This paper proposes an opportunistic nonorthogonal amplify-and-forward (ONAF) scheme, assisted by intelligent relay selection. Through analysing the mutual information of the scheme, the novel optimal relay selection criterion is proposed along with its implementation strategy. In order to reduce the system complexity, a sub-optimal selection criterion is then provided. The diversity-multiplexing tradeoff (DMT) analysis shows that the proposed scheme can achieve a diversity gain of the order of the number of candidate relays, and a maximal multiplexing gain of 1. Since the previous work on opportunistic relaying were established under the orthogonal constraint, ONAF is one of the most advanced opportunistic relaying schemes. Our numerical results show the ONAF scheme can outperform the existing nonorthogonal and opportunistic relaying schemes where the relays forward the message using the amplify-and-forward (AF) mode. More importantly, it is a flexible cooperative scheme that can reduce network power consumption, alleviate interference caused among relays' re-transmissions and avoid the negative impact of the weak source-relay-destination channels.

Distributed spatial diversity systems, such as multi-relay and multi-user networks, have drawn significant attention from the research community. However, their feasibility in a practical environment remains an open concern. Most notably, how to optimize cooperation between multiple users with individual interests and how practical systems issues can erode diversity gains. Whilst existing information theoretical analysis may yield insightful bounds, they provide an inadequate solution for optimal power allocation in realistic systems due to the mutual information saturation of non-Gaussian inputs. In our work, we use feasible modulation and error correction codes to implement a system and demonstrate how multiple users cannot only improve their performance through cooperation, but also optimize their performance through power allocation with imperfect feedback. We do so, by considering an evolution game theoretic (EGT) approach, whereby the status-quo between users change with each decision.

We consider decode-and-forward cooperative networks and we derive analytical expressions as well as tractable asymptotic approximations for the outage probability of a network node. Our analysis sheds more light on the interplay between the channel conditions, the network size and the adopted transmission scheme, and provides a useful tool for the design of cooperative networks.

This paper proposes a new distributed Amplify-and-Forward (AF) scheme which is integrated with the Ring-Trellis Coded Modulation (TCM) codes in order to achieve both high spectral efficiency and large diversity gain. In the distributed AF scheme, more users cooperate with each other. Fach user still uses half of its transmission freedom for relaying others' signal. However, different to the conventional AF scheme, each user further partitions its relay transmission into smaller divisions in order to help more users. As a result, for each user, the distributed AF scheme will have the same spectral efficiency as the conventional AF scheme, but creating more diverse transition paths and providing better diversity gain. In the scheme, output symbols are demultiplexed into several subframes, each of which will be relayed by a different user. As a result, each output symbol from a trellis transition branch can be relayed by a different user, assisting error-correction performance of the decoder. This distributed coding scheme is suitable for different wireless access systems, such as WiLAN and WiMAX systems. Our simulation results show that with the same spectral efficiency, the distributed coded AF scheme can significantly outperform the conventional coded AF scheme.

In this paper, we consider cooperative networks of users that implement an unselfish protocol to decode and forward packets of their partners. In unselfish cooperation, a user that has successfully retrieved the source data of a partner, will unconditionally assist that partner in its transmission to the destination. We use a threshold-based model to derive an analytical expression for the end-to-end packet error probability and we validate our approach comparing theoretical to simulation results. Furthermore, we explore the interplay between various network parameters, such as the number of users, the transmission scheme and the quality of the interconnecting channels, and we briefly discuss the impact of power allocation on the overall performance.

We derive an adaptive power control method for a collaborative network utilizing partner selection that aims to minimize the frame error rate (FER). We model a decode-and-forward (DF) collaborative network under block fading conditions, which contains M independent users utilizing codes, whose performance can be expressed by a signal to noise (SNR) threshold, such as turbo codes. We show that partner selection can reduce system complexity and power allocation can improve the FER performance. We use both a search method as well as a convex deterministic method to demonstrate our power allocation scheme. This research extends other work in which adaptive power allocation is only applied to limited scenarios. We conclude that power control can greatly benefit a DF collaborative network in a block fading environment.

