Preemptive scheduling provides an efficient mechanism for the coexistence of enhanced Mobile Broadband (eMBB) and Ultra-Reliable and Low-Latency Communication (URLLC) services in 5G networks. Due to differences in Quality-of-Service (QoS) requirements of the two services, it is necessary to investigate the trade-offs among energy-efficiency, throughput, latency, and reliability, in task offloading scenarios. Existing studies do not fully extend the preemptive scheduling mechanism for uplink task offloading while considering the interplay between all the QoS requirements of eMBB and URLLC User Equipment (UE). We address this gap by considering an edge network with eMBB and URLLC UE and formulate an objective function to improve energy-efficiency, throughput, and task queueing delay of eMBB UE while satisfying the transmission reliability of URLLC users. We also introduce the Twin Delayed Deep Deterministic Policy Gradient (TD3) to optimize task offloading. Simulation results show that the TD3 outperforms a widely used benchmark model in terms of convergence rate and variance. Results also highlight a very crucial aspect in reward shaping that embodies the trade-offs among the optimization variables and constraints.

This paper puts forth a proposal for a reconfigurable intelligent surface (RIS) enabled symbiotic backscatter system riding over a multiuser non-orthogonal multiple access (NOMA) carrier, where the RIS is employed as a substitute for the conventional backscatter device (BD) with the objective of enhancing both primary NOMA transmission and backscatter communications. In particular, a symbiotic mechanism is proposed to control the mutual interference by means of an adaptive adjustment of the reflection coefficient at the RIS. Moreover, a novel and effective multiuser decoding scheme is proposed, based on successive interference cancellation (SIC), with the objective of ensuring the successful transmission of the symbiotic system. To this end, analytical expressions re derived for the closed-form outage lower bounds, asymptotic outage behavior and outage error floors are derived. Furthermore, the upper bounds of the ergodic capacity and its asymptote at high signal-to-noise ratio (SNR) are developed in order to illustrate the spectral efficiency of the proposed symbiotic system. Theoretical analysis and numerical results demonstrate that a stronger backscatter channel with a greater number of elements deployed on a segmented RIS results in a reduction in transmission outage and an increase in system capacity. Additionally, numerical results illustrate the spectral efficiency advantage of the proposed symbiotic system over the conventional solutions.

In this paper, we present two low complexity algorithms to decode non-binary LDPC codes. The proposed decoding algorithms update iteratively the hard decision received vector to search for a valid codeword in the vector space of Galois field (GF). The selection criterion for the position of unreliable symbols is based on failed checks and the information from the Galois field structure. In the first proposed algorithm, the flipping function is calculated for all symbols of the received sequence and multiple symbols are flipped in each iteration while in the second proposed algorithm, a single symbol is flipped per iteration. In the second method, unreliable positions are short-listed by using a majority voting scheme, and then the flipping function is computed to predict candidate symbols from the set of symbols in GF(q) while not violating the field order q. The proposed methods reduce the decoding complexity and memory use. The results of the algorithms show appealing tradeoffs between complexity and bit error rate performance for non-binary LDPC codes.

This study investigates the performance of a cooperative non‐orthogonal multiple access cognitive network with imperfect successive interference cancellation under Rayleigh fading conditions. Specifically, the authors consider an underlay cognitive network that consists of a primary transmitter–receiver pair and a secondary system where a source node communicates with two destinations nodes directly and indirectly through a relay node selected from a set of decode‐and‐forward relays. A partial relay selection scheme is used to determine the best relay. The authors present an analytical framework, with closed‐form analytical expressions for the outage probabilities at the two destinations as well the primary destination. Moreover, to simplify the analysis and to provide further insights into the impact of key system parameters, asymptotic studies of the outage probabilities were carried out. To this end, the authors focus on two cases: (i) the maximum allowable transmit power of the secondary network grows sufficiently large and (ii) the interference power approaches infinity. Finally, Monte Carlo simulations are provided in an effort to assess the accuracy of the proposed mathematical framework.

Cluster based cooperative spectrum sensing (CSS) in cognitive radio networks provides for reduced sensing error, reporting delays and improved energy efficiency, in a practical network. However, achieving these advantages depend on suitably selecting a cluster head and adopting an appropriate fusion rule. This work investigates a new hard decision fusion rule, which makes the cluster heads non‐cooperative sensing result a necessary condition for cooperative decision making. The study also presents a comparative numerical study of three existing cluster head selection schemes with respect to their performance in CSS, under varying detection thresholds and cluster's heterogeneity. A robust and generalised cluster head selection scheme that overcomes the limitations of the existing schemes is thereafter proposed. The performance of the existing cluster head selection schemes depends on the distribution of secondary users relative to the primary user's position, and the detection threshold. Simulation results show that the proposed cluster head selection scheme can overcome the limitations of existing schemes. Furthermore, the hard decision fusion rule being proposed indicates improved performance compared with the OR rule in minimising the total error rate over Rayleigh fading channels.

