Due to the rapid growth of renewable energy and its integration into the existing grid, the future power grid may face several stability challenges. Sub-synchronous oscillation (SSO) is one of the critical stability aspects that can disrupt the normal operation of the grid within a few grid cycles. Although the methods of SSO detection and its mitigation in conventional power systems are well defined, the interfacing of large number of power electronics-based devices at generation, transmission and distribution level has regenerated SSO issue introducing several new factors that can trigger different types of SSO. Thus, this paper proposes an energy based SSO assessment that analyzes the energy of the measured signal before and after the disturbance to effectively determine SSO in a timely manner. This approach is validated on both simpler and more complex power systems including single AC bus integrated with type-4 wind farm and standard IEEE 39 Bus network with type 4 wind farm, respectively. Various simulation case studies are presented to validate the effectiveness of proposed scheme in determining different types SSOs.

Digital twins (DTs) are emerging as effective tools for power electronic converters, addressing important objectives such as real-time monitoring, fault detection and predictive maintenance. Among these power converters, the dual active bridge (DAB) stands out for DC-DC conversion applications. However, the non-linear dynamics of DABs pose considerable challenges to their accurate modeling. To address these challenges, this paper investigates the use of machine learning (ML) and deep learning (DL) models for DT implementation in DABs. Specifically, XG-Boost and dense neural network (DNN) models are employed to construct DTs compatible with low-cost microcontrollers. These DTs are operated in parallel with the physical DAB converter to predict its output voltage in real-time. Experimental results demonstrate that both of the models perform well in terms of accuracy and applicability to low-cost microcontroller. However, the DNN is more reliable and the XGBoost is simpler.

Electric vehicle (EV) charging stations have been evolving to offer better and more efficient power delivery methods. A key area of research in this field involves predicting the power consumption of EV charging stations. Many researchers have addressed this issue using machine learning and deep learning methods, however, forecasting models struggle to predict individual charging sessions with high resolutions. In this paper, a deep neural network (DNN) is constructed to forecast the EV charging current profile and state of charge (SoC). Charging current and SoC are mathematically formalized and embedded into the DNN’s loss calculation to build a physics-informed neural network (PINN). The performance of the models is assessed through analysis of their prediction error, utilizing actual data from real EV charging sessions.

The Controller Area Network (CAN) Bus is a commonly used communication protocol for different applications including vehicle controllers and power electronics converters which are the application focus in this paper. One drawback of CAN-bus is the lack of security measures in the protocol, which can be problematic if the communication line is exposed to attackers. This paper proposes a novel method to secure CAN-bus communication that is light-weight and applicable for power converters and microgrid applications. The proposed solution aims to protect against eavesdropping, false data injection, and replay attacks. The security scheme is implemented and deployed on a low-cost microcontroller that is used to control power sharing rectifiers. Experimental results are carried out to show that the proposed method effectively secures the channel against attacks with minimal time and space overhead.

The fog computing paradigm brings together storage, communication, and computation resources closer to users' end-devices. Therefore, fog servers are deployed at the edge of the network, offering low latency access to users. With the expansion of such fog computing services, different providers will be able to deploy multiple resources within a restricted geographical proximity. In this paper, we investigate an incentive-based cooperation scheme across fog providers. We propose a distributed cooperative algorithm amongst fog computing providers where fully collaborative fog nodes are subject to different loads. The proposed algorithm leverages the power-of-two result and exploits a cooperation probability, namely the probability that a given provider collaborates by accepting a computation request from another provider, as a mean to achieve a fair cooperation. We adopt an analytical approach based on exploiting a simplified performance model to demonstrate numerically that a set of optimal accepting probabilities exits when the number of server nodes goes to infinity. This result then drives the design of our distributed algorithm. Second, in our experimental approach, we perform a set of simulation analysis to verify the validity of the proposed solution when the number of servers is limited.

In this paper, we propose a new mode selection scheme for D2D enabled long term evolution-advanced (LTE-A) systems. The proposed scheme is based on a predefined threshold parameter related to the LTE sidelink (SL) received signal strength (RSS), where above this threshold, the D2D mode outperforms the cellular communication mode. Using the stochastic geometry, the system model is described and the expression of the proposed threshold parameter is derived. To evaluate the performance of the proposed scheme, the expressions of the probability of using D2D mode and the average ergodic capacity are detailed and derived. Based on that, Monte Carlo simulations are used to confirm the derived expressions and the advantages of the proposed scheme over related work in the literature.

In classical information and communication theory, channel capacity and achievable rate over Gaussian channels, whether for constant or fading channels and whether for single user or multiple users, are characterized as functions of the power that is used for the transmission of the information. The associated circuit power that is needed in real communication transceivers to power up the electronics and to do all required signal processing is typically not involved in the capacity characterization. However, to achieve global energy efficiency of the communication systems, the adaptation of the communication schemes should be based on total power consumption. In this paper, we characterize the maximum achievable rates over many fundamental channels taking total power constraints into considerations.

This paper investigates the impact of primary network interference on the performance of cognitive multihop secondary network under various multiple-input multiple-output (MIMO) approaches per hop. Specifically, the cognitive system involves a secondary network with MIMO relays that use the amplify-and-forward protocol, and each of which shares the same spectrum resources of multiple primary users (PUs) transmit and receive stations. Two different receive array conditions, and hence processing approaches, per hop in the secondary network are treated separately, which are maximal ratio combining for sufficiently spaced receive antennas to provide receive diversity gain and interference cancellation (IC) for insufficiently spaced antennas to reduce the effect of PUs interference. The latter approach involves two different algorithms that vary in terms of complexity and achieved performance, which are dominant receive IC and adaptive receive IC. Moreover, for both approaches, the transmit array gain is achieved per hop through the low-complexity transmit antenna selection. In doing so, new analytical results for multihop secondary network's end-to-end outage probability are developed. Moreover, simple asymptotic results for this outage performance in high SNR regime are provided, from which the achieved diversity and coding gains and the diversity-multiplexing tradeoff can be extracted. In addition, to further enhance the secondary network, optimal power allocation among hops is obtained based on the asymptotic outage performance under the constraints of transmit power of a secondary transmit station and interference limit on the primary network. The developed analytical results in this paper are validated through numerical and simulation results.

This paper studies the achievable secrecy performance of multiple-input multiple-output wiretap channels in the presence of imperfect channel state information (CSI) with practical low-complexity transmission schemes. In particular, we propose a general order transmit antenna selection and power-efficient output-threshold maximal ratio combining scheme. Two separate cases depending on the availability of the eavesdropper's CSI at the transmitter are considered. New closed-form expressions of the secrecy outage probability and the average secrecy rate are obtained. In addition, the secrecy diversity order and array gains, high signal-to-noise ratio slope, and power offset are characterized through asymptotic analysis, which enables the characterization of the effect of imprecise transmit antenna selection, output-threshold, and imperfect CSI on the secrecy performance. Numerical results are presented to validate the main outcomes of this paper.

We consider the design of space-time codes for the multiple-input multiple-output multicast communication systems with two classes of receivers. The first class comprises high-resolution (HR) receivers which have access to reliable channel state information (CSI) and can perform coherent detection, and the second class comprises low-resolution (LR) receivers which do not have access to CSI and can only perform non-coherent detection. We propose a layered encoding structure in which LR information available to both classes of receivers is encoded using Grassmannian constellations, and an incremental component, which is available only to the HR receivers, is encoded in the particular bases of the transmitted Grassmannian constellation points, thereby giving rise to constellations on the Stiefel manifold. The proposed structure enables reliable coherent communication of the HR information without compromising the reliability with which the basic LR information is non-coherently communicated. To effect rate-efficient communication of the incremental, HR layer, we use optimization methods on the Stiefel manifold to develop a novel technique for designing the unitary constellations directly. This approach alleviates the restriction imposed by the traditional techniques in which unitary space-time codes are constructed from scalar constellations. As such, this approach enables better control of the distance spectrum of the developed constellations and more effective utilization of the degrees of freedom that underlie the Stiefel manifold. For the LR receivers, we use maximum likelihood detection, whereas for the HR receivers, we develop a computationally-efficient two-step sequential detector which detects the LR information prior to detecting the incremental component superimposed on it. The detectors and the layered structure with the aforementioned constellations enable full diversity and maximum degrees of freedom to be achieved on the Grassmann and Stiefel manifolds.

The pervasiveness of small mobile devices equipped with multiple wireless interfaces enabled novel communication paradigms: opportunistic data transfer between the mobile devices. In this paper, we consider the heterogeneity in forwarding mechanisms as one of the major reasons which affects the performance of forwarding algorithms. Heterogeneity arises in different contexts, for example in device types (i.e., tablets vs. phones vs wearable), operating systems or node objectives. Each node may have its own objectives e.g. security, privacy, trust, battery life, etc. We specifically address the heterogeneity in nodes objectives and propose two different architectures, cooperative and collaborative. In the cooperative mode nodes can only communicate if they share the same forwarding objective such as saving energy or minimizing delays. In the collaborative mode, all nodes can communicate with other nodes after a negotiation phase within which they find objective trade-offs. We then present three different collaborative algorithms and evaluate all proposed algorithms using real mobility traces to find out the message delivery success rate.

In this paper, we provide a comprehensive analytical framework on the performance of multiple-input multiple-output (MIMO) mutlihop amplify-and-forward relay network employing transmit antenna selection (TAS) with receive maximal ratio combining (MRC) in the presence of randomly located interferers. The channel fading models per hop are assumed to be independent and follow exponential random distribution, and the interference is distributed according to the spatial Poisson point process PPP, which is further known as symmetric alpha stable distribution. The impact of spatial dependence across multiple antennas is facilitated by considering three different network interference models: 1) the isotropic model, where all receive antennas see interference belonging to the same Poisson point process (PPP); 2) the independent model, where each receive antenna sees interference belonging to a different independent PPP; and 3) the mixture model, where each receive antenna sees the superposition of the two previous models. The end-to-end transmission is performed using two TAS modes, which includes signal-to-noise ratio (SNR)-based selection, and signal-to-interference noise ratio (SINR)-based selection. The analysis provides new analytical results for the outage probability and symbol error rates (SER). In addition, the impact of feedback delay on the performance of the proposed system for SNR-based selection is investigated. We further study the optimum resource allocation strategies including power allocation, position allocation, and joint allocation for power and position. The obtained results are clarified through selected numerical and simulated examples.