We derive theoretical bit and frame error rate expressions for decode-and-forward (DF) collaborative networks containing M users, employing a variety of block codes over a Rayleigh block faded channel. With the aid of these expressions, we explore the performance of adaptive power control for such systems. This extends previous work by optimizing power allocation for all relay and direct channels. We further extend our work to a variety of cooperation mechanisms and we conclude that power control can greatly benefit a DF collaborative network in a fading environment.

In a cooperative communication network, individual users are encouraged not only to transmit their own data, but also relay other user's data. This relaying transmission creates spatial diversity to combat the effect of individual severe fading and path loss. Since cooperative users utilize some degree of their transmission freedom for relaying other user's data, cooperative transmission results in lowering each user's transmission spectral efficiency. Therefore, a coding scheme with high spectral efficiency and optimized performance would be desirable for a cooperative network. This paper proposes the Trellis Coded Modulation (TCM) scheme to be incorporated with the cooperative Amplify-and- Forward (AF) systems. A criterion for designing good TCM codes for AF systems is also derived and two cooperative AF systems achieving 1 bits/sec/Hz and 1.5 bits/sec/Hz for each user are presented. Analyses in this paper show that cooperative TCM schemes can not only achieve high spectral efficiency, but also outperform convolutional codes with a high order modulation scheme.

The quality of service (QoS) support for multimedia communications faces a big challenge in a fading wireless network. On one hand, conventional automatic repeat request (ARQ) schemes are not effective for small-scale fading channels with correlated errors due to consecutive retransmission failures. On the other hand, large-scale fading due to propagation loss or shadowing severely limits transmission range. A novel differentiated cooperative medium access control (MAC) protocol, called DC-MAC, is proposed to enhance the QoS support for multimedia communications while supporting service differentiation based on the IEEE 802.11e architecture. By enabling cooperative ARQ, the retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source. Since unnecessary and useless retransmissions may intensify the node contention and degrade the system performance contrarily, a novel negative acknowledgement feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Extensive simulations are conducted on the OPNET platform to analyse the performances of DC-MAC under both small-scale and large-scale fading. Simulation results show that the proposed scheme significantly improves the performances of both multimedia applications and best-effort data applications in terms of throughput, delay and coverage with moderate user contention.

The objective of this paper is two-fold. Initially, we present an analytic technique to rapidly evaluate an approximation to the union bound on the bit error probability of turbo codes. This technique exploits the most significant terms of the union bound, which can be calculated straightforwardly by considering the properties of the constituent convolutional encoders. Subsequently, we use the bound approximation to demonstrate that specific punctured rate-1/2 turbo codes can achieve a lower error floor than that of their rate-1/3 parent codes. In particular, we propose pseudo-random puncturing as a means of improving the bandwidth efficiency of a turbo code and simultaneously lowering its error floor.

Convolutional block codes, which are commonly used as constituent codes in turbo code configurations, accept a block of information bits as input rather than a continuous stream of bits. In this paper, we propose a technique for the calculation of the transfer function of convolutional block codes, both punctured and nonpunctured. The novelty of our approach lies in the augmentation of the conventional state diagram, which allows the enumeration of all codeword sequences of a convolutional block code. In the case of a turbo code, we can readily calculate an upper bound to its bit error rate performance if the transfer function of each constituent convolutional block code has been obtained. The bound gives an accurate estimate of the error floor of the turbo code and, consequently, our method provides a useful analytical tool for determining constituent codes or identifying puncturing patterns that improve the bit error rate performance of a turbo code, at high signal-to-noise ratios.

