Low latency communications is one of the key design targets in future wireless networks. We propose a queue aware algorithm to optimize resources guaranteeing low latency in multiple-input single-output (MISO) networks. Proposed system model is based on dynamic network architecture (DNA), where some terminals can be configured as temporary access points (APs) on demand when connected to the Internet. Therein, we jointly optimize the user-AP association and queue weighted sum rate of the network, subject to limitations of total transmit power of the APs and minimum delay requirements of the users. The user-AP association is viewed as finding a sparsity constrained solution to the problem of minimizing ℓq-norm of the difference between queue and service rate of users. Finally, the efficacy of the proposed algorithm in terms of network latency and its fast convergence are demonstrated using numerical experiments. Simulation results show that the proposed algorithm yields up to two-fold latency reductions compared to the state-of-the-art techniques.

With network slicing, physical networks are partitioned into multiple virtual networks tailored to serve different types of service with their specific requirements. In order to optimize the utilization of network resources for delay-critical applications, we propose a new multi-domain network virtualization framework based on a novel multipath multihop delay model. This framework encompasses a novel hierarchical orchestration mechanism for mapping network slices onto physical resources and a mechanism for dynamic slice resizing. The main idea is to locally redefine the delay requirements on each network domain depending on the conditions in the rest of the network. Delays larger than threshold (debt) are allowed in certain domains if there is a possibility to compensate such excessive delays in other segments of the network that can transmit the messages with less latency (credit). This tradeoff or delay threshold redefinition on different segments of the route is referred to as network latency equalization. For performance comparison, minimum cost routing with latency constraints is used as a baseline. We show that our approach enables significantly better utilization of the network resources measured in the number of slices with the same latency requirements that can be accommodated in the network.

We develop and analyze a new user-centric networking model for ubiquitous spectrum sharing where every user can share and use the spectrum under uncertainty of their traffic models. In this concept, users when connected to the Internet (wired/wireless) can dynamically serve as access points for other users in their vicinity. For this reason, the concept is referred to as user-centric distributed spectrum sharing. Each user in spectrum sharing mode utilizes a part of its available spectrum for its own traffic and remaining part to share with users in spectrum demanding modes. The model is designed as an operator supervised double-Stackelberg game with network operators, access points, and users as main players. We study network reliability and latency of the system under uncertainty of users' traffic patterns. The numerical results show that the proposed model, depending on different settings, can significantly improve both profit and utility for network operators and users, respectively. Furthermore, network reliability is significantly improved depending on the network parameters for both users and operators.

Dynamic network architectures (DNAs) have been developed under the assumption that some terminals can be converted into temporary access points (APs) anytime when connected to the Internet. In this paper, we consider the problem of assigning a group of users to a set of potential APs with the aim to maximize the downlink system throughput of DNA networks, subject to total transmit power and users' quality of service (QoS) constraints. In our first method, we relax the integer optimization variables to be continuous. The resulting non-convex continuous optimization problem is solved using successive convex approximation framework to arrive at a sequence of second-order cone programs (SOCPs). In the next method, the selection process is viewed as finding a sparsity constrained solution to our problem of sum rate maximization. It is demonstrated in numerical results that while the first approach has better data rates for dense networks, the sparsity oriented method has a superior speed of convergence. Moreover, for the scenarios considered, in addition to comprehensively outperforming some well-known approaches, our algorithms yield data rates close to those obtained by branch and bound method.

Small cell base stations deployment is a promising approach to offload traffic from macrocell, and improve the network capacity and coverage. However, interference management and providing seamless hand offs between access points (APs) for user equipments (UEs) remain main technical challenges especially in dense heterogeneous wireless networks. In this paper, a novel context-aware resource allocation (CARE) mechanism is proposed based on an adaptive space-time beamforming (ASTB) scheme, where different beam-widths (in time and space domains) are allocated to UEs according to their performance preferences with respect to delay tolerance, throughput, energy consumption and link robustness to the potential hand-off failure. We formulate CARE as a two-step matching game consisting of two many-to-one sub-matching games with externality for access and backhaul networks. We introduce two-step stable matching and Nash stability concepts as solutions of CARE. Our numerical results show that CARE with space-time beamforming provides at least two times higher capacity for UEs in comparison to space beamforming while the average delay and complexity are significantly decreased.

Tactile Internet (TI) will generate a variety of 5G-enabled use cases with different requirements for latency, throughput and reliability. In this paper, we propose a flexible cloud-based radio access network (FRAN) for TI, where traffic of user equipments (UEs) can be temporary offloaded from the operator-provided networks to user- provided networks if needed. Such a concept enables dynamic network slicing (DNS) where the network architecture is temporally augmented with slices of infrastructure borrowed from user provided network. FRAN is able to support Tactile applications without any basic change to the hardware/software infrastructure in the network. We model DNS system as a two-layer/slice traffic- aware resource allocation framework, where every layer uses a separate two-step matching game in order to serve Tactile users (TUs) and low- priority users (LUs). We propose a subgame Nash stable and two-sided exchange stable concepts as solutions of the proposed two-layer traffic-aware resource allocation. Our numerical results show that network operators and UEs (either TUs or LUs) significantly benefit from deploying the FRAN rather than conventional cloud-based radio access networks (CRANs).

In this paper, a novel paradigm of user-provided connectivity in wireless networks is introduced using certain class of wireless terminals that can be turned temporarily into access points at any time while connected to the Internet. We show that a DNA (Dynamic Network Architecture) model improves the connectivity and capacity of ultra-dense wireless access networks without need to reconfigure the network infrastructure. The DNA operators motivate terminals to participate in this concept by providing incentives. An example is to allow terminals to transmit additional free traffic volume if they share their free bandwidth by acting as access points. The DNA operators manage the dynamic network in order to maximize their own profit by adjusting jointly their price and incentive rate. In addition, we model the joint problem of operator pricing and user resource sharing as a non-cooperative game and the resulting game admits a unique Nash equilibrium solution. Simulation results show high gains in such networks for terminals acting as access points and operators.

A new paradigm in wireless network access is presented and analyzed. In this concept, certain classes of wireless terminals can be turned temporarily into an access point (AP) anytime while connected to the Internet. This creates a dynamic network architecture (DNA) since the number and location of these APs vary in time. In this paper, we present a framework to optimize different aspects of this architecture. First, the dynamic AP association problem is addressed with the aim to optimize the network by choosing the most convenient APs to provide the quality-of-service (QoS) levels demanded by the users with the minimum cost. Then, an economic model is developed to compensate the users for serving as APs and, thus, augmenting the network resources. The users' security investment is also taken into account in the AP selection. A preclustering process of the DNA is proposed to keep the optimization process feasible in a high dense network. To dynamically reconfigure the optimum topology and adjust it to the traffic variations, a new specific encoding of genetic algorithm (GA) is presented. Numerical results show that GA can provide the optimum topology up to two orders of magnitude faster than exhaustive search for network clusters, and the improvement significantly increases with the cluster size.

