Abstract The distributed Goppa coded spatial modulation (DGC‐SM) scheme is proposed in cooperative scenarios. In the proposed DGC‐SM scheme, the relay chooses the partial information from the source by using the idea of information selection, and then re‐encodes the selected information. At the destination, a distributed Goppa code is obtained corresponding to each selection. In order to get the best possible code, an optimal information selection algorithm is proposed at the relay. In the proposed optimal algorithm, all selections and source message sequences are considered, which results in high complexity. Thus, another optimized information selection algorithm with low complexity is proposed at the relay. To further enhance the capability to get the source information, two efficient joint decoding algorithms called smart decoding algorithm and improved smart decoding algorithm are proposed. Moreover, the bit error rate (BER) performance bound of the proposed DGC‐SM scheme is derived. Through the simulations, the effectiveness of the proposed two optimized information selection algorithms is confirmed. Also, it is observed that the simulation and analytical results closely match at high signal‐to‐noise ratio (SNR).

Abstract This paper discusses layered baud‐space modulation system under arbitrary spatial correlation both at the transmitter and the receiver. Layered baud‐space modulation provides better reliability in spatial modulation systems as well as flexibility in data rates compared to multiple‐active space modulation. Several transmissions occur asynchronously within the time slot. As a result, fractional sampling is employed at the receiver to detect the signals. For this scheme, it is more practical to analyse spatial correlation both at the transmitter and the receiver, since temporal correlation is a likely occurrence. However, asynchronous transmission will lead to higher probability of packet drops when synchronization errors are present. Lower bounds of bit error rates are derived from theoretical criteria based on mutual information and sample covariance of the joint spatial and modulation space. Analytical results for bit error probability are tightly verified from simulations. The channel is assumed to be of frequency‐flat Rayleigh fading form. The tests are carried out under different antenna spacing, amplitude and phase modulation schemes and various number of transmit and receive antenna configurations.

Abstract In this paper, two intelligent reflecting surface (IRS)‐assisted single‐input single‐output Golden codeword‐based modulation schemes for next‐generation networks are investigated. In Scheme 1, one pair of Golden codeword super‐symbols are transmitted over two consecutive time slots with the assistance of an IRS to maximise the received signal‐to‐noise ratio (SNR) in each slot. Scheme 2 applies component‐interleaving to the pair of Golden codeword super‐symbols and transmits the modified super‐symbols over four consecutive time slots with the assistance of an IRS to maximise the received SNR in each slot. A significant improvement in error performance is demonstrated over their counterparts, for both conventional/non‐access point (AP) or AP‐based IRSs. Scheme 2 exhibits superior error performance over Scheme 1, especially for small and medium IRSs. The theoretical average bit error probabilities for the proposed schemes are formulated and validated by simulation results. Low‐complexity detectors for the schemes under study are provided and the computational complexity imposed by these detectors are analysed and found to be extremely low.

This research article proposes a multiple relay‐based Reed–Muller network‐coded cooperative (MR‐RMNCC) scheme for wireless communication. In the MR‐RMNCC scheme, Hadamard transform construction is adopted to build Reed–Muller (RM) codes that effectively achieve network coded‐cooperation among multiple sources and multiple relays over slow and fast Rayleigh fading channels. In any network coded‐cooperative system, a proper encoding strategy at the relay nodes is vital for achieving an optimum code construction at the destination node. Therefore, the authors have proposed an efficient message bit selection algorithm at relay‐2 that optimally selects the message bits. The supremacy of the message bit selection algorithm is demonstrated by Monte–Carlo simulation. Furthermore, the performance bound for average error‐probability is also derived for the MR‐RMNCC scheme that validates its simulated bit‐error‐rate performance over a fast Rayleigh fading channel. At the destination node, the MR‐RMNCC scheme is jointly decoded by two different decoding strategies, i.e. joint soft maximum likelihood decoding and joint majority logic decoding. Monte–Carlo simulations suggest that the MR‐RMNCC scheme not only provides a significant bit‐error‐rate performance gain over its corresponding coded non‐cooperative scheme but also to the existing state‐of‐the‐art RM network‐coded cooperative scheme under identical conditions.