This paper proposes the first complete soft-decision list decoding algorithm for Hermitian codes based on the Koetter-Vardy's Reed-Solomon code decoding algorithm. For Hermitian codes, interpolation processes trivariate polynomials which are defined over the pole basis of a Hermitian curve. In this paper, the interpolated zero condition of a trivariate polynomial with respect to a multiplicity matrix M is redefined followed by a proof of the validity of the soft-decision scheme. This paper also introduces a new stopping criterion for the algorithm that tranforms the reliability matrix Pi to the multiplicity matrix M. Geometric characterisation of the trivariate monomial decoding region is investigated, resulting in an asymptotic optimal performance bound for the soft-decision decoder. By defining the weighted degree upper bound of the interpolated polynomial, two complexity reducing modifications are introduced for the soft-decision scheme: elimination of unnecessary interpolated polynomials and pre-calculation of the coefficients that relate the pole basis monomials to the zero basis functions of a Hermitian curve. Our simulation results and analyses show that soft-decision list decoding of Hermitian code can outperform Koetter-Vardy decoding of Reed-Solomon code which is defined in a larger finite field, but with less decoding complexity.

Cooperative communication is becoming a promising technology for wireless networks by exploiting two key characteristics of the wireless medium: broadcast nature and spatial diversity. To integrate cooperation into practical systems, efficient protocols are needed across the entire protocol stack. This paper presents a novel cooperative relay-based auto rate medium access control (MAC) protocol (CRBAR) for multirate wireless networks, in which low-rate stations can be adaptively assisted by high-rate stations. Different from state-of-the-art table-based proactive relay selection schemes, a reactive relay selection scheme is developed to adapt to dynamical channel variation and network topology in which the relay candidates adaptively select themselves as the relay nodes and determine the relay scheme and transmission rates based on the instantaneous channel measurements. In terms of relay schemes, cooperative relaying can be employed whenever possible in addition to simple relaying. The receiver can improve its capability to decode the original frame by combining the information from both the sender and the relay. We have developed analytical models of different schemes for a simple scenario and carried out further simulations under a realistic fading channel and mobility model. Both analysis and simulation show that CRBAR significantly outperforms the table-based proactive relay selection scheme and direct rate adaptation scheme.

The quality of service (QoS) support in wireless local area networks (WLANs) faces a big challenge due to time-correlated fading channel. Conventional automatic repeat reQuest (ARQ) schemes based on time diversity may result in consecutive retransmission failures degrading QoS severely. This paper proposes a novel Differentiated cooperative medium access control (MAC) protocol, called DC-MAC, to enhance QoS in WLANs based on the IEEE 802.11e architecture. The retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source to exploit spatial diversity. A novel negative acknowledgement (NAK) feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Simulations conducted on the OPNET platform show that the proposed scheme significantly improves the performances of both multimedia applications and data applications in terms of throughput and delay while supporting service differentiation.

Cooperative communication is becoming a promising technology for wireless networks by exploiting multipath fading instead of mitigating its impact. To integrate cooperative diversity into practical systems, efficient protocols are needed across the entire protocol stack. This paper presents a Cooperative Relay-Based Auto-Rate MAC protocol (CRBAR) to enhance the multi-rate capability along a long link. By leveraging the broadcast nature of the wireless medium and spatial diversity, a low-rate hop can be replaced by two high-rate hops via adaptive MAC-layer cooperation. To adapt to dynamical channel variation and network topology, the relay candidates adaptively select themselves as the relay nodes and determine the relay scheme and transmission rates based on the instantaneous channel measurements. System-level simulation study shows that CRBAR significantly outperforms traditional rate adaptation schemes in realistic scenarios.

Broadband fixed wireless access (BFWA) systems enable services such as high-speed data communication, high quality voice/video conferencing and high-speed internet access in areas where a wired link is not possible. However, the BFWA channel is a slow-fading channel having deep frequency-selective fading caused by clusters of scatterers in the environment that introduce inter-symbol interference (ISI) at the receiver. Low density parity check (LDPC) codes, optimised for the single-input single-output BFWA channel, are designed using the structured balance incomplete block design method. The use of both quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM) are investigated theoretically. To help overcome the ISI effects of the channel, equalisation techniques are employed separately with LDPC decoding for a system employing QPSK and 16-QAM modulation schemes. The equaliser single carrier approach is then replaced with orthogonal frequency division multiplexing (OFDM) and the performance of these two approaches is evaluated in terms of bit-error rate. The simulation results show that equalisation with LDPC coding has a measurable performance gain over LDPC coding with OFDM.