Future wireless networks are envisioned to integrate multi-hop multi-operator multi-technology (m3) components in order to meet the increasing traffic demand at an acceptable price for subscribers. The performance of such a network depends on the multitude of parameters defining traffic statistics, network topology/technology, channel characteristics, and business models for multi-operator cooperation. So far, most of these aspects have been separately addressed in the literature. Since the above parameters are mutually dependent and simultaneously present in a network, for a given channel and traffic statistics, a joint optimization of technology and business model parameters is required. In this paper, we present such joint models of complex wireless networks and introduce optimization with parameter clustering to solve the problem in a tractable way for large number of parameters. By parameter clustering, we compress the optimization vector and significantly simplify system implementation, and hence, the algorithm is referred to as the compressed control of wireless networks. Two distinct parameter compression techniques are introduced, namely, parameter absorption and parameter aggregation. Numerical results obtained in this way demonstrate clear maximum in the network utility as a function of the network topology parameters. The results, for a specific network with traffic offloading, show that the cooperation decisions between the multiple operators will be significantly influenced by the traffic dynamics. For typical example scenarios, the optimum offloading price varies by factor 3 for different traffic patterns, which justifies the use of dynamic strategies in the decision process. Besides, if user availability increases by multi-operator cooperation, network capacity can be increased up to 50% and network throughput up to 30%-40%.

Cellular networks are faced with serious congestions nowadays due to the recent booming growth and popularity of wireless devices and applications. Opportunistically accessing the unused licensed spectrum, cognitive radio can potentially harvest more spectrum resources and enhance the capacity of cellular networks. In this paper, we propose a new multihop cognitive cellular network (MC2N) architecture to facilitate the ever exploding data transmissions in cellular networks. Under the proposed architecture, we then investigate the minimum energy consumption problem by exploring joint frequency allocation, link scheduling, routing, and transmission power control. Specifically, we first formulate a maximum independent set (MIS) based energy consumption optimization problem, which is a non-linear programming problem. Different from most previous work assuming all the MISs are known, finding which is in fact NP-complete, we employ a column generation based approach to circumvent this problem. We develop an ϵ-bounded algorithm, which can obtain a feasible solution that are less than (1 + ϵ) and larger than (1 - ϵ) of the optimal result of MP, and analyzed its computational complexity. We also revisit the minimum energy consumption problem by taking uncertain channel bandwidth into consideration. Simulation results show that we can efficiently find ϵ-bounded approximate results and the optimal result as well.

Due to the emerging various data services, current cellular networks have been experiencing a surge of data traffic and are already overloaded; thus, they are not able to meet the ever exploding traffic demand. In this study, we first introduce a multi-radio multi-channel multi-hop cognitive cellular network (M$^3$C$^2$N) architecture to enhance network throughput. Under the proposed architecture, we then investigate the minimum length scheduling problem by exploring joint frequency allocation, link scheduling, and routing. In particular, we first formulate a maximal independent set based joint scheduling and routing optimization problem called original optimization problem (OOP). It is a mixed integer non-linear programming (MINLP) and generally NP-hard problem. Then, employing a column generation based approach, we develop an$\epsilon$-bounded approximation algorithm which can obtain an$\epsilon$-bounded approximate result of OOP. Noticeably, in fact we do not need to find the maximal independent sets in the proposed algorithm, which are usually assumed to be given in previous works although finding all of them is NP-complete. We also revisit the minimum length scheduling problem by considering uncertain channel availability. Simulation results show that we can efficiently find the$\epsilon$-bounded approximate results and the optimal result as well, i.e., when$\epsilon =0\%$in the algorithm.

Benefits of multi-operator spectrum sharing in wireless networks heavily depend on the traffic misbalance in the networks belonging to different operators. In this paper, we study the likelihood that such misbalance occurs in networks with high traffic dynamics. An extensive business portfolio for heterogeneous networks is presented to analyse the benefits due to multi-operator cooperation for spectrum sharing. High resolution pricing models are developed to dynamically facilitate price adaptation to the system state. By using queuing theory, we quantify the operators' gains in cooperative arrangements as opposed to non-cooperative independent operation. In addition, Markov model is used that can handle wider range of different distributions of traffic arrivals and service rates. A tractable analysis and quantitative results are provided for those gains as a function of the number of cooperating operators. Under the condition that there is a traffic underflow in one band, it has been shown that with capacity aggregation model, the operator operating in other band can take advantage of additional channels with probability close to 1. In capacity borrowing/leasing model, this advantage is not unconditional, and there is a risk that the operator leasing the spectra will suffer temporary packet losses. When cognitive models are used in a network with high traffic dynamics, 50–70% of the spectra may be lost due to channel corruptions caused by the return of primary users. The gains of traffic offloading from a cellular network to a WLAN are quantified by an equivalent increase in opportunistic capacity proportional to the ratio of aggregate coverage of cellular networks and WLANs. The results provide guidelines for business decision in multi-operator network management.

In this paper, we present an economic model for offloading data from subscribers of a large scale cellular operator to a small scale WLAN in a multi-hop cellular environment. We make use of a hexagonal tessellation deployed with relay elements to model the multi-hop capability. An incentive-based model helps to determine the behavior of the cellular and WLAN operator, as the cellular operator decides to offload its users depending upon the price charged by the WLAN operator for each offloaded user. The simulated results quantify the benefits of collaboration between the operators in terms of the offload ratio, network efficiency, and revenue gains.

With increasing mobile data demand there is a push towards heterogeneous networks. Small-scale operators (SSOs) of WLANs are becoming more prevalent, while Mobile Network Operators (MNOs) seek an outlet for their customers' data usage. These conditions prompt the need for an effective relationship between the two parties for the purpose of offloading cellular data traffic to WLANs in a way that is economically beneficial to all involved. This paper presents a model of such a relationship, in which the SSO sets a strategic offloading price per subscriber and the MNO chooses how many subscribers it wants to offload in order to minimize its costs. The application of this model is simulated in a real-world WLAN deployment in Oulu, Finland. Our findings can be used by both MNOs and SSOs to make informed network deployment decisions, even before engaging in an offloading relationship.

Spectrum trading creates more accessing opportunities for secondary users (SUs) and economically benefits the primary users (PUs). However, it is challenging to implement spectrum trading in multi-hop cognitive radio networks (CRNs) due to harsh cognitive radio (CR) requirements on SUs' devices, uncertain spectrum supply from PUs and complex competition relationship among different CR sessions. Unlike the per-user based spectrum trading designs in previous studies, in this paper, we propose a novel session based spectrum trading system, spectrum clouds, in multi-hop CRNs. In spectrum clouds, we introduce a new service provider, secondary service provider (SSP), to facilitate the accessing of SUs without CR capability and harvest uncertain spectrum supply. The SSP also conducts spectrum trading among CR sessions w.r.t. their conflicts and competitions. Leveraging a 3-dimensional (3-D) conflict graph, we mathematically describe the conflicts and competitions among the candidate sessions for spectrum trading. Given the rate requirements and bidding values of candidate trading sessions, we formulate the optimal spectrum trading into the SSP's revenue maximization problem under multiple cross-layer constraints. In view of the NP-hardness of the problem, we develop heuristic algorithms to pursue feasible solutions. Through extensive simulations, we show that the solutions found by the proposed algorithms are close to the optimal one.