In this study, the bit error rate (BER) performance of multiple‐input‐multiple‐output (MIMO) hierarchical quadrature amplitude modulation systems employing maximum ratio transmission (MRT‐HQAM) is investigated under the effects of imperfect channel state information (ICSI) due to the channel estimation error and feedback delay. Theoretical expressions for the BER performance of the MRT‐HQAM systems are derived using the two common ICSI models that exist in the current literature, specifically when studying the MIMO beam‐forming systems with ICSI, where the error term due to the ICSI is assumed to contribute to either the noise component or to the signal component. The BER results for the two ICSI models are presented and then compared. In addition, various antenna configurations are studied to illustrate the performance gains achievable with additional antennas, and to identify the ideal antenna configuration for a given number of antennas. Moreover, the hierarchical modulation parameter is varied to determine the varying levels of sensitivity of the hierarchical layers in the presence of ICSI. The theoretical BER expressions provided for both ICSI models are verified by simulation results.

A Plotkin‐based polar coded space–time spatial modulation scheme is proposed and its bit error rate (BER) performance over quasi‐static Rayleigh fading channel is evaluated. The exacerbated complexity in receiver design is ameliorated by employing a low complexity soft demapper for their proposed Plotkin‐based polar coded scheme. As there is a natural split present in the design of the considered Plotkin's construction, therefore the authors effectively extended their proposed scheme to coded‐cooperative scenarios. In any coded‐cooperative communication, the relay node always plays a pivotal role in determining the BER performance of communication system. Therefore, a rational selection criterion for selecting the information bits at the relay node is presented. The authors have also devised nested polar coded‐cooperative space–time spatial modulation (NPCCST‐SM) scheme as a useful benchmark. Monte‐Carlo simulated results revealed that their proposed coded‐cooperative scheme has triumphed conventional NPCCST‐SM scheme by a gain of 0.6–0.8 dB under identical conditions. Moreover, the proposed cooperative scheme outperforms its corresponding non‐cooperative counterpart scheme by a gain of 1–1.2 dB under identical conditions.

A multi‐level construction of polar‐coded single carrier frequency division multiple access (SC‐FDMA) with multiple input multiple output (MIMO) antennas scheme is proposed and its bit error rate performance over frequency selective Rayleigh fading channels has been evaluated. The existence of a parallel split in the design of multi‐level construction of polar code has enabled the authors to effectively extend the proposed scheme in coded cooperative scenarios. As in coded cooperation communication, the relay plays a crucial role in the design of communication system; therefore, an efficient selection criterion for reinforcing the bad channels has been adopted at the relay node. Moreover, the joint successive cancellation decoding is employed at the destination node. To check the efficacy in the performance of the proposed coded cooperative scheme, the authors have also upgraded the traditional nested polar‐coded cooperative scheme in the context of SC‐FDMA with MIMO antennas as a useful benchmark. Monte Carlo simulated results revealed that the proposed coded cooperative scheme have triumphed the conventional nested polar coded cooperative scheme based on SC‐FDMA system by gain of 0.5 dB under identical conditions. Moreover, the proposed cooperative schemes outperform their corresponding non‐cooperative counterpart schemes by the gain of 1 dB under identical conditions.

Spatial modulation (SM) is an efficient transmission scheme based on multiple‐input multiple‐output systems. SM, by nature, requires coherent detection to achieve optimal error performance. This requires that the receiver has full knowledge of the channel state information (CSI), however, determining the CSI results in an increase in the detection complexity at the receiver. Differential modulation systems are capable of performing detection without knowledge of the CSI at the receiver, however, they suffer a 3 dB error performance penalty as compared to their coherent counterparts. In this study, the authors present a generalised differential scheme for SM (GD‐SM) based on generalised differential modulation, which is capable of reducing the performance penalty incurred through optimal power allocation. Furthermore, they extend the architecture of GD‐SM and optimal power allocation to conventional differential SM. The architecture of the proposed systems, advantageously permits the use of either M ‐ary quadrature amplitude modulation or M ‐ary phase shift keying constellations. Simulation and theoretical results demonstrate that GD‐SM incurs only about 0.5 dB performance loss as compared to coherent SM when the frame length is 400.