This paper proposes a packet scheduling scheme that comprises a user scheduling and Physical Resource Blocking (PRB) mapping schemes for satellite LTE network with the adoption of MIMO technology. The Satellite Long Term Evolution (S-LTE) access network is able to provide worldwide coverage and hence supplement the terrestrial access network in the provision of mobile services to users in the LTE network. The user scheduling scheme is a vital Radio Resource Management (RRM) function that is needed in order to effectively utilize the available resources of the satellite LTE network. However, a user scheduling scheme without a scheme that will ensure effective mapping of the available PRBs to the selected users will undermine the utilization of the limited resources in a S-LTE network. Hence, the main goal of this paper is to propose a new joint scheme that is designed using cross-layer approach in order to improve the network throughput. This joint scheme will consists of user scheduling and PRB mapping algorithms. The proposed scheme will be compared with existing schemes through simulations, using known performance metrics.

In this paper, we analyze the performance of the generalized selection combining with Gaussian distributed weighting errors for physical-layer security of a wireless communication system. Exact closed-form expressions for the secrecy performance in terms of the secrecy outage probability and the probability of non-zero secrecy capacity are derived. Moreover, asymptotic expressions are obtained and provide insights on how the channel parameters affect the secrecy performance. Monte-Carlo simulations are conducted to assess the accuracy of our analytical framework.

This paper provides an analytical study on the bit-error rate (BER) of the turbo-coded cooperative relaying in spectrum-sharing systems subject to Rayleigh fading. It is assumed that a single relay that maximizes the received signal- to-noise ratio (SNR) is selected in a secondary multi-relay network. We consider that the transmit power conditions of the underlay system is controlled by the joint power constraint of the interference in the primary network and the maximum allowable transmission power at the secondary network. Moreover, the proposed scheme takes into account the effect of primary user (PU) interference on the neighboring secondary network. First, we derive an expression of a tight upper bound for the BER of the secondary network. Then, we investigate the cooperative diversity gain of the underlying scheme. Finally, the proposed analysis is validated by Monte-Carlo simulations.

Channel assembling (ChA) is a technique through which a user performs concurrent transmissions through multiple channels to maximize capacity in wireless networks. This paper proposes a hybrid ChA scheme for overlay and underlay secondary user (SU) transmissions in cognitive radio networks (CRNs). The main objective is to determine the optimal channel selection together with the associated power distribution. This aims to maximize SU capacity subject to total power constraint, minimum quality-of-service (QoS) requirement on capacity, collision constraint and transmission power constraint to protect primary user (PU) services. A Lagrangian framework is employed to reformulate the otherwise mixed integer nonlinear programming (MINLP) problem, based on which Lambert-W function with dual decomposition and subgradient iterative search methods are used to determine the optimal solution. In general, the presented simulation results illustrate significant performance improvement in terms of channel capacity, outage probability and collision probability when employing the proposed hybrid ChA scheme for SU transmissions.

This study proposes a near‐optimal packet scheduling scheme in the satellite long term evolution (LTE) network which uses multiuser multiple‐in multiple‐out technique. For the available resources in the satellite LTE network to be fully utilised and in order to meet the set targets of 4G standard, the need for an optimal scheduling scheme that will maximise the throughput without compromising the quality of service and fairness of users is very crucial. The aim of this study is to propose near‐optimal scheduling schemes that have been obtained using Karush–Kuhn–Tucker multipliers and compare their performances with other throughput‐optimal scheduling schemes. A new metric that can be used to compute the overall performance of the scheduling schemes is also presented. This work has adopted the use of a land mobile dual‐polarised GEO satellite system.

In this paper, we study the outage probability of the amplify-and-forward (AF) cognitive relaying in spectrum-sharing environments with outdated channel state information (CSI) over Rayleigh fading channels. A selection of the best relay in the secondary system with outdated channel information is considered. We derive a closed-form expression for the tight lower bound on the end-to-end outage probability using the cumulative density function (CDF) approach. Furthermore, the asymptotic behavior of the outage performance is investigated and reveals the diversity order of the underlying scheme. Finally Monte-Carlo simulations are provided to verify the analytical framework.