Wireless channel between power producer and power consumer will play an important role when designing future smart grids. In order to optimize the performance of a smart grid, the knowledge of power price information at the consumer end and the knowledge of power demand information at the power producer side is important. In this paper, the modeling of advanced power grid with different cooperative sources of conventional and renewable power generation and with different power price knowledge is proposed. The control problem is to exploit the available information in the power grid in such a way that the power grid adapts to changes both in power production and power demand minimizing the power losses in the system. We use dynamic optimization methods to implement a dynamic control policy, which optimizes the performance of the power grid, when only the power demand information is assumed to be available at the power producer side. In addition, using both the instantaneous power demand knowledge at the power producer side and the instantaneous power price information at the power consumer end, it is shown that the dynamic control policy not only minimizes the power losses but also the balance between the power generation and power demand is achieved. The basis for the models and analysis presented in this paper are the analogies between the power grid control and optimum information flow control in communication networks.

Cognitive radio technology enables secondary users (SUs) to opportunistically use the vacant licensed spectrum and significantly improves the utilization of spectrum resource. Traditional architectures for cognitive radio networks (CRNs), such as cognitive cellular networks and cognitive ad hoc networks, impose energy-consuming cognitive radios to SUs' devices for communication and cannot efficiently utilize the spectrum harvested from the primary users (PUs). To enhance the spectrum and energy efficiencies of CRNs, we have designed a new architecture, which is called the Cognitive Capacity Harvesting network (CCH). In CCH, a collection of relay stations (RSs) with cognitive capability are deployed to facilitate the accessing of SUs. In this way, the architecture not only removes the requirement of cognitive radios from SUs and reduces their energy consumption, but also increases frequency reuse and enhances spectrum efficiency. In view of the importance of the RSs on the improvement of spectrum and energy efficiencies, in this paper, we study the RS placement strategy in CCH. A cost minimization problem is mathematically formulated under the spectrum and energy efficiency constraints. Considering the NP-hardness of the problem, we design a framework of heuristic algorithms to compute the near-optimal solutions. Extensive simulations show that the proposed algorithms outperform the random placement strategy and the number of required RSs obtained by our algorithms is always within 2 times of that in the optimal solution.

When considering a multicell scenario with nonuniform traffic distribution in multihop wireless networks, the search for the optimum topology becomes an NP-hard problem. For such problems, exact algorithms based on exhaustive search are only useful for small toy models, so heuristic algorithms such as genetic algorithms (GA) must be used in practice. For this purpose, we present a novel sequential genetic algorithm (SGA) to optimize the relaying topology in multihop cellular networks aware of the intercell interference and the spatial traffic distribution dynamics. We encode the topologies as a set of chromosomes and special crossover and mutation operations are proposed to search for the optimum topology. The performance is measured by a fitness function that includes the throughput, power consumption and delay. Improvement in the fitness function is sequentially controlled as newer generations evolve and whenever the improvement is sufficiently increased the current topology is updated by the new one having higher fitness. Numerical results show that SGA provides both high performance improvements in the system and fast convergence (at least one order of magnitude faster than exhaustive search) in a dynamic network environment. We also demonstrate the robustness of our algorithm to the initial state of the network.

In this paper, we present a new approach to optimization of multicast in multihop cellular networks. We apply a hexagonal tessellation for inner partitioning of the cell into smaller subcells of radius$r$. Subcells may be several orders of magnitude smaller than, e.g., microcells, resulting in what we refer to as a nanoscale network model (NSNM), including a special nanoscale channel model (NSCM) for this application. For such tessellation, a spatial interleaving SI MAC protocol is introduced for context-aware interlink interference management. The directed flooding routing protocol (DFRP) and interflooding network coding (IFNC) are proposed for such a network model including intercell flooding coordination (ICFC) protocol to minimize the intercell interference. By adjusting the radius of the subcell$r$, we obtain different hopping ranges that directly affect the throughput, power consumption, and interference. With$r$as the optimization parameter, in this paper we jointly optimize scheduling, routing, and power control to obtain the optimum tradeoff between throughput, delay, and power consumption in multicast cellular networks. A set of numerical results demonstrates that the NSNM enables high-resolution optimization of the system and an effective use of the context awareness.

In this paper, we present a framework for self-management of mobile clouds, based on self organized distributed coalition formation process for spectrum sharing in interference channel for large scale ad hoc networks. In this approach we use concept of coalition clusters within the network where mutual interdependency between different clusters is characterized by the concept of spatial network correlation. Then by using stochastic models of the process we give up some details characteristic for coalition game theory in order to be able to include some additional parameters for network scaling. Applications of this model are: a) Estimation of average time τ to reach grand coalition and its variance στ2through closed form equations. These parameters are important in designing the process in dynamic environment. b) Managing the dimensioning the coalition cluster within the network c) Modelling the network spatial correlation characterizing mutual visibility of the interfering links. d) Modelling of the effect of the new link activation/inactivation on the coalition forming process. e) Modelling the effect of link mobility on the coalition forming process.

In this paper we present nonlinear 3 player game model for joint routing, network coding, and scheduling problem. To define such a game model, first routing and network coding are modeled by using a new approach based on compressed topology matrix that takes into account the inherent multicast gain of the network. Topology matrix includes the set of all possible paths, including network coded paths, from sources to their corresponding sinks. These paths are identified and compressed, and then by switching between some of them with appropriate usage rates (frequencies), achievable throughput is optimized. The scheduling is optimized by a new approach called network graph soft coloring. Soft graph coloring is designed by switching between different components of a wireless network graph, which we refer to as graph fractals, with appropriate usage rates. Therefore each link can be painted with more than one different colors selected with appropriate probabilities. In the proposed game which is a nonlinear cubic game, the strategy sets of the players are links, path, and network components. The outputs of this game model are mixed strategy vectors of the second and the third players at equilibrium. Strategy vector of the second player specifies optimum multi-path routing and network coding solution while mixed strategy vector of the third players indicates optimum switching rate among different network components or membership probabilities for optimal soft scheduling approach. Optimum throughput is the value of the proposed nonlinear cubic game at equilibrium. The proposed nonlinear cubic game is solved by extending fictitious playing method. Numerical and simulation results prove the superior performance of the proposed techniques compared to other conventional schemes.

In this paper, we present a framework for analysis of self organized distributed coalition formation process for spectrum sharing in interference channel for large scale ad hoc networks. In this approach we define coalition clusters within the network where mutual interdependency between different clusters is characterized by the concept of spatial network correlation. Then by using stochastic models of the process we give up some details which are characteristic for coalition game theory in order to be able to include some additional parameters for network scaling. Applications of this model are: a) Estimation of average time to reach grand coalition and its variance στ2through closed form equations. These parameters are important in designing the process in dynamic environment. b) Dimensioning the coalition cluster within the network c) Modelling the network spatial correlation characterizing mutual visibility of the interfering links. d) Modelling of the effect of the new link activation/inactivation on the coalition forming process. e) Modelling the effect of link mobility on the coalition forming process.

We study a problem of optimal resource allocation in cooperative communication network with finite state fading channels and queueing. The control problem is to assign resources dynamically within the cloud of mobile users subject to the longterm average power constraint in order to stabilize the queues and maximize the long-term average throughput of the system. By modeling the problem as a finite horizon Markov Decision Problem (MDP), we propose a dynamic control policy that making opportunistic cooperative control decisions adaptively allocates resources over time varying fading channels and maximizes the long-term average throughput of the system. In addition, the concept of inter system networking (InSyNet) is introduced to provide performance bound for the resource allocation policies of the cooperative communication network (CCN).