The use of radio frequency (RF) mirrors to improve spectral efficiency is a recently introduced technique. The authors investigate its application to single RF chain and inter‐channel interference‐free communications. The technique is first applied to improve the error performance of a conventional single‐input multiple‐output (SIMO) scheme, in the form of SIMO media‐based modulation (SIMO‐MBM) with single‐mirror activation pattern (MAP). Significant improvement in error performance is demonstrated. The theoretical average bit error probability (ABEP) of SIMO‐MBM with single MAP is formulated and serves to validate the Monte‐Carlo simulation results. The application of RF mirrors to further improve spectral efficiency in quadrature spatial modulation is then proposed, in the form of quadrature spatial media‐based modulation (QSMBM) and is able to achieve very large spectral efficiencies, while maintaining relatively good error performance. The theoretical ABEP of QSMBM is formulated and shown to agree well with Monte‐Carlo simulation results. Finally, MAP selection for QSMBM is investigated. Due to the high computational complexity and memory requirements of optimal MAP selection, low‐complexity suboptimal algorithms for MAP selection are investigated. A significant improvement in the error performance of QSMBM is demonstrated with these algorithms.

A new multiple‐ring star‐ M ‐ary quadrature amplitude modulation‐aided spatial modulation ( N R‐STAR‐ M QAM‐SM) scheme is proposed. The aim is to minimise the average bit error probability (ABEP) of the system. Then in the interest of further minimising the ABEP, the authors formulate a low‐complexity algorithm to achieve the optimum radii of N R‐STAR‐ M QAM‐SM. This algorithm is based on a specific multiple‐input multiple‐output configuration and the pairwise error probability function. To validate the results of the proposed scheme, a closed‐form union‐bound theoretical ABEP expression is derived. Finally, to improve the error performance of N R‐STAR‐ M QAM‐SM, the authors propose a low‐complexity Euclidean distance‐based antenna selection (EDAS) algorithm for N R‐STAR‐ M QAM‐SM (EDAS‐ N R‐STAR‐ M QAM‐SM). Since all amplitude/phase modulation schemes are considered to have rotational symmetry and symmetric constellation points have the same EDAS solution, the authors achieve EDAS‐ N R‐STAR‐ M QAM‐SM by searching only one constellation point per symmetric constellation set. The EDAS‐ N R‐STAR‐ M QAM‐SM solution exhibits a significant reduction in the computational complexity compared with the conventional EDAS solution.

A simple optimal error analysis of multiple‐branch equal gain combining (EGC) and selection combining (SC) in the presence of arbitrarily correlated Rayleigh fading channels is presented. It is shown that the error rates over correlated branches for diversity combining schemes can be analysed at the output of an eigenfilter splitter, which is placed at the output of the diversity combiner. Since the outputs of the splitter are uncorrelated, the error analysis of maximal ratio combining (MRC) technique is applied to EGC and SC. This analysis is possible since error performance of MRC with correlated branches is optimal and invariant to eigenfilter or eigenvector decorrelation and the decorrelated outputs can simply be analysed similar to independent branches. The authors exploit extensive simulations for average bit error probability, which show tight bounds with the proposed analytical approach. Channel correlations for different practical antenna spacing of 0.15, 0.2 and 0.5 of the signal carrier wavelength, λ are analysed.

