In this paper, we propose a cooperation framework in heterogeneous cloud radio access networks (H-CRANs) to mitigate inter-tier interference. Specifically, small cell remote radio head (S-RRH) acts as the cognitive relay for multiple macrocell users (MUEs) which are primary users, and obtains a fraction of time slot from multiple MUEs as a reward. Through the cooperation, the S-RRHs can obtain extra spectrum resource for serving secondary users-small cell users (SUEs), while the MUEs can improve their transmission rates. Moreover, the inter-tier interference between macrocell networks and small cell networks can be mitigated via cooperation. The cooperation problem is formulated as a binary integer programming problem which is NP-hard. To solve this problem, we transform it to an equivalent many-to-one matching problem. Then, we achieve the near optimal solution by proposing a two-sided cooperator selection algorithm, which takes the benefits of both S-RRHs and MUEs into consideration. Simulation results show that the performance of the macrocell networks as well as small cell networks can be improved by adopting the proposed scheme, and the cooperator selection result is stable and close to the optimal solution.

One of the major challenges, which prevents the coordinated multipoint (CoMP) communications concept from being widely deployed in new cellular systems, is timing synchronization. In order to achieve the gains promised by CoMP systems, the user equipment's signals in uplink (UL) or the base stations' signals in downlink should be synchronized, such that the time difference of arrivals do not exceed the cyclic prefix length of the transmitted signals; otherwise, the system suffers from unavoidable integer time offsets. These offsets lead to asynchronous interference in terms of inter-carrier, inter-block, and inter-symbol interference. This limits the percentage of area within a cell which can be covered by cooperation and imposes an upper bound on this area. In this paper, we investigate this problem in the UL, and by using geometrical and semi-analytical approaches, we define this upper bound. Also, by characterizing an accurate mathematical model for the asynchronous interference in Rayleigh fading channels, we were able to employ a standard MMSE-based receiver that mitigates this interference. Furthermore, a typical joint channel and delay estimation block is incorporated into the receiver to examine its performance with estimation errors.

In this paper, we study opportunistic traffic offloading in a vehicular environment, where the cellular traffic of vehicular users (VUs) is offloaded through carrier-WiFi networks deployed by the mobile network operator (MNO). By jointly considering users' satisfaction, the offloading performance, and the MNO's revenue, two WiFi offloading mechanisms are proposed: auction game-based offloading (AGO) and congestion game-based offloading (CGO). Moreover, we introduce an approach to predict WiFi offloading potential and access cost and incorporate it in the offloading mechanisms. Specifically, with the AGO mechanism, the MNO employs auctions to sell WiFi access opportunities; VUs decide whether to bid according to their utilities and are capable of using WiFi if the auction is won. With the CGO mechanism, a VU calculates utility considering other VUs' strategies and makes offloading decisions accordingly. We show that the AGO mechanism can maximize social welfare and increase the MNO's revenue, whereas the CGO mechanism can achieve a better performance of average VU utility and fairness. Additionally, both AGO and CGO mechanisms can improve the overall WiFi offloading performance. Through simulations, we demonstrate that both AGO and CGO mechanisms can achieve higher average utility of VUs and lower average service delay and offload much more cellular traffic compared with existing offloading mechanisms.

Abstract Millimeter wave (mmWave) communication is a promising technology to support high‐rate (e.g., multi‐Gbps) multimedia applications because of its large available bandwidth. Multipacket reception is one of the important capabilities of mmWave networks to capture a few packets simultaneously. This capability has the potential to improve medium access control layer performance. Because of the severe propagation loss in mmWave band, traditional backoff mechanisms in carrier sensing multiple access/collision avoidance (CSMA/CA) designed for narrowband systems can result not only in unfairness but also in significant throughput reduction. This paper proposes a novel backoff mechanism in CSMA/CA by giving a higher transmission probability to the node with a transmission failure than that with a transmission success, aiming to improve the system throughput. The transmission probability is adjusted by changing the contention window size according to the congestion status of each node and the whole network. The analysis demonstrates the effectiveness of the proposed backoff mechanism on reducing transmission collisions and increasing network throughput. Extensive simulations show that the proposed backoff mechanism can efficiently utilize network resources and significantly improve the network performance on system throughput and fairness. Copyright © 2014 John Wiley & Sons, Ltd.

Abstract In this paper, a cluster‐based two‐phase coordination scheme for cooperative cognitive radio networks is proposed considering both spectrum efficiency and network fairness. Specifically, candidate secondary users (SUs) are first selected by a partner selection algorithm to enter the two‐phase cooperation with primary users (PUs). In phase I, the selected SUs cooperate with PUs to acquire a fraction of time slot as a reward. In phase II, all SUs including the unselected ones share the available spectrum resources in local clusters; each of which is managed by a cluster head who participated in the cooperation in phase I. To improve the total network utility of both PUs and SUs, the maximum weighted bipartite matching is adopted in partner selection. To further improve the network performance and communication reliability, network coding is exploited during the spectrum sharing within the cluster. Simulation results demonstrate that, with the proposed cluster‐based coordination scheme, not only the PUs' transmission performance is improved, but also SUs achieve spectrum access opportunities. Copyright © 2015 John Wiley & Sons, Ltd.

This paper provides a detailed mathematical analysis of the impact of integer time offsets on the performance of OFDM systems. Although a number of approximate expressions for the probability of error in OFDM systems with integer time offset can be found in the literature, to the best of our knowledge, this work is the first that provides exact expressions. In particular, we derive exact closed-form expressions for the bit error rate (BER) and the symbol error rate (SER) of BPSK, QPSK, and 16-QAM modulation for transmission over both AWGN and Rayleigh fading channels. The effect of the fractional carrier frequency offset (CFO) is taken into consideration in the derivations. This makes the derived expressions more useful in evaluating the probability of error for OFDM systems with CFO only, especially in cases like 16-QAM modulation for transmission over Rayleigh fading channels where exact closed-form expressions are not available. For OFDM systems with a large number of subcarriers, an approximate method for evaluating the BER/SER is given. Finally, numerical results are included to demonstrate the exactness of the derived expressions and the accuracy of the approximate method.

Millimeter wave (mmWave) communication is a promising solution for future fifth generation (5G) cellular networks to offer extremely high capacity. Because of the propagation characteristics of mmWave band, 5G users with high mobility in metropolitan areas could suffer frequent link outages resulting in challenges on video quality provisioning. In this paper, a playout buffer is used to regulate and maintain the video playout quality. We formulate the problem of using dynamically allocated bandwidth to charge the buffer as a Markov decision process (MDP), aiming to maximize video playout quality for all the users moving in the whole coverage area. Dynamic programming is adopted to solve the MDP problem with state aggregation considering the characteristics of mmWave network. Numerical results demonstrate that the resultant optimal policy of the MDP model can effectively maintain video playout quality for high-mobility users with intermittent mmWave connection.

We study user cooperation to enhance the physical layer security. Specifically, the source cooperates with friendly intermediate nodes to transmit message securely in the presence of multiple eavesdroppers. We propose a cooperative framework, whereby the source selects multiple partners and stimulates them by granting an amount of reward. First, multiple cooperative relays and jammers are selected by the source using greedy or cross-entropy based approaches. Then, the source and the partners negotiate for the payment and transmission power, which is modeled as a two-layer game. At the top layer, a buyer-seller game is utilized, where the source buys the service provided by the partners. At the bottom layer, all the partners share the reward by determining their transmission powers in a distributed way, which is formulated as a non-cooperative power selection game. By analyzing the game, the partners can determine the transmission powers for cooperation, while the source can select the best payment. To further improve the utility of the source, a set of reward allocation coefficients are introduced and optimized using particle swarm optimization approach. Simulation results are provided to demonstrate the performance of the proposed schemes.

In this paper, we present an analytical framework for offloading cellular traffic by outdoor WiFi network in the vehicular environment. Specifically, we consider a generic vehicular user with Poisson data service arrivals to download/upload data from/to the Internet through the cost-effective WiFi network (want-to) or the cellular network providing full service coverage (have-to). Under this scenario, the WiFi offloading performance, characterized by offloading effectiveness, is analyzed in terms of desired average service delay which is the average time the data services can be deferred for WiFi availability. We establish an explicit relation between offloading effectiveness and average service delay by an M/G/l/K queueing model, and the tradeoff between the two is examined. We validate our analytical framework through simulations based on a VANET simulation tool VANETMobisim and real map data sets. Our analytical framework should be valuable for providing offloading guidelines to both vehicular users and network operators.

In this paper, we study channel-based authentication, where the receiver can identify and authenticate the senders through channel vectors estimated from their frames. The authentication process is formulated as a sequence of hypothesis test problems. In order to improve the detection probability and reduce the false alarm probability, two schemes are proposed based on different classification algorithms in machine learning. Specifically, support vector machine (SVM) based authentication schemes and the linear Fisher discriminant analysis (LFDA) based authentication scheme are proposed by exploiting three channel features, including the time-of-arrivals, received signal strengths, and cyclic-features of the channels. In SVM based schemes, the linear and nonlinear SVMs are used to generate classifiers to solve the hypothesis test problems. In LFDA based scheme, a linear combination of these three channel features is used as the test statistic, which is compared with a threshold to perform authentication. Simulation results demonstrate that the proposed schemes perform better in terms of the misdetection probability and the false alarm probability than several existing typical channel-based authentication schemes. Moreover, the time complexity and space complexity of the proposed schemes are analyzed, and the LFDA based scheme performs the best.

In this paper, cooperative sensing for multi-channel cognitive radio networks (CRNs) is studied, whereby the secondary users (SUs) cooperate with each other to sense the multiple channels owned by the primary users (PUs). The objective is to better protect the primary system while satisfying the SUs' requirement on the expected access time. A general scenario is considered, where the channels present different usage characteristics and the detection performance of individual SUs varies due to the channel conditions between the PUs and SUs. With the dynamics in the channel usage characteristics and the detection capacities, each SU chooses one channel for sensing to minimize the interference to the PUs. The problem is formulated as a nonlinear integer programming problem which is NP-complete in general. To find the solution efficiently, the original problem is transformed into a variant of convex bipartite matching problem by constructing a complete bipartite graph and defining proper weight vectors. Based on the problem transformation, a channel assignment algorithm is proposed for computing in polynomial time the solution in terms of the number of SUs, the number of channels, and the maximum value of weights. Simulation results are presented to validate the performance of the proposed algorithm.

Quality of service (QoS) aware resource allocation for the uplink of a decode-and-forward relay assisted Orthogonal Frequency Division Multiple Access (OFDMA) based cellular system is investigated. Incorporating relays in the system improves the cell-edge coverage and the system throughput. Resource (relay, subcarrier and power) allocation problem is formulated with the objective of maximizing the total system throughput subject to the satisfaction of user QoS requirements and individual total power constraints of the users and relays. The throughput of each end-to-end link is modeled considering both the direct and relay links. Due to non-convex nature of the original resource allocation problem, the optimal solution is obtained by solving a relaxed problem via two level dual decomposition. The performance of the proposed scheme is evaluated in the scenarios based on LTE-A network model. Numerical results reveal that the proposed scheme guarantees each user's QoS satisfaction at the expense of a slight degradation of the system throughput.

Providing various wireless connectivities for vehicles enables the communication between vehicles and their internal and external environments. Such a connected vehicle solution is expected to be the next frontier for automotive revolution and the key to the evolution to next generation intelligent transportation systems (ITSs). Moreover, connected vehicles are also the building blocks of emerging Internet of Vehicles (IoV). Extensive research activities and numerous industrial initiatives have paved the way for the coming era of connected vehicles. In this paper, we focus on wireless technologies and potential challenges to provide vehicle-to-x connectivity. In particular, we discuss the challenges and review the state-of-the-art wireless solutions for vehicle-to-sensor, vehicle-to-vehicle, vehicle-to-Internet, and vehicle-to-road infrastructure connectivities. We also identify future research issues for building connected vehicles.

There is a growing interest in the use of renewable energy sources to power wireless networks in order to mitigate the detrimental effects of conventional energy production or to enable deployment in off-grid locations. However, renewable energy sources, such as solar and wind, are by nature unstable in their availability and capacity. The dynamics of energy supply hence impose new challenges for network planning and resource management. In this paper, the sustainable performance of a wireless mesh network powered by renewable energy sources is studied. To address the intermittently available capacity of the energy supply, adaptive resource management and admission control schemes are proposed. Specifically, the goal is to maximize the energy sustainability of the network, or equivalently, to minimize the failure probability that the mesh access points (APs) deplete their energy and go out of service due to the unreliable energy supply. To this end, the energy buffer of a mesh AP is modeled as a G/G/1(/N) queue with arbitrary patterns of energy charging and discharging. Diffusion approximation is applied to analyze the transient evolution of the queue length and the energy depletion duration. Based on the analysis, an adaptive resource management scheme is proposed to balance traffic loads across the mesh network according to the energy adequacy at different mesh APs. A distributed admission control strategy to guarantee high resource utilization and to improve energy sustainability is presented. By considering the first and second order statistics of the energy charging and discharging processes at each mesh AP, it is demonstrated that the proposed schemes outperform some existing state-of-the-art solutions.

In this paper, risk-aware cooperative spectrum access schemes for cognitive radio networks (CRNs) with multiple channels are proposed, whereby multiple primary users (PUs) operating over different channels choose trustworthy secondary users (SUs) as relays to improve throughput, and in return SUs gain transmission opportunities. To study the multi-channel cooperative spectrum access, cooperation over single channel is investigated first, which involves a PU selecting the suitable SU and granting a period of access time to the selected SU as a reward, considering trustworthiness of SUs. The above procedure is modeled as a Stackelberg game, through which access time allocation and power allocation are obtained. Based on the above results, cooperation over multiple channels is studied from the perspectives of the primary network and secondary network, respectively. Two schemes are proposed accordingly: the primary network-centric matching (PCM) scheme and the secondary network-centric cluster-based (SCC) scheme. In PCM scheme, cooperating SU for each channel is determined to maximize the total utility of the primary network, which is formulated as a maximum weight matching problem. In SCC scheme, SUs first form a cluster to share the channel state information (CSI), and the best SUs are selected for cooperation with PUs over different channels to obtain the maximum aggregate access time for the secondary network. Then, SUs share the obtained resource using congestion game and quadrature signalling. Numerical results demonstrate that, with the proposed schemes, PUs can achieve higher throughput, while SUs can obtain longer average access time, compared with the random channel access approach.

In this paper, dynamic spectrum access (DSA) in multi-channel cognitive radio networks (CRNs) is studied. The two fundamental issues in DSA, spectrum sensing and spectrum sharing, for a general scenario are revisited, where the channels present different usage characteristics and the detection performance of individual secondary users (SUs) varies. First, spectrum sensing is investigated, where multiple SUs are coordinated to cooperatively sense the channels owned by the primary users (PUs) for different interests. When the PUs' interests are concerned, cooperative spectrum sensing is performed to better protect the PUs while satisfying the SUs' requirement on the expected access time. For the SUs' interests, the objective is to maximize the expected available time while keeping the interference to PUs under a predefined level. With the dynamics in the channel usage characteristics and the detection capacities, the coordination problems for the above two cases are formulated as nonlinear integer programming problems accordingly, which are proved to be NP-complete. To find the solution efficiently, for the former case, the original problem is transformed into a variant of convex bipartite matching problem by constructing a complete bipartite graph and defining proper weight vectors. Based on the problem transformation, a channel selection algorithm is proposed to compute the solution. For the latter case, the deterministic optimization problem is first transformed to an associated stochastic optimization problem, which is then solved by cross-entropy (CE) method of stochastic optimization. Then, the sharing of the available channels by SUs after sensing is modeled by a channel access game, based on the framework of weighted congestion game. An algorithm for SUs to select access channels to achieve Nash equilibrium (NE) is proposed. Simulation results are presented to validate the performance of the proposed algorithms.

In this paper, a spectrum sharing strategy in cooperative cognitive radio network (CCRN) is investigated. Specifically, a multi-phase cooperation architecture is proposed including cooperation partner selection and spectrum sharing among secondary users (SUs). The cooperation partners who are selected from SUs forward the data of primary users (PUs), and then acquire the spectrum access opportunities for their own transmissions as a reward. To improve the utility for the PU-SU cooperation pairs, the partner selection is modeled as an optimally weighted bipartite matching problem to maximize the total utility where energy efficiency is also considered. The partner SU further improves spectrum utilization by sharing the acquired spectrum with the surrounding SUs via cooperative network coding. Simulation results demonstrate that the proposed partner selection and spectrum sharing approach adapts well to the dynamic traffic loads in CCRN.

In this paper, an opportunistic channel access for cognitive radio networks (CRNs) with multiple channels is proposed, whereby the secondary users (SUs) cooperate with primary users (PUs) to improve the latter's throughput and gain transmission opportunities in return. Cooperation on single channel is studied first, which is modeled by the Stackelberg game. By analyzing the game, the access time allocation of the PU and the optimal transmission power of the SU can be obtained. Then, based on the outcome of the above game, cooperation on multiple channels in the network is studied. To better exploit transmission opportunities on different channels, a cluster-based cooperation scheme (CBC) is proposed, whereby SUs first form a cluster, select best SUs to obtain the maximum sum of the access time using maximum weight matching, and then share the obtained channels fairly using congestion game and quadrature signalling. The condition for Nash Equilibrium (NE) of the congestion game is provided and an algorithm for CBC scheme is proposed. Numerical results demonstrate that, with the proposed scheme, the SUs can get more average access time and achieve higher fairness, compared with the random channel access approach.

An orthogonal modulation enabled two-phase energy-efficient framework is presented for active cooperation between secondary users (SUs) and primary users (PUs) in a cognitive radio network. Since the PU has higher priority, and SUs compete for spectrum accessing, we model the power control problem as a Stackelberg game which incorporates throughput and energy consumptions into utility design. Due to the two-phase feature and SUs' power constraint, this game is played in an additive coupled sum constrained type. Unique Nash Equilibrium is achieved in analytical format, and simulations demonstrate the effectiveness of the proposed cooperation framework.

The booming smart grid produces a large amount of data that should be transmitted to the utility control center (UCC), typically by means of the cellular network. This may pose a prohibitive transmission cost and choke the cellular network. As an effort to address this issue, we propose a vehicle assisted data delivery method to offload the cellular network, in which vehicles are utilized to carry and deliver the data from distributed locations to the UCC through the deployed roadside units. Two data forwarding schemes are developed based on the theory of optimal stopping rules to increase the data delivery probability. Simulation results are given to demonstrate that the proposed method can achieve high data delivery ratio through the roadside network so that it can efficiently offload the cellular network and reduce the communication cost.

This work is concerned with enhancement of spectrum-energy efficiency whereby a primary user (PU) engages secondary users (SUs) to relay its transmission in an energy-aware cognitive radio network, i.e., forming a cooperative cognitive radio network (CCRN). The cooperation framework in CCRN can be multiple two-hop relaying with or without PU's direct link transmission using an amplify-and-forward or decode-and-forward mode. In the energy-aware CCRN, an individual cooperating partner attempts to maximize its own utility. The partner selection and parameter optimization, led by the PU, are formulated as two Stackelberg games, namely a sum-constrained power allocation game for two-phase cooperation and a power control game for three-phase cooperation, respectively. Unique Nash Equilibrium is proved and achieved in analytical format for each game. The optimal communication strategy is chosen which achieves the maximum PU utility among different optimal communication strategies. Moreover, an implementation scheme is presented to perform the partner selection and parameter optimization based on the analytical results. Theoretical analysis and performance evaluation show that the proposed CCRN model is a promising framework under which the PU's utility is maximized, while the relaying SUs can attain acceptable utilities.