In this paper, we present a joint optimization of power control, scheduling and relaying topology for multi-hop cellular networks aware of the intercell interference. To reduce the intercell interference in adjacent cells, cooperative diversity relaying scheme (COOR) is used in the system to reduce the transmission power needed to meet the same SINR threshold as the conventional relaying scheme (CONR). The resulting intercell interference management (I2M) protocols using COOR and CONR schemes will be referred to as I2M-COOR, and I2M-CONR respectively. In this complex scenario, for a given spatial traffic distribution we find the optimum scheduling and relaying topology in order to reduce the overall interference in the network and achieve a proper tradeoff between throughput and power allocation. Numerical results show that I2M-COOR offers an improvement in the network throughput of at least 150% and a reduction of power consumption of at least 130% compared to I2M-CONR. The optimum topology consumes in average 3 times less power than non-optimum options and the variation in throughput between the non-optimum solutions is by factor 5 inferior with respect to the optimum topology.

Although establishing cooperation in a wireless network is a dynamic process, most game theoretic coalition formation models proposed in the literature are static. We analyze a dynamic coalition formation game based on a Markovian model for the spectrum sharing problem in an interference channel. Our model is dynamic in the sense that distributed transmitter/receiver pairs, with partial channel knowledge, reach stable coalition structures (CSs) through a time-evolving sequence of steps. Depending on an interference environment, we show that the game process either converges to the absorbing state of the grand coalition or to the absorbing state of internal and external stability. We also show that, due to myopic links, it is possible that the core of the game is nonempty, but links cannot form the grand coalition to utilize the core rate allocations. We then formulate a condition for the formation of the stable grand coalition. Using simulation we show that coalition formation yields significant gains in terms of average rates per link for different network sizes. We also show average maximum coalition sizes for different distances between the transmitters and their own receivers. Finally, we analyze the mean and variance of the time for the game to reach the stable coalition structures.

In this paper, we use matrix games framework for joint optimization of routing and network coding under conflict free scheduling for multi-source wireless ad-hoc networks. The impact of multicast diversity on scheduling is controlled by using topology compression concept quantified through compressed multicast topology matrix. To define topology matrix, first a set of all possible paths, including network coded paths, is identified and compressed. Depending on the nature of data selected path can be unicast or multicast. Then by switching between these paths with appropriate rates (frequencies), achievable scaled throughput is maximized. A link conflict free environment is designed by appropriate conflict free network partitioning using network graph coloring algorithm. For each possible coloring scheme and considering priority assigned to each source, link scheduling partitions topology matrix into multiple sub-matrices, one for each partial topologies. Each sub-matrix is used as a payoff matrix for an asymmetrical matrix game where against any single move of the second player, first player has multiple (K) moves, corresponding to different partial topologies or their equivalent colors. The strategy sets for the players are links and paths respectively. Such a game will be formally referred to as Asymmetrical Matrix Game with notation AMG(2,K,1) and the value of this game is inverse of the scaled throughput. In this notation 2 indicates two dimensional games. At the equilibrium, mixed strategy vector of the first player indicates optimum percentage of time or optimum number of time slots dedicated to the selected partial topologies for a given partitioning of the network graph while, mixed strategy vectors of the second player is proportional to optimum usage rates of the paths. Numerical results are presented for a simple butterfly network including 6 nodes and 2 sources. One source transmits multicast and second one unicast data with different priority.

In this paper, we present a novel application of matrix game theory for optimization of link scheduling in wireless ad-hoc networks. Optimum scheduling is achieved by soft coloring of network graphs. Conventional coloring schemes are based on assignment of one color to each region or equivalently each link is member of just one partial topology. These algorithms based on coloring are not optimal when links are not activated with the same rate. Soft coloring, introduced in this paper, solves this problem and provide optimal solution for any requested link usage rate. To define the game model for optimum scheduling, first all possible components of the graph are identified. Components are defined as sets of the wireless links can be activated simultaneously without suffering from mutual interference. Then by switching between components with appropriate frequencies (usage rate) optimum scheduling is achieved. We call this kind of scheduling as soft coloring because any links can be member of more than one partial topology, in different time segments. To simplify this problem, we model relationship between link rates and components selection frequencies by a matrix game which provides a simple and helpful tool to simplify and solve the problem. This proposed game theoretic model is solved by fictitious playing method. Simulation results prove the efficiency of the proposed technique compared to conventional scheduling based on coloring.

In this paper we define the jointly optimum topology for the duplex transmission (uplink/downlink) in multihop cellular networks which is aware of the intercell interference and a protocol that reconfigures the optimum topology based on the observation of the temporal traffic in the network. In addition we also consider the application of network coding in cellular networks to combine the uplink and downlink transmissions and incorporate it into the optimum bidirectional relaying with intercell interference awareness resulting in a comprehensive solution for 4G common air interface.

In this paper, we present new methodology and results for joint routing and link scheduling optimization in multicast wireless ad-hoc networks. The impact of multicast diversity on scheduling is controlled by using topology compression concept quantified through compressed multicast topology matrix. To define topology matrix, first a set of all possible multicast paths, including network coded paths, is identified. A subset of these paths with appropriate rates is chosen to maximize achievable throughput or throughput per sum of transmitting powers on the route, in a conflict free environment created by proper scheduling. Therefore this optimization provides two improvement gains, throughput gain from scheduling on a compressed network topology and the gain from mixed path selection optimizations with a careful compromise between the multicast diversity and network coding. Numerical results, as illustration, are presented for a simple wireless butterfly network. If just throughput regardless of power consumption is maximized, then depending on the system parameters both a network coded structure or a plain routing can be optimum. On the other hand if throughput per power is maximized, a mixed set of plain routing paths is the optimum solution.

Cognitive wireless networks benefit from context awareness which is integrated in decision making process in different layers. In this paper, we modify the MAC layer transmission permission probability, for elastic traffic users, in such a way to discourage the transmissions from/to the users at the border of the cell where transmissions cause significant interference in adjacent cell. This will be referred to as spatial traffic shaping. By using the absorbing Markov chain theory, we provide, for such a concept, analytical models to analyze system performance, mainly probability of successful channel assignment and message delivery delay. The analysis shows that in the cellular network, with channel spatial reuse factor equal to one, the probability of successful channel assignment close to one can be achieved with acceptable message delivery delay.

The optimization of the relaying topology in multihop cellular network should provide the answer to the question who is transmitting to whom, and when, in such a way to insure the best system performance. In the case of temporally and spatially varying traffic distribution the optimal topology will also vary in time and an efficient way for topology control is needed in order to maximize the system performance. In this paper we present an algorithm for efficient relaying topology control, which is aware of the intercell interference, requiring coordinated action between the cells and resulting in multicell jointly optimal relaying topology. Numerical results demonstrate that an adaptive relaying topology control provides the network utility improvements and presents the framework for quantifying these improvements for spatially and temporally varying traffic.