In this study, symbol error probability of transmitted modulation signals for a single‐input–multiple‐output system is used to derive overall average bit error probability (ABEP) of multiple active‐spatial modulation (MA‐SM) system as a function of the number density of bits in error. Specifically, a theoretic method of determining the number density of bits in error in the joint detector of MA‐SM is proposed. Sample variance (SV) criterion uses the sample covariance of detector noise data, while mutual information (MI) criterion uses relative entropy derived from the Kullback–Liebler distance to compute the number density of bits in error. The choice for the better criterion is formulated as a model selection problem between the SV and the MI criteria. Analytical results for ABEP are tightly verified from simulations, which are carried out under arbitrarily correlated flat Rayleigh fading channels. Various data rates, antenna spacing and number of transmit and receive antenna configurations are tested, where it is also shown that SM is a special case of MA‐SM. Moreover, a basis spectral efficiency (BSE) formula for MA‐SM systems is proposed, which can be used to select a preferred antenna configuration without the need for simulations.

Euclidean‐distance antenna selection (EDAS) is an effective transmit AS technique for spatial modulation (SM). This study presents a low‐complexity (LC) EDAS scheme for the M ‐ary phase shift keying (MPSK) SM. The LC‐EDAS for MPSK SM (LC‐MPSK‐EDAS) is achieved by exploiting the rotational symmetry of the MPSK constellation and using singular value decomposition (SVD_EDAS) for factorisation of the modified channel matrix. A further reduction in complexity is achieved by eliminating the process of conditioning on elements of the MPSK symbol set. The complexity of the proposed scheme is independent of the order M of MPSK. Also, in this study, an LC near maximum likelihood (ML) detection scheme for MPSK SM systems, signal vector‐based detection (SVD), is implemented. Though this scheme provides poor results when using the M ‐ary quadrature amplitude modulation constellation, it is found that the error performance of this scheme for MPSK constellations has very near ML results. The simulation results show that even at high signal‐to‐noise values this scheme maintains near ML performance. To support the results, the closed‐form expression of the bit error rate for the MPSK constellation is derived.

Hierarchical quadrature amplitude modulation (HQAM) allows for transmission of multiple classes of data (such as voice, video and file transfer), provides flexibility in terms of coverage area and allows for network upgrades while maintaining backwards compatibility. However, the addition of hierarchical layers leads to higher‐order modulation schemes which make the system increasingly susceptible to noise and fading. To mitigate fading while maintaining backwards compatibility, maximum ratio transmission (MRT) is incorporated into the HQAM system to maximise signal‐to‐noise ratio for a given number of diversity branches. This study presents a theoretical bit error rate (BER) performance analysis of an MRT enhanced HQAM (MRT‐HQAM) system in Rayleigh fading. The BER performance gains of the proposed system over single‐input–single‐output and single‐input–multiple‐output HQAM systems are shown. The HQAM hierarchical modulation parameter is varied and the effects are presented. Furthermore, the authors present the effects of varying the number of antennas on the transmitting and receiving ends and discuss the optimal antenna configuration. The theoretical BER expressions used in the performance analysis are verified using simulation results.

Link adaptation in the form of Euclidean distance‐based antenna selection (EDAS) at the transmitter, has demonstrated a significant improvement in the error performance of spatial modulation (SM). However, when a large transmit antenna array is required, the computational complexity imposed by the EDAS scheme is inherently high. Thus, there is great motivation for the development of low‐complexity transmit antenna selection (LCTAS) schemes for SM. In this study, the authors propose several LCTAS schemes for SM. Assuming full knowledge of the channel at the receiver, the proposed schemes select a subset of the candidate transmit antenna elements based on channel amplitude, antenna correlation, Euclidean distance between transmit vectors or a combination of these; demonstrating a significant improvement in error performance compared with conventional SM, while imposing significantly lower computational complexity than EDAS‐SM. Moreover, the proposed schemes employ a novel complexity reducing technique, which allows parallel processing of algorithms and can easily be applied to existing schemes.