This paper presents an analytical study on the outage probability (OP) of cognitive amplify-and-forward (AF) with underlay spectrum-sharing systems subject to Rayleigh fading. In the underlying scheme, we consider a partial relay selection with outdated channel state information (CSI) and a spectrum-sharing system where the transmit power conditions are controlled by the combined interference power in the primary network and the maximum allowable transmission power at the secondary network. We first derive the end-to-end OP in closed form and then present asymptotic analysis for the high signal-to-noise ratio (SNR). Finally, Monte-Carlo simulations are provided to verify the accuracy of the theoretical analysis.

Abstract Recently, cooperative relaying techniques have been integrated into spectrum‐sharing systems in an effort to yield higher spectral efficiency. Many investigations on such systems have assumed that the channel state information between the secondary transmitter and primary receiver used to calculate the maximum allowable transmit secondary user transmit power to limit the interference is known to be perfect. However, because of feedback delay from the primary receiver or the time‐varying properties of the channel, the channel information may be outdated, which is an important scenario to cognitive radio systems. In this paper, we investigate the impact of outdated channel state information for relay selection on the performance of partial relay selection with amplify and forward in underlay spectrum‐sharing systems. We begin by deriving a closed‐form expression for the outage probability of the secondary network in a Rayleigh fading channel along with peak received interference power constraint and maximum allowable secondary user transmit power. We also provide a closed‐form expression for the average bit‐error rate of the underlying system. Moreover, we present asymptotic expressions for both the outage probability and average bit‐error rate in the high signal‐to‐noise ratio regime that reveal practical insights on the achievable diversity gain. Finally, we confirm our results through comparisons with computer simulations. Copyright © 2016 John Wiley & Sons, Ltd.

Channel assembling (ChA) has been proposed to maximize capacity in wireless communications. This paper determines the optimal channel selection and power distribution for secondary user (SU) transmissions under varying channel conditions, subject to power constraint, minimum quality of service (QoS) requirement for capacity, and collision probability threshold to protect primary user (PU) services. The nature of the optimization problem turns out to be in a form of mixed integer nonlinear programming (MINLP), which is generally nondeterministic in polynomial time. A Lagrangian framework is therefore employed to reformulate the optimization problem, based on which dual decomposition with subgradient and Newton-Raphson methods are used to determine a relaxed optimal solution. Thereafter, accelerated branch-and-bound (BnB) with sequential fixing (SF) is applied to determine an optimal solution to the original MINLP problem. The simulation results presented in this paper demonstrate that adaptive ChA with channel characterization improves performance in terms of channel capacity, outage probability and collision probability.

In this paper, the best relay selection in CSI-assisted variable gain amplify-and-forward (AF) with outdated channel state information (CSI) in the presence of co-channel interference (CCI) over Rayleigh fading channels is investigated. We first derive the cumulative density function (CDF) of the effective signal-to-interference-plus-noise ratio (SINR) of both the best source-to-relay and relay-to-destination links. Subsequently, a closed-form expression for the lower bound on the end-to-end outage probability (OP) of the system under study is obtained. Moreover, we present and discuss asymptotic expressions of the OP, which reveal the diversity gain of the underlying system. In particular, it is shown that for varying interference-to-noise ratio (INR), the diversity order is reduced to zero regardless of the nature of the desired CSI (i.e., outdated or ideal), and to full diversity or diversity one for fixed INR with ideal CSI or outdated CSI, respectively. Finally, Monte-Carlo simulation results are presented to validate the accuracy of the proposed analytical framework.

Future networks are to deliver any-traffic, anytime, anywhere with full quality of service (QoS) guarantees. They will evolve from typical heterogeneous networks (HetNets) into dense, organic, and irregular heterogeneous networks called DenseNets. They will be complex and face additional challenges of heterogeneity in many design dimensions like different radio access technologies (RAT's) shrinking in structure. Radio Resource Management (RRM) is one of the key challenges in providing for QoS for these networks. Connection Admission Control (CAC) scheme and intelligent scheduling techniques are employed on the links for RRM. In this paper a CAC scheme is developed that features multiple traffic classes, multiple admission parameters at both packet and connection level. The CAC scheme uses both signal to interference ratio (SIR) and delay as admission parameters since the single parameter based CAC algorithm is not adequate for the emerging traffic classes. The performance analysis of the model features Batch Markovian Arrival Process (BMAP) traffic, a better representative of the future traffic characteristics than the traditional Poisson traffic. A simple approximate Markovian analytical model is developed and used to analyze the complex network. The developed model with more admission parameters outperforms those with less admission control parameters for future networks traffic.