A model for the service capacity at link layer, for a wireless, link-adaptive system is presented. The model includes imperfections in the adaptation chain (estimation error, estimation delay, acquisition error), and implementation implications (switching hysteresis). Transceiver characteristics and imperfections are independently represented by separate matrices. The dependence of effective capacity Rmacrcon the impairments is discussed using analytical, numerical, and simulation results. Examples show that the above effects should not be neglected in realistic performance analysis at upper layers

In this paper we analyze the impact of system imperfections on the overall cellular code-division multiple access (CDMA) radio network performance. The theory is general and some examples of practical sets of channel and system parameters are used as illustration. A flexible signal model, based on the complex signal format, is used enabling us to model all wideband CDMA standards. For such a signal, we first derive a complex decorrelator structure. In the next step imperfections in the operation of a decorrelating space-time Rake combiner are modeled and analyzed. Relative capacity losses and the network sensitivity function are used as performance measures. Simulations are also performed to confirm some of the key assumptions made in the analysis. Numerical results show that the user capacity varies significantly depending on the multipath profile, diversity order, fading rate, and code crosscorrelations. It is shown that up to 97 % of the system capacity can be lost due to the system imperfections. More, advanced and robust parameter estimators and/or multiuser detectors are needed to alleviate these degradations at the cost of increased complexity

This paper presents a model for the link service capacity that an imperfect adaptive radio link provides to upper layers. As the main contribution of this paper, the model includes a number of imperfections in the link adaptation chain, as well as implementation implications. The average goodput is expressed also in compact form and its dependence on the impairments is discussed using analytical, numerical, and simulations results. The model, to be used for analyses at upper layers, integrates physical channel, transceiver characteristics, and imperfections in a flexible way, by independent, separate matrices

In this paper we analyze capacity losses in advanced code division multiple access (CDMA) network due to imperfections in the operation of the system components. In addition to the standard WCDMA technology both, base stations and mobile units use antenna beam forming and self steering to track the incoming (and transmitted) signal direction. By using high directivity antennas and antenna pointer tracking the level of multiple access interference (MAI) and the required transmitted power are reduced. In order to exploit the available propagation diversity signals arriving from different directions (azimuth psi elevation phi) and delay tau, are combined in 3D (psi phi, tau) RAKE receiver. This is expected to significantly improve the system performance. The main result of this work is a systematic mathematical framework for capacity evaluation of such CDMA network in the presence of implementation imperfections and fading channel. The theory is general and some examples of practical set of channel and system parameters are used as illustration. As an example, it was shown that in the case of voice applications and 2D (4 antennastimes4 multipaths) RAKE receive, up to 90% of the system capacity can be lost due to the system imperfections. Further elaboration of these results, including extensive numerical analysis based on the offered analytical framework, would provide enough background for understanding of possible evolution of advanced W-CDMA and MC-CDMA towards the fourth generation of mobile cellular communication networks

In this paper, we investigate code acquisition in the delay and angular domain in environments where interference and noise are nonuniformly distributed in the spatial (angular) domain. It is seen that performance is clearly degraded by the presence of nonuniform spatial distributions of interference. The degree of impairment is related to the actual shape of the distribution and becomes more significant when large amounts of interfering power are concentrated in one or more angular directions. As compared to a reference case with a uniform distribution of equivalent interfering power, the mean acquisition time could increase by factors of up to four. Some effective approaches to compensate for the loss of performance due to the uneven nature of interference are also studied. First, the effect of search strategies in the delay and angular domains on acquisition performance is assessed. A searching algorithm up-ranking angular cells according to the amount of associated interference is proposed as one solution to reduce the performance gap. It is shown that applying this search strategy can considerably reduce the mean acquisition time. Finally, two adaptive schemes based on setting integration times or threshold values according to the level of interference prevailing in each angular cell, are discussed. The former approach returns performance figures similar to those obtained with the uniform equivalent interference distribution while the latter provide moderate performance gains.

The authors analyze throughput-delay performance of an unslotted channel load sensing protocol (CLSP)/direct sequence (DS)-code division multiple access (CDMA) packet radio network (PRN) with adaptive packet length over burst-error correlated fading channels. CLSP controls the packet access in uplink of unslotted ALOHA/DS-CDMA systems so that contention is avoided and throughput is maximized. However, due to high uncertainty of radio channels, the performance of CLSP/DS-CDMA PRN may suffer from notable degradations. Using theoretical analysis and simulation, the authors show that in highly correlated fading environments adapting the length of radio packets to fading conditions significantly improves system performance and energy efficiency of mobile terminals. In their modeling, they study the relation between the fade statistics and the packet length in correlated Rayleigh fading channels. The effects of reception diversity, imperfect transmit power control (TPC), and user mobility are considered. The results are used to develop simple, energy-efficient, and robust adaptation mechanisms.

This paper presents a throughput-delay analysis of a centralized unslotted DS/CDMA packet radio network using rate adaptive channel load sensing protocol (CLSP). CLSP is an access control protocol used to limit the contentions, i.e. multiple access interference (MAI) of the CDMA unslotted ALOHA radio channel, under a certain threshold to improve the system throughput. A mobile-location (space) based rate adaptive extension of CLSP is proposed to: (i) compensate the near-far effects and transmitter power control (TPC) difficulty of datagram packet transmissions under changing channel conditions; (ii) enhance the system performance and coverage; (iii) increase the energy-efficiency of the mobile unit. An analytical method is developed based on a multi-rate loss network model, of which each system load state is described with a two-state hidden Markov model (HMM) taking into account the impacts of TPC inaccuracy, spatial user distributions and channel attenuation. The results show that the proposed rate/space adaptive CLSP system gains significant improvement in throughput-delay tradeoffs compared to the fixed rate counterpart with the same coverage, offered traffic and QoS requirements. Also, in the new system the mobile terminal can operate with much lower maximum power.

We analyse throughput-delay performance of an unslotted DS-CDMA packet radio network (PRN) using the channel load sensing protocol (CLSP) and packet-length adaptation. This paper shows that while error-correcting channel coding has not yet been effective in heavily correlated flat fading environments, adapting the length of radio packets to time-varying channel conditions is a simple adaptive technique for maintaining and improving the system performance and the energy efficiency of mobile terminals. In our modeling we study the correlation between fade duration statistics and packet length in a flat Rayleigh fading channel under the effects of imperfect power control and user mobility. The results are used to derive practical and robust adaptation mechanisms and performance characteristics. A number of numerical results is presented. This paper lays the groundwork for exploiting adaptive radio possibilities on media access control (MAC) layer in unslotted DS-CDMA PRN.

We introduce a new concept of multiple access called /spl tau/-CDMA. The abbreviation stands for code division multiple access with delay (or) modulation and hopping. The concept is based on a modification of direct sequence spread spectrum (DSSS) system where transmitted waveform includes multiple amplitude and delay replicas of DSSS signal. In general notation amM/spl tau/-DSDH is used for the DS signal that includes m delayed (/spl tau/) replicas of different amplitudes (a), sent in a limited delay window of M chip intervals. The position of the delay window is hopped (delay hopping-DH) in the range of the code length N. This provides resistance to near far effect without the need for complex multiuser detectors. The variable impacts of the near far effect, for different positions of the delay window and fading, are simultaneously reduced by interleaving. If the signal energy is split to m>1 separate components, making it more vulnerable to noise and fading, the overall flow of useful information will be still increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance. This system combines the good characteristics of DSSS and FHSS systems. The near far effect is mitigated without need for complicated multiuser detectors and at the same time the simplicity of the DSSS system is preserved. There is no need for a frequency synthesizer. The coherency for coherent RAKE reception is maintained in a much simpler way than in the FH system. Higher suppression of the multipath component is achieved than in a standard DSSS system. For the above signal formats this paper offers a number of receiver configurations ranging from very simple to more complex ones providing better and better performance. The application is energy aware software radio where a configuration control algorithm would chose the simplest configuration in order to provide the required QoS for the given environment with the minimum processing power resulting in minimum energy consumption.