A scheme is proposed, called polar coded spatial modulation (PCSM), to provide both detection/decoding of the transmitted symbol and the transmit antenna index in multiple‐input–multiple‐output (MIMO) antenna systems. Based on the free polar set and the frozen polar set in polar codes, the proposed PCSM scheme maps the transmitted information data in the free polar set and the transmit antenna index bits in the frozen polar set whose positions are known at the receiver. This has the advantage that the bits that identify the transmit antenna are not transmitted to the receiver and do not need to be detected as is the case in conventional spatial modulation (SM). Thus, PCSM presents a spectrally efficient and a power‐efficient system. For the simulations, MIMO channels with transmission over independent and identically distributed flat fading characteristics are exploited. Firstly, capacity results for coded SM which is a requirement for the construction of the codes are presented. Consequently, the bit error rate performances of the M‐ary quadrature amplitude modulation SM are analysed for various MIMO architectures after which the desirable MIMO architecture is proposed for the PCSM. In addition, the upper and lower bounds on probability of frame error for the transmitted symbol information, under successive cancellation decoding are derived and the PCSM scheme suits the bounds for the suiting architecture.

Space‐time block coded spatial modulation (STBC‐SM) is a recently proposed multiple‐input–multiple‐output transmission scheme, which combines spatial modulation (SM) and Alamouti's space‐time block code (STBC) in such a manner so as to retain the primary advantages of SM and STBC, while avoiding their drawbacks, resulting in an improved system error performance. In this study, the authors propose a soft‐output maximum‐likelihood (ML) detector (SOMLD) and a soft‐output low‐complexity near‐ML detector (SOLCD) for STBC‐SM transmission. Monte‐Carlo simulations demonstrate that the error performance of the proposed schemes are able to closely match that of the hard decision ML detector for uncoded channel conditions, while significant improvement in error performance is demonstrated for coded systems. Furthermore, compared with SOMLD, SOLCD imposes a significantly lower computational complexity, while achieving near‐ML error performance.

Spatial diversity schemes are often used to extract additional performance from wireless communication systems. Incorporating the partial relay selection (PRS) protocol into a distributed switch‐and‐stay combining (DSSC) cooperative communication network gives the benefit of diversity while simplifying hardware, processing and feedback requirements. Because only a single relay is ever active, the destination employs no combiner; the best relay is chosen based on first‐hop relay conditions. However, achieved performance is worse than other distributed protocols, such as distributed selection combining (DSC). In this study, signal space diversity (SSD) is added to the DSSC–PRS system to provide further diversity and error performance gains, at the expense of necessitating a maximum‐likelihood detector with increased complexity at the receiver. Analytical results are presented in the form of a lower bound based on the minimum distance lower bound for SSD systems and are verified with simulation. The DSSC–PRS–SSD system shows an improvement of 5 dB at a symbol error rate of 10 − 4 as well as a clear diversity order improvement. Spectral efficiency of the new system with SSD is slightly decreased at low signal‐to‐noise ratios, but is still an improvement over other distributed schemes, such as DSC.

Conventional hierarchical modulation (HM) only provides two levels of unequal error protection (UEP) for multimedia traffic transmission. An HM‐based scheme is proposed that provides multiple levels of UEP by exploiting the structure of the Alamouti scheme. A typical Alamouti scheme operates based on the assumptions that the modulation scheme used for the transmission at each antenna is the same and that the power in each antenna is equal. In the proposed system, these two operating assumptions are relaxed, in that the modulation schemes as well as the transmission powers for the two antennas are varied in order to propose a multiple level UEP mechanism for multimedia traffic. The concept is applied to a recently proposed system which uses the Alamouti space–time block code (STBC) structure with HM and signal space diversity (SSD), and it is shown via theoretical and simulation results how the simple UEP mechanism can accommodate the simultaneous transmission of multiple classes of multimedia traffic.