In this paper, we study the performance of relay selection in variable-gain amplify-and-forward (AF) turbo-coded cooperative network in the presence of channel estimation errors. In particular, we assume M-ary phase shift keying (MPSK) modulation and consider a dual multi-relay cooperative scenario where the relay selection requires global knowledge (end-to-end) of the relaying link. We derive the probability density function (PDF) of the received signal-to-noise ratio (SNR) for the underlying relaying link, and an upper bound expression of the average pairwise error probability (PEP). Furthermore, we present the diversity analysis study in which we show that the effect of erroneous channel estimates reduce the diversity order at high SNR to zero. Using these results, we evaluate the performance of the coded cooperation scenario under study in terms of bit-error rate (BER). Monte-Carlo simulation results are presented to validate the accuracy of the analytical results.

In this paper, we consider a cognitive radio network (CRN) with multiple primary users (PUs) and multiple SUs and propose a cooperative spectrum sensing and transmission for some selected SUs in order to avoid interference with PUs. The distributed collaboration strategy is done through a coalitional game and we present a distributed algorithm for the coalition formation. In the proposed scheme, the SUs that sense a particular channel with non-identical sensing times, form a coalition in which a coalition head is selected to determine whether or not the channel is idle. If a channel is not active, then the SU chosen as coalition head can transmit its packets through a cooperative scheme in the data transmission slot. Our simulation results show that the proposed scheme can significantly improve the average throughput compared to its non-cooperative counterpart. Moreover, it is shown that the proposed scheme is energy efficient in comparison to a scheme with fixed and identical sensing times.

Cooperation with channel coding also known as coded cooperation has been shown to be an efficient scheme for providing significant performance gains. However, relay selection in coded cooperation systems is seldom available in the existing literature. It is widely known that relay selection schemes in cooperative communications are dependent on the quality of the channel state information (CSI). In this paper, we study the impact of using outdated channel state information (CSI) for opportunistic relay selection (ORS) in turbo-coded cooperation over Rayleigh fading channels. A closed-form expression for the exact outage probability as a function of the correlation between the actual and delayed or outdated CSI is derived. Furthermore, diversity analysis is presented and it is noted that the diversity order is reduced to two regardless of the number of available relays, when the correlation factor is not equal to unity.

In this paper, we consider relay selection for turbo coded cooperative networks subject to Nakagami-m fading when the channel state information (CSI) is known at the receiver but is not necessarily ideal. This non-ideality may be due to a feedback delay caused by the difference between the instantaneous CSI during the transmission and the CSI at the time of relay selection, resulting in outdated CSI phenomena. The impact of the outdated CSI on the proposed scheme is well investigated. A closed-form expression for the exact outage probability is derived as well as its asymptotic expression in the high signal-to-noise (SNR) regime. Moreover, upper bounds on the bit-error rate (BER) are presented and a study of the diversity order reveals that for ideal CSI, full diversity in the number of relays and fading parameters m is achieved as opposed to outdated CSI where the achievable diversity is equivalent to the diversity of a coded cooperative network with a single relay.

We study the performance of distributed turbo-coded cooperative networks with multiple dual-hop relays over both identical and non-identical Nakagami-m slow fading channels. All the relays are equipped with error detection capabilities and only the reliable relays retransmit to the destination. In this paper, we derive the union bounds on the bit-error rate (BER) of the proposed scheme using the transfer function bounding and the limit-before-average techniques. Moreover, through the derived pairwise-error probability (PEP), we analyze the asymptotic behavior of this system at high signal-to-noise ratio (SNR). It is noted that the achievable diversity order depends on the number of cooperating relays and the fading parameters. Finally, performance evaluation of the proposed scheme is presented via error bounds and Monte Carlo simulations.

We investigate a power assignment scheme in multi-relay adaptive decode-and-forward (DF) cooperative-diversity networks over non-identical Rayleigh fading channels, that integrates truncated automatic repeat-request (ARQ) at the link layer. At the cooperative level, only the reliable relays participate in the retransmission phase if necessary. In this paper, we aim at maximizing the system throughput via power optimization and we show that this can be done by minimizing the symbol-error rate (SER) of the retransmission. We derive the closed- form expressions for the exact SER of the multi-relay adaptive DF over non-identical Rayleigh fading channels as well as the asymptotic bounds for the SER. Results show that the analytical bounds for the SER corroborate with the simulated SER at high signal-to-noise ratio (SNR) and maximum throughput is achieved through optimal power allocated at the source and various reliable relays.