Relaying in femtocell networks is a promising and economically viable option to reduce the co-channel interference while improving indoor coverage and the network capacity in the next generation wireless networks. However, efficient relay selection as well as subcarrier and power allocation are critical in such networks when multiple users and multiple relays are considered. In this paper, an optimal resource (relay, subcarrier and power) allocation algorithm for co-channel deployed orthogonal frequency division multiple access (OFDMA) based femtocell systems is proposed. The resource allocation problem is formulated as a joint relay, subcarrier and power allocation problem with the objective of maximizing the sum of the weighted rates of the femtocell system subject to protecting the macrocell network's communications. Due to the non-convex nature of the original resource allocation problem, we obtain an optimal solution for the original problem by solving a relaxed problem via dual decomposition. Simulation results demonstrate that our proposed resource allocation algorithm outperforms the resource allocation algorithms proposed in literature by achieving higher throughput at the expense of a slight increment of the system complexity.

To the best of our knowledge, the existing clustering schemes in coordinated multi-point (CoMP) systems do not take into consideration the timing synchronization requirements of the users' signals at the cooperating base stations. In this paper, a clustering scheme that can satisfy these requirements is proposed. With the aid of simulations, we compare this scheme to a clustering scheme that does not take these requirements into consideration and show that our scheme has better performance in high SNRs and it has less system complexity.

In this paper, we propose an electronic mail system, namely VeMail, for handling messages between vehicles and Intelligent Transportation Systems (ITS), to improve the efficiency of transportation management. After elaborating the reasons of using Internet email as a basis of messaging for ITS, we describe the key components of the VeMail system, including mail server, mail client, and mail proxy. Considering the intermittent connectivity of vehicles to the mail server, we propose an optimal probabilistic message retrieval (OPMR) scheme for VeMail, in which each vehicle optimally selects an online period for email retrieval. Simulation is used to evaluate the performance and the results demonstrate that the proposed scheme outperforms the regular mail retrieval method in terms of the connection time with the mail server.

The abundant bandwidth at 60 GHz band (around 7 GHz) offers the potential for multi-Gbps indoor wireless connections for bandwidth-intensive applications. However, 60 GHz millimeter wave (mmWave) links are highly susceptible to blockage since it is difficult to diffract around obstacles. In this paper, we propose multi-radio band integration framework to have 2.4/5 GHz band assist mmWave band to prevent drastic data rate reduction. Specifically, the problem of multi-radio band integration with TDMA-based MAC is formulated as an optimization problem. We decompose the problem into two sub-problems: radio band selection and space-time scheduling. Firstly, considering network load and mmWave channel status, we define start-integration threshold and stop-integration threshold to select an active radio band for data transmission. Secondly, a space-time scheduling scheme is proposed to allow multiple flows over different radio bands operate concurrently to exploit the spatial reuse. Simulation results of the proposed multi-radio band integration mechanism demonstrate significant improvements of network connectivity and the number of supported traffic flows.

In this paper, we investigate cooperative networking in cognitive radio networks (CRNs), which targets to help the primary users (PUs) for secure communications and provide transmission opportunities to secondary users (SUs). Two cooperation schemes: relay-jammer (R-J) scheme and cluster-beamforming (C-B) scheme, are proposed. In R-J cooperation scheme, two individual SUs, a relay and a friendly jammer, are leveraged by the PU to improve communication secrecy via cooperation; In return, the PU allocates a fraction of access time for SUs' transmission. To achieve the maximum secrecy rate, joint time and power allocation is considered. In C-B cooperation scheme, the PU cooperates with a cluster of SUs, which enhance the secrecy of primary link via collaborative beamforming and gain spectrum access opportunities as a reward. With the objective of maximizing the secrecy rate, the optimal weights and time allocation are studied. Numerical results validate the proposed schemes and demonstrate that the PU can significantly enhances the secrecy through cooperation with the cooperating SUs by allocating time and transmission power optimally.

This work is concerned with enhancement of spectrum utilization by using polarization enabled two-phase cooperation between primary users (PUs) and secondary users (SUs) in cooperative cognitive radio networking (CCRN). The use of orthogonally dual-polarized antennas (ODPAs) enables concurrent transmissions of multiple independent signals of PUs and SUs, and interference suppression via polarization zero-forcing and polarization filtering to obtain significant performance improvement. To maximize a weighted sum throughput of PUs and SUs under energy/power constraints, the problem is formulated and solved based on a multi-timescale Markov decision process, and two modified backward iteration algorithms are devised to attain the optimal policies. Numerical results validate the effectiveness of the proposed CCRN framework, showing that the obtained policy outperforms both greedy and random ones.

In cognitive radio networks (CRNs), secure information transfer is of paramount importance for primary users (PUs), while secondary users (SUs) mainly desire to ease the starvation for transmission opportunities. To meet such different requirements, cooperation between PUs and SUs can be leveraged and therefore create a win-win situation. In this paper, we investigate cooperative spectrum access for CRNs, which targets to improve the secure transmission of PUs via cooperating SUs that would be incented by certain transmission opportunities. Two types of cooperation schemes are proposed, whereby the PU either cooperates with two individual SUs or a cluster of SUs, which are referred to as relay-jammer (R-J) scheme and cluster-beamforming (C-B) scheme, respectively. In R-J scheme, two individual SUs act as a relay and a friendly jammer to improve the PU's secrecy; In return, the PU allocates a fraction of access time for the SUs' transmission. To achieve the maximum secrecy rate, joint time and power allocation is considered. Particularly, the cooperating relay and jammer determine the optimal transmission power, while the PU decides the optimal time allocation strategy. In C-B scheme, the PU cooperates with a cluster of SUs to enhance the secrecy of the primary link via collaborative beamforming, where three different approaches are proposed for the scenarios with one eavesdropper, with multiple eavesdroppers, and without eavesdroppers' information, respectively. To maximize the secrecy rate, the weight selection and time allocation are also studied. Simulation results are given to validate the proposed schemes and demonstrate that the PU can significantly enhance the secrecy through cooperation.

Access infrastructure, such as Wi-Fi access points and cellular base stations (BSs), plays a vital role in providing pervasive Internet services to vehicles. However, the deployment costs of different access infrastructure are highly variable. In this paper, we make an effort to investigate the capacity-cost tradeoffs for vehicular access networks, in which access infrastructure is deployed to provide a downlink data pipe to all vehicles in the network. Three alternatives of wireless access infrastructure are considered, i.e., cellular BSs, wireless mesh backbones (WMBs), and roadside access points (RAPs). We first derive a lower bound of downlink capacity for each type of access infrastructure. We then present a case study based on a perfect city grid of 400 km2with 0.4 million vehicles, in which we examine the capacity-cost tradeoffs of different deployment solutions in terms of capital expenditures (CAPEX) and operational expenditures (OPEX). The rich implications from our results provide fundamental guidance on the choice of cost-effective access infrastructure for the emerging vehicular networking.

The resource allocation problem is investigated for relay-based multi-user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) uplink system, considering heterogeneous services. A quality of service (QoS) aware optimal relay selection, power allocation and subcarrier assignment scheme under a total power constraint is proposed. The relay selection, power allocation and subcarrier assignment problem is formulated as a joint optimization problem with the objective of maximizing the system throughput, which is solved by means of a two level dual decomposition and subgradient method. To further reduce the computational cost, two low-complexity suboptimal schemes are also proposed. The performance of the proposed schemes is demonstrated through computer simulations based on LTE-A network. Numerical results show that the proposed schemes support heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation.

A novel polarization enabled two-phase cooperation framework for cognitive radio networking is proposed in this paper. By leveraging the degrees of freedom provided by orthogonally dual-polarized antennas, secondary users can relay the traffic of primary users and transmit their own in the same time slot without interference. To evaluate the performance of the proposed framework, a sum throughput maximization problem is formulated. By using the geometric programming algorithms, the nonlinear and non-convex optimization problem is solved by applying different power constraints for high and medium (or low) signal-to-noise ratio regimes. Simulation results validate the effectiveness of the proposed two-phase framework.

Millimeter-wave (mmWave) communications is a promising technology to provide high data rates (multiGigabit) for indoor multimedia applications. However, indoor mmWave links are highly susceptible to blockage because of the limited ability to diffract around obstacles such as the human body and furniture. In order to realize high-rate reliable transmission, cooperative communication is utilized to tackle with the scenarios where LOS link of source node and destination node is blocked. Specifically, with directional antenna, we first select the node in the feasible region with best achievable rate of cooperative communication as the cooperative relay. Then, cooperative concurrent transmission scheduling is formulated as an optimization problem to maximize the transmission efficiency. A flip-based heuristic scheduling algorithm is proposed to obtain the real-time solution. Extensive simulations demonstrate that the proposed cooperative concurrent transmission scheduling (CCTS) scheme can significantly increase the transmission throughput and utilize network resource efficiently while maintaining network connectivity.

A two-phase cooperative framework in Cognitive Radio Networks (CRNs), whereby the secondary users (SUs) can fully exploit the transmission opportunities through cooperation with primary users (PUs), is proposed. Specifically, the SU cooperates with the active PU to improve the PU's utility. As a reward, the period of time when the PU is inactive, is allocated to the cooperating SU for its own transmissions. During the cooperation, the PU and the cooperating SU use quadrature amplitude modulation (QAM) to attain orthogonal signaling to cooperate efficiently, while the SU selects the optimal power allocation coefficient to maximize the performance of the PU, when its own transmission requirement is satisfied. The SU selection and power allocation determination procedure is formulated as a nonlinear optimization problem. The closed-form solution is derived. Numerical results demonstrate that, with the proposed cooperative strategy, the PU can achieve optimal performance and the SU can gain transmission opportunities through cooperation.

Cooperative relaying is a promising technique for Long Term Evolution Advanced (LTE-A) networks to satisfy high throughput demand and support heterogeneous communication services with diverse quality-of-service (QoS) requirements. However, efficient relay selection as well as resource allocation are critical in such a network when multiple users and multiple relays are considered. In this paper, a resource allocation problem of maximizing the total achievable throughput for multi-user cooperative LTE-A uplink system considering heterogeneous services is investigated. An optimal joint relay selection, subcarrier assignment and power allocation scheme under total power constraint is proposed. The optimization problem is formulated as a convex optimization problem and solved by decomposing it into a hierarchy of subproblems with reduced computational complexity. The subgradient method is used to find the Lagrange multipliers, which helps to obtain the optimal solution. Numerical results show that our approach supports heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation.

In this paper, a concurrent transmission scheduling algorithm is proposed to enhance the resource utilization efficiency for multi-Gbps millimeter-wave (mmWave) networks. Specifically, we exploit spatial-time division multiple access (STDMA) to improve the system throughput by allowing both non-interfering and interfering links to transmit concurrently, considering the high propagation loss at mmWave band and the utilization of directional antenna. Concurrent transmission scheduling in mmWave networks is formulated as an optimization model to maximize the number of flows scheduled in the network such that the quality of service (QoS) requirement of each flow is satisfied. We further decompose the optimization problem and propose a flip-based heuristic scheduling algorithm with low computational complexity to solve the problem. Extensive simulations demonstrate that the proposed algorithm can significantly improve the network performance in terms of network throughput and the number of supported flows.

In this paper, a cooperative framework in cognitive radio networks, which addresses energy efficiency of the primary users (PUs) and trustworthiness of secondary users (SUs), is proposed. Specifically, the cooperation involves a PU selecting the most suitable SU as the cooperative relay and allocating the spectrum access intervals for relaying its message and rewarding the SU for its help in relaying the PU's message. Based on the PU's strategy, the selected SU determines its optimal transmission power. The above sequential decision procedure, with the PU as the leader and the SU as the follower, is formulated as a Stackelberg game. The outcomes of the proposed cooperative strategy, including partner selection, cooperation in an untrustworthy environment, and energy efficiency consideration, are analyzed. Numerical results demonstrate that, with the proposed relay selection scheme, the PU can achieve high energy saving through cooperation with the trustworthy SU.

A quadrature signaling based two-phase cooperation framework for cooperative cognitive radio networking is proposed. By leveraging the degrees of freedom provided by orthogonal modulation, secondary users are able to relay the traffic of primary users and transmit their own in the same time slot without interference. To evaluate the cooperation performance of the proposed framework, a weighted sum throughput maximization problem is formulated, and closed-form solutions of the optimal power setting/allocation are obtained in the amplify-and-forward and decode-and-forward relaying modes. Simulation results validate the efficiency of the proposed framework.

An adaptive medium access control (MAC) retransmission limit selection scheme is proposed to improve the performance of IEEE 802.11p standard MAC protocol for video streaming applications over vehicular ad-hoc networks (VANETs). A multi-objective optimization framework, which jointly minimizes the probability of playback freezes and start-up delay of the streamed video at the destination vehicle by tuning the MAC retransmission limit with respect to channel statistics as well as packet transmission rate, is applied at road side unit (RSU). Periodic channel state estimation is performed at the RSU using the information derived from the received signal strength (RSS) and Doppler shift effect. Estimates of access probability between the RSU and the destination vehicle is incorporated in the design of the adaptive MAC scheme. The adaptation parameters are embedded in the user datagram protocol (UDP) packet header. Two-hop transmission is applied in zones in which the destination vehicle is not within the transmission range of any RSU. For multi-hop scenario, we discuss two-hop joint MAC retransmission adaptation and path selection. Compared with the non-adaptive IEEE 802.11p standard MAC, numerical results show that the proposed adaptive MAC protocol exhibits significantly fewer playback freezes while introduces only a slight increase in start-up delay.

ABSTRACT A link adaptation (LA) scheme for the downlink of mobile hotspot, which is supported by an IEEE 802.16e or mobile WiMAX network, is proposed. The mobile WiMAX uses orthogonal frequency division multiple access (OFDMA) in its physical layer. The main function of the LA scheme is to select an appropriate burst profile, which includes a multiple input multiple output (MIMO) transmission mode, modulation technique, and coding scheme. We formulate a discrete optimization problem for the LA scheme by maximizing the throughput. An algorithm to implement the LA scheme is also proposed. Numerical results show that the proposed LA scheme exhibits good performance. Copyright © 2011 John Wiley & Sons, Ltd.

An adaptive MAC retransmission limit selection scheme is proposed to improve the performance of IEEE 802.11p MAC protocol for video streaming applications over vehicular area networks (VANETs). A multi-objective optimization framework is applied at road side unit (RSU) which jointly minimizes the probability of playback freezes and the start-up delay of the streamed video at the destination vehicle by tuning the MAC retransmission limit with respect to channel statistics as well as packet transmission rate. Periodic channel state estimation is performed at RSU which is video transmitter by information acquired from received signal strength (RSS) considering Doppler shift effect. Also, estimation of access probability between RSU and destination vehicle is done via information about the most recent location of the vehicle and considered in design of adaptive MAC scheme. The information is enclosed inside the user datagram protocol (UDP) packet header. Compared with non-adaptive IEEE 802.11p MAC, our scheme results in significantly less playback freezes while introducing slight increase in start-up delay.

Next generation communication networks are anticipated to make use of renewable energy sources, e.g., solar and wind power, to reduce carbon footprints and achieve an environmentally sustainable system. However, renewable energy sources have the limitation of unstable availability and capacity, which introduces new challenges for network planning and resource management. In this paper, adaptive resource management is introduced for wireless mesh networks that are powered by sustainable energy sources. The objective is to address the unreliability of the energy supply and to maximize the energy sustainability of the network, or equivalently, minimize the probability that mesh access points (APs) deplete their energy and go out of service. Specifically, the energy buffer of a mesh AP is modeled as a G/G/1 queue and a diffusion approximation is applied to analyze the transient evolution of the queue length and energy depletion duration. Based on the analysis, a resource management scheme is proposed to adaptively distribute traffic over various relay paths across the network and a distributed admission control strategy is applied to further guarantee high resource utilization under the energy sustainability constraint. By considering the first and second order statistics of the energy charging and discharging processes, it is demonstrated that the proposed scheme outperforms some existing state-of- the-art solutions.

Service-oriented vehicular networks face challenge to deliver delay-sensitive data such as video packets. Most research on video streaming consider network-centric quality of service (QoS) metrics rather than the user perceived quality. In this paper, we propose an application-centric routing framework for real-time video transmission over urban multi-hop vehicular ad-hoc network (VANET) scenarios. Queueing based mobility model, spatial traffic distribution and probability of connectivity for sparse and dense VANET scenarios are taken into consideration in designing the routing protocol. The numerical results demonstrate the gain achieved by the proposed routing protocol versus geographic greedy forwarding in terms of video frame distortion and streaming start-up delay in several urban communication scenarios for various vehicle entrance rate and traffic densities.

The inherent characteristics of vehicular networks, such as dynamic topology and high mobility, pose significant challenges for the deployment of delay-sensitive applications, e.g., video streaming, in urban Vehicular Ad-hoc Networks (VANET). In this paper, we propose an integrated network-layer scheme for seamless delivery of video packets in VANET. First, we propose a new quality-driven routing scheme for delivering video streams from a fixed network to a destination vehicle via multihop communications. The routing scheme aims to optimize the visual quality of the transmitted video frames by minimizing the distortion, the start-up delay, and the frequency of the streaming freezes. We further propose an efficient network mobility management scheme, which introduces a novel adaptation of Proxy Mobile IPv6 (PMIPv6) for multi-hop VANET scenarios, and incorporates a handover prediction mechanism. Numerical results are given to demonstrate that our integrated scheme can achieve a better performance for the video quality metrics, the handover delay and the signalling cost.

In this paper, we exploit the heterogeneity of wireless channels and propose an efficient opportunistic cognitive routing (OCR) scheme for dynamic spectrum access (DSA) networks. We first introduce a novel routing metric by jointly considering physical characteristics of spectrum bands and diverse activities of primary users (PU) in each band. To effectively explore the spectrum opportunities, a proper channel sensing sequence for fast and reliable message delivery is determined by secondary users (SU) in a distributed way. We then develop a greedy forwarding scheme that SUs can select the next hop relay based on the geometry information and channel access opportunity of their one hop neighbors. For the proposed OCR, as routing control messages are locally exchanged, SUs can efficiently make the routing decision and opportunistically access the available channels. We further evaluate the performance of OCR via extensive simulations. It is shown that our proposed scheme outperforms existing opportunistic routing schemes in DSA networks by exploiting the heterogeneity of spectrum bands for opportunistic channel access.

Millimeter-wave (mmWave) communications is a promising enabling technology for high rate (Giga-bit) multimedia applications. However, because of the high propagation loss at 60 GHz band, mmWave signal power degrades significantly over distance. Therefore, a traffic flow being transmitted over multiple short hops can attain higher throughput than that over a single long hop. In this paper, we first design a hop selection metric for the piconet controller (PNC) to select appropriate relay hops for a traffic flow, aiming to improve the flow throughput and balance the traffic loads across the network. We then propose a multi-hop concurrent transmission (MHCT) scheme to exploit the spatial capacity of mmWave WPANs by allowing nodes to transmit concurrently in communication links without causing harmful interference. The analysis of concurrent transmission probability and time division multiplexing demonstrates that the MHCT scheme is capable of improving the time slot utilization. Extensive simulations are conducted to validate the analytical results and demonstrate that the proposed MHCT scheme can improve the average traffic flow throughput and network throughput.