In this paper, the long-term average achievable rate over block-fading buffer-aided relay channels is maximized using a hybrid scheme that combines three essential transmission strategies, which are decode-and-forward, compress-and-forward, and direct transmission. The proposed hybrid scheme is dynamically adapted based on the channel state information. The integration and optimization of these three strategies provide a more generic and fundamental solution and give better achievable rates than the known schemes in the literature. Despite the large number of optimization variables, the proposed hybrid scheme can be optimized using simple closed-form formulas that are easy to apply in practical relay systems. This includes adjusting the transmission rate and compression when compress-and-forward is the selected strategy based on the channel conditions. Furthermore, in this paper, the hybrid scheme is applied to three different models of the Gaussian block-fading buffer-aided relay channels, depending on whether the relay is half or full duplex and whether the source and the relay have orthogonal or non-orthogonal channel access. Several numerical examples are provided to demonstrate the achievable rate results and compare them to the upper bounds of the ergodic capacity for each one of the three channel models under consideration.

Abstract In this paper, we examine the impact of antenna correlation on transmit antenna selection with receive maximal ratio combining (TAS/MRC) in multiple‐input multiple‐output multiuser underlay cognitive radio network (MIMO‐MCN) over a Nakagami‐m fading environment. The secondary network under consideration consists of a single source and M destinations equipped with multiple correlated antennas at each node. The primary network composed of L primary users, each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing paradigm, the transmission power of the proposed secondary system is limited by the peak interference limit on the primary network and the maximum transmission power at the secondary network. In particular, we derive exact closed‐form expressions for the outage probability and average symbol error rate of the proposed secondary system. To gain further insights, simple asymptotic closed‐form expressions for the outage probability and symbol error rate are provided to obtain the achievable diversity order and coding gain of the system. In addition, the impact of antenna correlation on the secondary user ergodic capacity has been investigated by deriving closed‐form expressions for the secondary user capacity. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. Copyright © 2016 John Wiley & Sons, Ltd.

The evolution of mobile devices into highly capable computing platforms that sense, store, and execute complex tasks is making them attractive candidates for edge computational micro-cloud settings. Such solutions are creating novel security challenges due to the increased push for more seamless computational cyber-foraging that leverages the exploding proliferation of mobile devices. A major concern is that security challenges stemming from these trends, are growing at a rate exceeding the evolution of security solutions. In this paper, we consider an environment in which computational offloading is performed among a set of mobile devices. We propose HoneyBot, a defense technique for device-to-device (d2d) malicious communication. While classical honeypots designed to isolate distributed denial of service (DDoS) botnet attacks fail to detect d2d insider attacks, HoneyBot nodes detect, track, and isolate such attacks. We propose and investigate detection and tracking algorithms that leverage insecure d2d infected communication channels to accurately and efficiently identify suspect malicious nodes and isolate them. Our data driven evaluation and analysis, based on 3 real world mobility traces, show that the number and placement of HoneyBot nodes (Hb) in the network considerably impact the tracking delay and the detection accuracy.

In this paper, we develop two approaches for designing unitarily-constrained space-time block codes, which are suitable for communicating high-resolution information in layered multiple-input multiple-output broadcast channels. Unlike existing space-time codes, which are usually synthesized from standard phase-shift keying (PSK) or quadrature amplitude modulation constellations, the space-time codes proposed herein are designed using direct optimization over the unitary group. In comparison with conventional unitary space-time block codes, including Alamouti code with PSK constellations, the space-time codes generated by the proposed approaches exhibit significantly better performance, more favorable distance spectra and more effective utilization of the degrees of freedom that underlie the unitary group.

This paper investigates the performance of multiuser mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The outdated channel information (OCI) on the first relaying hop and its effect on the system performance is also studied. Furthermore, a power allocation scheme is proposed. The considered system includes K sources (users) that communicate with the relay node through RF links and the relay is connected with the destination through an FSO link. In the analysis, the first hop channels are assumed to follow Rayleigh fading model and the second hop channel is assumed to follow Gamma-Gamma fading model with pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability (ASEP) and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio (SNR) regime. Using the asymptotic results, the power of users and relay are determined to minimize the system outage probability under a total power constraint. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.

In this paper, we examine the impact of antenna correlation on transmit antenna selection with maximal ratio combining (TAS/MRC)in multiple-input-multiple-output multiuser cognitive relay networks (MIMO-MCRNs). A single secondary user (SU) source communicates with M SU destinations via SU decode-and-forward (DF) relay over Rayleigh fading channels and in the presence of L PU destinations. Each node in the considered SU network is equipped with multiple correlated antennas as well as the L PU destinations. The SU network employs underlay spectrum sharing paradigm in which the SU transmission power is limited by peak interference temperature limit on the PU network and the maximum allowable transmission power at each node of the SU network. As a measure of performance, we derived an exact expression for the outage probability of the proposed SU network. To gain further insights, a simple asymptotic expression for the outage probability is provided to obtain the achievable diversity order and coding gain.

With the advent of wearable computing and the resulting growth in mobile application market, we investigate mobile opportunistic cloud computing where mobile devices leverage nearby computational resources in order to save execution time and consumed energy. Our goal is to enable generic computation offloading to heterogeneous devices forming a mobile-to-mobile opportunistic computing platform. In this paper, we adopt (1) an analytical approach and (2) an experimental approach to highlight the gain given by mobile-to-mobile opportunistic offloading compared to local execution. We also investigate multiple offloading strategies with regards to both computation time and energy consumption. We propose an auto-splitting and offloading algorithms that computes the optimal chunks sizes that could be offloaded remotely to neighboring mobile device. We show that our splitting and offloading algorithm succeeds in picking the optimal chunk sizes and distribution with up to 99.7% efficiency. In addition, the offloader device saves up to 80% energy while offloading the task remotely. For instance if the offloader device is running out of battery, offloading is the ultimate solution to increase its lifetime.

This work proposes a suboptimal multi-user scheduling scheme for Gaussian broadcast channels which improves upon the classical single user selection, while considerably reducing complexity as compared to the optimal superposition coding with successful interference cancellation. The proposed scheme combines the two users with the maximum weighted instantaneous rate using superposition coding. The instantaneous rate and power allocation are derived in closed-form, while the long term rate of each user is derived in integral form for all channel distributions. Numerical results are then provided to characterize the prospected gains of the proposed scheme.

In this paper, we present a comprehensive investigation on the secrecy performance of opportunistic relay selection systems employing the decode-and-forward protocol over Rayleigh fading channels. Considering a practical setting where direct link between the source node (Alice) and the destination node (Bob) is available, we study the secrecy performance of three different diversity combining schemes, namely, maximum ratio combining (MRC), distributed selection combining (DSC), and distributed switch-and-stay combining (DSSC). Throughout the analysis, we consider two different scenarios based on the availability of the eavesdropper's channel state information (CSI), i.e., Scenario A, where the eavesdropper's CSI is not available at Alice and the relay, and Scenario B, where Alice and the relay have knowledge about the eavesdropper's CSI. For Scenario A, we derive exact closed-form expressions for secrecy outage probability and simple asymptotic approximations for the secrecy outage probability, which enable the characterization of the achievable secrecy diversity order and coding gains. For Scenario B, we derive closed-form expressions for the achievable secrecy rates. For both scenarios, we investigate the impact of feedback delay (outdated CSI) on the secrecy performance wherein exact and asymptotic secrecy outage probability and closed-form expressions of the secrecy achievable rates are obtained. Our analytical findings suggest that both the MRC and DSC schemes achieve the maximum diversity order of K+1 where K is the number of relays. In addition, the feedback delay has a significant impact on the achievable secrecy performance by reducing the achievable diversity order to two.

The aim of this work is to maximize the long-term average achievable rate region of a primary and a secondary source-destination pairs operating in an overlay setup over block-fading channels. To achieve this objective, we propose an opportunistic strategy to grant channel access to the primary and secondary sources based on the channel conditions in order to exploit the available multiple-link diversity gains in the system. The secondary source has causal knowledge of the primary messages and it acts as a relay of the primary source in return for getting access to the channel. To maximize the gains of relaying, the relay and destination are equipped with buffers to enable the use of channel-aware adaptive link selection. We propose and optimize different link selection policies and characterize their expected achievable rates. Also, we provide several numerical results to demonstrate the evident mutual benefits of buffer-aided cooperation and adaptive link selection to the primary and the secondary source-destination pairs.

It is common practice for mobile devices to offload computationally heavy tasks off to a cloud, which has greater computational resources. In this paper, we consider an environment in which computational offloading is made among collaborative mobile devices.We call such an environment a mobile d

In this paper, we investigate the impact of multiple correlated antennas on the performance of transmit antenna selection with receive maximal ratio combining (TAS/MRC) model. Multiple correlated antennas are considered at the primary and secondary users in dual-hop underlay cognitive radio system. The transmit power condition of our proposed spectrum-sharing system is governed by interference temperature limit on the primary networks and the maximum transmission power at the secondary network. An exact expression for the outage probability of the proposed system is derived. To gain further insights, simple asymptotic expression for the outage probability is provided to obtain the achievable diversity order and coding gain of the system. All derived analytical results are corroborated by simulation results to show the correctness of our derived results.

This paper considers downlink multicast transmit beamforming for secure layered transmission systems with wireless simultaneous information and power transfer. We study the power allocation algorithm design for minimizing the total transmit power in the presence of passive eavesdroppers and energy harvesting receivers. The algorithm design is formulated as a non-convex optimization problem. Our problem formulation promotes the dual use of energy signals in providing secure communication and facilitating efficient energy transfer. Besides, we take into account a minimum required power for energy harvesting at the idle receivers and heterogeneous quality of service (QoS) requirements for the multicast video receivers. In light of the intractability of the problem, we reformulate the considered problem by replacing a non-convex probabilistic constraint with a convex deterministic constraint which leads to a smaller feasible solution set. Then, a semidefinite programming relaxation (SDR) approach is adopted to obtain an upper bound solution for the reformulated problem. Subsequently, sufficient conditions for the global optimal solution of the reformulated problem are revealed. Furthermore, we propose two suboptimal power allocation schemes based on the upper bound solution. Simulation results demonstrate the excellent performance and significant transmit power savings achieved by the proposed schemes compared to isotropic energy signal generation.

Mobile Device Clouds are becoming a reality with the quantitative and qualitative upgrades on mobile devices such as smart-phones and tablets. This proliferation renders mobile devices capable of initiating sophisticated cyberattacks especially when they coordinate together and form a distributed mobile botnets which we call “MobiBots”. MobiBots infect a large number of mobile devices and schedule targeted attacks by leveraging device-to-device (d2d) short range wireless communications. In this work, we first introduce MobiBots, the formation of MobiBots, their challenges, and limitations. We then make the case for MobiBots utilization. We show the potential for and impact of the large scale infection and coordination of mobile devices via short range wireless technologies in attacks against other mobile devices that come within proximity. We show that MobiBots are difficult to detect and isolate compared to common botnets. However, prevention techniques cost at least 40% of the network capacity.