The paper presents a throughput-delay analysis of an unslotted DS-CDMA packet radio network (PRN) using a mobile-location aware rate adaptive channel load sensing protocol (CLSP) for media access control (MAC) in a heavily correlated Rayleigh fading channel. In this adaptive CLSP scheme, which we proposed previously (see Phan, V.V. and Glisic, S., IEEE ICC'02, 2002), an uncorrelated fading model is used for investigating system performance. This paper shows that while the error-correcting capability of channel coding has not yet been effective in heavily-correlated fading environments, the rate adaptive CLSP still provides significant enhancement for efficiency of radio and battery resource utilization compared to the fixed rate counterpart. Through our modeling, a comprehensive study is presented of the correlation between fade duration statistics and packet-transmission duration, and the impacts of channel attenuation, user mobility, spatial user distribution (SUD), and transmitter power control (TPC) inaccuracy. This paper lays groundwork for understanding the possibilities and benefits of context-aware adaptation on MAC, the vital layer of PRNs.

This paper presents a simple and accurate analysis for performance evaluation and comparison of a class of queueing schemes for priority handoff and call admission control in mobile cellular PCNs. The handoff requests are allowed to queue up in a finite or infinite buffer if upon their arrivals no idle channel is found. The handoff dwell time that is needed for a mobile to pass through the handoff area is viewed as a random variable having a general probability distribution. The new call requests are accepted according to a generic guard channel policy given priority to handoff calls. The analytical model is developed based on a birth-death process with state-dependent Poisson arrivals, exponentially distributed and decomposed service-time, multiple servers, finite or infinite system capacity and general customer impatience until the beginning of service. The measures of interests include the probabilities of handoff forced terminations, handoff failure and new call blocking. The closed-form solutions are obtained and numerical results are presented for important modeling scenarios. This analysis is believed to have significant uses for network planning and performance optimization.

We analyze capacity losses in advanced wideband code division multiple access (WCDMA) networks due to imperfections in the estimation of the system and channel parameters. Key components in the analysis are multiple access intracell interference (MAI), intercell interference, efficiency of the interference cancellation, multipath intensity profile, efficiency of the RAKE combiner, inefficiency of signal and channel parameter estimation and additive white Gaussian noise. Receiver structures are based on a conventional matched filter RAKE combiner that can be supported by either a linear or nonlinear interference canceler. Both the equal gain and maximal ratio combining techniques are considered. Results show that significant capacity gains can be achieved by interference cancellation in comparison to the conventional techniques. However, the capacity gain may be completely lost in fast fading channels due to the estimation imperfections.

We present models for the code acquisition process in RAKE receivers. These models include multipath diversity, multiple transmitter (base station or satellite) diversity, and multiple access interference generated by other users in the network. This results in a different probability of false alarm for each cell of the code delay uncertainty region. The analysis is based on signal flow graph theory. By using these models, we elaborate different strategies for RAKE receiver synchronization and derive exact closed-form results for the average acquisition time. These strategies differ in how they organize initial (first RAKE finger) and postinitial search algorithms. If the channel is known, the initial synchronization may organize a parallel search for all fingers simultaneously by a proper set up of the local correlators' mutual delays. If not, then a serial search of different segments (partitioned among the different fingers) can be organized. In the postinitial search, sequential or random initializations are possible. A set of approximations is also included for practical applications where a quick assessment of the system performance is needed.

The extension of conventional delay-domain code acquisition to the angular domain is explored. The uncertainty region is partitioned into a number of delay and angular cells. In single-path channels where the interference is modeled as temporarily and spatially white, there exists an optimum number of angular cells minimizing the mean acquisition time. Mean acquisition times up to three times shorter can be attained with the two-dimensional approach. A rather similar behavior is in general found in Lth-order equal amplitude multipath channels, where paths are contiguous in the delay or angular domains. The strategy employed to search through the uncertainty region may have a considerable impact on acquisition performance. The results reveal that the search should proceed not in the direction of the multipath spread but in the other available domain. Proper selection of the search strategy can reduce the synchronization time by a factor of up to two. Two-dimensional code acquisition in scenarios with spatially nonuniform interference is also investigated. In general, the acquisition performance is degraded by the presence of nonuniform interference in the angular domain.

The system throughput, outage probability and packet delay are analyzed for a feedback channel state information (FCSI) based soft decision MAC protocol in a centralized asynchronous CDMA packet radio system with finite population. The relative system performance loss due to effects of the feedback delay, access delay and imperfect channel sensing is investigated in terms of sensitivity functions. The motivation behind this protocol is to control the access of data transmission by dynamically changing permission probability depending on FCSI. The channel state is defined as a number of packets currently being transmitted in up-link (UL) multiple access channel. The FCSI is sensed and emitted periodically by a central base station (BS). The UL interfering load is therefore softly controlled under a certain threshold for a QoS requirement. The system performance can be improved significantly compared with conventional ALOHA or statically hard decision MAC packet radio system. The system is modeled with a modified Erlang loss queuing system, which has a variable number of servers and Erlang distributed service function. Tradeoff of the system parameters and performance characteristics is discussed based on number of numerical results.

A wireless LAN standard developed by IEEE committee P802.11 operates in the unlicensed 2.4 GHz ISM band. This band is a very hostile environment due to many unpredictable interference sources, such as microwave ovens, utilizing the same frequency bands. At the same time the allowed signal power density that can be used is limited in order to minimize the interference to other users in the same band. In order to avoid these interference and keep a low signal power density the standard supports both direct sequence (DS) and frequency hopping (FH) modulation for these applications. The new test beds for multimedia wireless (WLANs) also use FH modulation. We analyze the performance of a modification of the FH multiple frequency shift keying (MFSK) system that includes a multitone multiamplitude MFSK signal, designated as amMFSK modulation. In this case, in order to meet the transmitted power density limits imposed in the ISM band, the signal energy is split into m separate tones. This makes the system more vulnerable to noise and fading, but still the overall flow of useful information will be increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance.

In this paper, we discuss modeling of the serial code acquisition process in a code division multiple access (CDMA) network. Due to multiple access interference (MAI), the process is characterized by a different probability of signal detection P/sub D/ and probability of a false alarm P/sub FA/ in each cell of the code delay uncertainty region. We derive exact expressions for average code acquisition time and its variance. In addition to this, we also present several useful approximations, which enable easy engineering use of these results for practical applications in future Universal Mobile Telecommunications System (UMTS) solutions. Numerical results based on this analysis are used for decision threshold optimization in code acquisition process for asynchronous CDMA networks.