We propose a distributed quality of service (QoS)-aware MAC protocol for multi-channel cognitive radio networks supporting multimedia applications. Specifically, based on the channel usage patterns of primary users (PUs), secondary users (SUs) determine a set of channels for channel sensing and data transmissions to satisfy their QoS requirements. We further enhance the QoS provisioning of the proposed cognitive MAC by applying differentiated arbitrary sensing periods for various types of traffic. An analytical model is developed to study the performance of the proposed MAC, taking the activities of both PUs and SUs into consideration. Extensive simulations validate our analysis and demonstrate that our proposed MAC can achieve multiple levels of QoS provisioning for various types of multimedia applications in cognitive radio networks.

A new cross layer path selection scheme with quality of service (QoS) support along urban areas is proposed. First, we introduce a cross-layer approach where the routing decision takes explicit consideration of the application layer objective function. Second, the queueing based mobility model, spatial traffic distribution and probability of connectivity for sparse and dense Vehicular Ad-Hoc Networks (VANETs) are taken into consideration for developing the cross-layer routing protocol. We focus on the video streaming application and optimize application layer performance metric, i.e., Peak Signal to Noise Ratio (PSNR). Video stream is downloaded from a Road Side Unit (RSU) deployed along the road and is transmitted to the destination vehicle via multi-hop communication. Simulation results show that the cross layer path selection scheme can achieve results close to the upper analytical bound.

A classification-based method is proposed to select an optimal path for video streaming over multi-hop mesh networks. Our main contribution is translating of path selection over multi-hop networks to a standard classification problem. The classification is based on minimizing average video packet distortion at the receiving nodes. We also consider long range dependence (LRD) characteristics of variable bit rate (VBR) video encoders by modeling the link as a fractional Brownian motion queue. In our method, a support vector machine is applied at each hop to optimally assign the next hop (partial path) for each video packet received at that hop. Wireless channel conditions (WCC) including packet loss probability of the channel and maximum achievable rate are used as class prototypes. Sample feature vectors include video content features (VCF) and video encoding parameters (VEP) extracted from video sequences. The classifiers are trained offline using a vast collection of video sequences and wireless channel conditions in order to yield optimal performance during real time path selection. Our method substantially reduces the complexity of conventional exhaustive optimization methods and results in high quality (low distortion). Simulations are conducted over an elementary multi-hop structure and cascades of such structure which not only proves the superiority of our method in terms of low complexity and high peak signal to noise ratio (PSNR) performance, but also provides important insights that can guide the design of network infrastructures and streaming protocols for video streaming.

Millimeter-wave (mmWave) transmissions are promising technologies for high data rate (multi-Gbps) Wireless Personal Area Networks (WPANs). In this paper, we first introduce the concept of exclusive region (ER) to allow concurrent transmissions to explore the spatial multiplexing gain of wireless networks. Considering the unique characteristics of mmWave communications and the use of omni-directional or directional antennae, we derive the ER conditions which ensure that concurrent transmissions can always outperform serial TDMA transmissions in a mmWave WPAN. We then propose REX, a randomized ER based scheduling scheme, to decide a set of senders that can transmit simultaneously. In addition, the expected number of flows that can be scheduled for concurrent transmissions is obtained analytically. Extensive simulations are conducted to validate the analysis and demonstrate the effectiveness and efficiency of the proposed REX scheduling scheme. The results should provide important guidelines for future deployment of mmWave based WPANs.

An adaptive regenerate and forward cooperative diversity (CD) system using quadrature amplitude modulation (QAM) for a two-user cooperation is proposed. The proposed system can achieve a maximum diversity order of two. The bit error probability (BEP) of a CD system depends primarily on the quality of the inter-user channel and user-to-destination channels, and the transmitted power of the cooperating users. Expressions which characterize the asymptotic behavior of the BEP as a function of the received signal-to-noise ratio (SNR) at the relay and the destination are derived. The transmit power is allocated optimally between the source and the relay according to the channel qualities and the CD system employed to achieve a prescribed BEP. Three power allocation strategies, each for a specific wireless communication scenario, which optimize the power consumption of the proposed CD system are introduced. The cooperative region, corresponding to each power allocation scheme, within which the partners must be located in order to yield a specified cooperative energy gain, is determined.

Millimeter-wave (mmWave) communication technologies can achieve up to several gigabit/sec data rate over a small range, using directional antenna. To enable high data rate wireless connectivity in a large area, a multi-hop routing protocol is needed. The rate-adaptiveness of mmWave link and the use

In this paper, a novel Kalman filter-based power allocation scheme is developed for cooperative networks with inaccurate channel state information (CSI). The channel estimation error is embedded in the power allocation model which results in uncertain linear and time varying system. The robust and constrained Kalman filter (RCKF) scheme adapts the allocated power to channel variation while satisfying the average bit error probability (BEP) requirements of each subscriber. The proposed scheme's low complexity and robustness to channel estimation inaccuracy make it practical for real networks implementations. Simulation results show that the proposed scheme converges to the optimal allocation with light computational burden despite of the inaccuracy in the received CSI.

This paper addresses practical implementation issues of resource allocation in OFDM A networks: inaccuracy of channel state information (CSI) available to the resource allocation unit (RAU) and diversity of subscribers' quality of service (QoS) requirements. The resource allocation problem in the considered point-to-multipoint (PMP) network is modeled as a network utility maximization (NUM) problem that allocates subcarriers, rate and power while satisfying orthogonal frequency division multiple access (OFDMA) constraints and QoS constraints defined in the service level agreement. Performance evaluation findings support our theoretical claims: a substantial data rate gain is achieved by considering the CSI imperfection and multiservice classes are supported with QoS guarantees by coordinating with a call admission control (CAC) scheme.

Ultra-wideband (UWB) communication is a promising enabling technology for future broadband wireless services. A simple, scalable, distributed, efficient medium access control (MAC) protocol is of critical importance to utilize the large bandwidth UWB channels and enable numerous new applications and services cost-effectively. In this paper, by investigating the characteristics of UWB communications, we propose a Distributed, EXclusive region (DEX) based MAC protocol. The proposed DEX protocol capitalizes on the spatial multiplexing gain of UWB networks by reserving exclusive regions (ER) surrounding the sender and receiver for data and acknowledgment (ACK) transmissions, so that users can efficiently and fairly share network resources in a distributed and asynchronous manner. We further quantify the network performance bounds and derive the optimal ER size to maximize the expected network transport throughput for a dense, multi-hop UWB network. Extensive simulation results demonstrate the efficiency and effectiveness of the DEX protocol. This work explores how to effectively utilize the wireless spatial capacity of distributed, multi-hop wireless networks by optimizing protocol parameters, instead of depending on more complicated control messages.

Multi-user multiple-input multiple-output (MIMO) systems have been emerging and attracting considerable attention recently for its potential to substantially improve system capacity via space division multiple access. In this paper, we propose a distributed multi-user (MU) medium access control (MAC) protocol for wireless local area networks (WLANs) with MIMO capability, using a leakage-based preceding scheme. By exploiting the multi-user degree of freedom in a MIMO system to allow the access point (AP) to communicate with multiple users in the same frequency band simultaneously, the proposed MU MAC can effectively minimize the AP-bottleneck effect in legacy WLANs. We then develop an analytical model to study the performance of the proposed MU MAC, in terms of the maximum number of users that can be supported and the network throughput. The analysis and simulation results show that the proposed MU MAC significantly outperforms the single-user MAC.

In this paper, a credit-based user authentication scheme is proposed for delay tolerant mobile wireless networks. The proposed authentication scheme isolates the uncertain network condition in the high-delay wireless backhaul with high error rate, and accelerates the overall authentication process when the mobile terminal roams in the visited network. The performance evaluation demonstrates that the proposed credit-based authentication scheme is secure and effectively reduces the overall delay and overhead in user authentication for delay tolerant mobile wireless networks.

By considering the characteristics of Ultra- wideband (UWB) communications networks, ie., short transmission range, accurate ranging, and low transmission/interference power, we propose a Distributed, Exclusive region (DEX) based MAC protocol for multi-hop UWB based wireless networks. DEX can effectively explore the spatial multiplexing gain of UWB networks and allow users to efficiently and fairly share network resources in a distributed manner by reserving exclusive regions (ER) around the sender and receiver for data and acknowledgment (ACK) transmissions. We further quantify the network performance bounds and derive the optimal ER size to maximize the expected network transport throughput for a dense multi-hop UWB network. Extensive simulation results demonstrate the efficiency and effectiveness of the DEX protocol.

Communications at 60GHz millimeter-wave (mmWave) band is a promising technology for future wireless personal area networks (WPAN) supporting high data rate applications. Internet Protocol TV (IPTV) is anticipated to be one of the next killer applications, which requires high data rate and st

The benefits of adaptive joint power control and rate allocation for uplink transmission in a wideband code division multiple access cellular system are investigated. Closed-loop power control (CLPC), to adaptively adjust the transmit power, has the effect of maintaining a target signal-to-interference ratio and bit error rate (BER) performance. On the other hand, rate adaptation requires less transmit power, although the BER performance may be poorer. The authors differentiate the power update interval from the data rate update interval, analyse and evaluate the performance of two joint rate/power adaptation algorithms in a fading environment: optimal spreading factor-power control (OSF-PC) and greedy rate packing-power control (GRP-PC). Numerical results show that GRP-PC exhibits superior throughput performance compared with other three adaptation schemes. CLPC alone exhibits throughput and BER performances comparable to those of the OSF-PC scheme, but consumes a significantly higher amount of transmit power. Rate adaptation only is not efficient in enhancing throughput, but its power consumption is minimal.

The impact of user relaying on the behavior of a relay node, which acts as the source node at the same time, is analyzed in a wireless relay network at the packet level. The analysis process models the behavior of the relay node as a queueing system and represents the service for its own packet transmission as an M/G/1-type Markov chain. By considering the fact that the maximum number of packet arrivals is ordinarily limited in a practical system, the M/G/1-type Markov chain is further reformatted into a quasi-birth-death (QBD) process through re-blocking so as to simplify the analysis and obtain the associated performance, such as average packet transmission delay. As an application of the results arising from the analysis, a new relay node selection scheme, based on a utility function approach that jointly considers the channel and the queue conditions at the relay node, is proposed. Numerical results show that the proposed analysis model is quite accurate and the proposed relay node selection scheme is effective in balancing cooperative diversity gain and packet transmission delay.

In this paper, designing an effective user relaying algorithm, in terms of relay node selection and power allocation, is discussed for amplify-and-forward wireless relay networks. The objective is to simplify the application of user relaying in practical wireless communication networks so that the system capacity can be improved with low computational complexity and system overhead. Beginning with the derivation of a tight threshold-based sufficient condition on the feasibility of a relay node, i.e., ensuring that user relaying via the node can achieve a larger channel capacity than direct transmission, a semi-distributed user relaying algorithm is proposed. In the proposed algorithm, each relay node can make decision on its feasibility individually, and the ultimate decision on the relay node selection among multiple feasible ones is made in a centralized manner. Since there is no need on exchanging channel state information among different network nodes, the proposed algorithm is simple for implementation and suitable for practical applications, which have stringent constraints on system overhead. By comparing with the centralized user relaying algorithm, which requires global channel state information of the whole network, the proposed semi-distributed algorithm can provide comparable system capacity, but has significantly reduced computational complexity.

In this paper, we propose a simple yet accurate analytical model for the slotted non-persistent carrier sense multiple access protocol with binary exponential backoff, as specified in the medium access control (MAC) protocol of the IEEE 802.15.4 standard for the contention access period. The model is based on a three-level renewal process, which leads to a general analytical framework applicable to the protocol variants of either single or double sensing, in a saturated or unsaturated case, under a general traffic arrival distribution and with various backoff policies. The analytical model can be used to obtain some important performance metrics, such as MAC throughput and average frame service time. The accuracy of the analytical model is demonstrated by extensive simulation results. The applicability of this model to the performance analysis of other slotted MAC protocols is also briefly discussed.

By integrating wireless wide area networks (WWANs) and wireless local area networks (WLANs), mobile hotspot technologies enable seamless Internet multimedia services to users on-board a vehicle. In this paper, we investigate the performance of TCP-Friendly Rate Control (TFRC) protocol supporting multimedia services in mobile hotspots. To quantify the throughput of TFRC flows in mobile hotspots, we first develop discrete-time queuing models for the WWAN link and the WLAN link. We then derive the steady state TFRC throughput using an iterative algorithm. Analytical and extensive simulation results reveal how the end-to-end TFRC throughput is affected by the number of users in a mobile hotspot, the vehicle velocity, the WWAN/WLAN link bandwidth, the retransmission limit, and the buffer size. It is found that the WWAN channel profile and link bandwidth have significant impacts on the TFRC throughput, and therefore suitable resource allocation and admission control are indispensable for the quality and efficiency of multimedia services in mobile hotspots.

A multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system with Rake receivers is considered. Based on the system capacity, an admission scheme at the connection level is formulated to relate the number of multipath fingers to the number of different classes of users that can be supported and to the blocking probability of each class in the system. With this analytical framework, the minimum number of multipath fingers that are needed in the physical layer while maintaining prescribed outage probability requirements in the link layer and prescribed blocking probability requirements at the connection level in the network layer for each traffic class can be determined. The outage probability in terms of bit error rate specification, with Gaussian monocycles supporting variable bit rate (VBR) multiclass services, is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Closed- form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active time hopping sequences from the interfering users on one pulse are explicitly derived. The indoor channel model used is based on IEEE 802.15.3a.

In this paper, real-time video transmission with quality of service (QoS) assurance over orthogonal frequency division multiplexing (OFDM) wireless systems is studied. Three quasi-optimal subcarrier allocation schemes, namely regular, delay tolerant and adaptive, are proposed. In the proposed schemes, effective throughput per subcarrier employing adaptive forward error correction (FEC) coding in a Rayleigh fading channel is evaluated, and a capacity matrix that governs all active users and all assignable subcarriers is formulated. The Munkres algorithm is used in the schemes to achieve optimal subcarrier assignment. Performance analyses in terms of spectral efficiency and packet loss probability are presented. Multi-user multichannel diversity is investigated to exploit the innate capacity gain in terms of fading variation and delay tolerance. The proposed schemes are scalable to both single-cell and multi-cell circumstances. Numerical results demonstrate that the proposed schemes can effectively achieve quasi-optimal spectral utilization and significantly improve system throughput.

Abstract To suppress narrowband interference (NBI) in an ultra‐wideband (UWB) communications environment, a null phase‐shift polarization (NPSP) filter is proposed. The proposed NPSP filter is a combination of a linear polarization‐vector transformer (PVT), a conventional single notch polarization (SNP) filter, and an amplitude and phase compensator (APC). The NBI, which has polarized states different from those of the UWB, can be suppressed completely and the UWB signal can be recovered without distortion if the polarized states can be estimated exactly. Analytical and simulation results indicate that the signal‐to‐interference ratio (SIR) can be improved effectively after NPSP filtering. The proposed NPSP filter can be implemented in a time‐hopping spread spectrum (TH‐SS) or a direct‐sequence spread spectrum (DS‐SS) UWB system. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper, the performance of a hybrid medium access protocol in IEEE 802.15.3 has been studied. An analytical model has been developed for the coordination between the contention access period (CAP) and the contention-free channel time allocation period (CTAP). Given the traffic characteristic and the number of contending devices, the piconet coordinator (PNC) determines the duration of the CAP. Based on the successfully received requests and the scheduling scheme, the PNC decides the duration of the CTAP. Extensive simulations are performed to validate our analysis.

An analytical model is proposed for the perfor- mance study of IEEE 802.11 distributed coordination function (DCF) with finite traffic load. Based on the model, average medium access control (MAC) sublayer service time of a frame and channel throughput are obtained. The model is further extended for the performance analysis of DCF with mixed voice and data traffic. The maximum number of voice connections supported in IEEE 802.11 WLAN under various background data traffic is derived. The results are useful for effective call admission control in IEEE 802.11 WLAN. Extensive simulations are performed to validate our analysis. I. INTRODUCTION The IEEE 802.11 standard (1) has been widely deployed around the world. Its medium access control (MAC) sublayer specifies two modes, the mandatory distributed coordination function (DCF) and the optional point coordination function (PCF). DCF is a distributed random access mechanism that is suitable for ad hoc networks, while PCF is a centralized polling based mechanism that can only work in infrastructure- based wireless LANs (WLANs). Due to its inefficient polling schemes and limited Quality-of-Service (QoS) provisioning, PCF is not widely implemented in practice. Therefore, in this paper, we study the performance of the dominant DCF in various scenarios. To date most research work in the literature (e.g., (2)-(4)) focuses on the study of DCF performance in the saturation case, in which every station in the network always has frames waiting for transmission. However, when there are more than In this paper, we first propose an analytical model to study the DCF throughput and average MAC service time under various load conditions for a single traffic type. It is based on the fundamental relationship between the mean MAC service time and the mean traffic arrival rate, and thus applicable to general traffic arrival processes. The proposed model improves the one in (10) in several aspects such as more accurate calculation of the average backoff time and the average number of transmission trials of a frame. Moreover, by comparing the obtained average MAC service time for a frame with the given average frame inter-arrival time, whether or not a station is in the saturated state can be accurately determined with the proposed model. The maximum number of stations that can be supported in such a network is also obtained. This information is critical to the design of admission control schemes that are usually adopted for QoS support in a network. It is worthy to note that this information cannot be readily obtained from the analysis of a saturation case. As VoIP over WLAN becomes more and more popular, it is instructive to study analytically the performance of DCF in a WLAN with mixed voice and data traffic. However, little work on this thread has been reported. In this paper, we carefully extend the proposed model to study the performance of DCF in such a situation. Using the extended model, the maximum number of voice stations that can be supported in the presence of a certain amount of data traffic can be obtained. On the other hand, the data throughput can also be obtained, given the number of voice stations in the WLAN. The rest of the paper is organized as follows. The IEEE 802.11 DCF is briefly reviewed in Section II. Section III presents the proposed analytical model for a single traffic type. Section IV extends the model to mixed voice and data traffic. Numerical results of both analysis and simulations for the two scenarios are given in Section V. Finally, we conclude the paper in Section VI.

In this paper, we investigate the unique characteristics of millimeter-wave (mmWave) communications and propose an exclusive region (ER) based resource management scheme to explore the spatial multiplexing gain of mm Wave WPANs. We develop an analytical model to study the performance of mm Wave WPANs in terms of the average number of concurrent transmissions and the spatial multiplexing capacity, considering the use of omni-directional and directional antennae. Extensive simulations are conducted to demonstrate the accuracy of the analytical model and the efficiency of the ER based resource management scheme. The analysis and simulation results should provide important guidelines for future deployment of mm Wave based WPANs. Our findings can also be extended to other wireless communications networks in general.

Distributed prioritized channel access mechanisms have been adopted by the IEEE 802.11e enhanced distributed channel access (EDCA) and the Multiband OFDM Alliance prioritized channel access (PCA) to support service differentiation. In this paper, we propose a novel analytical model for performance study of such mechanisms. The proposed model gives the average frame service time first and then the per station and network normalized throughput, which makes it applicable to both saturated and unsaturated stations. Furthermore, the model is especially helpful in understanding the different effects of the same prioritizing mechanisms in saturated and unsaturated conditions. To the best of our knowledge, there is no similar work reported in the open literature. The accuracy of the analytical model is demonstrated by extensive simulation.

In this paper, the performance of adaptive relaying schemes in cooperative diversity (CD) systems equipped with automatic repeat request (ARQ) is studied. Both selection relaying and incremental relaying are considered with a regenerate and forward CD system. The performance metrics of the CD-ARQ system such as efficiency, packet drop rate, average delay and jitter are presented. Numerical results show that selection relaying with a good partner outperforms incremental relaying. In addition, selection relaying performs better than incremental relaying without the ARQ scheme.