We consider the design of space-time codes for multi-resolution multiple-input multiple-output (MIMO) broadcast communication systems. Two classes of receivers are considered: high-resolution (HR) receivers, which have access to reliable channel state information (CSI) and can perform coherent detection, and low-resolution (LR) receivers which do not have access to CSI and can only perform non-coherent detection. We propose a layered encoding structure, whereby, for the LR receivers, the transmitted codewords are chosen to be points on the Grassmann manifold whereas, for the HR receivers, incremental information is encoded in the particular bases of the transmitted codewords, thereby representing points on the Stiefel manifold. For the HR receivers, we develop a computationally-efficient two-step detector. Using this detector, we show that the proposed structure enables reliable coherent communication of the incremental HR information without compromising the reliability with which the basic LR information is non-coherently communicated. We also show that this structure enables full diversity to be achieved for both LR and HR receivers. Finally, we show that this structure achieves the maximum number of degrees of freedom for non-coherent LR channels and coherent HR channels with unitarily-constrained input signals.

In this paper, we consider a fading relay channel where the source uses two layers source coding with successive refinement. The two source layers are transmitted using superposition coding at the source and relay with optimal power allocation, and successive interference cancellation at the receivers (i.e. relay and destination). The power allocation for the two layers at the source and relay is subject to optimization in order to maximize the expected user satisfaction that is defined by a utility function of the total decoded rates at the destination. We assume that only the channel statistics are known. The relay is half-duplex and applies decode and forward. We characterize the expected utility function in terms of the channel statistics of the fading channels, and we solve the optimization problem using the numerical random search method. We provide many numerical examples to show the prospected gains of using the relay on the expected utility for different channel conditions. Furthermore, we obtain that for some conditions, it is optimal to send only one layer.

In this paper, we analyze the performance of a multiple-input multiple-output (MIMO) multi-hop relay network using transmit antenna selection and maximal ratio combining (TAS/MRC) employing amplify-and-forward relay mode over a Rayleigh fading channels in the presence of Poisson field of interferers, that is applied practically in current cellular networks like LTE (Long Term Evolution). The aggregated interference per hop is modeled as shot noise with α-stable distribution, which is assumed to be non-identical per receive antenna. In particular, we derive compact analytical expressions for exact, and upper bound outage probability of the system. To gain further insights on the proposed system behaviors, we derive asymptotic outage probability at high signal-to-ratio (SNR) which explicitly characterizes the diversity order and coding gain of the network. All derived analytical results are corroborated by simulation results to show the correctness of our derived results.

Wireless sensor technologies can provide the leverage needed to enhance patient-caregivers collaboration through ubiquitous access and direct communication, which promotes smart and scalable vital sign monitoring of the chronically ill and elderly people live an independent life. However, the design and operation of BASNs are challenging, because of the limited power and small form factor of biomedical sensors. In this paper, an adaptive compression technique that aims at achieving low-complexity energy-efficient compression subject to time delay and distortion constraints is proposed. In particular, we analyze the processing energy consumption, then an energy consumption optimization model with constraints of distortion and time delay is proposed. Using this model, the Personal Data Aggregator (PDA) dynamically chooses the optimal compression parameters according to real-time measurements of the packet delivery ratio (PDR) or individual users. To evaluate and verify our optimization model, we develop an experimental testbed, where the EEG data is sent to the PDA that compresses the gathered data and forwards it to the server which decompresses and reconstructs the original signal. Experimental testbed and simulation results show that our adaptive compression technique can offer significant savings in the delivery time with low complexity and without affecting application accuracies.

In this paper, we examine the impact of antenna correlation on transmit antenna selection with receive maximal ratio combining (TAS/MRC) in multiple-input multiple-output multiuser network (MUN-MIMO) with single source, M destinations with underlay spectrum sharing over Nakagami-m fading environment. The secondary network under consideration is equipped with multiple correlated antennas at each node. The primary networks composed of L primary users (PUs) equipped with multiple correlated antennas. For the underlay spectrum sharing transmission, the transmit power condition of the proposed MU spectrum-sharing system is limited by peak interference temperature limit on the primary networks and the maximum transmission power at the secondary network. In particular, we derive an exact expression for the outage probability and SER of the proposed system. To gain further insights, simple asymptotic expression for the outage probability and SER are provided to obtain the achievable diversity order and coding gain of the system.

This paper studies secure layered video transmission in a multiuser multiple-input single-output (MISO) beamforming downlink communication system. The power allocation algorithm design is formulated as a non-convex optimization problem for minimizing the total transmit power while guaranteeing a minimum received signal-to-interference-plus-noise ratio (SINR) at the desired receiver. In particular, the proposed problem formulation takes into account the self-protecting architecture of layered transmission and artificial noise generation to prevent potential information eavesdropping. A semi-definite programming (SDP) relaxation based power allocation algorithm is proposed to obtain an upper bound solution. A sufficient condition for the global optimal solution is examined to reveal the tightness of the upper bound solution. Subsequently, two suboptimal power allocation schemes with low computational complexity are proposed for enabling secure layered video transmission. Simulation results demonstrate significant transmit power savings achieved by the proposed algorithms and layered transmission compared to the baseline schemes.

In this paper, we consider a novel layered coding approach with two layers. One of the two layers, denoted by the base-layer, can be received by any receiver even if it does not have reliable channel estimates. The other, refining-layer can only be received by any receiver that has channel state information. We propose signal constellations that allow the transmission of coherent and non-coherent information for the single-antenna transmitters. We derive upper bounds for the pairwise error probability for the coherent and non-coherent receivers and prove that our proposed signal constellations can achieve a diversity of order M for the 1 × M system, for both the coherent and non-coherent receivers.

This paper presents a comprehensive performance analysis of multiuser multiple antenna amplify-and-forward relaying networks employing opportunistic scheduling with feedback delay and co-channel interference over Rayleigh fading channels. Specifically, we derive exact as well as approximate closed-form expressions for the outage probability and average symbol error rate (SER) of the system. In addition, simple asymptotic expressions at the high signal-to-noise ratio (SNR) regime are obtained, which facilitate the characterization of the achievable diversity order and coding gain of the system. Moreover, two novel ergodic capacity bounds valid for general systems with arbitrary number of antennas and users are proposed. Finally, the optimum power allocation scheme in terms of minimizing the average SER is studied, and simple analytical solutions are obtained. Simulation results are provided to corroborate the derived analytical expressions, and it is demonstrated that the ergodic capacity bounds remain sufficiently tight across the entire range of SNRs and the proposed power allocation scheme offers significant improvements on the SER performance. The findings of the paper suggest that the full diversity order can only be achieved when there is ideal feedback, i.e., no feedback delay, and the diversity order always reduces to one in the presence of feedback delay. Also, the impact of key parameters such as the number of antennas and users on the system performance is intimately dependent on the level of feedback delay.

In this paper, we propose transmit antenna selection with maximal ratio combining (TAS/MRC) in dual-hop decode-and-forward spectrum-sharing relaying networks with the primary user's interference and outdated channel state information (CSI). In this network, a single antenna that maximizes the received SNR is selected at the secondary transmitter, and the MRC is adopted at the secondary receiver. To efficiently evaluate the impact of key parameters on the system performance, we derive the exact analytical expression for the outage probability of the secondary network in a Rayleigh fading channel. Moreover, we present simple asymptotic expressions for the outage probability in a high SNR regime, which reveal practical insights on the achievable diversity order and coding gain. The findings suggest that whether the outdated CSI concerning the secondary transmission links has significant impact on the outage probability of the system depends on the interference power constraint at primary receivers. Specifically, under the proportional interference power constraint, the achievable diversity order is affected by imperfect CSI regarding the secondary transmission links, and the diversity-multiplexing tradeoff is independent of the primary network. However, under the fixed interference power constraint, the error floor is displayed, and the achievable diversity order reduces to zero regardless of the CSI concerning the secondary transmission links.

In this paper, we obtain the optimal resource allocation scheme in order to maximize the achievable rate region in a dual-hop system that consists of two independent source-destination pairs sharing a single half-duplex relay. The relay decodes the received information and possesses buffers to enable storing the information temporarily before forwarding it to the respective destination. We consider both non-orthogonal transmission with successive interference cancellation at the receivers and orthogonal transmission. Also, we consider Gaussian block-fading channels and we assume that the channel state information is known and that no delay constraints are required. We show that, with the aid of buffering at the relay, joint user-and-hop scheduling is optimal and can enhance the achievable rate significantly. This is due to the joint exploitation of multiuser diversity and multihop diversity in the system. We provide closed-form expressions to characterize the average achievable rates in a generic form as functions of the statistical model of the channels. Furthermore, we consider sub-optimal schemes that exploit the diversity in the system partially and we provide numerical results to compare the different schemes and demonstrate the gains of the optimal one.

In this paper we consider joint optimization of rate and power for communication systems that use multilayer source coding with successive information refinement, accompanied with a broadcast approach at the physical layer of the system. We analyze the problem under the assumption of Rayleigh fading channels where rates and power ratios of the source layers are jointly optimized based on channel statistics information, with the objective of maximizing the expected user satisfaction which is usually defined by a differentiable concave increasing utility function of the total decoded rate. As special cases, we consider two utility functions; namely, the expected total decoded rate at the receiver and the expected rate distortion of a Gaussian source. We show that the optimal solution can be obtained using a two-dimensional bisection search for any number of layers. The outer bisection search is over the Lagrangian dual variable and the inner bisection search is over the decoding threshold of the layer. Moreover, we show that with a small number of layers, we can approach the performance upper bound that is achieved by transmitting an infinite number of layers.

In this paper, we investigate the outage behavior of a dual-hop Nth-best decode-and-forward (DF) relay system with co-channel interference (CCI) at both the relays and the destination. The source-relay and relay-destination channels as well as the interferers' channels at both the relay and the destination nodes are assumed to follow Rayleigh distribution. Exact closed-form expressions for the outage probability for both independent non-identically distributed (i.n.d.) and independent identically distributed (i.i.d.) cases of interferers' channels are derived in this paper. Furthermore, the system behavior at high signal-to-noise ratio (SNR) values is studied via deriving an approximate expression for the asymptotic outage probability as well as the diversity order and the coding gain. The analytical results are supported and validated by Monte-Carlo simulations. Our findings suggest that the diversity order linearly increases with the number of relays and linearly decreases with the order of the relay. Also, the results show that the system is still able to achieve full diversity gain in the presence of finite number of interferers with finite powers.