In this paper, we investigate a cross-layer relay selection approach for cooperative-diversity networks that employ the truncated automatic repeat request (ARQ) protocol. The key feature of the proposed scheme is that the criterion for the selection of relay subsets is the maximization of the link-layer throughput that takes into account both the physical and link layers characteristics. Results show that the proposed cross-layer approach which assigns transmission to relay combination that sees better channel conditions, outperforms the capacity-based cooperative transmission with the same number of reliable relays in terms of throughput gain. Furthermore, a joint optimization of constellation size and packet length is included to enhance the system throughput for both the cross-layer relay selection and capacity-based relay selection.

Multiple antennas are used to increase reliability and bit rate for a given bandwidth. For a fixed transmission rate, discrete input alphabets and no channel state information at the transmitter, optimal space-time codes (STCs) achieving both gains (full rate and full diversity) are well known. However, the complexity of maximum likelihood decoding increases exponentially with the number of space and time dimensions of the STC. Despite praiseworthy efforts to reduce the decoding complexity, optimal STCs are not used in practice in the case of more than two transmit antennas because of complexity reasons. It is generally accepted that reducing the dimension of the STC leads to a reduced diversity order. We show that this is not true for coded communication, assuming the presence of an outer error-correcting code with any coding rate. We propose a new class of full-rate full-diversity STCs; more specifically, time-varying space-only codes. This new class is referred to as EMI codes. Full diversity is proven in terms of outage probability, for the case where the number of receive antennas is larger than or equal to the number of transmit antennas, and is numerically verified in terms of outage and word error probability using LDPC codes.

Cross Layer Hybrid Automatic Repeat reQuest 2 (HARQ 2) Cooperative Diversityis an efficient transmission scheme, proposed in this paper. This cross layer design scheme, between the physical and data link layer, provides BER and throughput improvements over traditional Coded Cooperation due to the fact that in some cases the base station has already decoded a particular set of information bits using a user's initially transmitted parity and not all parity bits are required. The user however is not informed by the base station of this, during Coded Cooperation. With the proposed cross layer design users can then transmit incremental parity packets and await feedback from the base station to decide whether further parity is required for a particular set of information bits. Improvements in Bit Error Rate (BER) and throughput are observed by the cross layer design over Coded Cooperation. BER theoretical bound analysis is performed and is validated by simulations in a block fading channel. Throughput results are also presented.

Recently, cooperative diversity has been introduced where single-antenna mobiles achieve uplink transmit diversity helping each other by relaying one another's messages. A variation of this principle is coded cooperation which partitions the codeword of each mobile and transmits portions of each codeword through independent fading channels. Coded cooperation framework has been easily extended using turbo codes. In this paper we propose a new cooperative protocol that improves the performance of turbo coded cooperation from moderate to high signal-to-noise ratios. This method uses the forced symbol method in which the basic encoder structure remains unchanged. We present computer simulation results of the proposed scheme under various inter-user channel SNRs and compare to the union bound analysis.

Quality-of-service (QoS) guarantees are critical for the transmission of multimedia traffic over mobile wireless networks. Currently, wireless networks provide QoS guarantees using the legacy layered protocol architecture where each layer provides a separate, independent solution, with its own optimised adaptation and protection mechanisms. Cross-layer design has been proposed as a methodology to extend that paradigm in wireless links where there is interdependence between the layers and hence opportunity for information sharing. Recently, cross-layer adaptation mechanisms have been proposed which attempt to solve the QoS provisioning problem. However, most of these mechanisms only use the lower (physical and data link) layers and the possibility of using higher protocol layers remains unexplored. As a result, restrictions are placed on the system which introduces functional and efficiency limitations. Here, one such limitation is highlighted, namely the inability to insert more than one class of traffic in a physical layer frame. A physical and application layer cross-layer adaptation mechanism is then proposed, which overcomes this limitation. The performance results of the scheme show that the cross-layer mechanism can be efficiently applied for the purpose of providing QoS guarantees for multimedia traffic.