We study how to appropriately match users for two-user cooperative diversity systems that deploy optimal power allocation for anamplifyandforwardor aregenerateandforwardCD scheme. Optimized power allocation strategies, which minimize the total energy consumption for the cooperating pair, are proposed for both CD schemes. A novel matching algorithm with less computational complexity than, but with performance very close to the state-of-the-art optimal maximal weighted matching algorithm is developed. Numerical results show that, with optimal power allocation, the proposed matching algorithm can achieve 9 ~ 10 dB cooperative diversity gain, which is equivalent to prolonging the cell phone battery recharge time by 10 times.

In this paper, we investigate efficient data access algorithms in intelligent transportation system (ITS)-based networks with multi-hop wireless links. We introduce a proxy cache (PC) and propose PC-based poll-each-read (P-PER) and PC-based callback (P-CB) data access algorithms to reduce the transmission cost over the bottleneck wireless links. Extensive simulation results are given to demonstrate the performance of P-PER and P-CB. It is shown that P-PER and P-CB can improve the cache hit performance and reduce the transmission cost significantly. A tradeoff between P-PER and P-CB suggests the need to use a hybrid proxy-based approach to attain optimal performance of data access in ITS-based networks with multi-hop wireless links.

We consider downward and upward vertical handovers in integrated wireless LAN and cellular networks, and address wireless profiled TCP premature timeouts due to steep increase of round-trip time and false fast retransmit due to packet reordering. Specifically, we develop a mobile receiver centric loosely coupled cross-layer design, which is easy to implement and deploy, backward compatible with the wireless application protocol version 2 (WAP 2.0) architecture, and robust in the absence of cross-layer information. We propose two proactive schemes which prevent false fast retransmit by equalizing the round-trip delay experienced by all packets and suppress the premature timeouts by carefully inflating retransmission timeout time. We conduct extensive simulations to evaluate the performance in downward and upward vertical handovers. It is demonstrated that the proposed schemes significantly improve the performance in a wide range of network conditions.

In this paper, an agent based WLAN/cellular network integrated service model and relevant authentication scheme is proposed. The service model, or solution, does not require cumbersome peer-to-peer roaming agreements to provide seamless user roaming between WLAN hotspots and cellular networks, which are operated by independent wireless network service providers. Security analysis and overhead evaluation are given to demonstrate that the proposed service model and the supporting schemes are secure and effective.

In this paper, a versatile WLAN/cellular networks integrated roaming service framework with billing support is proposed, which can lift off the requirement of peer-to-peer roaming agreements to provide seamless user roaming between WLAN hotspots and cellular networks operated by independent wireless network service providers. Within the framework, an adaptive authentication and an event-tracking scheme have been developed considering the anonymity of the mobile users and allowing the integrated billing service to be applied to cellular network if it still uses a traditional authentication scheme. Security analysis and overhead evaluation demonstrate that the proposed roaming service framework is secure and efficient.

IEEE 802.15.3c has recently been formed for developing a millimeter-wave (mmWave)-based alternative physical layer (PHY) for the existing 802.15.3 wireless personal area network (WPAN) standard, using the unlicensed 57-64 GHz band. However, the existing resource management schemes are inherently inefficient and insufficient for mmWave-based WPANs, without the consideration of the unique features of mm Wave communications: high Oxygen absorption rate and atmospheric attenuation, limited communication range, stringent power control for unlicensed usage, and the use of directional antennae. In this paper, by capturing the unique physical characteristics of mm Wave communications and based on the use of omni-or directional antennae, we derive the exclusive regions (ER) to allow efficient concurrent transmissions and develop an ER based scheduling algorithm to improve the network throughput of mm Wave based WPANs by several folds. Extensive simulations are conducted to demonstrate the effectiveness and efficiency of the proposed ER scheduling algorithm. The analysis and simulation results can provide important guidelines for future deployment of mm Wave based WPANs.

This paper presents a novel, simple yet accurate analytical model for the IEEE 802.15.4 contention access period MAC protocol. The model is based on a three-level renewal process, which leads to a general analytical framework applicable for the protocol variants of either single or double sensing, in a saturated or unsaturated case, under a general traffic arrival distribution. The analytical model is used to obtain some important performance metrics, such as MAC throughput and average frame service time. The accuracy of the analytical model is demonstrated by extensive simulation results.

A novel polarization receiver for suppressing narrowband interference (NBI) in ultra-wideband (UWB) communication systems is proposed. A null phase-shift polarization (NPSP) filter, consisting of linear polarization vector transformation (PVT), conventional single notch polarization (SNP) filtering, and amplitude and phase compensation (APC), is utilized. The NBI, which has polarized states different from those of the UWB, can be suppressed completely and the UWB signal can be recovered without distortion. Analytical and simulation results indicate that the signal-to-interference ratio and BER performance can be improved effectively after NPSP filtering. The proposed receiver can be implemented in a time-hopping spread spectrum (TH-SS) or a direct-sequence spread spectrum (DS-SS) UWB system.

Mobility management is a key issue in mobile hotspots which enable ubiquitous Internet services while onboard a vehicle. In this paper, we compare two representative mobility management schemes for mobile hotspots: the network mobility (NEMO) basic support protocol at the network layer and the session initiation protocol (SIP)-based network mobility support protocol at the application layer. We evaluate their salient features and quantify their handoff latency over a wireless fading channel. It is shown that the SIP-based network mobility support protocol can be easily deployed and can reduce the tunneling overhead incurred in the NEMO basic support protocol. However, it can increase the handoff latency due to longer message length.

In this paper, a ticket ID system is proposed for service agent based WLAN/cellular network integrated service architecture. The proposed system accelerates the authentication process for the mobile terminal in the visited network, which effectively compensates the additional cost introduced by the service agent. The design of the ticket ID system also considers the user anonymity feature of the integrated service architecture. The performance evaluation demonstrates the ticket ID system effectively reduces the overall overhead in service agent based integrated service architecture.

In this paper, transmitting the real-time video with QoS provisioning over orthogonal frequency division multiplexing (OFDM) wireless channels is studied. Efficient subcarrier allocation schemes, namely regular, delay tolerant and adaptive, are proposed for real-time video streaming with QoS satisfaction to achieve near-maximal frequency efficiency. The Munkres algorithm is properly applied to the schemes to assure the optimality of subcarrier assignment. Multiuser multichannel diversity is investigated to exploit the innate multiplexing gain from fading variation and delay tolerance.

In this paper, the capacity of an orthogonal variable spreading factor code division multiple access (OVSF-CDMA) system supporting convergent variable rate video and data services is studied. An analytical approach for evaluating the system outage probability based on interference analysis is introduced. An optimization model to achieve maximum video and data throughput with QoS assurance and satisfactory outage probability is proposed. Numerical results demonstrate the effectiveness of the proposed approaches.

By introducing a mobility anchor point (MAP), Hierarchical Mobile IPv6 (HMIP6) reduces the signaling overhead and handoff latency associated with Mobile IPv6. However, if a mobile node (MN)'s session activity is high and its mobility is relatively low, HMIPv6 may degrade end-to-end data throughput due to the additional packet tunneling at the MAP. In this paper, we propose an adaptive route optimization (ARO) scheme to improve the throughput performance in HMIPv6 networks. Depending on the measured session-to-mobility ratio (SMR), ARO chooses one of the two different route optimization algorithms adaptively. Specifically, an MN informs a correspondent node (CN) of its on-link care-of address (LCoA) if the CN's SMR is greater than a predefined threshold. If the SMR is equal to or lower than the threshold, the CN is informed with the MN's regional CoA (RCoA). We analyze the performance of ARO in terms of balancing the signaling overhead reduction and the data throughput improvement. We also derive the optimal SMR threshold explicitly to achieve such a balance. Analytical and simulation results demonstrate that ARO is a viable scheme for deployment in HMIPv6 networks.

In this paper, we develop a novel analytical framework for modeling and quantifying the performance of window-controlled multimedia flows in a hybrid wireless/wired network. The framework captures the traffic characteristics of window-controlled flows and is applicable to various wireless links and packet transmission schemes. We show analytically the relationship between the sender window size, the wireless link throughput distribution, and the delay distribution. We then substantiate the analysis by demonstrating how to statistically bound the end-to-end delay of flows controlled by a TCP-like datagram congestion control protocol (DCCP) over an M-state Markovian wireless link. Simulation results validate the analysis and demonstrate the effectiveness and efficiency of the proposed delay control scheme. The scheme can also be applied to other window-based transport layer protocols

We are concerned with optimally grouping active mobile users in a two-user-based cooperative diversity system to maximize the cooperative diversity energy gain in a radio cell. The optimization problem is formulated as a non-bipartite weighted-matching problem in a static network setting. The weighted-matching problem can be solved using maximum weighted (MW) matching algorithm in polynomial time O(n3). To reduce the implementation and computational complexity, we develop a Worst-Link-First (WLF) matching algorithm, which gives the user with the worse channel condition and the higher energy consumption rate a higher priority to choose its partner. The computational complexity of the proposed WLF algorithm is O(n) while the achieved average energy gain is only slightly lower than that of the optimal maximum weighted- matching algorithm and similar to that of the 1/2-approximation Greedy matching algorithm (with computational complexity of O(n2log n)) for a static-user network. We further investigate the optimal matching problem in mobile networks. By intelligently applying user mobility information in the matching algorithm, high cooperative diversity energy gain with moderate overhead is possible. In mobile networks, the proposed WLF matching algorithm, being less complex than the MW and the Greedy matching algorithms, yields performance characteristics close to those of the MW matching algorithm and better than the Greedy matching algorithm.

A bandwidth and energy efficient cooperative diversity scheme based on quadrature signaling is proposed. The quadrature signaling is achieved by transmitting in the in-phase and quadrature components of QPSK modulation. The diversity gain and the bit error rate of the proposed cooperative diversity scheme improve with the inter-user channel quality. It is shown that the proposed scheme can achieve a diversity order of two for high inter-user signal-to-noise ratios, if the cooperating users are located within a region that permits successful cooperation. The cooperative region corresponding to a specified bit error rate is defined and derived

Mobile hotspot enabling Internet access services in moving vehicles is an important service for ubiquitous computing. In this paper, we propose an analytical framework for studying the packet loss behavior and throughput in a mobile hotspot with heterogeneous wireless links. We first develop a two-state Markov model for the integrated wireless wide area network (WWAN) and wireless local area network (WLAN). We then derive the expressions that describe the experienced packet loss probability, packet loss burst length, and throughput. Finally, we present simulation results to verify the accuracy of our analysis. It is concluded that adaptive and cross-layer approaches should be deployed to improve the performance of mobile hotspots.

In IEEE 802.11 WLANs, packet losses may be due to buffer overflow, transmission errors, or collisions. Therefore, the performance of TCP-Friendly Rate Control (TFRC) in IEEE 802.11 WLANs largely depends on its ability to differentiate packet losses resulting from network congestion (due to buffer overflow and collisions) and those from transmission errors. In this paper, an enhanced TFRC (E-TFRC) protocol is proposed to detect and identify the cause of packet loss events through a novel two-phase loss differentiation algorithm (TP-LDA). The packet losses due to buffer overflow and those due to failed transmissions in WLANs are first differentiated. For failed transmissions, the fraction of those due to collisions is obtained with the assistance of the lower layer. By employing TP-LDA, only the packet losses due to buffer overflow and collisions are notified to the sender for appropriate flow and congestion control. To quantify the performance of TFRC and E-TFRC over WLANs, a continuous-time Markov chain based on a new WLAN link model is developed by considering both collisions and transmission errors. Analytical and simulation results demonstrate that, with appropriate loss differentiation, E-TFRC can achieve higher throughput than TFRC in WLANs with different channel profiles.

An analytical framework for studying the performance of wireless profiled TCP (WP-TCP) flows over the integrated wireless LAN and cellular networks is proposed. The framework can be used to analyze the short-term performance during vertical handover and long-term performance of WP-TCP for a given set of network and protocol parameters. It captures the WP-TCP behavior under the influence of wireless channel errors, step change in network parameters and excessive packet losses due to vertical handovers. Extensive simulations are conducted to verify the accuracy of the analytical framework. The main findings in this study are: (1) when the network is subjected to hard handovers, increasing the maximum window size improves the efficiency in a high transmission error environment, but degrades the efficiency in a low transmission error environment; (2) increasing the congestion window reduces the chances of premature timeouts during soft upward vertical handover; and (3) depending on duplicate ACK threshold, increasing the congestion window can increase or reduce the chances of false fast retransmit during soft upward vertical handover.

The type of services and the manner with which multiple access is performed have a tremendous impact on the system capacity. The capacity region for video services Ui the uplink of a round-robin carrier-hopping multi-rate multi-carrier (MC) DS-CDMA cellular system is derived by formulating and analyzing the outage probabilities in terms of bit error rate specifications. The subcarriers of the MC-DS-CDMA system are dynamically allocated to evenly distribute their usage. Three management schemes are used to perform subcarrier allocation: complete sharing (CS), dynamic complete partitioning (DCP) and dynamic complete group partitioning (DCGP). The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. Numerical results show that the capacity of DCGP is larger than that of CS or DCP.

In this paper, adaptive transmission of scalable multi-layered video with quality of service (QoS) assurance over wireless channels is studied. By properly formulating the channel fading as a finite state Markov channel (FSMC) model, three rate adaptation schemes, namely, assured-rate-allocation, neighbor- interleaving, and swing-loaded schemes, are proposed to exploit the inherent multiplexing gain. An analytical model for QoS performance evaluation of video transmission over time-varying erroneous channels is derived. The accuracy of the analytical model is validated by simulations. Analytical and simulation results demonstrate that the proposed rate adaptation schemes can effectively improve the channel utilization and the system throughput.

Abstract The integration of wireless local area network (WLAN) hotspot and the 3G cellular networks is imminently the future mode of public access networks. One of the key elements for the successful integration is vertical handoff between the two heterogeneous networks. Service disruption may occur during the vertical handoff because of the IP layer handoff activities, such as registration, binding update, routing table update, etc. In this paper, the network interface switching and registration process are proposed for the integrated WLAN/cellular network. Two types of fast vertical handoff protocols based on bicasting and non‐bicasting supporting real‐time traffic, such as voice over IP, are modeled. The performance of a bicasting based handoff scheme is analyzed and compared with that of fast handoff without bicasting. Numerical results and the simulation are given to show that packet loss rate can be reduced by the bicasting during handoff scheme without increasing bandwidth on both wireless interfaces. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract In this paper, a self‐organizing map (SOM) scheme for mobile location estimation in a direct‐sequence code division multiple access (DS‐CDMA) system is proposed. As a feedforward neural network with unsupervised or supervised and competitive learning algorithm, the proposed scheme generates a number of virtual neurons over the area covered by the corresponding base stations (BSs) and performs non‐linear mapping between the measured pilot signal strengths from nearby BSs and the user's location. After the training is finished, the location estimation procedure searches for the virtual sensor which has the minimum distance in the signal space with the estimated mobile user. Analytical results on accuracy and measurement reliability show that the proposed scheme has the advantages of robustness and scalability, and is easy for training and implementation. In addition, the scheme exhibits superior performance in the non‐line‐of‐sight (NLOS) situation. Numerical results under various terrestrial environments are presented to demonstrate the feasibility of the proposed SOM scheme. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, a resource allocation scheme is proposed for wireless relay networks to achieve maximum system throughput in terms of achievable average mutual information with low computational complexity. A relay network, which has single source node, multiple relay nodes and single destination node, is analyzed from the information theory point of view. Both sufficient and necessary conditions are derived for the best relay node selection, and a close-form of optimal power allocation between the source and the relay nodes is obtained. Application of the proposed resource allocation schemes in practical relay networks with incomplete channel state information is also studied. Simulation results are presented to demonstrate the effectiveness of the proposed resource allocation schemes in wireless relay networks.

In this paper, an adaptive regenerate and forward cooperative diversity (CD) system based on quadrature signaling is proposed. The bit error probability (BEP) of the proposed CD system is derived in terms of the received signal-to-noise ratio (SNR) at the relay and the destination. The derived upper bound of the BEP is validated by simulations. Further, it is shown that the proposed CD system can achieve maximum diversity order of two and performs better even though the inter-user channel is poor. The power consumption of the CD system is location dependent for given BEP. To optimize the power consumption of the proposed CD system, an optimal power allocation strategy is proposed.

Mobile hotspot enabling Internet access services in moving vehicles is an important service for ubiquitous computing. In this paper, we propose an analytical framework for studying the packet loss rate and throughput in a mobile hotspot with heterogeneous wireless links. We present simulation results to verify the accuracy of our analysis. It is concluded that adaptive and cross-layer approaches should be deployed to improve the performance of mobile hotspots.

In this paper, second order statistical parameters at the maximum ratio combining output of two independent but not necessarily identically distributed Nakagami-m channels are studied. Specifically, generalized expressions of level crossing rate and average fade duration of the combined received envelope are derived. Sample simulation results are presented to verify the correctness of the derived expressions. In addition, numerical results given to demonstrate the behavior of the combined received envelope.

An analytical framework for studying the efficiency and throughput of WAP 2.0 Wireless Profiled TCP (WP-TCP) flows in an heterogeneous wireless environment is proposed. Explicit mathematical expressions that describe the WP-TCP long-run average efficiency and throughput are derived. Simulations are performed to validate the accuracy of the analytical results. It is shown that increasing the maximum window size improves the efficiency and throughput in high transmission error environment, but degrades the efficiency in low transmission error environment.

In this paper, efficient rate adaptation schemes for scalable multi-layered video transmission over wireless links with quality of service (QoS) assurance are proposed. An analytical model for QoS performance evaluation on video transmission over time-varying erroneous channels is derived. The accuracy of the analytical model is validated by simulations. Analytical and simulation results show that the proposed rate adaptation schemes can effectively improve the channel utilization and the system throughput.

We analyze the capacity of UWB networks supporting multimedia services by calculating the number of multimedia connections that can be supported in a UWB network based on IEEE 802.15.3 Medium Access Control (MAC) protocol, taking into consideration the overheads from different layers. We then propose how to increase the capacity by improving the MAC protocol design. To fully explore the potential of UWB technologies which favor concurrent transmissions if the interference is appropriately controlled, we study the capacity of cellular-like UWB networks. Our findings, which should provide important guidelines for UWB network planning, are a) the inter-cell interference of UWB networks is closely related to the Riemann Zeta function, and to guarantee the bounded inter-cell interference of UWB networks, the path loss exponent α must be larger than 2; b) the total throughput in an area is a concave function of the cell size; c) the best distance between adjacent cells is a function of path loss exponent, background noise level, and cross-correlation of the target signal and the interfering signal; and d) with the optimal cell size, a single flow's throughput is reduced by 2/α due to inter-cell interference. Simulation results are given to demonstrate the accuracy of the analysis.

The two-state Markov chain has been widely used to model fading channels in the performance study of upper-layer communication protocols in wireless networks. It can be used to model transmission success/failure based on the physical characteristics of the transmission channel. However, for shared wireless links, packet transmission depends on both the status of the link and the scheduling strategy used. In this poster, we propose a novel four-state Markov model, which takes into consideration the impacts of channel fading and scheduling on packet transmission over shared wireless links. It is further abstracted to an effective two-state Markov chain to facilitate analytical performance evaluation. To demonstrate the efficacy of the proposed model, we apply it to study the throughput, delay and delay jitter of a saturated traffic source, and the packet dropping probability at the network layer for data traffic under a buffer overflow dropping policy. Simulation results to demonstrate the reasonableness of the proposed model are also presented. © 2006 ACM.