In this paper we consider joint optimization of rate and power for communication systems that use multilayer superposition source coding with successive refinement of information. We assume a Rayleigh fading channel, where rates and power are jointly and optimally allocated between the source layers based on channel statistics information, with the objective of maximizing the expected total received rate at the end user. We show that the optimization problem possesses a strong duality, and hence we use the dual form to show that the optimal solution can be obtained using a two-dimensional bisection search for any number of layers. The outer bisection search is over the Lagrangian dual variable and the inner bisection search is over the decoding SNR threshold of the last layer. Moreover, we show that with a small number of layers, we can approach the performance upper bound, that is achieved by transmitting an infinite number of layers.

In this paper, we consider a two-way communication system in which two users communicate with each other through an intermediate relay over block-fading channels. We investigate the optimal opportunistic scheduling scheme in order to maximize the long-term average transmission rate in the system assuming symmetric information flow between the two users. Based on the channel state information, the scheduler decides that either one of the users transmits to the relay, or the relay transmits to a single user or broadcasts to both users a combined version of the two users' transmitted information by using linear network coding. We obtain the optimal scheduling scheme by using the Lagrangian dual problem. Furthermore, in order to characterize the gains of network coding and opportunistic scheduling, we compare the achievable rate of the system versus suboptimal schemes in which the gains of network coding and opportunistic scheduling are partially exploited.

We consider the problem of minimizing the expected distortion in the multilayer transmission of a Gaussian source using the broadcast approach with successive information enhancement. This minimization is contingent on the jointly optimal choice of the rates and power ratios of the different layers. This problem was tackled in the literature with the assumption that the fading channel has a finite number of states and the number of source layers matches the number of channel states. In this paper, we provide a more generic solution for a continuous Rayleigh fading channel, and for any predetermined number of layers. We prove that the primal optimization problem has a strong duality with the Lagrangian dual problem. Consequently, we propose a two-dimensional bisection search algorithm that can, for any number of layers, find the optimal solution of the dual problem which will be the same as the optimal solution of the primal problem. The complexity of the search algorithm has linear order with respect to the number of layers. We provide numerical results for the optimal rate and power allocation. Moreover, we show that with a small number of layers, we can approach the distortion lower bound that is achieved by transmitting an infinite number of layers.

In this paper, we maximize the achievable rate region of a dual-hop network with two sources serving two users independently through a single shared relay. We formulate the problem as maximizing the sum of the weighted long term average throughputs of the two users under stability constraints on the long term throughputs of the source-user pairs. In order to solve the problem, we propose a joint user-and-hop scheduling scheme, which schedules the first or second hop opportunistically based on instantaneous channel state information, in order to exploit multiuser diversity and multihop diversity gains. Numerical results show that the proposed joint scheduling scheme enhances the achievable rate region as compared to a scheme that employs multi-user scheduling on the second-hop alone.

In this paper, we analyze the performance of a dual-hop system with partial relay selection and feedback delay over Nakagami-m fading channels in the presence of multiple identical interferers at the destination. Based on the new closed-form expressions for the cumulative distribution function of the effective signal-to-interference plus noise ratio, we present closed-form expressions for the outage probability and average symbol error rate (SER) for both fixed and CSI-assisted gain relaying systems. To gain further insights, the asymptotic outage probability and average symbol error rates at the high signal to noise ratio regimes are examined. Our results reveal that increasing the number of relays does not provide any extra diversity gain due to the presence of the feedback delay. Specifically, we show that feedback delay as well as CCI only affect the coding gain of the system. The accuracy of the analytical results are supported Monte-Carlo simulations.

Co-channel interference (CCI) has an inevitable effect on the performance of cooperative systems. It is a result of sharing the same time slot among several nodes. In this paper, we address the impact of CCI at the destination node on the performance of a dual-hop fixed-gain amplify-and-forward (AF) relay system. A noise-limited relay and an interference-limited destination are assumed in the analysis. Furthermore, the source-relay and the relay-destination channels of the desired user are assumed to be Rician distributed and the interferers' channels are assumed to follow the Nakagami-m distribution. We derive approximate expressions for the outage probability and the symbol error rate (SER) for both the independent non-identically distributed (i.n.d.) and independent identically distributed (i.i.d.) cases of interferers' fading channels. Furthermore, a look into the asymptotical high signal-to-noise ratio (SNR) performance has been taken and the diversity order and coding gain of the considered system are determined. Monte-Carlo simulations are provided to validate the accuracy of the analytical results. Main results show that the system is still able to achieve full diversity in the presence of finite number of interferers with finite powers.

We propose joint user-and-hop scheduling over dual-hop block-fading broadcast channels in order to exploit multi-user diversity gains and multi-hop diversity gains all together. To achieve this objective, the first and second hops are scheduled opportunistically based on the channel state information. The joint scheduling problem is formulated as maximizing the weighted sum of the long term achievable rates of the users under a stability constraint, which means that in the long term the rate received by the relay should equal the rate transmitted by it, in addition to power constraints. We show that this problem is equivalent to a single-hop broadcast channel by treating the source as a virtual user with an optimal weight that maintains the stability constraint. We show how to obtain the source weight either off-line based on channel statistics or on real-time based on channel measurements. Furthermore, we consider special cases including the maximum sum-rate scheduler and the proportional fair scheduler. We also show how to extend the scheme into one that allows multiple user scheduling via superposition coding with successive decoding. Numerical results demonstrate that our proposed joint scheduling scheme enlarges the rate region as compared to scheduling schemes that exploit the diversity gains partially.

In this paper, we develop multiuser access schemes for spectrum sharing systems whereby secondary users are allowed to share the spectrum with primary users under the condition that the interference observed at the primary receiver is below a predetermined threshold. In particular, we devise two schemes for selecting a user among those that satisfy the interference constraint and achieve an acceptable signal-to-noise ratio level. The first scheme selects the user that reports the best channel quality. In order to alleviate the high feedback load associated with the first scheme, we develop a second scheme based on the concept of switched diversity where the base station scans the users in a sequential manner until an acceptable user is found. In addition to these two selection schemes, we consider two power adaptive settings at the secondary users based on the amount of interference available at the secondary transmitter. In the On/Off power setting, users are allowed to transmit based on whether the interference constraint is met or not, while in the full power adaptive setting, the users are allowed to vary their transmission power to satisfy the interference constraint. Finally, we present numerical results for our proposed algorithms where we show the trade-off between the average spectral efficiency and average feedback load for both schemes.

In this paper, we investigate the outage behavior of a dual-hop opportunistic decode-and-forward (DF) relay system with co-channel interference (CCI) at both the relay and the destination. The source-relay and relay-destination channels as well as the interferers' channels at both the relay and the destination nodes are assumed to follow Nakagami-m distribution. Exact closed-form expressions for the outage probability for both independent non-identically distributed (i.n.d.) and independent identically distributed (i.i.d.) cases of interferers' channels are derived in this paper. Furthermore, the system behavior at high SNR values is studied via deriving the asymptotic outage probability. Our finding suggest that the co-channel interferers do not reduce the diversity order of the system, instead, they degrade the outage performance by affecting the coding gain of the system. The accuracy of the analytical results are supported by Monte-Carlo simulations.

Multiuser switched-diversity scheduling schemes were recently proposed in order to overcome the heavy feedback requirements of conventional opportunistic scheduling schemes by applying a threshold-based, distributed, and ordered scheduling mechanism. The main idea behind these schemes is that slight reduction in the prospected multiuser diversity gains is an acceptable trade-off for great savings in terms of required channel-state-information feedback messages. In this work, we characterize the achievable rate region of multiuser switched diversity systems and compare it with the rate region of full feedback multiuser diversity systems. We propose also a novel proportional fair multiuser switched-based scheduling scheme and we demonstrate that it can be optimized using a practical and distributed method to obtain the feedback thresholds. We finally demonstrate by numerical examples that switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the ultimate network capacity of full feedback systems in Rayleigh fading conditions.

We investigate the power allocation problem in layered transmission with successive enhancement using the broadcast approach. This problem is particularly important for multimedia streaming applications and multicasting services over slowly fading channels with partial channel information at the transmitter. We consider the practical scenario of limited and pre-specified source layers, and we propose a generic and efficient solution to optimize the transmission power allocated to each layer in order to maximize the average user satisfaction defined by a utility function of the decoded layers. We assume a block-fading Rayleigh distributed channel model. However, our solution can be extended to a number of other channel distributions. Although the direct formulation of the problem is not convex, we propose change of optimization variable, and we use the dual problem and the perturbation analysis in order to obtain the optimal solution. The solution is based on a one-dimensional bisection search irrespective of the total number of layers. Our optimality analysis indicates that in some cases it may not be optimal to transmit all the layers.

In this paper, we analyze the performance of a dual- hop system with partial relay selection and feedback delay over Rayleigh fading channels in the presence of multiple identical interferers at the destination. Based on the new closed-form expressions for the cumulative distribution function of the effective signal-to-interference plus noise ratio, we present closed-form expressions for the outage probability and average symbol error rates for both fixed and CSI-assisted gain relaying systems. To gain further insights, the asymptotic outage probability and average symbol error rates at the high signal to noise ratio regimes are examined. Monte-Carlo simulation results confirm the accuracy of the our analytical results.

In this paper, we investigate the performance of a dual-hop amplify-and-forward relay system in Nakagami-\emph{m} fading channels in the presence of multiple interferers. Based on the new closed-form expression for the cumulative distribution function of a new type of random variable involving a number of independent gamma random variables, we present closed-form expressions for the outage probability, general moments for the end-to-end signal to interference and noise ratio and ergodic capacity of the system. In addition, we look into the high signal to noise ratio regime and characterize the diversity order and coding gain achieved by the system. Our result shows that the diversity of the system is limited by the hop experiencing more severer fading. Moreover, the interference does not reduce the diversity order of the system, instead, it degrades the outage performance by affecting the coding gain of the system.

In this paper, we investigate the outage performance of a dual-hop relaying systems with partial relay selection and feedback delay. The analysis considers the case of Rayleigh fading channels when the relaying station as well as the destination undergo mutually independent interfering signals. Particularly, we derive the cumulative distribution function (c.d.f.) of a new type of random variable involving sum of multiple independent exponential random variables, based on which, we present closed-form expressions for the exact outage probability of a fixed amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Numerical results are provided to illustrate the joint effect of the delayed feedback and co-channel interference on the outage probability.

A new multiuser scheduling scheme is proposed and analyzed in this paper. The proposed system combines features of conventional full-feedback selection-based diversity systems and reduced-feedback switch-based diversity systems. The new hybrid system provides flexibility in trading-off the channel information feedback overhead with the prospected multiuser diversity gains. The users are clustered into groups, and the users' groups are ordered into a sequence. Per-group feedback thresholds are used and optimized to maximize the system overall achievable rate. The proposed hybrid system applies switched diversity criterion to choose one of the groups, and a selection criterion to decide the user to be scheduled from the chosen group. Numerical results demonstrate that the system capacity increases as the number of users per group increases, but at the cost of more required feedback messages.