The general theory of adaptive self reconfigurable interference suppression schemes is applied to several specific practical problems mainly suppression of m-level m amplitude-shift keying, m phase-shift keying (PSK), and m quadrature amplitude modulation signals. This is a practical situation when a code-division multiple-access (CDMA) network is overlaid with standard microwave systems. Another example is a multirate CDMA network where a limited number of high bit rate CDMA signals are allowed to use much higher power level due to lower processing gain. The algorithm is well suited for a modular software radio concept, which we believe, will be more and more accepted in future wireless communications. Further modifications of the schemes necessary for these applications are described, and numerous results are presented to illustrate performance improvements. A general interpretation of these techniques based on so-called multilayer least mean squares (LMS) algorithm is introduced and discussed. The algorithm is based on estimating fast changing interfering signal parameters by using parallel structures, which are fast but complex. At the same time, estimation of slow-varying signal parameters over a large range is accomplished by using an LMS algorithm that is simple but slower. In this way, suppression of the interference occupying the same bandwidth as the CDMA signal is possible with reasonable implementation complexity. For this case, a BER0 dB for binary PSK interference, J/S>17 dB for 8-PSK, J/S>27 dB for 32-PSK, and J/S>40 dB for 128-PSK.

We analyze capacity losses in code division multiple access (CDMA) networks due to imperfections in the operation of the system components. The main result of this work is a systematic mathematical framework for capacity evaluation of CDMA-based networks in fading channels. This should be considered as an alternative tool to extensive simulations being used for these purposes at the moment. The intention is to provide simple approximate relations that simultaneously take into account: multiple access intracell interference (MAI), intercell interference, and near-far effect, including different sources of power control imperfections. In addition to this, the efficiencies of the major receiver components are also included in the analysis. A flexible complex signal format is used which enables us to model at currently interesting proposals for wideband CDMA (W-CDMA) standards. The theory is general, and some examples of practical set of channel and system parameters are used as illustration. Further elaboration of these results, including extensive numerical analysis based on the offered analytical framework, would provide enough background for the understanding of W-CDMA system performance in a realistic environment.

We analyze a new interference suppression structure in direct-sequence spread-spectrum (DSSS) systems that is based on two dimensional (frequency- and time-domain) notch filtering. In the first step, the filter is realized in the form of variable-step (function of estimation error-power /spl nu/) least mean square algorithm. This modification will improve the system performance in the transient period by making this period shorter. Unfortunately, in the steady-state regime, the performance will be slightly degraded. This suggests a modification that will include an algorithm with /spl nu/=2 in the transient state and /spl nu/=1 in the steady-state operation. Further modification of the algorithm will use time notching of the code division multiple-access (CDMA) receiver in the period when estimation error is larger than a given threshold. A comprehensive analysis and comparison of these modifications are presented and discussed. These results can be used either for performance enhancement of DSSS systems in the presence of jamming or for CDMA overlay-type mobile communication networks. In the latter case, the interfering signal comes from another user employing narrow-band modulation. The analysis does not include fading so that the results can be used in the case when the narrow-band modulated signal is not significantly distorted by fading. An example is line-of-sight microwave communications, which happens to be one of the most feasible applications.

In this paper we present a new approach to interference suppression in code-division multiple-access (CDMA) wireless networks. Depending on the interfering signal, these schemes adaptively change not only their parameters but their structures as well. For the relevant types of the interfering signal, suppression is also possible for the wideband interference occupying the same frequency band as the CDMA signal. Probability of error in these schemes is for several orders of magnitude better than in the existing solutions described in the open literature so far. The main applications are the CDMA overlay type wireless network collocated in the same frequency band with a high bit rate microwave communication system, and the multimedia CDMA network where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission.

A new approach to PN code acquisition is presented and analyzed. A recirculation loop is used to improve probability of synchro cell detection P/sub D/ in each retrace of the code uncertainty region. To further improve P/sub D/ and probability of false alarm P/sub fa/ simultaneously, code diversity (a number of synchro channels in parallel) is used. This is especially effective in the channel with multiple access interference and near-far effect. Typical applications are networks with very low signal-to-noise ratio. Examples are code division multiple access (CDMA) LEO satellite systems experiencing high Doppler or any CDMA network where the number of users is approaching capacity limits. Even if the carrier Doppler is compensated, in any asynchronous LEO satellite network, compensation of code Doppler is not feasible. For this reason, in order to cope with code Doppler (D) and delay (/spl tau/), a modification based on transforming the two-dimensional uncertainty region (D, /spl tau/) into a new uncertainty region (T/sub c/, /spl tau/) will be introduced. Parameter T/sub c/ is the period of the correlation pulses at the output of a sliding correlator. When Doppler rate is present, the three-dimensional uncertainty region (D, R/sub d/, /spl tau/) is transformed into a new one (T/sub c/, R/sub t/, /spl tau/) where R/sub d/ and R/sub t/ are Doppler rate and correlation pulse period change rate, respectively. The main motivation for this work is to find new algorithms suitable for all digital receiver implementation and operation at low signal-to-noise ratios. These algorithms make CDMA techniques feasible for direct communication between LEO satellite and small ground-based user terminals (handsets). A comprehensive performance study of the new PN code acquisition system is presented and discussed. The results obtained demonstrate that, for low signal-to noise ratios, the acquisition time achieved with the new algorithm is one order of magnitude shorter compared with standard techniques known so far.

In this paper we analyze the performance of wireless ad hoc networks based on mMFSK frequency hopping modulation. This modulation is a modification of the FH/MFSK system that includes a multitone MFSK signal which is designated as mMFSK modulation. In this case the signal energy is split to m separate tones making it more vulnerable to noise and fading but still the overall flow of useful information is increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance than the standard MFSK/FH system.

In this paper, we analyze the effect of wireless link characteristics on throughput, packet delay, and packet loss rate in code-division multiple-access (CDMA) networks using carrier-sense multiple-access (CSMA) protocols. Although CSMA protocols are being extensively considered for applications in wireless networks, there is no comprehensive analysis of the effect of the link characteristics on packet level QoS. In our paper, link parameters are incorporated into the analysis through the probability of correct channel sensing, the probability of packet correct demodulation, and the channel fading rate. Although the imperfect channel sensing degrades the system performance, the analysis demonstrates that the CSMA system outperforms ALOHA even if the probability of incorrect channel sensing is higher than 10/sup -1/. A number of numerical results quantitatively illustrates the impact of the channel fading rate and spatial correlation of the fading on packet level QoS. These results can be used for practical network design.

We present a model of serial code acquisition process in code-division multiple-access networks. The difference between this model and the existing work is in using the assumption that in each cell of delay uncertainty region the probability of false alarm, is different. This is caused by the fact that in each cell cross correlations between the local code and the codes used by the other users in the network are different. A closed-form expression for the average acquisition time is derived and discussed.

The performance analysis of a new concept of a code-division multiple-access (CDMA) based low Earth orbit (LEO) satellite network for mobile satellite communications is presented and discussed. The starting point was to analyze the feasibility of implementing multisatellite and multipath diversity reception in a CDMA network for LEO satellites. The results are used to specify the design parameters for a system experimental test bed. Due to the extremely high Doppler, which is characteristic of LEO satellites, code acquisition is significantly simplified by using a continuous wave (CW) pilot carrier for Doppler estimation and compensation. The basic elements for the analysis presented are: the channel model, the pilot carrier frequency estimation for Doppler compensation, and multipath and multisatellite diversity combining.