The performance of turbo codes in quasi-static fading channels both with and without antenna diversity is investigated. In particular, simple analytic techniques that relate the frame error rate of a turbo code to both its average distance spectrum as well as the iterative decoder convergence characteristics are developed. Both by analysis and simulation, the impact of the constituent recursive systematic convolutional (RSC) codes, the interleaver size and the number of decoding iterations on the performance of turbo codes are also investigated. In particular, it is shown that in systems with limited antenna diversity different constituent RSC codes or interleaver sizes do not affect the performance of turbo codes. In contrast, in systems with significant antenna diversity, particular constituent RSC codes and interleaver sizes have the potential to significantly enhance the performance of turbo codes. These results are attributed to the fact that in single transmit–single receive antenna systems, the performance primarily depends on the decoder convergence characteristics for Eb/N0 values of practical interest. However, in multiple transmit–multiple receive antenna systems, the performance depends on the code characteristics.

List decoding Hermitian codes using the Guruswami-Sudan (GS) algorithm can correct errors beyond half the designed minimum distance. It consists of two processes: interpolation and factorisation. By first defining a Hermitian curve, these processes can be implemented with an iterative polynomial construction algorithm and a recursive coefficient search algorithm respectively. To improve the efficiency of list decoding Hermitian codes, this paper presents two contributions to reduce the interpolation complexity. First, in order to simplify the calculation of a polynomialiquests zero condition during the iterative interpolation, we propose an algorithm to determine the corresponding coefficients between the pole basis monomials and zero basis functions of a Hermitian curve. Second, we propose a modified complexity reducing interpolation algorithm. This scheme identifies any unnecessary polynomials during iterations and eliminates them to improve the interpolation efficiency. Due to the above complexity reducing modifications, list decoding long Hermitian codes with higher interpolation multiplicity becomes feasible. This paper shows list decoding algorithm can achieve significant coding gain over the conventional unique decoding algorithm.

Broadband fixed wireless access (BFWA) is an ideal solution for providing high data rate communications where traditional landlines are either unavailable or too costly to be installed. In this paper we consider a number of alternative techniques to achieve high data rate and high quality of services requirements in these systems, including orthogonal frequency division multiplexing (OFDM), turbo equalization as well as multiple-input multiple-output (MIMO) techniques. In particular, the frequency domain OFDM scheme and time domain turbo equalization will be studied and compared in a MIMO BFWA context, in an attempt to provide some guidelines on how to design high data rate BFWA applications.

The list decoding algorithm can outperform the conventional unique decoding algorithm by producing a list of candidate decoded messages. An efficient list decoding algorithm for algebraic-geometric (AG) codes and Reed-Solomon (RS) codes has been developed by Guruswami and Sudan, called the Guruswami-Sudan (GS) algorithm. The algorithm includes two steps: Interpolation and Factorisation. To implement interpolation, Koetter proposed an iterative polynomial construction algorithm for RS codes. By redefining a polynomial over algebraic function fields, Koetter's algorithm can also be applied to AG codes. To implement factorisation, Roth and Ruckenstein proposed an efficient algorithm for RS codes and later Wu and Siegel extended it to AG codes. Following on from their previous work, we propose a more general factorisation algorithm which can be applied to both AG and RS codes. This algorithm avoids rational function quotient calculations required by Wu and SiegePs algorithm, making it more efficient to implement. As well as employing this algorithm to list decode AG and RS codes this paper also presents the first simulation results evaluating the list decoding performance comparison between AG and RS codes of a similar code rate defined over the same finite field.