In this letter, we investigate the performance of dual-hop channel state information-assisted amplify-and-forward relaying systems over Nakagami-mfading channels in the presence of multiple interferers at the relay. Assuming integer fading parameterm, we derive closed-form expressions for the exact outage probability and accurate approximation for symbol error rate of the system. Furthermore, we look into the asymptotical high signal to noise ratio regime, and characterize the diversity order achieved by the system. All the analytical results are validated via Monte Carlo simulations.

We consider multiuser MIMO systems with some of the users having target-rate requirements while the other users are working on best-effort data transmission. Both multiple-access channels (MAC) and broadcast channels (BC) are considered. We show that the best-effort users can achieve higher rates when the data streams of any user are not restricted to be decoded consecutively and when time-sharing between different decoding orders is allowed. For MIMO-MAC, we show that the problem can be formulated as a convex optimization problem, and hence efficient algorithms can be used to obtain the globally optimal solution. We also show that in some cases it is possible to reduce the transmission power of some users without affecting the optimal solution, and we show that the power minimization problem is convex. We also exploit the MAC-BC duality in order to solve the same problem for the MIMO-BC channel.

We provide the solution for optimizing the power and resource allocation over block-fading relay-assisted broadcast channels in order to maximize the long term average achievable rates region of the users. The problem formulation assumes regenerative (repetition coding) decode-and-forward (DF) relaying strategy, long-term average total transmitted power constraint, orthogonal multiplexing of the users messages within the channel blocks, possibility to use a direct transmission (DT) mode from the base station to the user terminal directly or a relaying (DF) transmission mode, and partial channel state information. We show that our optimization problem can be transformed into an equivalent "no-relaying" broadcast channel optimization problem with each actual user substituted by two virtual users having different channel qualities and multiplexing weights. The proposed power and resource allocation strategies are expressed in closed-form that can be applied practically in centralized relay-assisted wireless networks. Furthermore, we show by numerical examples that our scheme enlarges the achievable rates region significantly.

In this paper we consider multicast systems that use layered source coding with successive refinement in a Rayleigh fading environment. For this kind of systems, we optimally allocate the transmission power, and hence the decoding threshold of each layer, in order to maximize the expected satisfaction defined by a utility function of the decoded rates of the users. In particular, we use the Lagrangian dual problem in order to efficiently solve the primal non-convex problem for any number of layers. Furthermore, we show that for some channel statistics, it is not optimal to transmit all the layers, rather we should allocate zero power to some of the upper layers in order to maximize the expected user satisfaction.

The base station in IEEE 802.16, or WiMAX, networks allocates contention-based time slots for the mobile stations to transmit their requests for additional bandwidth. Using a technique called subchannelization, multiple concurrent transmissions by mobile stations can be admitted by the base station during the same contention period. For transmission during this period, each station employs a contention-resolution mechanism. In this paper, we develop an analytical model for the bandwidth request and resolution mechanism during this contention period when subchannelization is employed. The model is shown to accurately model the contention period when subchannelization is enabled. Performance metrics, such as throughput, average waiting time, and contention period capacity, show that adding more subchannels to the contention time slots increases throughput and reduces average waiting time. Several simulation results are carried out to validate the model.

IEEE 802.16 wireless networks, known as WiMAX, employ a mechanism for guaranteed time allocation to mobile stations in order to meet the different quality of service requirements for service flows. The base station allocates contention-based time slots for the stations to transmit their requests for additional bandwidth. Each contention time slot can accommodate a single transmission if there is no sub-channelization or multiple concurrent transmissions if the base station enables sub-channelization during the contention period. For transmission during this period, each station employs a contention-resolution mechanism. In this paper, we develop an analytical model for the bandwidth request and resolution mechanism during this contention period when sub-channelization is employed. The model is shown to accurately model the contention period when sub-channelization is enabled. Performance metrics, such as throughput and capacity, show that adding more subchannels to the contention time slots increases both the throughput and the capacity of the contention period carrying more successful bandwidth requests. Simulations with different parameter sets are carried out to validate the proposed model.

Chip-Level Modulated Binary Pulse Position Modulation (CLM-BPPM) is proposed as a modulation scheme for Fiber-Optic Code Division Multiple Access (FO-CDMA) systems using Optical Orthogonal Code (OOC) for time domain signal spreading. The proposed scheme provides better synchronization and source activity detection at the receiver side as compared to On-Off Keying (OOK). A mathematical expression is derived for the BER of CLM-BPPM using a combinatorial interference pattern analysis approach. The mathematical model is verified using simulation. Numerical results demonstrate that CLM-BPPM has a BER that is very close to OOK. Moreover, increasing the average source activity causes the performance of the CLM-BPPM to approach that of the OOK system with an asymptotic BER equal to the BER of OOK at full user activity.

3G long term evolution (LTE) has emerged as a comprehensive evolution of the Universal Mobile Telecommunications System (UMTS). LTE system uses resource blocks which are the basic unit of exchanging information in both downlink and uplink. However, resource allocation scheme, which is a crucial component to guarantee quality of service, remains as an open issue. In this paper, we propose a novel cross-layer scheduling algorithm for LTE system that allocates resources, both as resource blocks and a modulation and coding scheme, among users with different traffic load. The algorithm minimizes the overall average packet delay and takes into account queueing theory, modulation and coding scheme supported by each user, channel condition, and available transmit power. Simulation results shows that the proposed algorithm provides substantial reduction in average delay compared to conventional algorithm.

In this paper, we introduce a new Differentiated Successive Interference Cancellation (DiffSIC) ordering technique for up-link multi-user Multiple-Input Multiple-Output (MIMO) systems. Unlike classical SIC, DiffSIC is capable of differentiating users according to their priority or class of service by selecting a detection order that best fits the users' service profiles. In addition, DiffSIC is able to achieve the optimal SIC detection order that results in the best overall system performance. In order to develop DiffSIC, we introduce analytical methods towards finding instantaneous symbol error rates (SER) for the Zero Forcing SIC (ZF-SIC) and Minimum Mean Square Error SIC (MMSESIC) detectors. We present a number of numerical results which clearly demonstrate the ability of DiffSIC to accomplish service differentiation and overall performance improvement in general.

Existing medium access control (MAC) schemes for wireless local area networks (WLAN) have been shown to lack scalability in crowded networks, and efficiency in supporting heterogeneous traffic types. These issues are mostly due to the use of random multiple access techniques in the MAC layer. The design of these techniques is highly linked to the choice of the underlying physical (PHY) layer technology. The advent of new PHY schemes that are based on orthogonal frequency division multiple access (OFDMA) provides new opportunities for devising more efficient MAC protocols. We propose a new adaptive MAC design based on OFDMA technology. The design uses OFDMA to reduce collision during transmission request phases, and makes channel access more predictable. To improve efficiency, we combine the OFDMA access with a carrier sense multiple access (CSMA) scheme. Data transmission opportunities are assigned through an access point that can schedule traffic streams in both time and frequency (subchannels) domains. We demonstrate the effectiveness of the proposed MAC and compare it to existing mechanisms through simulation experiments and by deriving an analytical model for the operation of the MAC in saturation mode.

In this paper, we propose a cross-layer optimization scheme for delivery of scalable video over variable bit-rate wireless networks, in particular 802.11 based wireless local area networks (WLAN). For scalable video streaming applications, the conventional solution to reduced throughput due to channel distortions is to reduce the video bitrate by dropping the higher enhancement layers of the scalable video. We show that video quality can be improved, without adding to traffic load, when the WLAN link adaptation scheme uses a temporal fairness criterion along with scalable video distortion estimates to adjust its physical (PHY) layer modulation and coding parameters used for delivering each video layer. We formulate the problem as an optimization problem for assigning different PHY modes to different layers of scalable video under temporal fairness constrains; the solution to this problem provides a set of PHY configuration parameters that achieve the highest possible video quality while meeting the admission control constraints. Performance evaluations demonstrate the effectiveness of our method and the accuracy of the models.

In this paper, we propose a cross-layer optimization scheme for delivery of scalable video over multirate wireless networks, in particular the popular 802.11 based wireless local area network (WLAN). The 802.11 based networks use a link adaptation mechanism in the physical layer (PHY) to maintain the reliability of transmission under varying channel conditions. When channel condition worsens, the reliability is maintained by employing more robust modulation and coding schemes, at the cost of reduced PHY bit rate. The reduced bit rate will result in lower available throughput for applications. For scalable video streaming applications, the conventional solution to this problem is to reduce the video bit rate by dropping the higher enhancement layers of the scalable video. We show in this article that the video quality can be improved, if the link adaptation scheme uses more intelligent reliability criteria and adjusts the PHY parameters used for delivering each video layer, according to the relative importance of that layer. Our scheme achieves better video quality without increasing the traffic load of the WLAN. For this purpose we present temporal fairness constraints and formulate an optimization problem for assigning different PHY modes to different layers of scalable video; the solution to this problem provides a set of PHY configuration parameters that achieve the highest possible video quality while meeting the admission control constraints in the network. Performance evaluations demonstrate that our method outperforms the existing mechanisms.

Supporting Multimedia applications, such as video, over 802.11 wireless local area networks (WLAN) is a challenging task due to the inefficiency of the 802.11 MAC layer and the constant fluctuations in channel error rates. Therefore, specific measures must be taken in both application and delivery layers in order to achieve efficient and satisfactory quality for multimedia applications. Advanced video compression technologies, such as H.264, provide new data partitioning error resiliency feature that allows delivery of the video data in different streams with different levels of importance. There are several possible schemes for mapping these streams to the services of the IEEE 802.1 le MAC. In this article we examine the existing schemes and propose new mechanisms that improve the performance of the video communications system. We propose to use scheduled access schemes in MAC, along with aggregation of packets in the application layer to achieve the best results. We evaluate our proposed mechanisms using simulation experiments.

Heterogeneous multicast is an efficient communication scheme especially for multimedia applications running over multihop networks when multicast receivers in the same session require service at different rates commensurate with their capabilities. In this paper, we address the problem of resource allocation for a set of heterogeneous multicast sessions over multihop wireless networks. We propose an iterative algorithm that achieves the optimal rates for a set of heterogeneous multicast sessions such that the aggregate utility for all sessions is maximized. We present the formulation of the multicast resource allocation problem as a non-linear optimization model and highlight the cross-layer framework that can solve this problem in a distributed ad hoc network environment with asynchronous computations. Our simulations show that the algorithm achieves optimal resource utilization, guarantees fairness among multicast sessions, provides flexibility in allocating rates over different parts of the multicast sessions and adapts to changing conditions such as dynamic channel capacity and node mobility. Our results show that the proposed algorithm not only provides flexibility in allocating resources across multicast sessions, but also increases the aggregate system utility and improves the overall system throughput by almost 30% compared to homogeneous multicast.