This study presents a novel approach to an Alamouti transmission scheme for hierarchical modulation (HM) with signal space diversity (SSD) in a Nakagami‐ m fading channel. The bit‐error‐rate (BER) performance of the proposed system is determined using the nearest neighbourhood (NN) approximation approach and is briefly discussed. In addition, a reduced complexity maximum likelihood‐based decoder is proposed. Simulation results verify a significant BER improvement of the proposed system when compared with previously implemented schemes as well as the accuracy of the NN approximation and the proposed detector. Specifically, gains of up to 8 dB at a BER of 1 × 10 −5 for both base and refinement bits have been observed when comparing the proposed HM SSD Alamouti scheme with an HM SSD scheme without Alamouti transmit diversity at a hierarchy of α = 4, channel conditions at m = 1 and N = 1 receiver antennas. Additional results for varying hierarchy at increasing number of receiver antennas and improving channel conditions is also presented. The performance of the proposed reduced complexity decoder is also presented as well as its complexity reduction analysed.

Space‐time block coded spatial modulation (STBC–SM) has been proposed to exploit the advantages of both spatial modulation and space‐time block codes. The first objective of this study is to introduce a very simple near‐maximum‐likelihood (ML) low‐complexity detection scheme for N t × N r M‐ary quadrature amplitude modulation (M‐QAM) STBC–SM. Simulation results validate that the proposed simple detection scheme achieves near‐ML detection error performance. Furthermore, in comparison to existing schemes, the computational complexity of the proposed detector was demonstrated to be independent of the modulation size, hence exhibiting a very low computational complexity. The second objective of this study is to present an asymptotic bound to quantify the average bit‐error rate performance of M‐QAM STBC–SM over independent and identically distributed Rayleigh flat fading channels. The analytical frameworks are validated by Monte Carlo simulations.

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.

The authors apply spatial modulation over multiplicative complex fading wireless channels, where the multiplicative complex fading is represented by the product of K statistically independent and identically distributed standard complex Gaussian random variables, where K ≥ 2. The analytical bit‐error rate (BER) approximation of symbol estimation is obtained in terms of a Meijer's G function. The conditional pairwise error probability (PEP) of transmit antenna index estimation is a function of a stochastic parameter with an unknown distribution function. The authors propose a lognormal distribution to approximate the distribution of this stochastic parameter. Based on the lognormal distribution, the average PEP and the analytical error probability upper bound of transmit antenna index estimation are derived. A goodness of fit test successfully validates the proposed lognormal distribution being the approximate distribution of the stochastic parameter. The derived analytical BER approximations for both symbol and transmit antenna index estimation are successfully validated via Monte Carlo simulations.

This study combines hierarchical modulation with signal space diversity (SSD) to present an unequal error protection scheme with improved bit‐error rate (BER) performance for single as well as multiple antenna reception by employing maximal ratio combing in Nakagami‐ m fading channels. The optimal rotation angles for different constellation priority parameter α are derived. A theoretical BER expression in Nakagami‐ m fading channels using the nearest neighbour approximation approach is also derived. This is confirmed as a valid performance approximation for single and multiple antenna reception through simulations. The resultant scheme produces improved BER performance for both important and less important data without consuming any additional power than a non‐SSD system at the cost of increased complexity at detection. Specifically, performance gains of up to 18 and 17 dB at a BER of 1 × 10 − 5 for base and refinement bits, respectively, are observed for single receive antenna with Nakagami m = 1. A further improvement of roughly 3 dB at a BER of 1 × 10 − 6 for base bits at N = 3 receiver antennas is found as hierarchy is increased. Although the gain is observed to decrease as m increases, a gain of 14 dB at 1 × 10 − 6 for α = 4 is achieved even as m increases from m = 1 to m = 3.

This study proposes an low density party check (LDPC)‐coded multi‐relay cooperation with receive multi‐antenna in the destination over a Rayleigh‐fading channel, where maximal ratio combining and belief propagation algorithm (BP)‐based joint iterative decoding based on the introduced multi‐layer Tanner graph are effectively designed to detect and decode the corrupted received sequence at the destination. The overall code rate from the destination is derived mathematically in relation to all the constituent LDPC codes employed by source and multiple relays. Theoretical analysis and numerical simulation show that the proposed approach can well combine diversity and coding gains, which consequently result in significant advantage over the conventional cooperations under the same conditions.