In this letter, a low complexity decoding algorithm for binary linear block codes is applied to low-density paritycheck (LDPC) codes and improvements are described, namely an extension to soft-decision decoding and a loop detection mechanism. For soft decoding, only one real-valued addition per code symbol is needed, while the remaining operations are only binary as in the hard decision case. The decoding performance is considerably increased by the loop detection. Simulation results are used to compare the performance with other known decoding strategies for LDPC codes, with the result that the presented algorithms offer excellent performances at smaller complexity.

In this letter, an improved bit-flipping decoding algorithm for high-rate finite-geometry low-density parity-check (FG-LDPC) codes is proposed. Both improvement in performance and reduction in decoding delay are observed by flipping multiple bits in each iteration. Our studies show that the proposed algorithm achieves an appealing tradeoff between performance and complexity for FG-LDPC codes.

This paper presents a new method that improves the performance of coded cooperation, especially in the error floor region. This method uses a modified repeat-punctured turbo code or double repeat-punctured turbo code with the cooperative scheme, where the modified repeat-punctured turbo code uses a repeater and an interleaver for both the first and second recursive systematic encoders. The analysis and simulation results of the proposed scheme are given and a comparison is made with the conventional turbo coded cooperative diversity scheme and the coded cooperation with repeat-punctured turbo code.

The performance analysis of high rate space–time trellis-coded modulation (HR-STTCM) using the Gauss–Chebyshev quadrature technique is presented. HR-STTCM is an example of space–time codes that combine the idea used in trellis coded modulation (TCM) design that is signal set expansion and set partitioning into its construction. HR-STTCM construction is based on the concatenation of an outer TCM encoder and inner space–time block code. This paper evaluates the exact pairwise error probability of HR-STTCM based on the Gauss–Chebyshev quadrature formula. Comparison of numerical and simulation results shows that the proposed method is accurate. The method used is shown to be computationally simpler than those in the literature.

Token passing medium access control (MAC) protocols are gaining interest amongst wireless ad hoc network researchers as they provide unrivalled advantages over the existing IEEE 802.11 standards. This paper introduces a hybrid Token-CDMA MAC protocol that is based on a token passing scheme with the incorporation of code division multiple access (CDMA). With its unique CDMA feature, the proposed MAC is able to support multiple, simultaneous transmissions. The proposed protocol provides both Quality of Service (QoS) and high network resource utilization, while ensuring the stability of the network. This paper examines the performance of the proposed MAC scheme by simulation, and compares its performance against that of other MAC protocols that have appeared in the literature. Simulation results demonstrate that our proposed MAC scheme is effective in decreasing the packet delay and significantly shortens the length of the queue. The input traffic model used in the simulation is a two-state Markov Modulated Poisson Process (MMPP). The data rate QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC scheme. The simulation also takes into account channel link errors caused by the wireless link by implementing a multi-layered Gilbert-Elliot model.

In this paper, a modified bit-flipping decoding algorithm for low-density parity-check (LDPC) codes is proposed. Both improvement in performance and reduction in decoding delay are observed by flipping multiple bits in each iteration. Our studies show that the proposed algorithm achieves an appealing tradeoff between performance and complexity for many constructions of LDPC codes.

This paper presents the performance analysis of a hybrid token-CDMA MAC protocol. The protocol is based on a token passing scheme with the incorporation of code division multiple access (CDMA). The protocol provides both QoS guarantee and high network resource utilization. The performance of the MAC scheme is analyzed by event-driven simulations. Markov-modulated Poisson process (MMPP) is modeled for the traffic input sources and the issue on the channel link error caused by the wireless link has been taken into consideration by implementing multi-layered Gilbert-Elliot model which takes into account the number of interfering codes for simulating bit errors on a wireless link. Various performance metrics are used to demonstrate effectiveness of the hybrid protocol.

A major attraction for differential modulation is in non-coherent reception for a communication system propagating over fast fading channels. However, conventional differential modulation (CDM) leads to a 3 dB loss over coherent modulation. To overcome this with minimal complexity, iterative decoding employing hard decision feedback and bit-interleaved coded modulation have been suggested. The channel encoder often employs convolutional codes which may require low rates or high constraint length to reduce the flooring effect in CDM. In this paper we propose residual arithmetic codes for channel coding. We show through simulated results that the arithmetic codes can achieve similar or better bit error rate (BER) performance than convolutional codes of the same rate and asymptotic coding gain at t = 1, 2 error correcting capability with minimal complexity. We invoke the Chase algorithm to provide the soft input to the hard decision algebraic decoder for the arithmetic codes