A new adaptive multiple access scheme based on the theory of order statistics is introduced. Because the proposed low-complexity method requires relatively small channel information overhead and processing delays, it can be feasible in fast-fading environments and systems with large number of users. Numerical results reveal significant system performance improvement over conventional approaches.

In this paper, we propose a novel simplified mathematical analysis technique for modeling and calculating the effect of multiple access interference on bit error rate in optical code division multiple access (OCDMA) systems. Our technique applies to OCDMA systems using optical orthogonal codes (OOC) with optical time-domain spreading. The proposed analysis uses combinatorial methods on the combined signal at the output of the optical correlator decoder to derive a mathematical expression for the bit error rate.

Multicast-based data communication is an efficient communication scheme especially in multihop ad hoc networks where the MAC layer is based on one-hop broadcast from one source to multiple receivers. The problem of resource allocation for a set of homogeneous multicast sessions over multihop wireless network is addressed. An iterative algorithm is proposed that achieves the optimal rates for a set of multicast sessions such that the aggregate utility for all sessions is maximised. The authors demonstrate analytically and through simulations that the algorithm achieves optimal resource utilisation while guaranteeing fairness among multicast sessions. The algorithm in network environments with asynchronous distributed computations has been further analysed. Two implementations for the algorithm based on different network settings are presented and show that the algorithm not only converges to the optimal rates in all network settings but it also tracks network changing conditions, including mobility and dynamic channel capacity.

Generalized multi-protocol label switching (GMPLS) is a multipurpose control-plane paradigm that extends the MPLS scheme allowing switching without recognizing packet boundaries. In this paper, we present a novel extension that exploits a new physical layer for switching in optical GMPLS. The proposed extension is achieved through adding an optical code switching layer, or code switch capable (CSC) layer, to the existing label mapping layers. Our proposal enables finer granularity at sub-wavelength level in all-optical GMPLS core switches, resulting in significant enhancements to traffic isolation capabilities for all-optical GMPLS core switches. We employ mathematical analysis to derive performance bounds for the proposed scheme, from both the labeling capacity and network throughput points of view. We use our analytical model to derive several optimum operating points for the network, and show that our techniques significantly improve the overall performance of all-optical core networks

Multicast-based data communication is an efficient communication scheme especially in multihop ad hoc networks where the MAC layer is based on one-hop broadcast from one source to multiple receivers. In this paper, we address the problem of resource allocation for a set of homogeneous multicast sessions over multihop wireless networks. We propose an iterative algorithm that achieves the optimal rates for a set of multicast sessions such that the aggregate utility for all sessions is maximized. We demonstrate analytically and through simulations that the algorithm achieves optimal resource utilization while guaranteeing fairness amongst multicast sessions. We further analyze the algorithm in network environments with asynchronous distributed computations. We present two implementations for our algorithm based on different network settings and show that the algorithm not only converges to the optimal rates in all network settings but it also tracks network changing conditions including mobility and dynamic channel capacity.

Inherent difficulties in millimeter-wave radio operations, such as higher atmospheric attenuation, especially during rainy times, motivated the use of mesh architecture in millimeter-wave band for broadband fixed wireless access (BFWA) networks. When used with highly directional antennas, these mesh networks also provide better frequency reuse. A recent proposed architecture for such networks shows how a link can have multiple radio channels. This paper exploits this property to present a solution that uses distributed dynamic channel allocation (DDCA) to reconfigure the link capacities to achieve better Traffic Engineering. DDCA works by adding or removing channels from a link while satisfying interference constraints, based on current network conditions. The paper proposes a DDCA algorithm and then integrates it with routing. The distributed dynamic nature of the algorithm provides true scalability with fast and dynamic reconfiguration of the network. Simulation results show that the proposed solution provides better performance than solutions that employ a fixed channel allocation.

Transmission opportunity, or TXOP, is a channel control method introduced in the IEEE 802.11e wireless LAN standard for improving channel utilization. In this paper, we propose an analytical model to evaluate the performance of TXOP as a method for achieving efficient burst transmissions in IEEE wireless LANs. We show how the model can be used to estimate the throughput of different access categories as a function of the TXOP limit value, and how to calculate the total throughput achieved under basic-access and RTS/CTS access modes. We also show that improved service differentiation can be achieved by using a novel scheme based on TXOP thresholds. Our model demonstrates how the combined used use of TXOP with other MAC parameters can lead to higher aggregate throughput and improved service differentiation.

We consider the problem of QoS-based partitioning of traffic streams for a link model with adjustable service levels. Specifically, we consider a link model with variable service levels which may be mapped to a finite number of MPLS Label- Switched-Paths (LSPs). Our target is to partition a set of traffic streams each with arbitrary local QoS-demand into a small number of classes and find the service level for each class while optimizing the residual-allocated-resources as a result of the traffic partitioning. The residual allocated resources will be measured by the service quantization overhead which is the summation of the differences between the required QoS and the offered service level for all traffic streams. We formulate the partitioning process as a Dynamic Programming problem. We then present two polynomial time algorithms to obtain the QoSbased optimal partition with bandwidth allocation. Our results indicate that using 4 or 5 service levels will accomplish the tradeoff between complexity and granularity irrespective of the distribution of the QoS requirements.

Several enhancements to the Medium Access Control (MAC) layer of the IEEE 802.11 standard have been recommended in the new 802.11e standard. One main enhancement is the possibility to send bursts of frames during a limited duration called Transmission Opportunity (TXOP). Similar MAC efficiency enhancements such as Frame Aggregation have also been proposed for the upcoming 802.11n standard. We analyze the application of this feature to the existing 802.11 MAC and evaluate its performance under different network conditions. The frame bursting feature can increase the total capacity of an 802.11 network by reducing the contention and collision for bursty traffic sources. We extend the established 802.11 analytical models to include the frame bursting feature. Through simulation experiments we analyze the delay performance of the network under different frame bursting options and show that while in general frame bursting is useful and can increase the system capacity, it might cause excessive unfairness in certain cases. Using the findings of this article we present guidelines for implementing fair adaptive algorithms that use TXOP.

Multicast-based data communication is an efficient communication scheme especially in multihop ad hoc networks where the MAC layer is based on one-hop broadcast from one source to multiple receivers. In this paper, we discuss a framework of rate allocation for a set of homogeneous multicast sessions over multihop wireless networks. We propose a framework that facilitates the online calculation of the optimal rates for a set of multicast sessions such that the aggregate utility for all sessions is maximized. This framework is used to steer the entire network of ad hoc nodes towards the optimal point in real time using a totally distributed and asynchronous environment settings. We present a series of implementations based on different network settings and show that not only convergence to the optimal rates is attained in all these network settings but also network changing conditions such as mobility and dynamic channel capacity can be tracked in real time

In this paper, we introduce a new channel allocation scheme for up-link code division multiple access (CDMA)-based multi-user multiple-input multiple-output (MIMO) systems. In such a system, different users are treated as multiple antennas and space-time multi-user detection algorithms are used at the receiver to separate users sharing the same channel. In our allocation scheme, users are allowed to share multiple up-link codes simultaneously. This improves the overall up-link system capacity and fairly equalizes the bit error rate (BER) performance of different users

The widespread deployment of IEEE 802.11 based wireless local area networks (WLAN) has made broadband access a reality for many consumers. As a result, supporting a wide range of applications, in particular networked multimedia applications, has become of increasing importance. Since specific delay and bandwidth requirements of multimedia applications cannot be fulfilled by the current IEEE 802.11-based WLANs, new enhancements are being introduced to the medium access control (MAC) layer of the 802.11 standard under the framework of the IEEE 802.11e. Nevertheless, the 802.11e only provides the means of supporting quality of service (QoS) in the MAC layer and does not mandate a final solution for QoS issues. We present a QoS solution that employs the controlled access features of the 802.11e to provide per-session guaranteed QoS. Our design comprises of a scheduler that assigns guaranteed service times to individual sessions using a fair scheduling algorithm. Through analysis and experiments we prove the fairness of the algorithm and show that the proposed solution outperforms other methods that are contention or priority based

This paper presents a new analytical model for calculating the blocking probability in Just-Enough-Time (JET)-based optical burst switching networks. Relationship to the problem of calculating the reservation probability in advance reservation systems is also discussed. The proposed analytical model takes into consideration the effects of the burst offset time and the burst length on the blocking probability. We use a (M+1)-state non-homogenous Markov chain to describe the state of an output link carrying M wavelength channels. In addition, we model each wavelength channel by a 2-state Markov chain. The offset time is drawn from a specified distribution so that wavelength reservation requests, made before a given time, build up to be a workload whose mean value declines with the reservation starting time. Furthermore, we express the blocking probability in terms of first passage time distributions to account for the burst length. To verify its accuracy, the model results are compared with the results of a sophisticated discrete-event simulation model. The model results were found to be in satisfactory agreement with simulation results.

The use of optical CDMA as a labeling mechanism in generalized multi-protocol label switching (GMPLS) optical networks significantly increases the traffic isolation capabilities. These networks, referred to as optical code labeled GMPLS (OC-GMPLS), have higher resource utilization due to the finer flow granularity introduced into the network. In this paper we present a cross-layer mathematical model for the throughput of OC-GMPLS networks, which provides a quantitative measure for the performance of optical networks throughput taking into consideration the effect of the physical layer. The proposed mathematical model incorporates the physical layer effects on the network layer performance by expressing the throughput as a function of the physical layer bit error rate, as well as the network traffic parameters such as the number of users and the packet length. Using the developed analytical model we were able to demonstrate the significant enhancement in the network performance due to the use of OC-GMPLS. We also used our analytical model to derive several optimum network operating points, which are of great importance to network designers and researchers.

This paper proposes a novel algorithm for constructing optical orthogonal codes (OOC). The proposed algorithm is a modified element-by-element greedy algorithm based on the extended set representation of optical orthogonal codes. The algorithm employs a technique that reuses previously rejected delay elements during the construction process. We call this method the rejected delays reuse (RDR) greedy algorithm. We show that employing the RDR method leads to code lengths that are significantly shorter than those achieved for OOCs constructed using the classical greedy algorithm for the same code weight and the same number of simultaneous codes constraints. To quantify the effect of the reduction in the code length on sub-wavelength multiplexing, we introduce a factor called the expansion efficiency factor and use it to show that the RDR generated codes have higher efficiency

The broad spread of packet data networks and the emergence of applications in multimedia communications, has created a driving force towards an improved quality of service (QoS) model for today's Internet. A primary component of this model is packet schedulers. We introduce a new frame-based scheduling technique called mini round robin (MRR) that is primarily designed for providing lower latency bounds, and lower start-up latency bound for low-rate but high-priority flows. This enables applications such as voice-over-IP to demand low delay despite the low reserved bit rate of the voice sessions.