It is already known that the performance of narrowband interference adaptive filtering in DS spread spectrum systems is additionally degraded in the presence of a frequency hopped jamming signal compared to the case with CW interference. Even so, the adaptive filter can be rather efficient because during the hopping interval, while the jamming signal parameters are constant, the filter adjusts its weights; and if the hopping rate is not too high, there are time periods when the interfering signal is suppressed. In order to have a better insight into the performance of these systems, we analyze the DS spread spectrum receiver behavior, when the jamming signal frequency is continuously changing (chirp signal). We find that this is a reasonable step for a jammer that is trying to be more efficient. In such a case, a two-sided filter structure shows worse overall performance than a prediction error structure. As the jamming frequency sweeping rate or bandwidth is increased, the system performance is degraded. The analysis provides an insight into how much the system performance will be degraded as a function of the interfering (frequency sweeping) signal parameters.>

The performance of a direct sequence QPSK spread-spectrum receiver using adaptive filters in the presence of frequency hopped interference is analyzed. The analysis includes both the adaptive prediction error filters and the adaptive transversal filters with two-sided taps. If the product of the instantaneous frequency offset /spl Omega//sub l/, between the jamming signal and the carrier of the spread-spectrum signal, and the sampling period /spl Delta/ is 360/spl deg/ (/spl Omega//sub l//spl middot//spl Delta/=360/spl deg/), the filter gain is reduced to zero. The filter gain G highly depends on the filter adaptation rate /spl mu/. Depending on /spl mu/, G can vary from zero to more than 20 dB for a jammer/signal power ratio (J/S) of 20 dB. If /spl Omega//sub l//spl middot//spl Delta/ is small enough (/spl les/10/spl deg/), the performance of the transversal filter is better than that of the prediction error filter, in the case when /spl mu/ is small. For larger values of /spl mu/ or /spl Omega//sub l//spl middot//spl Delta/, these performances are approximately the same. Numerical results for the hopping sequence of the jamming signal are also presented. Besides the filter gain the analysis of the adaptation rate (time constant) filter misadjustment and the system bit error probability is also included.>

An algorithm for automatic decision threshold-level control in direct-sequence spread-spectrum systems is presented and analyzed. Using this algorithm, instantaneous setting of the threshold is possible. An additional loop called a threshold loop is used to improve the system performance. This loop is based on a constant false alarm rate (CFAR) criterion. The purpose of the algorithm is to set a decision threshold in the system which will provide a small probability of false alarm (P/sub 3/ to 0) and a large probability of signal detection (P/sub d/ to 1) at the same time. The analysis has shown that the threshold probability distribution function (PDF) is narrower (equaling better performance) in the case of the CFAR algorithm, but this comes at the cost of a considerably larger integration time for the system (the system time response is slower). As a compromise, the instantaneous algorithm is modified so that k successive samples of the signal are used to determine the value of the threshold. This permits better control of the shape and position of the threshold PDF with respect to the P/sub 3/ and P/sub d/ curves. At the same time, the time response of the system is good and can be easily controlled.>

A comprehensive analysis of a 1-persistent carrier-sense multi-access (CSMA) system using a radio channel with imperfect carrier sensing is presented and discussed. It is shown that a careful optimization of the channel state detector parameters must be performed in order to get good system performance. If the threshold of the detector is too high, the system will tend to behave like an unslotted ALOHA; if the threshold is too low, the system throughput will be zero. It is also shown that for the larger average packet rate G the system throughput is decreased. This is because for the same probability of correct channel sensing, the probability of incorrect transmissions from the waiting mode is increased.>

A novel approach to slow frequency hopping (FH) spread-spectrum signal tracking is presented and analyzed. This approach is based on utilization of additional synchronization data carrying information for FH signal tracking purposes which is added to the digital data stream. Using a renewal process model, the steady-state probability mass function for the phase error process is derived, along with expressions for the tracking error variance, and the mean time to lose lock. Results are presented for several different tracking algorithms and a rough comparison with a standard early-late gate tracking loop is made.>

For pt.I see ibid., vol.39, no.2, p.304 (1991). A novel algorithm for discrete tracking of slow frequency hopping spread-spectrum signals is described and analyzed. In this system, each Mth hopping interval is completely used for transmission of synchronization data. The motivation for introducing this algorithm is that it allows a large degree of flexibility with respect to trading off system performance, complexity, and the redundancy introduced for tracking purposes. The analysis of the system performance is based on the utilization of results from discrete renewal process theory. However, because of the difficulty in obtaining the exact values for the transition probabilities, approximate results are presented.>

The symbol synchronizer presented is an all-digital data transition tracking loop which permits simple implementation and voltage control of the loop bandwidth. The equivalent loop integration constant is changed by changing the threshold level of a comparator at the output of the loop phase error detector. Phase error probability distribution function, its variance, and the average probability of cycle slipping are analyzed analytically for the general case. The theory of finite Markov chains is used to analyze statistical properties of the tracking error, primarily with regard to the phase error distribution and its variance, the average probability of the cycle slipping, the synchronizer time response, and bandwidth. As an example, numerical results for generalized tamed frequency modulation (GTFM with B=0.62 and r=0.36) are presented and discussed.>

The applicability of standard symbol synchronization schemes in digital communication systems using partial-response CPM (continuous phase modulation) signaling has been analyzed. Using the theory of maximum a posteriori estimation of the unknown parameter in Gaussian noise, a theoretical structure for the optimum symbol synchronizer in a system using partial-response CPM signaling is derived. As the first approximation, a closed-loop configuration, known as the early-late loop, is derived and discussed. Due to signal correlation in adjacent symbol time intervals, even this configuration is impractical for a hardware realization. For these reasons, different approximations of the general maximum-likelihood function, leading to the discrete bit timing loop realizations, are derived and discussed. The influence of the carrier phase synchronization error on these synchronizers is also discussed.>

An automatic decision threshold level control (ADTLC) algorithm for direct-sequence spread-spectrum systems is described and analyzed. Two parameters of interest, probability of false alarm P/sub a/ and probability of correct signal detection P/sub d/, are controlled simultaneously. As an example, the implementation of the algorithm in several practical direct-sequence spread-spectrum receivers is discussed. A considerable advantage of this algorithm compared to the classical approach (constant false alarm probability control) to the problem is demonstrated.>

A novel criterion for digital synchronous communication system efficiency estimation is defined. All system attributes such as bit error probability, coding efficiency, initial system synchronization time, efficiency of detection of timing anomalies and system sync recovery, reliability of the lock indication, and the amount of redundancy insertion in the data stream for synchronization and error-correcting coding purposes are included in a single parameter called "system efficiency." The expression for this parameter is derived under the assumption of signal ergodicity and steady-state system operation. In its final form, this parameter seems obvious almost by inspection. Even so, until now, it has not been used in the analysis of communication system efficiency. The analysis of this parameter for several different systems is presented as an illustration.

An analytical expression for the power density spectrum of the product of two time-displaced versions of a maximum-length binary pseudonoise signal is derived. This expression is valid for any value of the pseudorandom sequence length. This provides a possibility for evaluating the effect of correlator self-noise on the serial synchronization decision circuitry of the spread-spectrum receiver for all possible values of the time difference between the pseudonoise modulation on the carrier and the pseudonoise waveform generated at the receiver.