In this paper, the construction of new families of error-correcting codes adapted from Boutros and Lentmaier's generalized low-density (GLD) codes, which we called generalized irregular low-density (GILD) codes, is investigated. By introducing irregular base matrices, significant improvements on Boutros and Lentmaier's results are achieved. Two cases are considered; in the first case, the same constituent code is used, and in the second case, different constituent codes are used. It is proved by an ensemble performance argument that these codes exist and are asymptotically good in the sense of the minimum-distance criterion. It is also proved that the performance of GILD codes approaches the binary symmetric channel capacity limit. Iterative decoding of GILD codes for communication over an additive white Gaussian noise channel is also studied. The high flexibility in selecting the parameters of GILD codes and their better performance and higher rate make them more attractive than GLD codes, and hence, suitable for small and medium block lengths forward-error-correcting schemes. Comparisons of simulation results between some GILD codes and some good low-density parity-check codes show very close performances

In this paper extrinsic information transfer (EXIT) charts are proposed to design non-binary low-density parity-check (LDPC) codes for the AWGN channel. A new metric is presented to describe the mutual information of the non-binary messages. The a priori information is modelled using a Gaussian mixture distribution. Analytical expressions are given for the EXIT curves of the variable and check node decoders for both regular and irregular LDPC codes. The analytical expressions are shown to agree well with simulation results. Finally, by matching the variable and check node EXIT curves, it is shown that good nonbinary LDPC can be designed for the AWGN channel.

New cyclic multiuser detection (MUD) algorithms are presented in this paper which are based on blind adaptive MUD algorithms but have been modified such that they operate directly on the frequency shift (FRESH) architecture. The operation of both stochastic gradient descent (SGD) and recursive least squares (RSL) algorithms are examined. Suboptimal FRESH architectures are also investigated. The relative performance of the adaptive algorithms on the FRESH architecture is compared with an implementation on the filter bank architecture. This paper also investigates the relative sensitivity of the adaptive algorithms to timing jitter on these competing architectures.

In this paper, reduced-complexity trellis-based soft-input soft-output (SISO) decoding of linear block codes is considered. A new low-weight subtrellis based SISO decoding algorithm for linear block code to achieve near optimal error performance with a significant reduction in decoding complexity is presented. The proposed scheme is suitable for iterative decoding of linear block codes when used as component codes in compound or concatenated coding schemes. It has the following important features. An initial candidate codeword is first generated by a simple decoding method that guarantees a successful decoding. A low-weight subtrellis diagram centered around the candidate codeword is constructed. The maximum a posteriori probability (MAP) algorithm is then applied to the subtrellis. The generated extrinsic information is then used as a priori information to improve the generation of a candidate codeword for the next stage of iteration. Simulation results in the case of the newly introduced generalized irregular low-density (GILD) codes indicate that the proposed algorithm achieves practically optimal performance with a significant reduction in decoding complexity.

This paper derives the closed form expressions for the excess mean square error (EMSE) of code constrained blind adaptive multiuser detectors (MUD) in a non-stationary channel, using the feedback approach. The tracking performance of those algorithms is thus quantified. Closed form expressions are derived to quantify the transient performance of the adaptive algorithms. It is shown that the exact time evolution of the signal to interference plus noise ratio (SINR) may be predicted from initialization to steady-state. The accuracy of the analysis is confirmed via simulation.

We propose an iterative multiuser detector for turbo coded direct sequence CDMA (DS-CDMA) systems in the uplink channel. The receiver is derived from the maximum a-posteriori (MAP) estimation of the single user's transmitted data, conditioned on the information about the estimate of the multiple access interference (MAl) and the received signal from the channel. The complexity of the proposed receiver increases linearly with the number of users. Error rate performances of the receiver is found to be better than those of the receiver in which a direct subtraction of the estimated multiple access interference is performed. The performance of the developed iterative multiuser receiver is investigated in the multipath fading environment with and without the knowledge of the side information. It was observed that the performance of the proposed receiver improves in a multipath fading channel when the channel side information is considered in the development of the receiver.

Wireless communication systems employing multiple antennas at both the transmitter and receiver have been shown to offer significant gains over single antenna systems. Recent studies on the capacity of multiple-input multiple output (MIMO) channels have focused on the effect of spatial correlation. The joint effect of spatial and temporal correlation has not been well studied. In this paper a geometric channel model is presented which considers motion of the receiver and non-isotropic scattering at both ends of the radio link. A joint space-time cross-correlation function is derived and variates with this correlation are generated using the vector autoregressive stochastic model. The outage capacity of this channel is considered where the effects of antenna spacing, antenna array angle, degree of non-isotropic scattering and receiver motion are investigated. When n transmit and n receive antennas are employed, it is shown that capacity still increases linearly with respect to n despite the presence of spatial and temporal correlation.

Mobility management is the highest contributor of signaling traffic in mobile networks. Messages generated by the insert subscriber data procedure during a location update are not only large but more will be required in future third generation (3G) networks to allow for the transfer of large subscriber profiles. This paper compares the mobility management protocol used in GSM and 3G networks with that proposed for super-charged networks by examining the network's performance under normal conditions and during signaling transfer point congestion.

A class of pseudo-random compound error-correcting codes, called generalized low density (GLD) parity-check codes, has been proposed recently. As a generalization of Gallager's low-density parity check (LPDC) codes, GLD codes are also asymptotically good in the sense of minimum distance criterion and can be effectively decoded based on iterative soft-input soft-output (SISO) decoding of individual constituent codes. The code performance and decoding complexity of GLD codes are heavily dependent on the employed SISO decoding algorithm. In this paper, we present an efficient SISO decoding algorithm for GLD codes. The proposed algorithm utilizes Kaneko's decoding algorithm for soft-input hard-output decoding. These hard outputs are converted to soft-decision using reliability calculations. The algorithm proposed here presents a major advantage over existing decoding algorithms for GLD codes by being applicable even when long and powerful component codes are used. The complexity of the proposed algorithm is less than that of trellis-based decoding algorithms with a performance degradation of only 0.3 dB.

Classically cellular networks have been analysed using Poisson call arrivals and negative exponential channel holding times. This approach has been reasonable for the circuit-switched voice traffic carried by the earlier cellular networks. However, with the advent of GPRS networks, packet switched data traffic now competes with circuit-switched voice traffic for the available resources on the air-interface. We analyse the merging of voice and data traffic in the radio layer of the GSM Phase 2+ (GPRS) networks.

This paper introduces a novel protocol for the transport of WATM cells over the reverse link of DS-CDMA cell. The QoS is offered in terms of the BER, and a cell deferring method is introduced and analysed. A new method to regulate the offered load in the ABR section is also described, which increases the throughput of ABR cells. Monte-Carlo simulations of the protocol, backed up by Markov analysis results, are also presented.

Classically cellular networks have been analysed using Poisson call arrivals and negative exponential channel holding times. However, measurements on live networks have generally invalidated these assumptions. We propose a method for analysing cellular networks under more generalised arrival processes and more realistic channel holding time distributions. We present a model for accurately characterising the hand-off traffic offered by a cell to its neighbour in a simple two-cell scenario. Our two-cell model easily lends itself to be used as building blocks for analysing more general cellular network layouts. The results of the two-cell scenario may be used to determine customer-orientated grade of service parameters such as new call blocking and forced termination probability. We illustrate the accuracy of our analysis using comparison with simulation results.

The main contribution of this paper is an analytical method for characterising the hand-off traffic generated under generalised call arrival and generalised channel holding time distributions. Our proposed model forms an integral part of a larger performance analysis algorithm that may be used to determine typical grade of service parameters such as new call blocking, hand-off call blocking and forced termination probability. The classical teletraffic assumptions of Poisson call arrivals and negative exponential channel holding times may not apply for future PCS networks. Instead, we employ a more realistic finite population Engset arrival process to model the new call arrival process. We model the hand-off call arrival process in the cellular network as a generalised arrival process and represent it using the mean and variance of its offered traffic distribution. We characterise the channel holding times using a more generalised distribution that we have labelled the det-neg distribution.

We present and analyse a distributed channel access control protocol in a direct sequence CDMA network. In this protocol, every channel is available for use in every cell and channel access decisions are made by the mobiles based on information broadcast from the base stations. This is different from the access strategies which have appeared in the literature where call requests are processed solely by the base stations. Narrainen and Takawira (see IEEE Military Commun. Conf., Virginia, USA, p.384-8, 1996) analysed the distributed protocol using a M/M//spl infin/ queuing model. A drawback of this model is its failure to accurately represent the protocol for small values of channel access update intervals. In this paper, we present an enhanced analytical model based on semi-Markov embedded processes. The performance of the network is also determined through simulation of a 30 cell network. We model closed-loop power control and include propagation effects such as path loss with distance, log-normal shadowing, and Rayleigh fading. Teletraffic performance is computed in terms of call blocking, probability of forced termination, and grade of service.