This paper proposes a novel class of wavelength scheduling algorithms in optical burst switching networks. The proposed wavelength scheduling algorithms process a batch of data bursts together instead of processing them one by one. When a control burst with a reservation request arrives to a batch scheduler, the scheduler waits for a small amount of time, called the acceptance delay, before deciding to accept or reject the reservation request. After the acceptance delay has passed, the scheduler processes all the reservation requests that have arrived during the acceptance delay, then it accepts the requests that will maximize the utilization of the wavelength channels. We describe an optimal batch scheduler that serves as an upper bound on the performance of batch scheduling algorithms. Furthermore, we introduce four novel heuristic batch scheduling algorithms. The bursts of the proposed algorithms is evaluated using a discrete-event simulation model. Simulation results suggest that batch schedulers could decrease the blocking probability by 25% compared the best previously known wavelength scheduling algorithm.

Most of the recent research on TCP over heterogeneous networks has concentrated on differentiating between packet drops caused by link congestion versus drops caused by link errors. Handling the two types of packet drop differently avoids significant throughput degradations caused by frequent TCP window shut downs due to non-congestive drops. However, TCP also exhibits inherent unfairness for connections with long round-trip times and connections that traverse multiple congested routers. In heterogeneous networks, the difference in bit error rates between wireless and wired links aggravates the situation even more. In this paper, we propose a new TCP bandwidth allocation (NTBA) algorithm to solve these problems. The primary contribution is a wireless access node algorithm with a simple new shadow price scheme provided by the network node. The advantage of our algorithm is that it simplifies the TCP sender-side implementation and keeps the receiver-side protocol stack unchanged. We propose to apply wireless explicit congestion notification (WECN) to decouple congestion control from loss recovery in wireless networks. Simulation results show that not only can the combined NTBA/WECN mechanism improve TCP fairness, but it can also maintain very good throughput performance in the presence of wireless channel losses.

The broad spread of packet data networks and the emergence of applications in multimedia communications, created a driving force towards an improved quality of service (QoS) model for today's Internet. A primary component of this model is packet schedulers. We introduce a new frame-based scheduling technique called mini round robin (MRR) designed primarily for providing lower latency bounds, and lower start-up latency bound for low-rate but high-priority flows. This enables applications such as voice-over-IP to demand low delay despite the low reserved bit rate of the voice sessions.

Inherent difficulties in millimeter-wave radio operations, such as higher atmospheric attenuation, especially during rainy times, motivated the use of mesh architecture in millimeter-wave band for broadband fixed wireless access (BFWA) networks. When used with highly directional antennas, these mesh networks also provide better frequency reuse. In a recent proposed architecture for such networks, a link can have multiple radio channels. However, to provide traffic engineering with scalability, it is needed to develop a distributed dynamic channel allocation algorithm to allocate channels to these links. This paper proposes a distributed dynamic channel allocation algorithm that is scalable and able to provide traffic engineering if invoked periodically. The proposed solution provides traffic engineering by optimizing link capacities by adding or removing channels from a link while maintaining interference constraints, based on current network conditions. Simulation results suggested that proposed algorithm performs better than a solution based on fixed channel allocation

We investigate the QoS-based classification of traffic streams for a multi-class link model with predetermined service levels. Specifically, we consider a link model with fixed service levels or fixed class weights which may be represented by a finite number of MPLS label-switched-paths (LSPs). Our target is to classify a set of traffic streams each with arbitrary local QoS-demand into a small number of service levels while optimizing the residual-allocated-resources as a result of the traffic classification. The residual-allocated-resources are measured by the service-quantization-overhead which is the summation of the differences between the required QoS and the offered service level for all traffic streams. We formulate the classification as a dynamic-programming problem. We then present a group of polynomial-time-algorithms to obtain the optimal classification for soft and hard QoS requirements. We also present the concept of "differentiation factor" and show the effect of this factor on minimizing the quantization-overhead

We propose a novel and cost-effective approach for the deployment of third generation (3G) wireless systems over hybrid fiber coaxial (HFC) CATV networks. The main goal is to facilitate 3G deployment over the existing CATV plant and reduce the large cost required for building a dedicated last mile infrastructure for 3G access networks. Our proposal reduces the last mile cost by sharing the existing CATV network and using the standard equipment and protocols of data-over-cable systems interface specifications (DOCSIS). This allows rapid deployment of 3G wireless systems, facilitates convergence of wireless and wireline networks and paves the way towards all IP wireless networks. Enhancements to the DOCSIS medium access control (MAC) protocol must be implemented in order to support Quality of Service (QoS) guarantees for 3G data and signaling traffic. This paper presents the proposed 3G over CATV network architecture and DOCSIS medium access control (MAC) enhancements for enabling the support of QoS guarantees for 3G data and signaling traffic. The proposed MAC enhancements can reduce the access delay for delay-sensitive traffic by 30 to 40% over existing DOCSIS MAC without compromising QoS guarantees for other traffic classes, or the DOCSIS channel utilization. Copyright © 2004 John Wiley & Sons, Ltd.

Supporting real-time multimedia applications in any network requires scheduling techniques that can provide guaranteed delay and/or bandwidth to media streams. Coordinating access to the wireless medium in an IEEE 802.11 wireless LAN is different from network layer scheduling since it requires scheduling traffic flows in a distributed manner. We introduce a new scheduling framework called multiple access hybrid scheduling (MAHS) that utilizes the concept of virtual packet and emulates stations packets in the access point in order to centralize the scheduling process. This way the main scheduling function is performed solely in the access point thus enabling the use of conventional schedulers to for scheduling both uplink and downlink packets (hybrid scheduling). We deploy a modified version of weighted fair queuing (WFQ) as this internal scheduler. Performance evaluation and analysis of the proposed framework is described in this article.

This paper presents a detailed architecture for providing quantitative QoS guarantees in labeled optical burst switching (LOBS) networks. Packets are assembled into data bursts based on their respective forwarding equivalence class (FEC) at ingress nodes. The burst assembly algorithm employs two parameters to control the burst blocking probability and burst assembly delay. We deploy a fair packet queueing (FPQ) algorithm in each edge node to regulate access to a wavelength scheduler. For LOBS core nodes, we present a novel approach that applies FPQ scheduling algorithms to the control plane of these nodes to guarantee fair bandwidth allocation. Based on the information provided by the queued control bursts, the core FPQ algorithm creates a virtual queue of data bursts in core nodes, then it selects the eligible control burst to be processed by the wavelength scheduler. In addition, we present analytical expressions for the worst case delay and the blocking probability in the proposed architecture. Simulation results demonstrate that the proposed architecture provides accurate and controllable service differentiation in LOBS networks.

We propose a low-complexity constraint-based routing algorithm for traffic engineering in packet networks that route end-to-end packet flows. The proposed fuzzy routing algorithm (FRA) modifies the well-known Dijkstra's single-source shortest paths algorithm by using fuzzy-logic membership functions in the path-cost update process. The main objective of FRA is to reduce path-request blocking and increase overall network utilization. To achieve this objective, the algorithm computes new routes based on network-wide load balancing constraints. Simulation results show that FRA outperforms several earlier algorithms in terms of load balancing and path-request blocking.

We propose a novel extension to the label mapping space in GMPLS networks by exploiting further physical layer properties. The proposed extension, OC-GMPLS (optical code enabled GMPLS), is a modified version of the standard GMPLS. OC-GMPLS relies on adding an optical CDMA code switching layer called code switch capable (CSC) layer to the existing label mapping layers. OC-GMPLS provides a larger label mapping space and enhances the QoS capabilities for optical networks through increasing the granularity of traffic identification. In our extension, we use Manchester signaling to allow for more robust clock recovery while providing enhanced performance over conventional on-off keying (OOK) schemes. We also provide a reference architecture for the label switching layers in our OC-GMPLS architecture capable of performing labelling through optical CDMA. We analyze the performance of the proposed scheme and show that our proposal significantly enhances the overall network performance.

In this paper we present a new analytical model for evaluating the blocking probability in Just-Enough-Time-based optical burst switching networks. The proposed analytical model takes into consideration the effects of the burst offset time and the burst length on the blocking probability. We use a (M+1)-state nonhomogenous Markov chain to describe the state of an output link carrying M wavelength channels. In addition, we model each wavelength channel by a 2-state Markov chain. The offset time is drawn from a specified distribution so that wavelength reservation requests, made before a given time, build up to be a workload whose mean value declines with the reservation starting time. Furthermore, we express the blocking probability in terms of first passage time distributions to account for the burst length. To verify its accuracy, the model results are compared with the results of a sophisticated discrete-event simulation model. The model results were found to be in satisfactory agreement with simulation results.

This paper presents two fundamental theorems that show that the O(N) complexity for updating the virtual time in a weighted fair queuing (WFQ) scheduler with N sessions is caused mainly by simultaneous departures of packets, and not by iterated deletion as was previously claimed. Iterated deletion is caused by an "avalanche" of consecutive, but not necessarily simultaneous, departures that incur more departures due to increments in available bandwidth from idling sessions. Iterated deletion potentially leads to large numbers of consecutive departures within a given time period. The number of departures is, however, a function of such implementation details as the resolution of the time-stamp and the scheduler clock. On the other hand, the problem of simultaneous time-stamps can not be solved by an increase in the time resolution of virtual-time update. Essentially, all equal time-stamps must be processed during a single virtual-time update operation. We present a proof to show that O(N) simultaneous departures can occur during a single virtual-time update. We also show that this is a fundamental property of WFQ that holds even under the most restrictive conditions, viz. all packets arrive serially to the scheduler (no simultaneous arrivals), and the input bit-rate does not exceed the output bit-rate.

This work presents a new analytical model for calculating the blocking probability in just-enough-time (JET)-based optical burst switching networks. Relationship to the problem of calculating the reservation probability in advance-reservation systems is also discussed. The proposed analytical model takes into consideration the effects of the offset time and the burst length on the blocking probability. We model the wavelength channel by a 2-state nonhomogenous Markov chain. The offset time is drawn from a specified distribution so that wavelength reservation requests, made before a given time, build up to be a workload whose mean value declines with the reservation starting time. In addition, we express the blocking probability in terms of first passage time distributions to account for the burst length. To verify its accuracy, the model results are compared with the results of a discrete-event simulation model. The model results were found to be in satisfactory agreement with simulation results.