Maximum‐eigenvalue‐detection (MED) and maximum‐eigenvalue geometric‐mean (ME‐GM) are attractive eigenvalue‐based spectrum sensing (EBSS) schemes for cognitive radio (CR). The first objective of this paper is to present an analytical probability of detection (PD) expression for MED. The evaluated expression matches the simulation results well. Many of the existing analytical results for EBSS schemes are based on the asymptotic Tracy‐Widom (TW) distribution; however, for small or moderate sample length, N and secondary users, M the distribution lacks accuracy. Recently, adjusted centring and scaling parameters have been presented to improve the accuracy of the TW distribution for this practical scenario; thus, the second objective is to present the adjusted‐TW expressions (probability of false alarm (PFA), threshold and PD) for MED and ME‐GM. The proposed results show an improved accuracy for moderate N when M is small. To improve the accuracy for small N the authors propose to use an exact cumulative distribution function of the maximum eigenvalue. Hence the third objective of the paper is to present the exact analytical expressions for MED. The exact approach is then applied to ME‐GM, where an asymptotic expression for the GM is employed. The exact analysis exhibits a higher accuracy for both MED and ME‐GM.

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.

Spatial modulation (SM) is a low complexity, highly spectral efficient multiple-input–multiple-output scheme that has been proposed in the literature. The authors apply adaptive modulation to conventional SM in order to maximise the average throughput of the scheme. For this to be possible, the equivalent received signal-to-noise ratio (SNR) needs to be defined and is done so via two proposed approaches: using the first-order statistics SNR and using the average statistics SNR. Average theoretical bit-error-rate (BER) bounds are derived for both of these SNR approaches. Also, adaptive M-ary quadrature amplitude spatial modulation switching levels are determined to maximise the throughput while meeting the average target BER. The Monte Carlo simulation results successfully validate the derived theoretical BER bounds and also prove that the average throughput is improved in comparison to conventional SM. The two proposed definitions for the equivalent received SNR are confirmed to yield comparable BER and throughput performances via simulations, implying that the equivalent received SNR can be defined using either approach.

Spectrum sensing for cognitive radio allows a secondary user to detect spectrum ‘holes’ and to opportunistically exploit this space for unlicensed communication. Blind spectrum sensing has the advantage that it does not require any knowledge of the transmitted signal, the channel or the noise-power, which are usually unknown at the receiver. In this study, the simulation and performance results for the maximum–minimum-eigenvalue and energy-minimum-eigenvalue sensing methods are presented for the Nakagami-m fading channel. The simulation and performance results are presented for the maximum-eigenvalue-to-trace method and the arithmetic-to-geometric-mean method together with the analytical expressions for the threshold, probability of detection and probability of false alarm. In addition, another algorithm, maximum-eigenvalue-geometric-mean is proposed and is investigated in terms of the analytical and simulation results for Nakagami-m fading channels. Improved performance is shown compared to the other schemes when the number of samples is decreased and when the number of cooperating users is increased such that the ratio of the latter to the former is positive and less than unity. Analytical expressions are also presented. The eigenvalue detection methods exhibit good performance in noisy environments and are matched by their bounds.