The capacity of a multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system with Rake receivers and Gaussian monocycles supporting variable bit rate (VBR) multiclass services is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. The indoor channel model used is based on IEEE 802.15.3a. The analytical work leads to the determination of the system capacity of an MTH binary PPM UWB system with VBR traffic in an indoor multipath environment. Numerical results of the system capacity region are also presented.

A two-level fractional guard channels (TLFGC) scheme to efficiently provide priority access for handoff calls over new calls in cellular systems is proposed. The switching between the levels is controlled by a dropped call. The first level has a small number of guard channels like the fixed guard channel (FGC) scheme, while the second level has a larger number of guard channels and a smaller number of fractional guard channels. An analytical formulation of the steady state probabilities, new call blocking probability, handoff call blocking probability, system utilization, probabilities in each level and the equivalent number of guard channels is presented. Numerical results show that the performance of TLFGC is almost the same as a fixed guard channels (FGC) scheme under light load. However, the advantage of the TLFGC scheme is demonstrated under heavy load where the handoff call blocking probability is much better than that of a FGC scheme, giving more priority and protection to handoff calls over new calls.

We study how to optimally group active users in an infrastructure-based wireless network employing two-user- based cooperative diversity technology in order to maximize the cooperative diversity gain in the network. The optimization problem is formulated as a non-bipartite weighted-matching problem, which can be solved with the state-of-the-art maximum weighted-matching algorithm in polynomial time O(n 3 ) .T o reduce the computational complexity, we develop a Worst-Link- First (WLF) matching algorithm, which gives the user with the worse channel condition and the higher energy consumption rate a higher priority to choose its partner. The computational complexity of the proposed WLF algorithm is O(n 2 ) while the achieved average energy gain is only slightly lower than that with the optimal maximum weighted-matching algorithm. Numerical results demonstrate that, with the WLF matching algorithm, 5 ∼ 7 dB energy gain can be achieved.

We propose a TCP-friendly Additive Increase and Multiplicative Decrease (AIMD) based Datagram Congestion Control Protocol (DCCP) protocol for supporting multimedia traffic in hybrid wireless/wired networks. We further demonstrate how to select the protocol parameters to fairly and efficiently utilize network resources with the consideration of quality of service (QoS) requirements. Since the parameter selection procedure requires only the exchange of parameters among the application, the transport layer protocol, and the link layer protocol, our approach preserves the end-to-end semantics of the transport layer protocol and the layered structure of the Internet. Extensive simulations are performed to evaluate the proposed protocol. It is shown that the AIMD protocol can appropriately regulate multimedia traffic to efficiently utilize the wireless link and fairly share the network resources with coexisting TCP flows, and it can provide satisfactory QoS for delay-sensitive multimedia applications. In addition, AIMD protocol can outperform the non-responsive User Datagram Protocol (UDP) when transporting multimedia traffic over hybrid wireless/wired networks. With satisfactory QoS provisioning, end-systems have more incentives to voluntarily regulate multimedia traffic with an AIMD-based congestion controller, which is vital for network stability, integrity, and future proliferation.

In this paper, the utilization of real-time video service in the downlink of an orthogonal variable spreading factor code division multiple access (OVSF-CDMA) system is studied. By modeling the video traffic and wireless channel as a joint Markov modulated process, and properly partitioning the states of the Markov process, an adaptive rate allocation scheme is proposed for real-time video transmission with quality of service provisioning while achieving high channel utilization. The scheme is applicable for packet switching and frame-by-frame real-time video transmission, and incorporates both the physical layer and network layer characteristics. For QoS provisions, the closed form expressions of packet delay and loss probability are derived based on the Markov model. Analytical and simulation results demonstrate that the proposed scheme can significantly improve the channel utilization over the commonly used effective bandwidth approach.

A unified approach for power distribution and allocation in a multirate wideband CDMA system is investigated. It is shown that the traffic demand and the background disturbance fully govern the feasibility of the system and the optimal power distribution solutions, where the traffic demand is specified by the user QoS requirement, data rate, and spread spectrum bandwidth; the background disturbance includes the background noise and the intercell interference. Closed form expressions of the optimal power allocation, subject to power constraints in the practical system design, are derived. Convergent conditions are applied to evaluate the capacity region of the system. Numerical examples are provided to illustrate the applications of the obtained theoretical results.

A two-phase soft handoff scheme, which includes an initial power allocation phase followed by a power redistribution phase, is proposed. The initial power allocation phase makes a handoff decision for each connection by assigning a connection to the BS with the best link quality and allocating a minimum amount of power from the BS for the connection. The initial handoff decisions are made for individual connections independent of other connections or the BS power availability. Therefore, there might be heavily loaded and lightly loaded BSs because (i) traffic load may not be equally distributed in all cells, and (ii) the channel condition of the connections is random. The power re-distribution phase is to smooth out the loading on the system by coordinating the power allocations among neighboring BSs so that more connections can receive reliable transmissions. We then develop an analytical model for studying the connection reliability with the proposed soft handoff scheme. Our results show that the proposed two-phase soft handoff scheme can significantly improve connection reliability and increase system capacity in downlink transmissions.

A two-phase power distribution scheme for supporting quality-of-service (QoS) and best effort traffic is proposed. We first formulate the power distribution for QoS traffic as an optimization problem so that the number of simultaneously transmitting connections is maximized. Optimum power distribution is difficult to implement in practice due to both the computational complexity and the requirement for global information about the mobile station (MS) locations, connection channel conditions, and traffic load in the system. We then propose a heuristic scheme of power distribution for soft handoff (SHO) connections. The full scheme includes an initial power distribution (IPD) and a power distribution adjustment (PDA). IPD allocates BS power resource based on the channel condition of each individual connection, while PDA further coordinates the power distribution between neighboring base stations (BSs) in order to accommodate more connections. The proposed power distribution scheme can achieve a capacity close to that of the optimum power distribution, while providing much higher transmission throughput for best effort data traffic. The proposed power distribution scheme can be applied to existing SHO schemes for efficient BS power resource usage. The scheme does not require global information, and its implementation can be further simplified by performing IPD only with slight performance degradation.

An analytical model for studying the performance of the delayed acknowledgement (Dly-ACK) mechanism in IEEE 802.15.3 over a fading channel is developed. A three-state Markov channel model is used to approximate both correlated and uncorrelated error processes. Explicit mathematical expressions for the goodput and efficiency of Dly-ACK are derived. It is found that the Dly-ACK mechanism yields higher goodput in a burst error environment than in a random error environment. The goodput tends to increase as the size of the burst increases; however, the amount of increase depends on the underlying delay. Simulations results are given to validate the analytical results.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-code direct-sequence ultra-wideband (DS-UWB) system is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple spreading codes are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active spreading codes from the interfering users on one pulse are explicitly derived. The analytical work leads to the determination of the capacity region of a multi-code DS-UWB system supporting VBR services. Numerical results of the capacity region are also presented.

A TCP-friendly additive increase and multiplicative decrease (AIMD) protocol is proposed to support time-sensitive applications in hybrid wired/wireless networks. By analyzing the performance of AIMD-controlled flows in hybrid networks, we propose a cross-layer procedure to select the AIMD protocol parameters with consideration of wireless link characteristics and application QoS requirements, in terms of delay, loss, and throughput. Since the cross-layer interaction only exchanges parameters among the application, the transport layer protocol, and the link layer protocol, our approach preserves the end-to-end semantics of the transport protocol and the layered structure of the Internet, and it is applicable to supporting various multimedia applications over heterogeneous wireless links. With appropriate parameters, AIMD-controlled flows can fairly share network resources with TCP flows, efficiently utilize wireless resources, and statistically guarantee end-to-end delay for time-sensitive applications. Extensive simulations are performed to validate the analytical results, evaluate the protocol performance, and demonstrate that the AIMD protocol can outperform the unresponsive UDP protocol when transporting multimedia traffic in hybrid networks. With satisfactory QoS, end systems have more incentives to voluntarily regulate multimedia traffic with an AIMD-based congestion controller, which is vital for network stability, integrity, and future proliferation.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-code direct-sequence ultra-wideband (DS-UWB) system with Rayleigh monocycles is derived via an outage probability analysis. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple spreading codes are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active spreading codes from the interfering users on one pulse are explicitly derived for Rayleigh monocycles. The analytical work leads to the determination of the capacity region of a multi-code DS-UWB system supporting VBR services. Numerical results of the capacity region are also presented.

This paper proposes a practical joint power allocation and scheduling scheme for medium access control (MAC) layer design in ultra-wideband (UWB) networks. The scheme increases system spectral efficiency and reduces power consumption by fully considering the properties of the UWB, such as its capacity in supporting parallel transmission and providing accurate positioning, and its stringent constraint on computational complexity. Practical implementations of the proposed scheme are achieved by introducing a margin based power allocation scheme and an exclusive region based scheduling scheme. The margin based power allocation scheme is carried out based on each link's own information, and is simple to implement, while the exclusive region based scheduling scheme takes into account the interaction among different links. Simulation results show that the proposed power allocation and scheduling schemes exhibit good performance in terms of the average number of slots per frame and the power consumption reduction.

We evaluate the performance of voice transmission over a single-AP WLAN analytically and via simulation. Given the parameters of the medium access control protocol and different voice codecs, the voice capacity of the WLAN, in terms of the maximum number of voice connections that can be supported by the WLAN with satisfactory user-perceived quality, is obtained. Our analysis is applicable for unsaturated-station scenarios, and considers the practical issue induced by the unbalanced traffic. Extensive simulations have been performed to validate the analytical results.

Summary form only given. Over the ages, research in wireless communications has been evolving through a quest for answers to the fundamental questions: why, what and how? Why do people, separated by physical distances, cannot hear each other talking? Alexander Graham Bell's invention of the telephone was driven by this curiosity; so was Guglielmo Marconi's telegraphic signalling across the Atlantic Ocean in 1901. Societal evolution has also been driven by curiosity, especially in the pursuit for quality of life (QoL). The quest for QoL invariably creates conflicts, since greediness is a human trait (or perhaps fraud). Conflicts lead to warring among humans, and the need to observe the battle front in Europe during World War II was the pedal-stone on which research in wireless technology escalated. Through the cold war and subsequent relatively peaceful periods, wireless communications research continues to flourish. QoL becomes synonymous with wealth and health creation. With the ability to provide information in large volume and high-speed to enrich wealth creation, telecommunications research becomes the front banner in societal evolution. Quality of service (QoS) provided by an effective and efficient information transport platform becomes synonymous with QoL. To achieve global communications, it is necessary to interwork different domains of telecommunications. Interworking of different domains, however, has profound ramifications on the formulation of the building blocks and the glues needed to construct an information transport platform, and interdependency issues amongst the different layers of the information transport platform. This talk will provide an exposition and a critical look at future evolution of wireless communications and networking, beginning with a brief historical perspective of wireless technology, a critical look at the obstacles posed by nature, and then an examination of the building blocks and the glues necessary for the construction of the information transfer vehicle capable of delivering large volume of information at high-speed, and with end-to-end QoS satisfaction

In this paper, a bandwidth efficient and energy efficient cooperative diversity scheme is proposed based on orthogonal signaling. Orthogonal signaling is achieved by transmitting in the in-phase and quadrature components of a phase shift keying modulation system. The bit error rate performance of the proposed cooperative diversity scheme increases with interuser signal strength. Numerical results show that the proposed cooperative diversity scheme can achieve the diversity order of two for high interuser signal-to-noise ratio.

An analytical framework for studying the latency of wireless application protocol (WAP 2.0) over wireless links for short transfers is developed. In particular, a Markov channel model, which approximates both correlated and independent packet losses, is introduced. For a given wireless link and protocol parameters, an explicit mathematical expression, which represents a reasonable estimate of the minimum WAP 2.0 latency in terms of file transfer time, is derived. Simulation results are given to demonstrate the validity of analytical results. It is shown that for large file sizes (>20 KB), WAP 2.0 is more sensitive to bursty packet losses than random packet losses. It is also shown that the latency of WAP 2.0 can be improved by increasing the size of the initial window in a low rate bursty error environment, but degrades in a high rate bursty error environment.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple time hopping sequences are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active time hopping sequences from the interfering users on one pulse are explicitly derived. The analytical work leads to the determination of the capacity region of an MTH binary PPM UWB system with VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

The paper studies downlink channel utilization for real-time video traffic transmission in an orthogonal variable spreading factor code division multiple access (OVSF-CDMA) system. By modeling video traffic as a Markov modulated process and properly partitioning the states of the Markov process, an adaptive rate allocation scheme is proposed for real-time video transmission with quality of service (QoS) satisfaction while achieving high channel utilization. The scheme is applicable for packet switching and frame-by-frame real-time video transmission, and incorporates both physical layer and network layer characteristics. The QoS requirements include stringent packet delay and packet loss rate. Analytical and simulation results demonstrate that the proposed scheme can significantly improve the channel utilization over the commonly used effective bandwidth approach.

Power control and rate allocation are two radio resource management functions that can be used to enhance system utilization. In a time-varying environment, these functions need to be made adaptive. We consider certain implementation restrictions which cause deviations from ideal conditions in adaptive processing. An integrated power control and rate allocation approach to enhance system throughput is proposed. Simulation results show that by using closed-loop power control in conjunction with rate allocation in the presence of the Doppler effect and delay in feeding back channel state information (CSI), significant throughput and BER performance improvement over rate adaptation alone is obtained.

A dynamic fair resource allocation scheme is proposed to efficiently support real-time and non-real-time multimedia traffic with guaranteed statistical quality of service (QoS) in the uplink of a wideband code-division multiple access (CDMA) cellular network. The scheme uses the generalized processor sharing (GPS) fair service discipline to allocate uplink channel-resources, taking into account the characteristics of channel fading and intercell interference. In specific, the resource allocated to each traffic flow is proportional to an assigned weighting factor. For real-time traffic, the assigned weighting factor is a constant in order to guarantee the traffic statistical delay bound requirement; for non-real-time traffic, the assigned weighting factor can be adjusted dynamically according to fading, channel states and the traffic statistical fairness bound requirement. Compared with the conventional static-weight scheme, the proposed dynamic-weight scheme achieves capacity gain. A flexible trade-off between the GPS fairness and efficient resource utilization can also be achieved. Analysis and simulation results demonstrate that the proposed scheme enhances radio resource utilization and guarantees statistical QoS under different fairness bound requirements.

In this paper, a novel call admission control (CAC) scheme using fuzzy logic is proposed for the reverse link transmission in wideband code division multiple access (CDMA) cellular communications. The fuzzy CAC scheme first estimates the effective bandwidths of the call request from a mobile station (MS) and its mobility information, then makes a decision to accept or reject the connection request based on the estimation and system resource availability. Numerical results are given to demonstrate the effectiveness of the proposed fuzzy CAC scheme in terms of new call blocking probability/handoff call dropping probability, outage probability, and resource utilization.

In this paper, the performance of TCP-friendly generic AIMD (Additive Increase and Multiplicative Decrease) algorithms for Web-based playback and multirate multimedia applications is investigated. The necessary and sufficient TCP-friendly condition is derived, and the effectiveness and responsiveness of AIMD are studied. Due to practical implications, a Dynamic TCP-friendly AIMD (DTAIMD) algorithm is proposed. Extensive simulation results are given to verify the derived necessary and sufficient condition, and to demonstrate the performance of the proposed DTAIMD algorithm.

In this paper, an optimal downlink resource management scheme for heterogeneous packet transmission in orthogonal frequency-division multiplexing (OFDM) wireless communication systems is proposed. By making use of the channel impulse response and the properties of the OFDM physical layer, a resource management scheme is developed by integrating power distribution, subcarrier allocation, and the generalized processor sharing (GPS) scheduling. The scheme can: 1) maximize system throughput; 2) guarantee the required signal-to-noise ratio for heterogeneous traffic; 3) provide fairness to all the traffic admitted in the system; and 4) satisfy the total transmission power constraint. For practical implementation, a simplified power and subcarrier allocation algorithm, a robust H/sub /spl infin// channel estimation algorithm, and a truncated GPS (TGPS) scheduling scheme are introduced. Simulation results show that the proposed resource management scheme exhibits good throughput performance.

A self-organizing map (SOM) scheme for mobile location estimation in a direct-sequence code division multiple access (DS-CDMA) system is proposed. The scheme performs nonlinear mapping between the measured pilot signal strengths from nearby base stations and the user's location. It is shown that the proposed scheme has the advantage of robustness and scalability, and is easy in training and implementation. In addition, the scheme exhibits superior performance in the non-line-of-sight (NLOS) situation. Numerical results under various terrestrial environments are presented to demonstrate the feasibility of the proposed SOM scheme.

An adaptive handoff priority scheme is proposed for a packet switching multicode (MC)-CDMA cellular network supporting multimedia applications. The scheme jointly considers the physical, link and network layer characteristics, and gives service priority to handoff calls by exploiting the transmission rate adaptability of multimedia services over the available radio resources. Based on the proposed scheme, an admission region is derived for call admission control (CAC) and handoff management with quality of service (QoS) satisfaction for all multimedia traffic, where the QoS parameters include the wireless transmission bit error rate (BER), packet loss rate (PLR) and delay requirement. Simulation results substantiate the viability of the proposed scheme.

Analytical formulations of the outage probability in terms of bit error rate specification using Chernoff bound and central limit Gaussian approximation for variable bit rate (VBR) multiclass services in the downlink of a round-robin carrier-hopping multirate multicarrier (MC) DS-CDMA cellular system is presented The analytical framework is formulated for the general case in which different traffic classes have different data rates in each of the subcarriers. The analytical work leads to the determination of the capacity region of the downlink in a round-robin carrier-hopping multirate MC-DS-CDMA system for VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

Analytical formulations of the outage probability in terms of bit error rate specification using Chernoff bound and central limit Gaussian approximation for variable bit rate (VBR) multiclass services in the downlink of a dynamic complete partitioning (DCP) round-robin carrier-hopping multirate multi-carrier (MC) DS-CDMA cellular system is presented. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. The analytical work leads to the determination of the capacity region of a dynamic complete partitioning round-robin carrier-hopping multirate MC-DS-CDMA system for VBR traffic. Numerical results show that the system capacity with DCP can be larger than that with complete sharing (CS) of the subcarriers.

In this paper, a downlink resource management scheme with adaptive modulation and dynamic generalized processor sharing (DGPS) scheduling is proposed for orthogonal frequency-division multiplexing (OFDM) wireless communication systems. By making use of the frequency diversity among the subcarriers allocated to the same user and the inherent delay tolerance of the nonreal-time traffic, the proposed scheme can achieve maximum system throughput while guaranteeing the required symbol-error-rate (SER), providing fairness to all multimedia traffic, and satisfying the total transmission power constraint. Simulation results show that the proposed resource management scheme exhibits desirable performance.

An analytical formulation of the outage probability in terms of bit error rate specification for video services in the uplink of a round-robin carrier-hopping multirate multi-carrier (MC) DS-CDMA cellular system is presented. The video model used in this paper accounts for scene changes. In the model, each video source is modeled by a two-dimensional Markov chain. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. The analytical work leads to the determination of the capacity region of the uplink in a round-robin carrier-hopping multirate MC-DS-CDMA system for video traffic that accounts for slow and fast motions, numerical results of the capacity region corresponding to typical parameter values are also presented.

A dynamic fair resource allocation scheme to efficiently support realtime and nonrealtime multimedia traffic with guaranteed statistical QoS in uplinks of wideband CDMA cellular networks is proposed. The scheme uses the generalized processor sharing (GPS) fair service discipline to allocate uplink channel resources, taking into account the characteristics of channel fading and inter-cell interference. For realtime traffic, the weight of each user is assigned according to a required delay bound. For nonrealtime traffic, the weight of each traffic flow is adjusted dynamically according to fading channel states and a statistical fairness bound requirement. The capacity gain achieved by the proposed dynamic-weight scheme is analyzed for different fairness bound requirements. Simulation results are presented to demonstrate the performance of the proposed dynamic-weight scheduling scheme in terms of radio resource utilization and guaranteed statistical QoS, in comparison with the conventional static-weight scheme.

The variability of the wireless channel requires adaptive techniques for efficient, radio resource service The throughput gains for ideal rate adaptation over nonadaptation in a wideband CDMA communication system is analyzed. The result is obtained by using the derived probability density functions of service ratio. We further investigate how performance degrades with adaptation restrictions, which include adaptation interval, Doppler effect, delays associated with channel state information feedback, and finite number of spreading factors. Our results show that rate adaptation with restrictions does not always bring gains over nonadaptation.

Power distribution for a multirate wideband CDMA system is investigated. The target power vector is expressed in terms of the spread bandwidth, user data rates, and user QoS specifications. The power distribution problem is solved via a decomposition of the traffic demand matrix, subject to a power constraint. Based on the power distribution law and the corresponding convergence conditions, simple yet efficient strategies for call admission and capacity evaluation are proposed.

Based on the zero crossing rate of the slope (first derivative) of the underlying fading process, a mobile speed-estimation scheme, constructed by counting the average number of sampling steps in a positive-going (and/or negative-going) fade envelope slope, is proposed. The proposed speed-estimation approach requires neither knowledge of the average fade power nor a variable temporal observation window. The computational complexity and the required memory storage are negligibly small. Simulation results show that the proposed speed estimator yields good estimation accuracy, with relatively small estimation error.

The use of rate-compatible punctured turbo and rate-compatible punctured convolutional (RCPT/RCPC) codes as channel codes in a direct-sequence code-division multiple-access system where the system bandwidth expansion is fixed is investigated. The best RCPC and RCPT code rate in terms of maximizing the system spectral efficiency and minimizing the optimal power allocation where the receiver is either a matched filter (MF) or a minimum mean-square error (MMSE) device is assessed. It is shown that for the MF receiver, the coding-spreading tradeoff favors a code-rate reduction. In the case of the MMSE receiver, when the E/sub b//N/sub 0/ value and the system load are increased, the best code rate also increases. By examining the slope of the performance curves, it is deduced that, under similar operating conditions, the best code rate of the RCPT codes is lower than that of the RCPC codes. Also, the best code rate for a Rayleigh fading channel is lower than that for an additive white Gaussian noise channel.

In this paper, the joint time-frequency domain channel estimation problem in orthogonal frequency-division multiplexing (OFDM) wireless communication systems is transformed to a set of independent time-domain estimation problems. A robust channel estimation algorithm based on the H/sub /spl infin// filtering approach is proposed to estimate the channel fading in the time domain. The estimation criterion is to minimize the worst possible amplification of the estimation errors in terms of the exogenous input disturbances such as multiplicative and additive noise. The criterion is different from the traditional minimum estimation error variance criterion for the Kalman estimation algorithm, and requires no a priori knowledge of the disturbance statistics. It is shown that the proposed channel estimation algorithm is more robust compared with the Kalman estimation counterpart in terms of model uncertainty, and is more suitable to practical OFDM wireless communication systems.

A class of dynamic fair scheduling schemes based on the generalized processor sharing (GPS) fair service discipline, under the generic name code-division GPS (CDGPS), is proposed for a wideband direct-sequence code-division multiple-access (CDMA) cellular network to support multimedia traffic. The CDGPS scheduler makes use of both the traffic characteristics in the link layer and the adaptivity of the wideband CDMA physical layer to perform fair scheduling on a time-slot by time-slot basis, by using a dynamic rate-scheduling approach rather than the conventional time-scheduling approach. Soft uplink capacity is characterized for designing an efficient CDGPS resource allocation procedure. A credit-based CDGPS (C-CDGPS) scheme is proposed to further improve the utilization of the soft capacity by trading off the short-term fairness. Theoretical analysis shows that, with the C-CDGPS scheme, tight delay bounds can be provided to delay-sensitive traffic, and short-term unfairness can be bounded so that long-term weighted fairness for all users can still be satisfied. Simulation results show that bounded delays, increased throughput, and long-term fairness can be achieved for both homogeneous and heterogeneous traffic.

A closed-loop power control strategy, which includes both power control and power allocation functions, for a code-division multiple-access system is proposed. The target power level for a minimum mean squared error (MMSE) or a matched filter (MF) linear receiver is iteratively computed, and the power control command (PCC) is generated by comparing the received power with the generated target power. The PCC history and the channel fade slope information, which contains the Doppler effect, are used to generate variable stepsizes for regulating the transmit power level. Closed-loop power control is based on a criterion that minimizes the average transmit power and the standard deviation of the received power/signal-to-interference ratio. The power control strategy also tends to reduce the bit error rate. Simulation results demonstrate the effectiveness of the proposed power control algorithm. The results also indicate that the tracking ability of the MMSE and MF receiver is essentially similar, except that the average transmit power is lower with the MMSE receiver but is more complex to implement.

In this paper, downlink resource management scheme is proposed for heterogeneous packet transmission in orthogonal frequency-division multiplexing (OFDM) wireless communication systems. By making use of the properties in the physical layer of the OFDM system, the resource management scheme is developed by integrating power allocation, subcarrier allocation, and generalized processor sharing (GPS) scheduling. With the scheme, maximum system throughput can be achieved, while guaranteeing the required signal-to-noise ratio (SNR) for heterogeneous traffic, providing fairness to all the traffic in the system, and satisfying the total transmission power constraint. For practical implementation, a truncated GPS (TGPS) scheduling and a simplified power and subcarrier allocation algorithm are introduced. Simulation results are given to demonstrate the performance of the proposed resource management scheme.

End-to-end delay and delay jitter are critical QoS (quality of service) parameters for time sensitive applications. In wireless/IP hybrid networks, the wireless link is presumably the bottleneck. Because of the time-varying and error prone channel, the wireless channel throughput is random. On the other hand, with closed-loop AIMD (additive increase and multiplicative decrease) congestion control, the arrival process to a queue is not on-off. In this paper, given the measured channel profile and the transmission scheme used in the link layer, the wireless channel throughput distribution is derived. By analyzing the queue in the wireless domain with an AIMD controlled flow, the queuing delay distribution is derived. It is found that by appropriately setting the protocol parameters for TCP-friendly AIMD flows, the wireless spectrum can be efficiently utilized, and the QoS requirements of time sensitive applications can be statistically guaranteed.

To guarantee network stability while supporting multimedia applications over the Internet, a new dynamically adjusted TCP-friendly additive increase and multiplicative decrease (AIMD) congestion control algorithm, DTAIMD, is proposed. By studying the competition behavior of TCP and AIMD flows, the TCP-friendly condition for the AIMD (/spl alpha/, /spl beta/) congestion control is analytically derived. Quality of service (QoS) for multimedia playback applications is enhanced by choosing an appropriate parameter pair of (/spl alpha/, /spl beta/). Simulation results show that the proposed DTAIMD congestion control scheme is TCP-friendly and suitable for supporting multimedia playback applications.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in the uplink of a wideband CDMA-based cellular system is presented. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains. The analytical work leads to the determination of the capacity region of a wideband CDMA system with VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

In this paper, an expectation and maximization (EM) channel estimation algorithm is proposed for orthogonal frequency-division multiplexing (OFDM) wireless communication systems. The algorithm provides minimum mean square error channel fading estimates without requiring a priori knowledge of the channel fading statistics. Simulation results show that the proposed EM channel estimation algorithm without information on channel fading statistics can provide nearly the same performance as the Kalman estimation algorithm with perfect information on channel fading statistics, and is more suitable for practical OFDM wireless communication systems.

An asynchronous multicode multicarrier code-division multiple-access (CDMA) scheme for the uplink of wireless communication systems is considered in order to support multimedia services. The uncoded bit error rate of the system is analyzed after taking account of the intercarrier interference due to time-varying fading channels, inter-code interference due to the multicode assignment, and multiple access interference. Numerical results indicate that the system performance is improved with increasing the number of parallel data substreams and the processing gain. The two parameters have to be sufficiently large for supporting multimedia services.

An analytical formulation of the outage probability in terms of bit error rate specification for video services in the uplink of a multirate DS-CDMA-based cellular system is presented. The video model used in this paper accounts for scene changes. In the model, each video source is modeled by a two-dimensional Markov chain. The analytical framework is formulated for the general case in which different traffic classes have different low- and/or high-bit-rate spreading gains. Furthermore, each class has a combination of low- and high-bit-rate spreading codes for each user. The analytical work leads to the determination of the capacity region of a multirate DS-CDMA system with video traffic that accounts for slow and fast motions.

Soft handoff and call admission control (CAC) in a packet switching CDMA wireless cellular system are studied. A normal cell area is divided into an inner cell area and a handoff area, based on which a cell capacity vector and a call admission region are derived for uplink transmission to satisfy user quality of service (QoS) requirements and to minimize the grade of service (GoS) function. The QoS parameters under consideration arc the transmission bit error rate (BER) and packet loss rate (PLR). The BER requirement is guaranteed by properly arranging simultaneous packet transmissions, whereas the PLR requirement is satisfied by proper packet scheduling for calls in the inner cell and handoff areas. The GoS function is minimized by considering both new call blocking and handoff call dropping probabilities. By taking traffic characteristics and dynamic scheduling of nonhandoff and handoff calls into account, the proposed packet scheduling scheme achieves fair packet transmissions and greatly enlarges the call admission region.

A light weight authentication scheme is proposed to accommodate the secure authentication requirement for wireless Internet applications. The scheme can adapt to various authentication scenarios in mobile wireless Internet applications and provide secure and private communication sessions from other parties, including foreign networks. It is applied at the application layer as an add-on module, and virtually requires no modifications to the current Internet applications.

A novel call admission control (CAC) scheme using fuzzy interference for a wideband code division multiple access (CDMA) cellular system is proposed. The fuzzy CAC first estimates the newly arriving mobile station's (MS) effective bandwidth and its mobility information, and then makes a decision to accept or reject the MS's connection request based on the estimates and the system status. Numerical results are given to demonstrate the performance of the proposed fuzzy CAC scheme in terms of new call blocking probability, handoff call dropping probability, outage probability and resource utilization.

A novel resource reservation scheme for handoff priority in code division multiple access (CDMA) wireless cellular networks is proposed. The reservation scheme is derived by minimizing a grade of service (GoS) objective function which adjoins new call blocking probability and handoff call dropping probability through an arbitrary multiplier. The system capacity is optimized by minimizing the GoS function and jointly taking call level GoS and packet level quality of service (QoS) into consideration. The resultant reservation scheme is implemented adaptively using user mobility information and variation in traffic load. Numerical results show that, with the satisfaction of new call blocking probability and GoS performance, cell capacity and cell utilization are significantly improved relative to a resource reservation scheme in which only the call level characteristics are taken in to account.

An approximate analytical formulation of the resource allocation problem for handling variable bit rate multiclass services in a cellular direct sequence code-division multiple-access (DS-CDMA) system is presented. The novelty in this paper is that all grade-of-service (GoS) or quality-of-service (QoS) requirements at the connection level, packet level, and link layer are satisfied simultaneously, instead of being satisfied at the connection level or at the link layer only. The analytical formulation shows how the GoS/QoS in the different layers are intertwined across the layers. A complete sharing (CS) scheme with guard channels is used for the resource sharing policy at the connection level. The CS model is solved using a K-dimensional Markov chain. Numerical results illustrate that significant gain in system utilization is achieved through the joint coupling of connection/packet levels and link layer. This can translate to more revenues for network providers and/or lower charges for mobile users.

A novel radio resource management (RRM) scheme for the support of packet-switched transmission in cellular CDMA systems is proposed by jointly considering the physical, link, and network layer characteristics. The proposed resource management scheme is comprised of a combination of power distribution, rate allocation, service scheduling, and connection admission control. Power distribution allows individual connections to achieve their required signal-to-interference-plus-noise ratio, while rate allocation guarantees the required delay/jitter for real-time traffic and the minimum transmission rate requirement for non-real-time traffic. Efficient rate allocation is achieved by making use of the randomness and burstiness; of the packet generation process. At the link layer, a packet scheduling scheme is developed based on information derived from power distribution and rate allocation to achieve quality of service (QoS) guarantee. Packet scheduling efficiently utilizes the system resources in every time slot and improves the packet throughput for non-real-time traffic. At the network layer, a connection admission control (CAC) scheme based on the lower layer resource allocation information is proposed. The CAC scheme makes use of user mobility information to reduce handoff connection dropping probability (HCDP). Theoretical analysis of the grade of service performance, in terms of new connection blocking probability, HCDP, and resource utilization, is given. Numerical results show that the proposed RRM scheme can achieve both effective QoS guarantee and efficient resource utilization.

A novel intercarrier interference (ICI) cancellation scheme for orthogonal frequency-division multiplexing (OFDM) wireless communication systems is proposed. By equivalently representing the OFDM system with a synchronous code-division multiple access (SCDMA) model, the schemes for the multiple access interference (MAI) cancellation in the SCDMA model can be directly applied to the ICI cancellation in the OFDM system. In addition, the signal detection delay can be further improved by making use of the correlation between the neighboring subcarriers. Simulation results to demonstrate the effectiveness of the proposed ICI cancellation scheme are presented.

A dynamic fair scheduling scheme, named aggressive code-division generalized processor sharing (A-CDGPS) scheme, is proposed to guarantee quality of service (QoS) for multimedia traffic in the uplinks of direct-sequence wideband code division multiple access (CDMA) cellular networks. The scheme performs slot-by-slot fair scheduling of the physical channel rates in response to the variation of multimedia traffic rates, and maximizes the utilization of the 30-called soft capacity of the CDMA uplinks. With the A-CDGPS scheme, deterministic delay bounds for heterogeneous traffic are derived. Simulation results show that the A-CDGPS is able to guarantee the delay requirement for delay-sensitive traffic, assure the weighted fairness among all the users, and maximize the throughput of delay-insensitive traffic.

A rate adaptation scheme for data traffic in direct-sequence code-division multiple-access (DS-CDMA) system is studied. With the scheme, the received power of each active data user is maintained constant by using transmission power control to compensate for channel fading and path loss, while the transmission rate is dynamically adjusted to guarantee a target bit energy-to-equivalent noise spectral density (E/sub b//N/sub e/) when interference varies. A continuous-time Markov chain (CTMC) with state-dependent parameter is used to model the user activities in the system. Analysis and simulation results show that the rate adaptation scheme outperforms the conventional SIR based power control scheme, in terms of a power gain and lower average delay for the data users to achieve the same throughput. Moreover, by applying back-off access control, the performance of the rate adaptation scheme can be further improved.

An analytical model is proposed to study the grade-of-service (GOS) performance for cellular communication systems supporting heterogeneous services, where GOS includes handoff connection dropping probability (HCDP), new connection blocking probability (NCBP) and system resource utilization. In the analytical model, a higher priority is given to a handoff connection than a new connection by resource reservation. The amount of the reserved resource depends on the current traffic load, and can be adjusted to achieve different HCDP. Numerical results are given to demonstrate the GOS performance.

The delay jitter performance of voice traffic, modeled using an exponential on/off source, in a cellular wireless ATM network is analyzed. The uplink MAC (medium access control) protocol is implemented by a P-TDMA/DR (prioritized time division multiple access with dynamic reservation) MAC protocol. Voice, compressed video and data are used as test traffic. The delay jitter (or cell delay variation) of an exponential on/off voice is evaluated using approximate analysis and computer simulation. Numerical results indicate that, with very high probability of 0.92 (simulation) or 0.96 (analysis), the voice delay jitter is practically zero and, with very low probability, it is at other values. 99.1% of the voice delay jitter are within /spl plusmn/10 TDMA frame intervals. This shows that the voice delay jitter is well-behaved due to the excellent design of the P-TDMA/DR MAC protocol for voice traffic.

An approximate analytical formulation of the resource allocation problem for handling multiclass services in a cellular system is presented. Complete partitioning (CP) and complete sharing (CS) schemes with guard channels are used for the resource sharing policies at the call level. The CP model is solved explicitly using a one-dimensional Markov chain while the CS model is solved using a K-dimensional Markov chain. Call and packet level qualities of service (QoS) are considered. The performance of fast and slow mobile users and the effect of cell size are evaluated. The agreements between the analytical and simulation results for the CP and CS cases are good for low blocking probabilities. Numerical results illustrate that higher gain in system utilization is achieved through the joint optimization of call/packet levels.

A novel channel estimation algorithm for a fast fading channel in multicarrier code-division multiple-access (MC-CDMA) systems is proposed. The estimation algorithm considers the interchannel interference (ICI). With the channel estimation, the system performance in terms of the signal-to-interference plus noise ratio (SIR) is analyzed. Simulation results are given to demonstrate the effectiveness of the proposed estimation algorithm.

Resource allocation plays an important role in call admission control (CAC). In a wireless environment where resource is scarce, an efficient resource allocation scheme is of critical importance. A movable boundary (NO) resource allocation scheme for handling real-time (RT) and non-real-time (NRT) traffic at the base station is proposed. Numerical results show that this scheme reduces the resource requirement and increases the utilization of NRT traffic significantly while maintaining the service performance of RT traffic.

We consider rate and power adaptations for homogeneous data traffic in the uplink of direct-sequence code-division multiple-access (DS-CDMA) cellular systems, where the transmission power and the transmission rate of each data user are adapted in accordance to the random activities of users and varying data traffic. The performances in terms of data throughput, average packet delay and average power consumption, are analyzed and compared between adaptive rate and power control schemes. In the rate-adaptive system, the received power of each data user is fixed while the transmission rate is dynamically adjusted to maintain a target bit energy-to-equivalent noise spectral density ratio (E/sub b//N/sub e/). On the other hand, in the power-adaptive system, the transmission rate is fixed and the received power is adapted to maintain the target E/sub b//N/sub e/. Analytical results show that the rate-adaptive scheme provides a significant power gain and lower average packet delay over the power-adaptive scheme for the data users to achieve the same throughput.

The variability of the wireless channel requires adaptive error control. Conventional approaches use either link adaptation (LA), which adjusts the coding scheme based on the estimated channel condition, or incremental redundancy (IR), which adjusts the code rate by incrementally transmitting redundancy until decoding is successful. IR usually achieves a higher effective throughput than that of LA, but a larger delay compared to LA. A protocol which combines the advantages of LA and IR to enhance data transmission is proposed. In contrast to the conventional IR with a highest starting code rate, the proposed approach adaptively adjusts the starting code rate based on the current channel condition. Three schemes are proposed to accomplish adaptation. Simulation results show that the average number of transmissions is significantly reduced, with a small sacrifice in the average throughput compared with those of IR.

Quality-of-service (QoS) support by power distribution and rate allocation for heterogeneous services in multicode code division multiple access (MC-CDMA) systems is studied. Power distribution among all participating connections achieves high resource utilization subject to satisfaction of SINR specifications for the allocated transmission rates. Rate allocation ensures that the required delay/jitter and loss requirements for different connections, while efficiently utilizing the system resources by statistically multiplexing the random and bursty traffic streams. The resultant call level grade of service (GOS) performance, including resource utilization and connection blocking probability (CBP), is derived. Numerical results are given to demonstrate the GOS performance.

Power distribution for multicode code division multiple access (MC-CDMA) systems supporting heterogeneous services is investigated. Power distribution laws under perfect and imperfect power control conditions are derived for the MC-CDMA systems to satisfy the required quality-of-service (QoS) while supporting more simultaneously transmitting users. Numerical results calculated based on the analyses are shown to demonstrate the impact of imperfect power control on the required receive powers.

The best tradeoff between coding and spreading in a single-cell direct-sequence code division multiple access (DS-CDMA) system is investigated. The best code rate in terms of the system spectral efficiency for a single-class system and the optimal power allocation for a multi-class system is analyzed by applying both a matched filter (MF) receiver and a minimum mean square error (MMSE) receiver. It is shown that for the MF receiver, the coding-spreading tradeoff favors a code rate reduction. In the case of the MMSE receiver, the spectral efficiency vs. code rate curve is convex, so there is a best code rate corresponding to a given E/sub b//N/sub 0/ specification. Numerical results show that the best code rate is a function of the system load, the required bit error rate, and the steepness of the required SIR vs. the code rate curve, i.e., the error correction capability of the applied coding codes. The best code rate to maximize the spectral efficiency is further related to the system design parameter E/sub b//N/sub 0/.

In this paper, highly reliable data transmission using concatenated Reed-Solomon (RS) /convolutional coding for a direct-sequence code division multiple access system is studied. The study is based on the analysis of the tradeoff between coding and spreading, and on the compromise between RS outer code and convolutional inner code under the constraint of a fixed bandwidth expansion for each service class. Some insightful observations about the mechanism of the concatenated coding scheme and their explanations are presented. Numerical results show that a best outer/inner code rate pair exists. By applying this best code rate pair over a slow Rayleigh fading channel, depending on the system load and the constraint length of the inner code, a gain of 2dB to more than 9dB in received power reduction for each user can be achieved, compared to the conventionally used code rate pair (outer/inner code rate = 0.8/0.5).

A method for resource allocation to facilitate call admission control based on simultaneous satisfaction of packet-level and call-level QoS constraints is proposed. It is shown that the incorporation of the non-persistent traffic characteristics in the packet-level analysis increases the statistical multiplexing gain and improves the system utilization when compared to resource allocation based on the packet-level and call-level control in isolation. The method is equally applicable to fixed networks ( such as ATM networks) and cellular networks (TDMA and CDMA-based systems) with user mobility. Numerical results for both cases, demonstrating the improvement in utilization, are presented.

TCP performs reasonably well over the Internet where packet losses are mainly due to network congestion. However, TCP suffers significant throughput degradation over hybrid wireless/IP networks where packet losses are also due to transmission errors in wireless segments and during end-host handovers. In this paper, the micro-scale behavior and packet-level performance of four popular TCP variants over wireless links are assessed, and a modified TCP sender which incorporates a heuristic segment-in-flight estimation algorithm to improve the TCP throughput is proposed. Extensive simulations show that the modified TCP achieves better end-to-end performance, and still keeps the fairness and the compatibility with ordinary TCP variants.

We consider a system configuration consisting of both an uplink MAC (medium access control) protocol and a UPC (usage parameter control) at the base station for supporting heterogeneous services. The MAC is implemented by an enhanced TDMA/DR (time division multiple access with dynamic reservation) MAC protocol while the UPC is implemented by a leaky bucket device. Voice, compressed video and data are used as test traffic. The performance metrics are delay and cell loss. Numerical results based on approximate analysis and simulation are used to draw conclusions regarding the size of input buffers of the leaky bucket needed to yield a prescribed packet loss rate.

A distributed call admission control (CAC) scheme for heterogeneous services is proposed. The scheme is based on a non-preemptive priority polling scheme and takes advantages of statistically multiplexing user mobility information. It is shown that the scheme can achieve both high resource utilization and low handoff dropping probability.

Code division multiple access (CDMA) is an interference limited multiple access technology. The signal-to-interference (SIR) ratio, in the form of E/sub b//I/sub 0/, is an important parameter in CDMA systems and has a profound effect on the system capacity and utilization. They in turn affect the network level QoS in terms of new call blocking probability and forced termination probability. A relationship between the link layer E/sub b//I/sub 0/ specification and the network layer QoS parameters in the presence of user mobility is established. Numerical results which display the linkages between the link layer and network layer QoS parameters are presented and discussed.

As a multiple access technology, DS-CDMA operates in an interference limited environment so the system capacity is dominated by multiple access interference (MAI). Since MAI is proportional to the transmit power strengths of other users, the level of transmit power by all participating users requires careful planning and control in order to attain maximum system capacity. The power distribution under a multirate wideband CDMA environment is investigated. It is shown that power control is a function of the spread bandwidth, user data rates, and the user QoS requirements. A power control algorithm, based on a convergence criterion, is proposed. Numerical results which demonstrate the viability of the power control algorithm are presented.

Rate allocation for available bit-rate (ABR) services in ATM networks has received a considerable amount of attention, but important issues such as bandwidth fairness, MCR rate guarantees, and queue control still require further investigation. In light of these concerns, an enhanced rate allocation algorithm is proposed for congestion management using explicit rate feedback control. The algorithm uses fast, exact rate computations and is capable of achieving a variety of MCR-related fairness criteria. The scheme handles transient effects and can function in heterogeneous networks carrying higher priority real-time traffic. Simulation results for a wide range of network scenarios demonstrate that the algorithm effectively controls queue buildups and achieves good fairness. Performance scalability to large networks under challenging conditions is also shown for a given control parameter set.

A piggy-backed profile format for a feedback-based handoff algorithm is proposed to reduce the impact of profile information on radio bandwidth. An efficient identification scheme for mobile switching centers and access points, which reduces the size of the identifiers required for the profile, is also proposed. Furthermore, the sojourn time and the feedback interval of the profile are analyzed extensively and evaluated by simulations using the OPNET Modeler/Radio package. Numerical results indicate that feedback-based handoff is a viable approach.

A salient feature of wireless networks is the ability to support roaming. However, user mobility has a profound effect on QoS provisioning. A queueing model which forms the basis for analytically evaluating the performance characteristics of a generic radio cell is proposed. The effect of mobility on (i) degradation in utilization and (ii) excess capacity requirement when the mobile user's prescribed QoS requirements are maintained is examined. Numerical results pertaining to homogeneous traffic are presented and discussed.

A novel feedback-based handoff scheme, which makes use of information fed back from the mobile, is presented. The proposed scheme attains fast handoff, with relatively small buffer requirements at both the base station and the mobile terminal. The signaling involved in the handoff scheme is described in detail. Simulation results obtained using the OPNET Modeler/Radio package are presented.

Dynamic paging area schemes that use a distance threshold is can significantly reduce the cost of location management. A distance-based location management scheme that uses a mobility model which incorporates various user movement patterns is proposed. Performance characteristics of the proposed location management scheme using the new mobility model are presented and compared with those of the IS-41 standard.

A virtual connection tree (VCT) concept has been proposed to avoid the need to involve the network call processor for every cell handoff attempt in cellular ATM networks. Acampora and Naghshineh (see IEEE Journal on Selected Areas in Communications, vol.12, no.8, p.1365-75, 1994) propose a model for connection admission control (CAC) to the virtual connection tree is for a homogeneous system. With wireless ATM perceived for supporting multimedia services, it is necessary to consider heterogeneous traffic models. We propose two CAC approaches for admission to the VCT based on equivalent capacity for heterogeneous traffic. We study the performance of one of these approaches by mathematical analysis and the other approach by computer simulation. The quality of service performance are the overload probability in a base station and the % overload period in a base station.

An algorithm that dynamically maximizes the CDMA capacity usage by adjacent cell load sharing is proposed and investigated via simulation. For comparison purposes, the scheme proposed by Hanly (see IEEE J. Select. Areas Commun., vol.14, no.7, p.1332-41, Sept. 1995) is reviewed and a set of criteria is established for the comparison. It is conjectured that the proposed algorithm is amenable to practical implementation. A multiprocessed simulation methodology used to obtain the numerical results is also presented.

An approximate queueing analysis of a distributed explicit rate allocation algorithm for the flow control of available bit rate (ABR) service, which captures the effect of bandwidth-delay, is described. Attention is focused on bounding the worst case transient queueing behaviour in a strictly-ABR environment with persistent start-up sources. At each switch, resource management (RM) cells are enqueued using a buffer separate from the data cells, and are served with a higher priority than data cells. Both single and multiple node network cases are treated for connections with differing delays. The approximate analysis shows relatively good agreement with simulation results for single node networks, but gives looser estimates for the multiple node case.

The salient properties of a work-conserving, rate-based service scheduling scheme for ATM networks, called the head-of-the-line earliest due date (HOL-EDD), are described. The major feature of HOL-EDD is that it does not use cell stamping. Instead, it uses an integer decision variable for each VC to schedule cells for transmission. It is shown that the HOL-EDD has a connectionist implementation of O(1) computational complexity. The flexibility of the scheme is shown by generalizing it to schedule the CBR, ABR and UBR service classes.

We describe the architecture design of a wireless cellular ATM access network. A MAC protocol that has been designed to take into consideration the traffic characteristics of different service classes to provide bandwidth efficiency, good QoS for real-time traffic, and reasonable QoS for non-time-critical traffic is also described.

A statistical multiplexer supporting a number of bursty sources is modeled as a discrete time, single server queueing system with an infinite buffer. The probability generating function (PGF) method is used to analyze the queueing behavior. The PGF method requires the determination of a large number of boundary values and, hence, the roots of the characteristic equation. An iterative algorithm to evaluate the characteristic roots is proposed. When the arrival process is a superposition of independent processes, a decomposition approach is used to reduce the state space involved in the computational algorithm. Additionally, the computational algorithm is made efficient through the establishment of conditions under which all the roots are either real or nonnegative real numbers. A set of equations to recursively compute the moments of the queue length are established. Sample applications of the computational methods to evaluate the performance of a multiplexer supporting voice and video sources, modeled by two-state Markov and L-state MMPP processes, respectively, demonstrate the viability of the proposed methods.

Two asymptotic analyses of the queue length distribution at a statistical multiplexer supporting heterogeneous exponential on-off sources are considered. The first analysis is performed by approximating the cell generation rate as a multidimensional Ornstein-Uhlenbeck process and then applying the Benes queueing formula. In the second analysis, we start with a system of linear equations derived from the exact expressions of the dominant eigenvalue of the matrix governing the queue length distribution. Assuming that there are a large number of sources, we obtain asymptotic approximations to the dominant eigenvalue. Based on the analyses, we define a traffic descriptor to include the mean and the variance of the cell generation rate and a burstiness measure. A simple expression for the quality of service (QoS) in cell loss rate is derived in terms of the traffic descriptor parameters and the multiplexer parameters (output link capacity and buffer size). This result is then used to quantify the factors determining the required capacity of a call taking the statistical multiplexing gain into consideration.

A credit-based controller (CBC), which has a provision for cell tagging, is proposed for usage parameter control (UPC). Similar in concept to the leaky bucket, the CBC has a credit counter and a data buffer. Credits are accumulated at a rate initiated from the network (equivalent to the sustainable cell rate), and depleted at a rate pertaining to the network traffic load. A source has the prerogative whether or not to send its cells as tagged cells when the credit level is nonpositive. The queueing behavior of the CBC fed by a Marcov modulated source, is analyzed using a stochastic fluid flow model. It is shown that the performance of the CBC can be altered by tuning the weighting parameter within the CBC. Also, adjustments can be made to balance the ratio of tagged and untagged cells sent into the network.

Discusses the allocation of the available capacity of a statistical multiplexer to serve a number of heterogeneous on-off sources, with the cell loss rate as the performance criterion. In order to avoid using potentially lengthy simulations, the authors have derived computationally efficient bounds and asymptotic approximations for the cell loss rate. The union of all partitions of the available capacity which satisfies the capacity bound and the performance criterion is defined as the capacity region. Both linear approximation and nonlinear approximation of the capacity region are investigated. It is shown that the linear approximation is reasonably accurate when the activity factors of the sources are not too high (less than 0.8). For the case where the linear approximation appears too optimistic, a simple nonlinear approximation for determining the capacity region is suggested. The accuracy of the method is demonstrated using numerical examples.>

Buffer allocation to provide an efficient and fair use of the available buffer spaces is critically important for ATM networks. A complete sharing with virtual partition (CSVP) strategy for buffer management at a multiplexer or an output port of an output buffered switch is proposed and analyzed. The total buffer space is partitioned based on the relative traffic loads (measured or estimated). Virtual partition allows a newly arriving cell belonging to an oversubscribed type to occupy the spare space of an undersubscribed type, and to be overwritten when necessary. Using a fluid flow approach, a set of partial differential equations with a triangular stability region is established to characterize the dynamics of a system supporting two traffic flows. Under a buffer full condition, the system behavior is described by a set of non-homogeneous ordinary differential equations. The cell loss probability for each traffic type is obtained by solving the ordinary differential equations. Numerical examples indicate that by appropriately selecting the partitions, the CSVP method may be used to provide differential cell loss rate requirements by the different traffic types.

An adaptive coding scheme, based on a modification of the discrete cosine transformation, is used to encode image signals. The coding performance is compared with those of the DCT and the Walsh-Hadamard transform. The proposed coding scheme is simpler than the DCT, but its performance is quite close to that of the DCT. The adaptivity in our coder is achieved by using a suitable classification method and distributing the available channel capacity to different classes according to their energy level.>

SCOQ, a high performance fast packet switch with shared concentration and output queueing supports, point-to-point transmissions only. The incorporation of multicast (point-to-multipoint) functions require packet duplications. If the copy network were placed on the feedforward path of the switch, it is not transparent to, and can interfere with, point-to-point switching. By placing the copy network in the feedback position, its operation can be made transparent to the point-to-point information transfer. The copy network incorporated onto the SCOQ switch is non-blocking even without an arbitration or selection network. Contrary to the feedforward approach in which the input buffers must be centrally controlled, with the copy network in the feedback loop, the input buffers all operate independent of each other.>

The distributed queue dual bus (DQDB) protocol, which has been specified by the IEEE 802.6 as the metropolitan area networks (MANs) standard, has an undesirable feature that busy slots that have been already received (i.e. read) continue to propagate downstream unnecessarily. The use of special nodes, known as erasure nodes, allows conversion of read slots to empty, so that downstream nodes may reuse these slots. This should result in an increase of the total throughput of the network. In the paper, the authors introduce and evaluate the performance of an erasure node algorithm. The algorithm keeps track of past activities on both buses to effectively balance the slot erasure and the request cancellation functions. They show that this algorithm possesses a number of features which make it superior to existing algorithms.>

The authors are concerned with the allocation of the available capacity of a statistical multiplexer to serve a number of heterogeneous on-off sources, with the cell loss rate as the performance criterion. In order to avoid using potentially lengthy simulations, they have derived computationally efficient bounds and asymptotic approximations for the cell loss rate. The union of all partitions of the available capacity which satisfies the capacity bound and the performance criterion is defined as the capacity region. Both linear approximation and nonlinear approximation of the capacity region are investigated. It is shown that the linear approximation is reasonably accurate when the activity factors of the sources are not too high (less than 0.8). For the case where the linear approximation appears too optimistic, a simple nonlinear approximation for determining the capacity region is suggested. The accuracy of the method is demonstrated using numerical examples.>

The SCOQ switch is a Batcher-banyan based high performance fast packet switch with shared concentration and output queueing, with a maximum of L(>

A method for designing a vector quantizer by first partitioning the residual image vector space into concentric shells and then searching for the smallest possible codebook to represent the residual image vector space, while adhering to the visual perceptive qualities such as edges and textures in the image representation, is described. The coding method involves the decomposition of the image vector into relatively independent components, each with a small dynamic range, to permit the design of a small fixed codebook for the vector quantizer. Optimal partitioning amounts to optimally selecting the set of shell radii, which is achieved using a modified form of simulated annealing. The results obtained in the coding of images show that the concentric-shell partition vector quantizer compares favourably with the gain-shape vector quantizer in terms of subjective image quality at the same bit rate while achieving higher SNR and lower computational complexity.>

An approximate model is considered for characterizing aggregated cell arrivals from heterogeneous sources which may generate cells in a highly time correlated manner. The model consists of two types of on-off sources and provides enough degrees of freedom to match a number of moments of cell arrival rates as well as the time correlation of the aggregated cell arrivals. Numerical examples are presented to illustrate the accuracy of the queue length distributions obtained using the model compared with the exact results.>

A space-division, nonblocking packet switch with data concentration and output buffering is proposed. The performance of the switch is evaluated with respect to packet loss probability, the first and second moments of the equilibrium queue length and waiting time, throughput, and buffer overflow probability. Numerical results indicate that the switch exhibits very good delay-throughput performance over a wide range of input traffic. The switch compares favorably with some previously proposed switches in terms of fewer basic building elements used to attain the same degree of output buffering.>

The SCOQ switch is a Batcher-banyan-based high-performance fast packet switch with shared concentration and output queuing, with a maximum of L(>

The integrated transmission of voice and data at a time-division multiplexer (TDM) is discussed and analyzed. The system operates in a frame format and the channel capacity is governed by the frame size. The allocation of channel capacity for the transmission of voice and data is performed by a controller. Digital speech interpolation (DSI) and embedded coding techniques are used to enhance the transmission efficiency and to facilitate the implementation of multiplexing. Using a dynamic programming approach, a capacity allocation policy which jointly optimizes the voice/data performance is introduced. Numerical results indicate that the aggregate throughput of the system can be improved with a slight degradation in voice quality.>

A method is described for designing a vector quantizer by first partitioning the image vector space into concentric shells and then searching for the smallest possible codebook to represent it, while adhering to the visual perceptive qualities such as edges and textures in the image representation. The coding method involves decomposition of the image vector space into relatively independent components, each with a small dynamic range. Optimal partitioning amounts to optimally selecting the set of shell radii, using a modified form of simulated annealing. The results show that the concentric-shell partition vector quantizer outperforms the gain-shape vector quantizer in terms of computational complexity and coded image quality.>

A space-division, nonblocking packet switch with data concentration and output buffering is proposed. The performance of the switch is evaluated with respect to packet loss probability, the first and second moments of the equilibrium queue length and waiting time, throughput, and buffer overflow probability. Numerical results indicate that the proposed switch exhibits very good delay-throughput performance over a wide range of input traffic. The proposed switch compares favorably with the knockout switch of Y. Yeh et al. (1987) in terms of implementation complexity and packet concentration performance, and with the sunshine switch of J. Giacopelli et al. (1989) and the modular architecture proposed by T. Lee (1990) in terms of fewer basic building elements used to attain the same degree of output buffering.>

A matrix-analytic method is used to analyze the queueing behavior of small time division multiplexing (TDM) integrated services systems. Such systems have priority services for time-critical traffics in which adjacent packets exhibit a strong interdependency. The TDM frame with a capacity of M packets is used to transmit the high-priority packets at every time step. Any unused capacity is utilized to transmit low-priority packets. The system can be modeled as a discrete-time system with a fluctuating number of servers for the low-priority packets. Because the number of servers is small and adjacent packets are dependent, the birth-and-death analysis is not appropriate. An algorithm, based on a modification of Neuts' method, is used to determine the boundary points required in the queuing analysis. Numerical results for two integrated services systems, each with different characteristics, are presented to demonstrate the feasibility of the analysis method and the computational algorithm.>

A vector-adaptive vector quantization (VAVQ) scheme, which may be viewed as a generalization of gain-adaptive vector quantization, is described. The proposed scheme adjusts each component of the encoding signal vector according to a statistical estimate of the signal characteristics. The VAVQ scheme can cope with large input dynamic ranges. It can be used in either the time domain or the transform domain, and exhibits approximately 4 dB improvement in segmental signal-to-noise ratio (SNR) over the fixed VQ.>

A media access control (MAC) protocol for integrated services on a dual-ring high-speed LAN is proposed. The protocol supports real-time synchronous voice and video services and multilevel priority asynchronous data traffic types using a packet-switched operation. The most important service requirement for packetized real-time traffic is guaranteed periodic access to the network with a small delay variation. The requirement is met by periodic generation of synchronous service tokens. The effect of service interruptions due to the synchronous traffic, i.e. voice and video, on the asynchronous data traffic is investigated by means of analytical and simulation methods.>

A discrete-time queuing analysis is presented for integration of multiple traffic types in a packet-switched TDM (time-division multiplexing) system. The correlation of each traffic type is represented in terms of the power spectral density. The general expression obtained for the aggregate mean queue size indicates that slowly varying traffic types exert the largest effect on the queuing process. Also, a lengthy-steady traffic is highly predictable. An adaptive flow control and routing scheme, based on signal prediction, which successively adjusts the short-burst traffic arrival rate at each TDM node, is introduced and analyzed. The analytical results indicate a substantial reduction in the correlation effect on the system queuing behavior.>

A model of multiuser variable rate subband coding of speech incorporating digital speech interpolation (DSI) is presented and analyzed. A dynamic bit assignment algorithm which minimizes the mean squared reconstruction error is presented. A backward estimation of subband variances which makes the bit assignment algorithm backward-adaptive and greatly reduces the need to send side information is proposed. A novel switched-stepsize adaptation algorithm is used at the coders to improve system performance. With adaptive buffer control, buffer overflow is completely prevented. It has been shown by simulation means that a 2:1 DSI gain can be obtained with a relatively small buffer size.>

The integrated transmission of voice and data at a time-division multiplexer (TDM) is discussed and analyzed. The system operates in a frame format and the channel capacity is governed by the frame size. The allocation of channel capacity for the transmission of voice and data is performed by a controller. Digital speech interpolation and embedded coding techniques are used to enhance the transmission efficiency and to facilitate the implementation of multiplexing. Using a dynamic programming approach, a capacity allocation policy that jointly optimizes the voice/data performances is introduced. Numerical results indicate that the aggregate throughput of the system can be improved with a slight degradation in voice quality.>

For pt.1 see ibid., vol.COM-35, p.1329-41 (1987). A performance evaluation is presented for selective diversity with feedback for frequency-hopping M-ary frequency-shift-keyed systems operating over Rayleigh faded channels in the presence of partial-band noise and partial-band tone jamming. The behavior of uncoded and coded systems is studied. For coded systems, the performance is evaluated for hard-decision receivers without channel state information and soft-decision receivers with perfect jammer state information. The results demonstrate that the performance of uncoded FH/MFSK with selective diversity is unacceptable. However, this diversity technique can offer definite improvements for coded FH/MFSK systems. Specifically, the effectiveness of selective diversity signaling depends on the provision of a feedback channel between the transmitter and receiver to provide the transmitter with the fading gains of the independently faded channels. To obtain an improvement from the selective diversity signaling scheme described here, there must be multiple independently faded channels between the transmitter and receiver. If not, the performance of the selective diversity signaling scheme will be identical to the performance of FH/MFSK without diversity.>

A traffic model in which the interruption traffic is a correlated process is introduced. In this model the effect of correlation is culminated in a parameter that is the sum of all the imbalances of the autocorrelation function of the interruption process. Based on this model, the queueing analysis of integrated services on a packet switched TDM system is developed. It is shown that the presence of correlation increases the mean queue length. An adaptive flow control scheme that successively adjusts the short-bursty traffic arrival rate at each TDM node to reduce the correlation effect on the queue length build-up is proposed.>

Time-invariant trellis codes for stationary, ergodic, discrete-time sources are designed by unconstrained, nonlinear optimization of the performance in a simulated source encoding with the Viterbi algorithm. A nonderivative conjugate directions algorithm and a conjugate gradient algorithm with restarts are applied to design low-constraint-length, unit-rate, binary codes for the memoryless Gaussian source. The latter algorithm is also used to design codes for the memoryless Laplacian source and a third-order autoregressive model for speech. Good codes are tabulated and compared to other known results on a performance versus complexity basis. Those for the Gaussian source are tested in a joint (tandem) trellis-coding system with known convolutional channel codes.>

Previous results on a single integrated-services TDM (time-division multiplexer) node are extended to the modelling and analysis of a network of integrated-service TDMs. Different interconnections of the integrated-services TDM nodes are studied by means of computer simulation. The results indicate that a Poisson assumption for the internal data arrivals is reasonable. With this assumption, the mean queue analysis at an individual node can be separated from the rest of the network, so that solution of the entire network can be obtained by combining the separate solutions.>

The voice cutoff fraction and mean data waiting time of an integrated burst-switched system are analyzed. Several approximate approaches are proposed for the analysis. Comparison between simulation and approximate results shows that the accuracy of the approximations depends on the relationship between mu /sub d/ and mu /sub v/ where 1/ mu /sub d/ and 1/ mu /sub v/ are the mean lengths of data and voice packets (bursts), respectively. In general, the approximations give good accuracy for mu /sub d/mu /sub v/, the approximations for the mean data waiting time give less accurate but adequate results. From the analysis, it is found that a burst-switched system can achieve a higher bandwidth efficiency when data traffic has a shorter burst length (e.g. interactive data). Furthermore, it is also observed that the relative burst lengths between voice and data can significantly affect the characteristic of the voice clipping process. The analysis shows that, under normal operating condition where voice traffic is predominant and the constraint that the voice cutoff fraction is less than 0.5%, the data queue is always stable.>

The authors present a feedback rate control technique for FH/BFSK (frequency-hop/binary phase-shift keying) signaling over a jammed flat-flat fading channel. An algorithm is developed for tracking the channel fade level, dynamically adjusting the transmitted data rate, and mitigating the effects of partial-band noise jamming. Simulation studies indicate that improvements of about 2 dB can be obtained in the coded performance with the proposed adaptive rate system, when compared to a nonadaptive system operating over the same communication medium with identical power and bandwidth resources.>

The design of time-invariant trellis codes for stationary ergodic discrete-time sources is cast as an unconstrained, nonlinear optimization problem, where the objective function and its derivatives are evaluated by simulation. Using classical real analysis and the ergodic theorem, convergence of the sample encoding distortion and its partial derivatives (with respect to the code quantization levels) to their ensemble average values is investigated. It is found that in the common code design situation, the expected per-symbol distortion and its first derivatives are available and piecewise continuous, but second-derivative information is unreliable. This indicates that efficient optimization should be performed using a nonderivative or first-derivative method that does not compute approximate second derivatives to determine search directions.>

This paper gives an evaluation of the performance of adaptive signaling techniques for jammed fading channels. These techniques perform remarkably well for fading channels with AWGN. The performance of both uncoded and coded systems is examined in the presence of jamming. Adaptive signaling schemes are shown to offer little improvement for uncoded antijam systems. However, for coded antijam systems, they provide improvements in the performance and, in some cases, simplify the receiver implementation.

The performance of diversity and/or coding is evaluated for FH/MFSK signaling over Rayleigh fading channels in the presence of jamming. The effects of partial-band tone and partial-band noise jamming on uncoded and coded systems are considered. The results indicate that FH/MFSK signaling with diversity provides satisfactory performance for jammed fading channels. For coded FH/MFSK signaling over fading channels, noise jamming may be more effective than tone jamming. The amount of improvement resulting from the use of diversity in conjunction with coding depends upon many factors, including the nature of the channel, the degree of channel state information available at the decoder, the type of decoding, and the modulation alphabet size.

Data queueing is of primary concern in a voice/data integrated TDM system. The data queueing model is represented in the discrete-time domain with multiple servers and voice is given a higher priority than data. The data arrival process is assumed to be Poisson and the voice arrival process is characterized by a Markov chain. The correlation coefficient of the number of on voice calls between consecutive frames is used to measure the correlation behavior of the voice process. While the generating function approach may be used to analyze the queueing process, it involves the evaluation of a large number of boundary terms. On the assumption that the voice traffic consists ofNi.i.d. two-state Markov chains, we derive a simple expression for the mean queue size as a function of two variables in the form of the traffic departure processes. The results clearly reveal a significant influence of the correlation coefficient on the data queueing process. Then, an approximate analysis based on the departure processes is introduced. The numerical and simulation results indicate that this approximate approach yields reasonably accurate results.

The theoretical issues of scheduling for capacity allocation in multiple access networks using in-band and out-of-band signaling are addressed. The analysis is carried out under the hypothesis that the "scheduling epochs" consist of bandwidth-dependent and bandwidthindependent components. The ultimate limitation on channel capacity rests with the bandwidth-independent component. It is shown that over the range of practical interest, scheduling using a separate side channel is superior to in-band scheduling in that, under similar conditions, the former attains a higher usable channel capacity.

Network performance is investigated at an isolated node which we call the switching node (SN). An equal (outgoing) link utilization constraint is introduced to enhance the robustness of a minimum delay routing algorithm applied to the SN in the network. Input traffic to the SN is grouped into classes in accordance with the radial distance from the SN to their destinations. It is shown that under an equal link utilization constraint a four-class traffic admission scheme displays a smaller probability of buffer overflow compared to an unconstrained routing algorithm. Also, with the equal link utilization constraint, the buffer overflow characteristics are similar for both balanced and unbalanced loads. It is shown that the four-class traffic admission model exhibits an "almost" deadlock free characteristic, e.g., with a total buffer size of 4, the probability of deadlock is about 10-10.

The idea of combining the desirable features of random access (at low utilization) and reservation access (at high utilization) motivated the proposal of a combined random/reservation multiple access (CRRMA) scheme for a global beam satellite described in [13] and a multispot beam satellite described and analyzed in this paper. A key element in the proposed CRRMA protocol is the assumption of an onboard processing capability to interrogate uplink headers, to buffer successful requests, and to create and broadcast channel assignments to enhance system performance. A scheduling algorithm is introduced to enable a proper division of packet transmissions via random access and reservation access. Numerical results indicate that the proposed CRRMA protocol indeed exhibits good delay-throughput performance over a wide range of utilization.

A mini-slot, appended to the data slot in the distributed scheduling multiple access (DSMA) protocol described in [1], for the transmission of acknowledgement packets is described and analyzed. The resulting DSMA with fixed slot acknowledgement (DSMA/FSA) presents a better alternative to sending a separate acknowledgement packet for each received data packet. With priority requests, DSMA/FSA appears to be a viable media access protocol for integrated voice and data services in a local area network.

A combined random/reservation multiple access (CRRMA) scheme for packet-switched communication over a global beam satellite with on-board processing is proposed and analyzed. Channel time is divided into contiguous slots; each slot containsNminislots for transmission of request packets andN'minislots for data. WithNsubstantially smaller than the number of earth stations, collisions will occur in request packet transmissions. Two channel access algorithms for the CRRMA model are proposed: uncontrolled channel access (UCA) and controlled channel access (CCA). UCA is simpler but has an inherent stability problem particularly when the number of minislotsNis small. The CCA algorithm restricts the transmission of request packets for new arrivals to take place only when the slot is in the FREE state. WithN = 3, the CCA algorithm exhibits good delay-throughput characteristics. AsNincreases, the UCA algorithm offers stable operation. ForN \geq 5the simpler UCA algorithm is preferred over CCA.

A construction technique is given for complex sequences, each component of magnitude unity, with Iow autocorrelation and cross correlation. The construction is based on an application of the Carlitz-Uchiyama theorem to cyclic equivalence classes of maximal period of Reed-Solomon codes over GF(p),pbeing an odd prime.

A conflict-free distributed scheduling multiple access (DSMA) scheme using a high-speed main channel for data transmission and a subchannel for distributed decision scheduling is described and analyzed. DSMA, which has a variable cycle length and employs a slow speed subchannel for scheduling, is suitable for local area communication networks which employ a data bus as transmission support. With the data rate of the main channel and subchannel represented, respectively, by rpand rq, the maximum channel occupancy is given byC_{max} = r_{p}/(r_{p} + r_{q}). Numerical results show that DSMA is very efficient and exhibits a delay-throughput characteristic close to that of theM/D/1perfect scheduling lower bound over a wide range of throughput values. DSMA guarantees each active user one slot per cycle. In addition, DSMA permits priority scheduling.

A coded multiple access protocol (CMAP) to improve the delay-throughput performance of a global scheduling multiaccess model for data communication over a broadcast channel, which exhibits a short propagation delay, is described and analyzed. Upper and lower bounds on delay-throughput characteristics are obtained. It is shown that CMAP reduces system delay compared to the 1-out-of-Mcode. This reduction is attained at the expense of a dialogue exchange between the central scheduler and the users.

A satellite packet switching multiaccess model which employs a global scheduling assignment scheme is described and analyzed for batch Poisson arrivals. System performance in terms of buffer overflow probability and system delay is analyzed and simulated. The numerical results, presented in graphical form, indicate that the performance improves as the population size M increases. For large value of M the queueing delay decays approximately exponentially as the buffer length increases. Our results indicate that the system delay performance of our dynamic assignment (DA) algorithm is significantly better than that of a synchronous time-division multiplexing scheme.

A global scheduling multiple access (GSMA) scheme for data communication via a high speed bus is described. The GSMA scheme, which has a variable length frame format and the desirable property of guaranteeing each active user a minimum service per frame, attains conflict-free multiaccess and has the flexibility of providing more channel capacity to the large users. An expression for the mean system delay under a Poisson arrival law and an imbalanced loading (multi-rate) environment is derived. Numerical results indicate that the GSMA scheme offers substantially higher channel utilization compared to the synchronous time-division multiple access (STDMA) scheme, particularly at the low throughput region. It is shown also that the GSMA system offers superior delaythroughput performance to an STDMA or POLLING system.

A reference code, with an associated bound on the code rate, for the encoding of correlated digital sources is introduced. The reference code is adaptive and simple to implement. Image coding results obtained using concatenated trellis and reference encoding are presented. For the images studied, the reference code attains an average code rate of approximately 0.64 bits/bit, or a reduction in information rate of approximately 36%.

The multiaccess model for satellite packet switching proposed by the authors [1] employs a frame format, with scheduling assignments broadcast from the satellite. The total delay recurred by a data packet in traversing the satellite channel consists of queueing delay, scheduling delay, transmission delay and propagation delay. In this paper we analyze the queueing and scheduling delays and compare the analytical and simulation results. For the queuemg delay analysis we model the multiaccess scheme using anM/D/Nqueue, whereNis the number of slots per frame. For the scheduling delay analysis we emply a round-robin scheduling assignment algorithm. We treat the cases with and without random transmission; our results indicate that random transmission improves the queueing delay performance.

An adaptive trellis-encoding scheme, using the Viterbi algorithm for trellis search and the Kalman algorithm for adaptive adjustment, is described. The encoder is comprised of a fixed precoder and a time-varying trellis coder in tandem. The source decoder is timevarying with the time-varying part being represented by a feed forward finite-state machine (FSM). Adaptive trellis encoding requires the presence of a local FSM to monitor the adaptive encoding operation. The absence of the source signal at the decoder requires the transmission of a side-information for the mechanization of the adaptive operation of the source decoder. The transmission rate of the proposed adaptive trellis-encoding scheme is(1 + 1/K_{p})/Mbits per source symbol, whereMis the block size which the precoder maps source symbols onto an intermediate signal set before trellis coding and Kpis the update period. Results obtained in the encoding of iid binary, autoregressive, and video sources are presented.

A multiaccess model for packet switching with a satellite having the capability of interrogating the uplink header and creating the downlink header is proposed. The satellite broadcasts slot assignments, based on the users' reported queue status, to the users for transmission in the next frame. With the protocols being done at both the earth stations and at the satellite, the proposed multiaccess model avoids collisions that are prevalent in schemes of the ALOHA type. The actual model is too complex to handle analytically. We derive analytical equations for a two-group model. Calculated and simulated buffer overflow probabilities as a function of traffic intensity and buffer size are compared. We also evaluate the performance of the actual model in terms of average system delay as a function of traffic intensity by means of computer simulation.

This concise paper deals with variable length source coding for binary memoryless sources with a fidelity criterion. The encoding scheme under consideration is an (M_{c}, N, K) code consisting of a distortionless run-length inner code of size Mcand an outer code that maps each source vector of lengthNto a codeword of length less than or equal toK. The encoding of the outer code is accomplished by means of a trellis search, and the distortion measure used is a Hamming distance. For composite binary memoryless sources an adaptive (M_{c}, N) code can be constructed by varying the constraintKon codeword length according to the source statistics. The (M_{c}, N, K), and (M_{c}, N) codes are insensitive to the inaccuracy in estimating the source probabilities. Rate-distortion curves, obtained by computer simulation, are plotted along with the theoretical rate-distortion functionR(D).

An analog-digital hybrid decoder which combines amplitude and duration threshold detection and bipolar violation sensing capabilities for decoding bipolar signals is described. The main features of the decoder are: 1) a preamplifier with automatic gain control (AGC), 2) amplitude and duration threshold detectors, 3) a bipolar violation sensor, and 4) a unipolar pulse generator. The decoder is extremely robust and is self-synchronizing. If, during operation, burst errors occur, introducing bipolar violations in the received signal, the decoder decides that, where a violation has occurred, a binary "0" was transmitted. If, for some reason, the decoder is perturbed from its synchronous condition, it requires at most 1-b duration to reacquire synchronization. That is, the decoded message contains at most one erroneous bit.

An innovations approach to data compression as a viable method to improve the efficiency of data transmission is proposed. The correlated source is modeled by a ratio of polynomials with slowly time-varying coefficients. Data compression is achieved in three steps by: 1) dithering the source signal with a zero mean white noise process to enable the application of the innovations concept, 2) transforming the dithered signal to an innovations process (correlation removal), and 3) quantizing the resultant innovations process to remove unnecessary fidelity. An adaptive implementation of the data compression system using tapped-delay lines (TDL's) is obtained using the steepest descent method. Preliminary computer simulation demonstrates that, for binary data transmission, a reduction in mean square signal value of approximately 3 is attained with no observable error at a 31-dB signal-to-noise ratio (SNR).

It is shown that a suitable adaptive receiver for digital communication over noisy dispersive unknown channels consists of an adaptive prefilter followed by an adaptive equalizer. The adaptive receiver is optimized by a minimization of the overall receiver mean-square error. The resultant adaptive receiver requires a dummy equalizer to supply a control signal for adjusting the tap gains of the prefilter.

A linear receiver for digital communication over unknown dispersive and noisy channels obtained by jointly optimizing the prefilter and equalizer has been described by the authors in a recent paper [4]. An extension to incorporating a decision-feedback equalizer is made. Performance of the new receiver is evaluated by means of computer simulation. Comparison of the performance of the new receiver, the matched filter-equalizer receiver, and the fixed low-pass filter-equalizer receiver is made both with respect to convergence rate and error rate. It is conjectured that the new receiver exhibits performance superior to both the matched filter-equalizer receiver and the fixed low-pass filter-equalizer receiver.

Bipolar signal waveforms for digital communication are normally accomplished by coding the message sequence first and then pulse shaping the bipolar signal. The coding is relatively simple to mechanize; the pulse shaping may present some difficulty and approximation techniques may have to be used. A hybrid digital-analog mechanization of a bipolar signal waveform generator in which the bipolar encoding and pulse-shaping operations are combined is described.