Classical approaches to quality-of-service (QoS) provisioning in IP networks are difficult to apply in all-optical networks. This is mainly because there is no optical counterpart to the store-and-forward model that mandates the use of buffers for queuing packets during contention for bandwidth in electronic packet switches. Since plain IP assumes a best effort service model, there is a need to devise mechanisms for QoS provisioning in IP over wavelength-division-multiplexing, or IP-over-WDM, networks. In this paper, we propose a new scheme; called preemptive prioritized just enough time (PPJET), for QoS provisioning in buffer-less optical burst switching (OBS) networks. PPJET provides strict priority for high priority traffic by dropping reservations belonging to lower priority traffic using a new channel scheduling algorithm called preemptive latest available unused channel with void filling (PLAUC-VF). Furthermore, we study the performance of PPJET through simulation experiments, and we show that PPJET outperforms prioritized just enough time (PJET) in terms of dropping probability and end-to-end delay.

This paper presents the architecture and implementation of a multi-service streaming system for broadcast of MPEG-4 elementary streams. The proposed system promotes the use of the push channels model for information distribution. The system architecture accommodates two main layers for broadcast service management and media delivery. The broadcast service management layer uses the publisher-subscriber model for service announcement and clients' subscription. The proposed media delivery layer of the MPEG-4 media streams is based on the recommendations made by part 6 of the MPEG-4 standard, Delivery Multimedia Integration Framework (DMIF). However, the elementary specification of the standard's control plane for broadcast instance motivated the design of separate layer for broadcast service management. The paper also presents the contributive features that motivated our client/server implementation for broadcast of MPEG-4 streams including the "client random access", and the "inter-streams synchronization". These features allow clients to access the MPEG-4 media streams at any time during the presentation of the broadcast service.

This paper presents a novel recursive algorithm for generating higher order multidimensional (m-D) discrete cosine transform (DCT) by combining the computation of 2/sup m/ identical lower order (smaller size) DCT architectures. One immediate outcome of our results is the true "scalability" of the DCT computation. Basically, an m-D DCT computation can be constructed from exactly one stage of smaller DCT computations of the same dimension. This is useful for both hardware and software solutions, in which a very efficient smaller size m-D DCT core has been developed, and a larger DCT computation is required. The resulting DCT networks have very simple modular structure, highly regular topology, and use simple arithmetic units.

This paper presents efficient coding and mapping algorithms that lead to a significant speed improvement in low bit rate H.263/H263+ video encoding while maintaining high video-reproduction quality. First, by exploiting the statistical properties of low resolution and slowly varying video sequences, we reduce significantly the computation times of the most computationally intensive components of video coding, particularly the discrete cosine transform, the inverse discrete cosine transform, quantization, and motion estimation. We also map some of the single instruction multiple data (SIMD)-oriented functions onto Intel's MMX architecture. The developed algorithms are implemented using our public-domain H.263/H.263+ encoder/decoder software. Using the above algorithms, our H.263/H.263+ baseline video-encoder implementation can encode more than 15 fps in QCIF resolution on a Pentium MMX 200-MHz computer.

The explosive growth of Internet users, the increased user demand for bandwidth, and the declining cost of technology have all resulted in the emergence of new classes of high-speed distributed IP-router architectures with packet-forwarding rates of the order of gigabits, or even terabits, per second. This paper develops an analytical framework for modeling and analyzing the impact of technological factors on the cost-performance tradeoffs in distributed-router architectures. The main tradeoff in a distributed router results naturally from moving the main packet-forwarding and processing power from a centralized forwarding engine to an ensemble of smaller forwarding engines, either dedicated to or shared among the line cards. Processing packets in these smaller engines can be much cheaper (by as much two to three orders of magnitude) than in a centralized forwarding engine. Therefore, the main goal of our modeling framework is to determine an optimal allocation of processing power to the forwarding engines (in a distributed router) to minimize overall router cost while achieving a given level of packet-forwarding performance. Two types of router models are analyzed using the proposed framework: a distributed-router architecture and parallel-router architecture.

FPGA-based computing systems provide a feasible and cost-effective platform for implementing fast parallel arithmetic circuits for digital signal and image processing. This paper reports the results obtained from embedding a highly parallel convolution algorithm on an FPGA-based computer. Such a computer is intended to serve as a transformable co-processor for a standard microprocessor system. However, the transformable co-processor is reconfigurable and is capable of exploiting the concurrency of computations more than the sequential microprocessor. Our experiments show that a significant gain in speed can be achieved by using the transformable coprocessor. We present an example of performing a sequence of (independent) 16-point convolutions on 8-bit data, and show that the speed factor improves significantly as the number of convolutions to be performed increases.

This paper presents highly parallel VLSI structures for linear convolution. Our methodology implements Toom's algorithm and is based on mapping a modified version of the tensor product factorization proposed by Granata et al. (1991). The resulting networks have very simple structure, highly regular topology, and use simple bit-serial devices. Additionally, the proposed networks have very small depth and contain only a single stage of multipliers, while all other stages contain adders only.

This short note presents constant-time algorithms for labeling the connected components of an image on a network of processors with a wide reconfigurable bus. The algorithms are based on a processor indexing scheme which employs constant-weight codes. The use of such codes enables identifying a single representative processor for each component in a constant number of steps. The proposed algorithms can label an N/spl times/N image in O(1) time using N/sup 2/ processors, which is optimal. Furthermore, the proposed techniques lead to an O(logN/loglogN)-time image labeling algorithm on a network of N/sup 2/ processors with a reconfigurable bus of width log N bits. It is shown that these techniques on be applied to labeling an undirected N-vertex graph represented by an adjacency matrix.>

Network folding is a technique for realizing permutations on N elements using interconnection networks with M input (and output) terminals, where M>

This paper presents a methodology for designing folded VLSI networks for implementing tensor-product forms. Using tensor-products leads to very efficient expressions for a large number of computations in digital signal processing and matrix arithmetic. The resulting networks can trade-off total time delay with I/O bandwidth and chip area. The main goal is to parametrize the VLSI architecture so that it can be implemented under various packaging constraints including the available number of I/O pins, available chip-area, and certain restrictions on maximum wire length. Our methods result in folded VLSI networks with optimal AT/sup 2/ trade-off for digital filtering and multidimensional transforms, where A is the total area of the VLSI circuit (or chip) and T is its total time delay.>

A constant-time algorithm for labeling the connected components of an N/spl times/N image on a reconfigurable network of N/sup 3/ processors is presented. The main contribution of the algorithm is a novel constant-time technique for determining the minimum-labeled PE in each component. The number of processors used by the algorithm can be reduced to N/sup 2+(1/d/), for any 1/spl les/d/spl les/log N, if O(d) time is allowed.>

This paper presents a new class of AT/sup 2/-optimal networks for computing the multidimensional discrete Fourier transform. Although optimal networks have been proposed previously, the networks proposed in this paper are based on a new methodology for mapping large K-shuffle networks, K/spl ges/2, onto smaller area networks that maintain the optimality of the DFT network. Such networks are used to perform the index-rotation operations needed by the multidimensional computation. The resulting networks have simple regular layouts, and can be easily partitioned among several chips in order to reduce the number of input-output pins per chip.>

Minimum-area very large scale integration (VLSI) networks have been proposed for sorting N elements in O(log,N) time. However, most of such networks proposed have complex structures, and no explicit network construction is given in others. New designs of optimal VLSI sorters that combine rotate-sort with enumeration-sort to sort N numbers, each of length w (1+ in )logN bits (for any constant in >0), in time T in ( Omega (logN), Theta square root (NlogN)). The main attributes of the proposed sorters are a significantly smaller number of sorting nodes than in previous designs and smaller constant factors in their time complexity. The proposed sorters use a new class of reduced-area K-shuffle layouts to route data between sorting stages. These layouts can be also used to provide explicit designs for the column-sort technique developed by F.T. Leighton (1985).>

A survey and a characterization of the various parallel algorithms and architectures developed for the problem of labeling digitized images over the last two decades are presented. It is shown that four basic parallel techniques underly the various parallel algorithms for this problem. However, because most of these techniques have been developed at a theoretical level, it is still not clear which techniques are most efficient in practical terms. Parallel architectures and parallel models of computation that implement these techniques are also studied.>

Article Free Access Share on Optimal bounded-degree VLSI networks for sorting in a constant number of rounds Author: Hussein M. Alnuweiri Department of Electrical Engineering, The University of British Columbia, Vancouver, B.C., Canada V6T 1Z4 Department of Electrical Engineering, The University of British Columbia, Vancouver, B.C., Canada V6T 1Z4View Profile Authors Info & Claims Supercomputing '91: Proceedings of the 1991 ACM/IEEE conference on SupercomputingAugust 1991 Pages 732–739https://doi.org/10.1145/125826.126169Published:01 August 1991Publication History 2citation134DownloadsMetricsTotal Citations2Total Downloads134Last 12 Months4Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

A new parallel algorithm is proposed for fat image labeling using local operators on image pixels. The algorithm can be implemented on an n*n mesh-connected computer such that, for any integer k in the range (1, log (2n)), the algorithm requires Theta (kn/sup 1/k/) bits of local memory per processor and takes Theta (kn) time. Bit-serial processors and communication links can be used without affecting the asymptotic time complexity of the algorithm. The time complexity of the algorithm has very small leading constant factors, which makes it superior to previous mesh computer labeling algorithms for most practical image sizes (e.g. up to 4096*4096 images). Furthermore, the algorithm is based on using stacks that can be realized using very fast shift registers within each processing element.>

A new parallel architecture is presented which has p processors and N=n/sup 2/ memory locations, each consisting of 2s bits. The proposed organization can sort N s-bit numbers, where s=O((1+ epsilon ) log N), epsilon >0, in time t=O(N log N/p), for p in the range 1 to square root N log square root N. This result is optimal in the sense that the product of the number of processors and the parallel sorting time is equal to the sequential complexity of sorting. Also, the constant factors involved in the algorithm complexity are relatively small. When p= square root N log square root N, the time required for sorting N numbers on the proposed organization is O( square root N), which is the same time required by a two-dimensional mesh array, a mesh of trees organization, or a pyramid computer, all with O(N) processors, to sort N numbers.>

Processor-time optimal algorithms are presented for several image and vision problems. A parallel architecture which combines an orthogonally accessed memory with a linear array structure is used. The organization has p processors and a memory of size O(n/sup 2/) locations. The number of processors p can vary over the range (1,n/sup 3/2/) while providing optimal speedup for several problems in image analysis and vision. Such problems include labeling connected regions, computing minimum convex containers of regions, and computing nearest neighbors of pixels and regions. Optimal algorithms are presented for histogramming and computing the Hough transform. Such problems arise in medium-level vision and require global operations or dense data movement. It is shown that for these types of problems, the proposed organization is superior to the mesh and pyramid organizations.>

Optimal parallel solutions are presented to several geometric problems on an n*n image on a fixed-size linear array with p processors, where 1>