The detection of spectrum ‘holes’ is one of the primary tasks of a cognitive radio (CR). Blind detection techniques using eigenvalues have attracted a great amount of interest because of the fact that no a-priori knowledge is needed. The majority of the literature only considers the effect of thermal noise in detector performance; however in practice, man-made noise also exists and degrades detector performance. This motivated one to consider the performance of blind eigenvalue-based spectrum sensing for the dual condition of thermal (Gaussian) and man-made (impulse) noise. In the literature, most of the sensing schemes perform very well for large sample length. This can be achieved either by increasing the sensing duration or by oversampling the signal. The former increases the frequency of missed opportunities, whereas the latter causes samples to become highly correlated thus degrading the detector performance. Hence, the authors are motivated to investigate algorithms that perform well for smaller sample length. Three new eigenvalue-based sensing algorithms are proposed, viz. maximum-eigenvalue-harmonic-mean (ME-HM), maximum-eigenvalue-contra-harmonic-mean-p (ME-CHM-p) and contra-harmonic-mean-minimum-eigenvalue (CH-ME). ME-HM outperforms all existing eigenvalue-based sensing schemes including the maximum-eigenvalue-geometric-mean (ME-GM) algorithm previously presented by the authors of this paper, for smaller sample length, low signal-to-noise ratio (SNR) and increased number of cooperative secondary users. The ME-CHM-p algorithm, which only allows negative values of p, the filter order, performs identically to ME-HM when p=−1. However, for smaller values of p the probability of detection (PD) improves significantly more until p=−5. The CH-ME algorithm also exhibits an improvement in PD but does not outperform ME-GM. In addition, the proposed schemes and ME-GM exhibit a significant degree of immunity to impulse noise compared to existing schemes. The analytical and simulation results are presented for the proposed schemes and ME-GM for the Gaussian and impulse noise scenario in the Nakagami-m fading channel. In addition, the algorithms are evaluated for wireless microphone (WM) signals and show improved performance. The ME-CHM-p algorithm performed the best compared with other algorithms, for small and large sample lengths, low SNR, correlated signals and for increased number of cooperating secondary radios, with and without impulse noise.

In this study, the authors propose a simplified maximum likelihood (ML)-based detection scheme for Nt×Nr M-ary quadrature amplitude modulation (M-QAM) spatial modulation (SM) that is computationally less complex than the conventional ML detection scheme. Instead of searching for the transmit antenna index and transmitted symbol pair among all possible NtM pairs as in the ML-based optimal detection, the proposed simplified ML-based detection scheme firstly searches for pairs of transmit antenna index and transmitted symbol in level-one subsets which the transmitted signal most probably belongs to, and secondly searches for pairs of transmit antenna index and transmitted symbol in level-two subsets among those pairs in level-one subsets. We also extend the simplified ML-based optimal detection into multistage detection. Simulation results validate that the bit error rate (BER) performance of the proposed simplified ML-based detection schemes is almost the same as that of conventional ML detection with significant complexity reduction until a BER of 10−6.

In this study, the authors propose a simple low-complexity detection scheme for Nt×NrM-ary quadrature amplitude modulation spatial modulation that exhibits a much lower computational complexity compared to the conventional maximum-likelihood (ML) detection scheme. The proposed simple low-complexity detection scheme firstly detects the transmitted symbol for each transmit antenna based on modified suboptimal detection, and secondly chooses N (N≤Nt) pairs of the most probable transmit antenna index and transmitted symbol subset, which the transmitted signal most probably belongs to, and finally searches the pair of transmit antenna index and transmitted symbol among these pairs. To further reduce detection complexity of the proposed simple detection scheme the authors also propose an adaptive detection scheme. Simulation results validate that the average bit-error-rate (BER) performance of the proposed simple detection scheme is almost the same as that of the conventional ML optimal detection with significant complexity reduction. Simulation results also show that the adaptive detection scheme can achieve optimal detection BER performance with further complexity reduction compared to the proposed simple low-complexity detection scheme.

Spatial modulation (SM) is a recent multiple-input multiple-output transmission technique, which entirely avoids inter-channel interference as well as the need for transmit antenna synchronisation. The first objective of this study is to present an asymptotic bound to quantify the average bit error rate (BER) performance of M-ary quadrature amplitude modulation (M-QAM) SM with optimal-based detection over independent and identically distributed Rayleigh flat fading channels. The analytical frameworks are validated by Monte Carlo simulation results, which show that the derived lower bounds are increasingly tight for large signal-to-noise ratio values. The second objective is to introduce a novel SM detection scheme, termed multiple-stage (MS) detection. Performance and complexity comparisons with existing SM detectors show two main benefits of MS detection: near-optimal BER performance and up to a 35% reduction in receiver complexity as compared to the maximum likelihood-based SM detector.

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.

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.

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.