A novel equalization algorithm utilizing improper nature of the intersymbol interference (ISI) is introduced in this paper. We show that full exploitation of the available information on the second-order statistics of the observed signal entails widely linear processing and that previously known linear minimum mean square error (MMSE) equalizers represent sub-optimum solutions. The proposed scheme is generally applicable for both real and complex signal constellations. The results show that accounting for the improper nature of the ISI leads to significant performance gain compared to conventional equalization schemes.

It has been observed that particular rate-1/2 partially systematic parallel concatenated convolutional codes (PCCCs) can achieve a lower error floor than that of their rate-1/3 parent codes. Nevertheless, good puncturing patterns can only be identified by means of an exhaustive search, whilst convergence towards low bit error probabilities can be problematic when the systematic output of a rate-1/2 partially systematic PCCC is heavily punctured. In this paper, we present and study a family of rate-1/2 partially systematic PCCCs, which we call pseudo-randomly punctured codes. We evaluate their bit error rate performance and we show that they always yield a lower error floor than that of their rate-1/3 parent codes. Furthermore, we compare analytic results to simulations and we demonstrate that their performance converges towards the error floor region, owning to the moderate puncturing of their systematic output. Consequently, we propose pseudo-random puncturing as a means of improving the bandwidth efficiency of a PCCC and simultaneously lowering its error floor.

With the convergence of mobile telephony and the Internet, it seems that future telephony data will be transferred on VoIP datagram. Mobility will affect the overall system performance especially for voice communication. Thus, maintaining the quality of voice is necessary. It is important to guarantee that the end-to-end delay must be kept at a certain level. This paper investigates the performance of voice in traffic mix environment. Handover which is based on incoming traffics may cause the system to be unbalanced. A load balancing scheme was deployed to optimise the system capacity and to improve performance. The throughput, end-to-end delay and packet loss are used in measuring the performance. The results show that a better performance can be achieved by deploying this scheme. In addition, the system is able to support more number of connected users.

In this paper, we investigate in detail the performance of iterative demapping and decoding techniques over quasi-static fading channels both with and without antenna diversity. In particular, we consider the effect on the system performance of various mapping schemes, different coding schemes, the inter- leaver size as well as space diversity. Results demonstrate that over quasi-static fading channels characterized by significant antenna diversity, mappings traditionally optimized for iterative receivers (e.g., Boronka mapping) outperform mappings more appropriate for non-iterative receivers (e.g., Gray mapping). In contrast, over quasi-static fading channels characterized by limited antenna diversity, Gray mapping always outperform Boronka mapping for all Eb/N0and all iterations. Strikingly, this situation is in sharp contrast to that in the AWGN case. We note that we can further improve the performance of non-iterative systems (e.g., Gray mapping) having limited antenna diversity by increasing the memory size and removing the interleaving.

List decoding is a novel method for decoding Reed–Solomon (RS) codes that generates a list of candidate transmitted messages instead of one unique message as with conventional algebraic decoding, making it possible to correct more errors. The Guruswami–Sudan (GS) algorithm is the most efficient list decoding algorithm for RS codes. Until recently only a few papers in the literature suggested practical methods to implement the key steps (interpolation and factorisation) of the GS algorithm that make the list decoding of RS codes feasible. However, the algorithm's high decoding complexity is unsolved and a novel complexity-reduced modification to improve its efficiency is presented. A detailed explanation of the GS algorithm with the complexity-reduced modification is given with simulation results of RS codes for different list decoding parameters over the AWGN and Rayleigh fading channels. A complexity analysis is presented comparing the GS algorithm with our modified GS algorithm, showing the modification can reduce complexity significantly in low error weight situations. Simulation results using the modified GS algorithm show larger coding gains for RS codes with lower code rates, with more significant gains being achieved over the Rayleigh fading channels.

The systems under investigation are broadband fixed wireless access (BFWA) systems operating in multipath fading channels. Conventional detection methods, for example, coherent detection for single-input single-output systems and the Alamouti algorithm for multiple-input multiple-output systems are examined theoretically and shown to yield unsatisfactory performance. The theoretical analyses are validated by Monte-Carlo simulations and are demonstrated to be accurate. The asymptotic performance of the space–time block coded (STBC) system with the–Alamouti transmission scheme is also evaluated. However, the results indicate that the performance lower bound cannot be obtained in an uncoded system due to the error propagation problem, which can be tackled by concatenating the STBC system with an outer channel code and applying the turbo processing principle. Theoretical performance analysis provides an insight into the physical limitations imposed by BFWA channels and suggest solutions to improve the capacity and performance of future BFWA systems.

In this correspondence, we present a new method for the iterative equalization and decoding of multilevel trellis coded modulation (TCM) signals over frequency selective channels. Results show that the proposed algorithm achieves better performance compared to the previous work on the MMSE filter- based turbo equalization for a non-binary coded modulation scheme. The performance gain is accomplished by utilizing the combined modulation and coding nature of TCM and passing the refined signal obtained from different paths to the TCM decoder as the channel value in addition to the a priori probabilities.

The asymptotic performance of the space-time block coded systems using two transmit antennas over a broadband wireless fixed access (FWA) frequency selective channel is studied in this paper. The conducted theoretical analysis gives us an insight into the physical limitations imposed by the FWA channels and suggests solutions to improve the capacity and performance of future FWA systems.

A novel approach for the calculation of the transfer function of a terminated punctured convolutional code, which can be seen as a convolutional block code, is presented in this paper. The transfer function of the convolutional block code can be then used to evaluate the transfer function of a punctured turbo code and derive a tight upper bound on the bit error probability. Furthermore, the approach is used to find puncturing patterns that generate punctured turbo codes with optimal performance.

This paper presents the enhanced frame-based video coding scheme. The input source video to the enhanced frame-based video encoder consists of a rectangular-sized video and shapes of arbitrarily shaped objects on video frames. The rectangular frame texture is encoded by the conventional frame-based coding technique and the video object's shape is encoded using the contour-based vertex coding. It is possible to achieve several useful content-based functionalities by utilizing the shape information in the bitstream at the cost of a very small overhead to the bit-rate.

In this paper, we presents a novel method of turbo equalization and decoding multi-level trellis coded modulation (TCM) signals over frequency selective channels. Results show that the proposed algorithm achieves better performance with reduced complexity compared to previous work on the MMSE filter-based turbo equalization for non-binary coded modulation scheme. The performance gain is accomplished by passing the refined signal from different paths to the TCM decoder as channel value in addition to the a prior information. While the computational complexity is reduced by avoiding matrix inversion for each symbol estimate.

In this paper, we provide a theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a DS-CDMA system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time-varying multipath Rayleigh fading channel. Unequal powers are assumed among different paths, which is usually the case in practical situations. The proposed analysis gives insight into the performance and capacity one can expect from the PIC based receivers under different situations.

In this paper, we investigate in detail the performance of turbo codes in quasi-static fading channels both with and without antenna diversity. First, we develop a simple and accurate analytic technique to evaluate the performance of turbo codes in quasi-static fading channels. The proposed analytic technique relates the frame error rate of a turbo code to the iterative decoder convergence threshold, rather than to the turbo code distance spectrum. Subsequently, we compare the performance of various turbo codes in quasi-static fading channels. We show that, in contrast to the situation in the AWGN channel, turbo codes with different interleaver sizes or turbo codes based on RSC codes with different constraint lengths and generator polynomials exhibit identical performance. Moreover, we also compare the performance of turbo codes and convolutional codes in quasi-static fading channels under the condition of identical decoding complexity. In particular, we show that turbo codes do not outperform convolutional codes in quasi-static fading channels with no antenna diversity; and that turbo codes only outperform convolutional codes in quasi-static fading channels with antenna diversity

We present the channel estimation algorithms for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing the orthogonal signalling formats and long scrambling codes. The performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigated channel estimation algorithms under different conditions. The estimated channel information is used to enable the coherent data detection to combat the detrimental effect of multipath propagation of the transmitted signal as well as multiple access interference (MAI). Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of the channel estimate and the bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems.