Reconfigurable holographic surfaces (RHS) have emerged as a promising enablers for Integrated Sensing and Communication (ISAC) owing to their ultra-dense electromagnetic control capability. In this work, we consider near-field multi-user localization as a key ISAC function. However, hardware-induced phase-shift constraints and complex-plane coupling effects severely degrade the performance of classical subspace-based estimators such as multiple signal classification (MUSIC). In this work, we analytically characterize the impact of practical phase-shift constraints on the MUSIC spectrum and reveal the resulting pseudo-peak and angular bias phenomena. To address these challenges, we propose a hierarchical sensing framework that integrates subspace estimation with sparsity-aware recovery. Specifically, we introduce a regularized orthogonal matching pursuit (ROMP)-assisted multi-sector sensing mechanism that exploits directional sparsity and sector-level structural partitioning of RHS, enabling robust multi-user angle-of-arrival (AoA) estimation under limited-resolution hardware. Furthermore, to alleviate near-field distance estimation bias, we design a nonlinear fusion estimator that aggregates angle observations from multiple local far-field sectors using confidence-weighted integration based on sector-specific priors. A confidence-aware sector selection scheme is also developed to suppress unreliable observations without relying on data-driven learning models. Extensive Monte Carlo simulations demonstrate that our method achieves over 80% reduction in root mean square error (RMSE) localization compared to conventional MUSIC and least-squares schemes, and maintains meter-level accuracy even under severe hardware distortions and sector limitations.

Reconfigurable intelligent surfaces (RISs) are eminently suitable for improving the reliability of wireless communications by jointly designing the active beamforming at the base station (BS) and the passive beamforming at the RIS. Therefore, the accuracy of channel estimation is crucial for RIS-aided systems. The challenge is that only the cascaded two-hop channel spanning from the user equipments (UEs) to the RIS and spanning from the RIS to the BS can be estimated, due to the lack of active radio frequency (RF) chains at RIS elements, which leads to high pilot overhead. In this paper, we propose a low-overhead linear minimum mean square error (LMMSE) channel estimation method by exploiting the spatial correlation of channel links, which strikes a trade-off between the pilot overhead and the channel estimation accuracy. Moreover, we calculate the theoretical normalized mean square error (MSE) for our channel estimation method. Finally, we verify numerically that the proposed LMMSE estimator has lower MSE than the state-of-the-art (SoA) grouping based estimators.

Reconfigurable holographic surfaces (RHS) are expected to play a key role in future mobile networks. However, the substantial increase in antenna aperture and operating frequency brings new challenges for near-field communication. We propose a near-field multi-user 3D hierarchical beam training scheme tailored for RHS-based multi-input multi-output (MIMO) systems, supporting both near-field and far-field user deployment, while considering hardware constraints. Since the hierarchical beam training scheme involves activating varying numbers of transmitting elements at each search layer, and RHS elements are densely packed, significant mutual coupling effects may arise. To mitigate this, we propose two element activation strategies: centered activation and sparse activation based on different RHS element positioning patterns within the hierarchical beam training framework. Furthermore, we design a practical beam training approach tailored to a hybrid digital–holographic architecture, optimized through an alternating algorithm that accounts for both binary and coupled amplitude-phase hardware constraints on RHS meta-elements. Simulation results demonstrate strong robustness under various hardware and channel state information (CSI) imperfections, achieving performance close to that of fully digital systems. Finally, we further analyse the asymptotic orthogonality of near-field beam focusing vectors under different RHS surface geometries. The results show that rectangular surfaces offer superior beam orthogonality for beams steered in the same direction but located at different distances.

Intelligent metasurfaces may be harnessed for realizing efficient holographic multiple-input and multiple-output (MIMO) systems, at a low hardware-cost and high energy-efficiency. As part of this family, we propose a hybrid beamforming design for stacked intelligent metasurfaces (SIM) aided wideband wireless systems relying on the near-field channel model. Specifically, the holographic beamformer is designed based on configuring the phase shifts in each layer of the SIM for maximizing the sum of the baseband eigen-channel gains of all users. To optimize the SIM phase shifts, we propose a layer-by-layer iterative algorithm for optimizing the phase shifts in each layer alternately. Then, the minimum mean square error (MMSE) transmit precoding method is employed for the digital beamformer to support multi-user access. Furthermore, the mitigation of the SIM phase tuning error is also taken into account in the digital beamformer by exploiting its statistics. The power sharing ratio of each user is designed based on the iterative waterfilling power allocation algorithm. Additionally, our analytical results indicate that the spectral efficiency attained saturates in the high signal-to-noise ratio (SNR) region due to the phase tuning error resulting from the imperfect SIM hardware quality. The simulation results show that the SIM-aided holographic MIMO outperforms the state-of-the-art (SoA) single-layer holographic MIMO in terms of its achievable rate. We further demonstrate that the near-field channel model allows the SIM-based transceiver design to support multiple users, since the spatial resources represented both by the angle domain and the distance domain can be exploited.

Low Earth Orbit (LEO) satellite networks are capable of improving the global Internet service coverage. In this context, we propose a hybrid beamforming design for holographic metasurface based terrestrial users in multi-altitude LEO satellite networks. Firstly, the holographic beamformer is optimized by maximizing the downlink channel gain from the serving satellite to the terrestrial user. Then, the digital beamformer is designed by conceiving a minimum mean square error (MMSE) based detection algorithm for mitigating the interference arriving from other satellites. To dispense with excessive overhead of full channel state information (CSI) acquisition of all satellites, we propose a low-complexity MMSE beamforming algorithm that only relies on the distribution of the LEO satellite constellation harnessing stochastic geometry, which can achieve comparable throughput to that of the algorithm based on the full CSI in the case of a dense LEO satellite deployment. Furthermore, it outperforms the maximum ratio combining (MRC) algorithm, thanks to its inter-satellite interference mitigation capacity. The simulation results show that our proposed holographic metasurface based hybrid beamforming architecture is capable of outperforming the state-of-the-art antenna array architecture in terms of its throughput, given the same physical size of the transceivers. Moreover, we demonstrate that the beamforming performance attained can be substantially improved by taking into account the mutual coupling effect, imposed by the dense placement of the holographic metasurface elements.

High-precision indoor positioning has been viewed as a crucial challenge for 6G integrated communication and sensing networks, where the visible light-based positioning can provide a cost-efficient solution due to its line-of-sight. However, it is susceptible to high blockage, where the light of light-emitting diode (LED) can be blocked by obstacles and moving objects and then the conventional positioning methods do not perform well. In this paper, we propose a low-complexity machine-learning based visible light positioning (VLP) method in the context of the high-blockage scenario. In the proposed design, we explore the positioning accuracy of various machine-learning algorithms including the K-nearest neighbor (KNN), the extreme learning machine (ELM) and the random forest (RF), based on the channel impulse response. Furthermore, we establish the fingerprint database and vary the weights for these machine learning methods, to achieve a mean square error (MSE) as low as 0.046 m, while achieving precise positioning within 10cm with an 85% probability. We also demonstrate that all three methods can support high-precision indoor positioning through simulation analysis.

Abstract This paper proposes a novel machine learning (ML) assisted low‐latency low density parity check (LDPC) coded adaptive modulation (AM) system, where short block‐length LDPC codes are used. Conventional adaptive modulation and coding (AMC) system includes fixed look‐up table method, which is also called inner loop link adaptation (ILLA) and outer loop link adaptation (OLLA). For ILLA, the adaptive capability is achieved by switching the modulation and coding modes based on a look‐up table using signal‐to‐noise ratio (SNR) thresholds at the target bit error rate (BER), while OLLA builds upon the ILLA method by dynamically adjusting the SNR thresholds to further optimize the system performance. Although both improve the system overall throughput by switching between different transmission modes, there is still a gap to optimal performance as the BER is comparatively far away from the target BER. Machine learning (ML) is a promising solution in solving various classification problems. In this work, the supervised learning based k‐nearest neighbours (KNN) algorithm is invoked for choosing the optimum transmission mode based on the training data and the instantaneous SNR. This work focuses on the low‐latency communications scenarios, where short block‐length LDPC codes are utilized. On the other hand, given the short block‐length constraint, we propose to artificially generate the training data to train our ML assisted AMC scheme. The simulation results show that the proposed ML‐LDPC‐AMC scheme can achieve a higher throughput than the ILLA system while maintaining the target BER. Compared with OLLA, the proposed scheme can maintain the target BER while the OLLA fails to maintain the target BER when the block length is short. In addition, when considering the channel estimation errors, the performance of the proposed ML‐LDPC‐AMC maintains the target BER, while the ILLA system's BER performance can be higher than the target BER.

In contrast to the conventional reconfigurable intelligent surfaces (RIS), intelligent omni-surfaces (IOS) are capable of full-space coverage of smart radio environments by simultaneously transmitting and reflecting the incident signals. In this paper, we investigate the ergodic spectral efficiency of IOS-aided systems for transmission over random channel links, while considering both realistic imperfect channel state information (CSI) and transceiver hardware impairments (HWIs). Firstly, we formulate the linear minimum mean square error estimator of the equivalent channel spanning from the user equipments (UEs) to the access point (AP), where the transceiver HWIs are also considered. Then, we apply a two-timescale protocol for designing the beamformer of the IOS-aided system. Specifically, for the active AP beamformer, the minimum mean square error combining method is employed, which relies on the estimated equivalent channels, on the statistical information of the channel estimation error, on the inter-user interference as well as on the HWIs at the AP and UEs. By contrast, the passive IOS beamformer is designed based on the statistical CSI for maximizing the upper bound of the ergodic spectral efficiency. The theoretical analysis and simulation results show that the transceiver HWIs have a significant effect on the ergodic spectral efficiency, especially in the high transmit power region. Furthermore, we show that the HWIs at the AP can be effectively compensated by deploying more AP antennas.

Reconfigurable holographic surfaces (RHSs) constitute a promising technique of supporting energy-efficient communications. In this paper, we formulate the energy efficiency maximization problem of the switch-controlled RHS-aided beamforming architecture by alternately optimizing the holographic beamformer at the RHS, the digital beamformer, the total transmit power and the power sharing ratio of each user. Specifically, to deal with this challenging non-convex optimization problem, we decouple it into three sub-problems. Firstly, the coefficients of RHS elements responsible for the holographic beamformer are optimized to maximize the sum of the eigen-channel gains of all users by our proposed low-complexity eigen-decomposition (ED) method. Then, the digital beamformer is designed by the singular value decomposition (SVD) method to support multi-user information transfer. Finally, the total transmit power and the power sharing ratio are alternately optimized, while considering the effect of transceiver hardware impairments (HWI). We theoretically derive the spectral efficiency and energy efficiency performance upper bound for the RHS-based beamforming architectures in the presence of HWIs. Our simulation results show that the switch-controlled RHS-aided beamforming architecture achieves higher energy efficiency than the conventional fully digital beamformer and the hybrid beamformer based on phase shift arrays (PSA). Moreover, considering the effect of HWI in the beamforming design can bring about further energy efficiency enhancements.

Large-scale multiple-input and multiple-output (MIMO) systems are capable of achieving high date rate. However, given the high hardware cost and excessive power consumption of massive MIMO systems, as a remedy, intelligent metasurfaces have been designed for efficient holographic MIMO (HMIMO) systems. In this paper, we propose a HMIMO architecture based on stacked intelligent metasurfaces (SIM) for the uplink of cell-free systems, where the SIM is employed at the access points (APs) for improving the spectral- and energy-efficiency. Specifically, we conceive distributed beamforming for SIM-assisted cell-free networks, where both the SIM coefficients and the local receiver combiner vectors of each AP are optimized based on the local channel state information (CSI) for the local detection of each user equipment (UE) information. Afterward, the central processing unit (CPU) fuses the local detections gleaned from all APs to detect the aggregate multi-user signal. Specifically, to design the SIM coefficients and the combining vectors of the APs, a low-complexity layer-by-layer iterative optimization algorithm is proposed for maximizing the equivalent gain of the channel spanning from the UEs to the APs. At the CPU, the weight vector used for combining the local detections from all APs is designed based on the minimum mean square error (MMSE) criterion, where the hardware impairments (HWIs) are also taken into consideration based on their statistics. The simulation results show that the SIM-based HMIMO outperforms the conventional single-layer HMIMO in terms of the achievable rate. We demonstrate that both the HWI of the radio frequency (RF) chains at the APs and the UEs limit the achievable rate in the high signal-to-noise-ratio (SNR) region.

We propose a hybrid beamforming architecture for near-field reconfigurable holographic surfaces (RHS) harnessed in cell-free networks. Specifically, the holographic beamformer of each base station (BS) is designed for maximizing the channel gain based on the local channel state information (CSI). By contrast, the digital beamformer at the central processing unit is designed based on the minimum mean squared error criterion. Furthermore, the near-field spectral efficiency of the RHS in cell-free networks is derived theoretically by harnessing the popular stochastic geometry approach. We consider both the phase shift error (PSE) at the RHS elements and the hardware impairment (HWI) at the radio frequency (RF) chains of the transceivers. Furthermore, we theoretically derive the asymptotic capacity bound, when considering an infinite physical size for the RHS in the near-field channel model. The theoretical analysis and simulation results show that the PSE at the RHS elements and the HWI at the RF chains of transceivers limit the spectral efficiency in the high signal-to-noise ratio region. Moreover, we show that the PSE at the RHS elements and the HWI at the RF chains of BSs can be compensated by increasing the number of BSs. Finally, we also demonstrate that the ergodic spectral efficiency based on the near-field channel model is higher than that based on the far-field channel model assumption.

Reconfigurable intelligent surfaces (RISs) are capable of enhancing the wireless propagation environment of the future Internet of Things (IoT). Recently, they have also been configured as a transmitter to realize information modulation at low hardware complexity. In this article, we conceive a transmitter relying on a single radio frequency (RF) chain for low-complexity RIS-aided multiuser downlink communication. More explicitly, in the proposed architecture, the multiuser information is transmit precoded and modulated at the RIS by appropriately configuring the phase shift and amplitude of each RIS element. We assume that the distribution of multiple users obeys on a Poisson point process (PPP), where we jointly optimize the total power reflected from the RIS and the power allocation fraction assigned to each user, under the practical constraint of a realistic amplitude limitation of each RIS element. Additionally, we theoretically analyze the ergodic rate, symbol error probability, outage probability, and coverage range of the proposed RIS-aided single-RF downlink and confirm the accuracy of our analysis by simulations. Finally, we compare its performance to that of the conventional multiple-input-multiple-output (MIMO) systems employing multiple RF-chains.

Reconfigurable intelligent surfaces (RIS) are capable of beneficially ameliorating the propagation environment by appropriately controlling the passive reflecting elements. To extend the coverage area, the concept of simultaneous transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) has been proposed, yielding supporting 360° coverage user equipment (UE) located on both sides of the RIS. In this paper, we theoretically formulate the ergodic sum-rate of the STAR-RIS assisted non-orthogonal multiple access (NOMA) uplink in the face of channel estimation errors and hardware impairments (HWI). Specifically, the STAR-RIS phase shift is configured based on the statistical channel state information (CSI), followed by linear minimum mean square error (LMMSE) channel estimation of the equivalent channel spanning from the UEs to the access point (AP). Afterwards, successive interference cancellation (SIC) is employed at the AP using the estimated instantaneous CSI, and we derive the theoretical ergodic sum-rate upper bound for both perfect and imperfect SIC decoding algorithm. The theoretical analysis and the simulation results show that both the channel estimation and the ergodic sum-rate have performance floor at high transmit power region caused by transceiver hardware impairments.

To alleviate the explosive growth of data traffic caused by the increased use of smart devices, new transmission techniques are needed to increase the utilization of limited bandwidth resources and for providing high transmission rates in future wireless networks. On the other hand, due to their flexibility and autonomy, unmanned aerial vehicles (UAVs) are considered as a potential candidate to support ubiquitous connectivity and operate as flying base stations, where the deployment of UAVs can affect the quality of experience (QoE) of users. Hence, in this paper, we employ UAVs as aerial base stations to transmit data to ground users (GUs) via air to ground (A2G) communication links, where we show how content awareness can help improve the data rate. Specifically, we design two content-sharing (CS) data transmission schemes to improve the average data rate of the GUs. Additionally, two UAV deployment strategies, namely the fixed-point deployment scheme and traverse-search deployment scheme, are proposed based on the proposed CS transmission schemes. The simulation results demonstrate that our proposed data transmission schemes combined with their proposed deployment schemes outperform the traditional transmission scheme by 26 bits/s/Hz and 51 bits/s/Hz, respectively.

As a low-cost solution for the 5G communication system, centralised radio access network (C- RAN) has been implemented in the ultra-dense environment, where radio over fiber (RoF) technology can enable reduced operational cost as well as coordinated multi-point (CoMP) despite its less-robustness and reduced system performance. On the other hand, machine learning has been recognised as an efficient method for accelerating the fiber-optic communications with the aid of the advancements of the learning algorithms as well as the available high processing capabilities. In this paper, we propose a supervised learning-aided A - RoF system, where the logistic regression classification is invoked for removing the A-RoF module's need for re-customization and for boosting its performance. As a result, we can adaptively select the modulation format according to the optical power and the RF voltage, where we obtain an enhanced spectral efficiency and dynamic range (DR) by a factor of 4/3 and 19/13, respectively, while the learning network can be updated online.

Energy harvesting (EH) devices without batteries can enable the Internet of Things (IoT) to reach new and challenging scenarios. Multihop routing is needed to extend the range but, when low EH causes intermittency, it has been overlooked and is not possible with existing protocols. Also, whilst wake-up receivers (WuRxs) have been used to enable star networks, the cost of another EH node sending wake-ups, required for multihop communication, has not been considered. This paper adapts the opportunistic RPL (ORPL) protocol to make possible multihop routing between intermittently-powered devices. Furthermore, the benefit of using WuRx to enable networks is measured, considering different sensitivity devices and associated range. Comparing ORPL to RPL, we show that opportunistic routing enables multihop communication where RPL cannot. If WuRx are used for routing towards a central hub, the more sensitive WuRx perform better, but routing cross-network benefits from lower sensitivity, lower power WuRx.

This paper analyzes the successful communication probability between two intermittently-powered nodes in a homogeneous energy harvesting (EH) mesh network. Powering devices using EH can enable networks to operate indefinitely; however, with limited energy storage and in scarce EH conditions, nodes may only be intermittently-powered. This reduces the effectiveness of conventional networking techniques, where listening modes of radios deplete the storage too quickly, rendering nodes useless. This is particularly problematic in the deployment of mesh networks, where there is no provision of a high-power coordinator. To counter this, wake-up receivers (WuRxs) provide extended listening time without the need for a high power conventional radio, but with a cost to sensitivity. Therefore, listening time must be balanced with transmission and wake-to-receive cost, where if all the harvested energy is spent listening none remains to transmit, and vice versa. From stochastic analysis and simulation of the energy usage in mesh nodes, we obtain the optimum transmission load to maximize goodput, which is the rate of successful communications. We include the cost of each wake-up based on the network size in our goodput analysis. Simulations for a fixed number of homogeneous nodes verify this. Furthermore, we model and evaluate the energy consumption trade-off between transmit power and WuRx sensitivity to enable the maximum goodput.

In this paper, we conceive a compressed sensing (CS)-aided multi-dimensional index modulation (IM) scheme, where the benefits of space-time shift keying, orthogonal frequency-division multiplexing relying on the frequency domain IM, and spatial modulation are explored. Explicitly, extra information bits are transmitted through the active indices of both the transmit antennas and subcarriers, while striking a flexible design tradeoff between the throughput and the diversity order. Furthermore, CS is invoked in both the transmitter and the receiver of our multi-dimensional system for the sake of improving the system's design flexibility, while reducing the detector's complexity. We first present the maximum likelihood (ML) detector of the proposed CS-aided multi-dimensional IM system for characterizing the best-case bound of the proposed system's performance. Specifically, an upper bound is derived for the average bit error probability, and it is observed that the derived theoretical upper bound becomes very tight with the ML detector simulation curves as the signal-to-noise ratio increases. Then, we propose a reduced complexity detector imposing only a modest bit-error-ratio degradation, where we analyze the computational complexities of both the ML detector and the reduced complexity detector. Furthermore, a soft-input soft-output decoder is proposed for attaining a near-capacity performance, which is analyzed with the aid of extrinsic information transfer (EXIT) charts. The maximum achievable rate of the proposed CS-aided multi-dimensional IM system relying both on the ML detection and on our reduced-complexity-based detector is also evaluated using EXIT charts. In addition, the discrete-input continuous-output memoryless channel capacity of the proposed CS-aided multi-dimensional IM scheme is formulated.

Space-time shift keying (STSK) constitutes a beneficial multiple-input-multiple-output (MIMO) technique that strikes a compelling trade-off between the multiplexing and diversity gains attained. Its close relative, namely layered multi-group STSK (LMG-STSK) combines the concepts of multi-user MIMO, STSK and beamforming for simultaneously conveying information to multiple users. Generalized frequency division multiplexing (GFDM) has been proposed as a promising multicarrier modulation candidate for dispersive wideband channels since it benefits from its time-frequency domain structure when combined with a powerful MIMO scheme. As a further evolution, we propose a novel GFDM-aided adaptive layered multi-group STSK (LMG-STSK) system for the downlink of millimeter wave communications systems. The proposed system tackles the propagation challenges of the high pathloss at millimeter wave frequencies, where multiple users are clustered into groups served by different antenna layers at the transmitter. We propose an adaptive scheme that can adapt both the number of transmit antennas (TAs) per layer based on the number of users in each user group in order to maximize the number of users served and also the STSK codeword in order to maximise the achievable user throughput.

Millimeter wave (mmWave) communications has gained considerable attention due to the availability of large bandwidths, which can be harnessed to meet the ever-increasing data rate demands. Directional beamforming combined with baseband precoding should be used owing to the high propagation losses encountered at mmWave frequencies. This is typically referred to as hybrid beamforming. In hybrid beamforming arrangements, the adjacent antenna elements are closely spaced, typically at half-wavelength spacing in order to compensate for the propagation losses. In this antenna array configuration, the mutual coupling between the adjacent antenna elements becomes significant and may limit the performance of the system. Therefore, in this paper, we propose a reduced-complexity near-optimal detection scheme, namely the so-called Element-based Lattice Reduction algorithm, for hybrid beamforming in mmWave communications and we investigate its performance in the presence of mutual coupling. We demonstrate that the mutual coupling affects the spatial correlation of the channels between the different antennas depending on the distance between the antenna elements, which has a direct effect on the achievable rate as well as bit error ratio (BER) performance of the system.

The Internet of Things (IoT) will support a massive number of devices, which will be connected to the wireless network. In the wireless IoT, the base station serves a wide variety of devices in the same time-frequency resource, where it is expected that the number of devices will be greater than the number of base station antennas. This results in a rank-deficient system. In this paper, we propose a minimum bit error ratio (MBER) precoder for rank-deficient MIMO systems in the context of the IoT, where the IoT devices are generally stationary. We invoke the particle swarm optimization (PSO) algorithm for solving the non-linearly constrained MBER problem and we show that the PSO assisted MBER precoder outperforms the conventional zero forcing and linear minimum mean squared error (LMMSE) precoders, which produce an error floor in these challenging rank-deficient scenarios.

In order to solve the security problem for fading channel, a pragmatic physical layer encryption (PLE) scheme is proposed, which utilises diversity technique elaborately. Different from the conventional PLE schemes based on phase rotation for the modulated symbol, the proposed scheme changed phase and amplitude together for a block of symbols each time, which can be defined as multi‐dimensional PLE (MPLE). Unconventional constellation obfuscates eavesdropper, which can be seen as the first level security in the physical layer. The correct probability based on chosen plaintext attacks and known plaintext attacks is deduced. It can be seen from the simulation results that the MPLE scheme can achieve lower attack success probability because of multi‐level security and better performance based on diversity under fading channel.

Millimeter wave (mm-Wave) communications has been considered as a strong candidate for future wireless standards, due to the large available bandwidth in the order of gigahertz. As a result, a plethora of future services and application-oriented scenarios can be conceived, under suitable propagation conditions. Accurate physical layer (PHY) design plays a vital role in the deployment of robust transmission systems able to efficiently exploit the large bandwidth portions available in the mm-Wave frequencies. In this paper, we propose Space-Time Shift Keying (STSK) MIMO coding combined with Cyclic-Prefixed Single Carrier (CP-SC) block transmission for broadband data exchange over frequency-selective mm-Wave channels. STSK facilitates exploiting transmit and receive diversity resulting in enhanced performance, when compared with state-of-the-art MIMO techniques only relying on receive diversity, such as Spatial Modulation (SM). In this paper, we assess the performance of CP-SC-STSK and CP-SC-SM in the presence of phase noise and imperfect channel estimation, considering 2 and 4 elements MIMO systems and Line of Sight (LoS) indoor versus non-LoS (nLoS) outdoor 73 GHz multipath channels. We show that the STSK-based solution using MMSE Frequency-Domain Equalization (FDE) is very robust against the aforementioned impairments and clearly outperforms CP-SC-SM at the price of a slight increase of receiver complexity and a throughput reduction of 50% when 4 × 4 MIMO systems are considered.

In this paper, we analyze the effect of time-varying channels on the performance of a non-coherent massive single-input multiple-output (SIMO) uplink system based on M-ary Differential Phase Shift Keying (M-DPSK), when amalgamated with bit-interleaved coded modulation relying on iterative decoding (BICM-ID). Additionally, we study the number of receive antennas (R) required in hostile time-varying channels for attaining a similar performance to that achieved for stationary channels. Furthermore, we analyze the maximum achievable rate (MAR) in conjunction with the specific modulation and coding schemes considered. The analysis is based on extrinsic information transfer (EXIT) charts parametrized by R, which varies with the signal to interference-plus-noise ratio (SINR). Our numerical results show that the system is robust to the effects of the channel's temporal correlation and that the simulation-based MAR closely matches the semi-analytical achievable rate obtained using EXIT charts. Hence,our system can be applied to scenarios associated with the short coherence time of high-speed railway systems, for example.

The millimeter wave (mmWave) frequency band offers substantial hitherto unused spectral resources for future wireless communication systems in order to meet the increasing capacity demand. However, mmWave frequencies suffer from high propagation losses, which may be mitigated by directional beamforming in addition to baseband precoding. This is usually referred to as hybrid beamforming. In this paper, we investigate the so-called discrete Fourier transform- mutually unbiased bases (DFT-MUB) aided codebook design conceived for limited-feedback mmWave systems, where the MUB aided codebook is applied in the baseband, while the DFT codebook is invoked for RF analog phase shifters. We demonstrate that our DFT- MUB codebook design performs similarly to the optimal digital precoding matrix, where the precoder is selected as the right singular matrix of the channel. However, our solution significantly reduces the search complexity in the baseband, while performing within 2.5 dB from the optimal digital precoder.

Optical single sideband (OSSB) signals are conventionally generated using a dual‐drive Mach–Zehnder modulator (MZM) or by using a single‐drive MZM in conjunction with a fibre Bragg grating filter. In this study, the authors propose and mathematically characterise a novel radio over fibre downlink in which an OSSB signal is generated using a single‐drive, rather than dual‐drive, MZM without any additional filter. Additionally, their proposed scheme can achieve optical upconversion of the electronic signal. Furthermore, in addition to cost advantages, the proposed scheme's bit error ratio (BER) performance is better than the classical OSSB signal generation scheme.

In this study, the authors consider a two‐hop network, where multiple source nodes (SNs) transmit to a destination node (DN) with the aid of a relay node (RN). The RN is equipped with a buffer, which is capable of storing multiple frames received from the SNs. During each time slot, the proposed protocol activates either the SN–RN hop or the RN–DN hop, depending on the channel quality of each hop and the buffer state at the RN. To optimise the hop activation for the network, they design a hop quality metric and propose a multi‐user buffer‐aided‐relaying uplink (MU‐BR‐UL) protocol, with the aid of the minimum signal‐to‐noise power ratio approximation. The benefits of the proposed protocol are analysed in terms of the end‐to‐end (e2e) outage probability and the e2e transmission delay. Then, the optimal power allocation is proposed for minimising the e2e outage probability under the total power constraint. The results indicate that the outage performance is significantly improved when the proposed power allocation is utilised in the MU‐BR‐UL protocol.

We analytically characterize the data-aided error vector magnitude (EVM) performance of a single-input multiple-output (SIMO) communication system relying on maximal ratio combining (MRC) having either independent or correlated branches that are nonidentically distributed. In particular, exact closed form expressions are derived for the EVM in$\eta\text{-}\mu$fading and$\kappa W\mu$shadowed fading channels and these expressions arevalidatedby simulations. The derived expressions are expressed in terms of Lauricella’s function of the fourth kind$F_D^{(N)}(.)$, which can be easily computed. Furthermore, we have simplified the derived expressions for various special cases such as independent and identically distributed branches, Rayleigh fading, Nakagami-mfading, and$\kappa\text{-}\mu$fading. Additionally, a parametric study of the EVM performance of the wireless system is presented.

In this study, the authors investigate the benefits of phase‐rotation‐assisted precoding (PRP) technique in spatial modulation (SM) systems, which are based on maximum free distance d min . First, a closed‐form solution of the maximum‐ d min PRP matrix is derived for the scenario of having two transmit antennas ( N t = 2). Moreover, two numerical methods are proposed for dealing with the case of N t > 2. The complexity of the proposed algorithms is presented. The authors simulation results show that the proposed PRP algorithms provide beneficial bit error ratio performance improvements compared with both the conventional SM and with the existing adaptive SM.

Radio over Fiber (RoF) distribution aided co-operation of Remote Access Points (RAPs) is proposed for jointly transmitting data to the users in the downlink (DL) of a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Joint transmission is performed with the aid of Block Diagonalization (BD), where the transmitted signal is pre-distorted in order to overcome the non-linearity imposed by the optical modulator. We demonstrate that with adequate design, the users can obtain high data rates with very small degradation introduced by the RoF transmission. Quantitatively, when M=7 RAPs, each equipped with t=2 transmit antennas (TAs) each, cooperate to serve N=7 simultaneous users, also equipped with r=2 receive antennas (RAs), the SNR degradation is kept below 0.1 dB compared to a system assuming a perfect RoF channel. On the other hand, the SNR performance degradation is around 1.2 dB, when the number of antennas at the transmitters and the receivers is increased to t=r=8.

A novel adaptive turbo-coded soft-decision aided differential detection (ATSDD) scheme is proposed for cooperative uplink wireless and Radio-over-fiber (ROF) transmission in a Fractional Frequency Reuse (FFR) based multicell, multiuser system. More specifically, the ATSDD scheme is employed by the Mobile Station (MS) for reliably conveying the source bits to a pair of Remote Antennas (RAs) by appropriately adjusting the modulation mode according to the near-instantaneous wireless and ROF channel conditions. The ATSDD switching thresholds are specifically adjusted for ensuring that the Bit Error Ratio (BER) remains below 10^(-5). We also investigated the effect of phase-rotations, which is routinely inflicted by practical imperfect ROF links. We demonstrate that our ATSDD scheme increases the overall throughput.

Layered video coding is capable of progressively refining the reconstructed video quality with the aid of multiple layers of unequal importance. When the base layer (BL) is corrupted or lost due to channel impairments, the enhancement layers (ELs) must be discarded by the video decoder, regardless whether they are perfectly decoded or not, which implies that the transmission power assigned to the ELs is wasted. To circumvent this problem, we proposed a bit-level inter-layer forward error correction (IL-FEC) scheme for layered video transmission in our previous work, which implanted the systematic bits of the BL into the systematic bits of the ELs using exclusive-OR operations (XOR). This allowed the receiver to exploit the implanted bits of the ELs for assisting the BL's decoding and hence improved the overall system performance of our IL-FEC aided layered video scheme. In this treatise, we find the specific FEC coding rates in a real-time on-line fashion for the sake optimizing the overall system performance. The proposed procedure is widely applicable to diverse wireless transceivers and FEC codecs. Our simulation results show that the proposed optimized IL-FEC system outperforms the traditional optimal UEP by about 1.9 dB of Eb/N0at a peak signal-to-noise ratio (PSNR) of 38 dB. Viewing the improvements in terms of the video quality, 3.3 dB of PSNR improvement is attained at an Eb/N0of 10 dB, when employing a recursive systematic convolutional (RSC) code.

In layered video streaming, the enhancement layers (ELs)must be discarded by the video decoder, when the base layer (BL) is corrupted or lost due to channel impairments. This implies that the transmit power assigned to the ELs is wasted, when the BL is corrupted. To combat this effect, in this treatise we investigate the inter-layer turbo (IL-turbo) code, where the systematic bits of the BL are implanted into the systematic bits of the ELs at the transmitter. At the receiver, when the BL cannot be successfully decoded, the information of the ELs may be utilized by the IL-turbo decoder for the sake of assisting in decoding the BL. Moreover, for providing further insights into the IL technique the benefits of the IL-turbo scheme are analyzed using extrinsic information transfer (EXIT) charts in the scenario of unequal error protection (UEP) coded layered video transmission. Finally, our data partitioning based experiments show that the proposed scheme outperforms the traditional turbo code based UEP scheme by about an Eb=N0 of 1.1 dB at a peak signal-to-noise ratio (PSNR) of 36 dB or 3 dB of PSNR at an Eb=N0 of -5.5 dB at the cost of a complexity increase of 13%.

In this treatise, we investigate an inter-layer (IL) decoded self-concatenated coded system conceived for scalable video coding (SVC). In SVC, when the base layer (BL) is corrupted due to channel-induced decoding errors, the enhancement layers (ELs) are discarded by the SVC decoder. The proposed IL coding technique implants the systematic information of the BL into the systematic bits of the ELs using exclusive-OR (XOR) operations. The IL coding is combined with a self-concatenated code, which is a near-capacity iterative detection aided channel codec using a single encoder and a single decoder. At the receiver, the IL decoding technique is activated for correcting the errors residing in the error-infested BL. In our experiments, the proposed system is combined with a number of the traditional unequal error protection (UEP) arrangements for benchmarking the system performance. Our simulation results demonstrate that the proposed technique is capable of further improving the system performance of the traditional UEP assisted system by an Eb/N0of about 3 dB at a peak signal-to-noise ratio (PSNR) of 36 dB. When viewed from a different perspective, the attainable gain can be quantified as a PSNR improvement of 2.9 dB at Eb/N0= -5 dB, while imposing a marginal complexity increase of 1.5%.

We design distributed multiple-component turbo-codes (MCTCs) for cooperative automatic repeat request (CARQ) aided systems, which are capable of attaining both a similar performance and throughput as the conventional twin-component turbo code (TCTC) aided system, while imposing a significantly lower decoding complexity. The reduction in the decoding complexity of the MCTC-CARQ scheme is a direct benefit of using low-memory MCTC component encoders, combined with the novel principle of deferred iteration (DI), where the decoding process is only initiated when sufficient information has been accumulated at the receiver so that an open tunnel exists in the Extrinsic information transfer (EXIT) charts. In the presence of multiple collaborating relay nodes (RNs), the specific RN which succeeds in decoding the source message, and additionally, has the highest signal-to-noise ratio at the destination node is selected as the retransmission node. Our numerical results demonstrate that the proposed MCTC-CARQ protocol is capable of reducing the decoding complexity by up to 40% compared to its TCTC-CARQ counterpart, while achieving the same throughput and reliability.

A novel detect-and-forward (DeF) relaying aided cooperative SM scheme is proposed, which is capable of striking a flexible tradeoff in terms of the achievable bit error ratio (BER), complexity and unequal error protection (UEP). More specifically, SM is invoked at the source node (SN) and the information bit stream is divided into two different sets: the antenna index-bits (AI-bits) as well as the amplitude and phase modulation-bits (APM-bits). By exploiting the different importance of the AI-bits and the APM-bits in SM detection, we propose three low-complexity, yet powerful relay protocols, namely the partial, the hybrid and the hierarchical modulation (HM) based DeF relaying schemes. These schemes determine the most appropriate number of bits to be re-modulated by carefully considering their potential benefits and then assigning a specific modulation scheme for relaying the message. As a further benefit, the employment of multiple radio frequency (RF) chains and the requirement of tight inter-relay synchronization (IRS) can be avoided. Moreover, by exploiting the benefits of our low-complexity relaying protocols and our inter-element interference (IEI) model, a low-complexity maximum-likelihood (ML) detector is proposed for jointly detecting the signal received both via the source-destination (SD) and relay-destination (RD) links. Additionally, an upper bound of the BER is derived for our DeF-SM scheme. Our numerical results show that the bound is asymptotically tight in the high-SNR region and the proposed schemes provide beneficial system performance improvements compared to the conventional MIMO schemes in an identical cooperative scenario.

Layered video coding creates multiple layers of unequal importance that enables us to progressively refine the reconstructed video quality. When the base layer (BL) is corrupted or lost during transmission, the enhancement layers (ELs) must be dropped, regardless of whether they are perfectly decoded or not, which implies that the transmission power assigned to the ELs is wasted. In this treatise, we propose an inter-layer forward error correction (FEC) coded video transmission scheme for mobile TV. At the transmitter, the proposed interlayer (IL) coding technique implants the systematic information of the BL into the ELs by using exclusive-OR operations. At the receiver, the implanted bits of the ELs may be utilized for assisting in decoding the BL. Furthermore, the data partition mode of H.264 video coding is utilized as the source encoder, where the type B and type C partitions will assist in protecting the type A partition. The IL coded bitstream will then be modulated and transmitted over a multifunctional multiple input multiple output (MF-MIMO) scheme for the sake of improving the system's performance in mobile environments. The proposed system may be readily combined with the traditional unequal error protection (UEP) technique, where extrinsic mutual information (MI) measurements are used for characterizing the performance of our proposed technique. Finally, our simulation results show that the proposed system model outperforms the traditional UEP aided system by about 2.5 dB of Eb/N0or 3.4 dB of peak signal-to-noise ratio (PSNR) at the cost of a 21% complexity increase, when employing a recursive systematic convolutional code. Furthermore, unlike the traditional UEP strategies, where typically stronger FEC-protection is assigned to the more important layer, employing our proposed IL coding technique requires weaker FEC to the more important layer. For example, the system relying on channel coding rates of 0.85, 0.44, and 0.44 for the type A, type B, and type C H.264 video partitions, respectively, achieves the best system performance when employing a recursive systematic convolutional (RSC) code.

Robust video transmission using iteratively detected Self-Concatenated Coding (SCC), multi-dimensional Sphere Packing (SP) modulation and Layered Steered Space-Time Coding (LSSTC) is proposed for H.264 coded video transmission over correlated Rayleigh fading channels. The self-concatenated convolutional coding (SECCC) scheme is composed of a Recursive Systematic Convolutional (RSC) code and an interleaver, which is used to randomise the extrinsic information exchanged between the self-concatenated constituent RSC codes. Additionally, a puncturer is employed for improving the achievable bandwidth efficiency. The convergence behaviour of the MIMO transceiver advocated is investigated with the aid of Extrinsic Information Transfer (EXIT) charts. The proposed system exhibits an $E_b/N_0$ gain of about $9~dB$ at the PSNR degradation point of $1~dB$ in comparison to the identical-rate benchmarker scheme.

Classic Shannon theory suggests that the achievable channel capacity increases logarithmically with the transmit power. By contrast, the MIMO capacity increases linearly with the number of transmit antennas, provided that the number of receive antennas is equal to the number of transmit antennas. With the further proviso that the total transmit power is increased proportionately to the number of transmit antennas, a linear capacity increase is achieved upon increasing the transmit power, which justifies the spectacular success of MIMOs. Hence we may argue that MIMO-aided transceivers and their cooperation-assisted distributed or virtual MIMO counterparts constitute power-efficient solutions. In a nutshell, since the conception of GSM in excess of three orders of magnitude bit-rate improvements were achieved in three decades, which corresponds to about a factor ten for each decade, because GSM had a data rate of 9.6 Kb/s, while HSDPA is capable of communicating at 13.7 Mb/s. However, the possible transmit power reductions remained more limited, even when using the most advanced multistage iterative detectors, since the required received signal power has not been reduced by as much as 30 dB. This plausible observation motivates the further research of advanced cooperation-aided wireless MIMO transceivers, as detailed in this treatise.

It is widely recognised that the choice of a specific bit-to-symbol mapping scheme or a beneficial constellation labelling is an influential factor, when designing bit-interleaved coded modulation using iterative decoding (BICM-ID) for the sake of achieving a high iteration gain. Generally, a larger constellation size of a higher-dimensional space renders the bit-to-symbol mapping design more flexible. In this paper, we first define a flexibility measure based on the extrinsic information transfer (EXIT) characteristics of bit-to-symbol mapping schemes. Secondly, we investigate the effect of expanding the constellation to a higher-dimensional space on our proposed EXIT characteristic flexibility index, when transmitting diverse numbers of bits per joint symbol.

The conventional two-stage turbo-detection schemes generally suffer from a Bit Error Rate (BER) floor. In this paper we circumvent this deficiency by proposing a three-stage turbo detected Sphere Packing (SP) modulation aided Layered Steered Space-Time Coding (LSSTC) scheme for H.264 coded video transmission over correlated Rayleigh fading channels. The soft-bit assisted H.264 coded bit-stream is protected using low-complexity short-block codes (SBCs), combined with a rate-1 recursive inner precoder is employed as an intermediate code which has an infinite impulse response and hence beneficially spreads the extrinsic information across the constituent decoders. This allows us to avoid having a BER floor. Additionally, the convergence behaviour of this serially concatenated scheme is investigated with the aid of Extrinsic Information Transfer (EXIT) Charts. The proposed system exhibits an Eb/N0gain of about 12 dB in comparison to the benchmark scheme carrying out iterative source-channel decoding as well as Layered Steered Space-Time Coding (LSSTC) aided Sphere Packing (SP)demodulation, but dispensing with the optimised SBCs.

The achievable performance of a jointly optimised iterative source and channel decoding (ISCD) arrangement invoking the Adaptive MultiRate Wideband (AMR-WB) speech codec is characterized, which exploits the intentional redundancy imposed by the proposed Over-Complete source-Mapping (OCM) scheme. The resultant OCM-aided AMR-WB bitstream is protected by a Recursive Systematic Convolutional (RSC) code and mapped to a Differential Space-Time Spreading (DSTS) arrangement using Sphere Packing (SP) modulation for transmission over narrowband temporally correlated Rayleigh fading channels. The effect of appropriately apportioning the total amount of redundancy between the source and channel codecs on the attainable system performance is demonstrated, while keeping the overall coding rate constant. The decoding convergence of the proposed scheme is studied with the aid of Extrinsic Information Transfer (EXIT) charts. Explicitly, our experimental results show that the specific scheme using a 2/3-rate channel encoder and a 3/4-rate OCM scheme exhibits an Eb/N0gain of 0.7 dB at the SegSNR degradation point of 1 dB, when compared to the system that assigns all the redundancy to the OCM scheme. By contrast, the scheme using a 3/4-rate channel encoder and a 8/9-rate OCM results in an Eb/N0gain of 1.0 dB.

In this treatise we propose a three-stage twin-transmit-antenna assisted Multiuser (MU) Direct Sequence Code-Division Multiple Access (DS-CDMA) system employing both a Unitary Rate Code (URC) and a Recursive Systematic Code (RSC) to carry out iterative turbo detection. A Space-Time Block Code (STBC) is used to provide second-order diversity gain in conjunction with a novel soft-output (SO) ant-colony-optimization (ACO) based space-time multiuser detection (ST/MUD) algorithm, which is capable of carrying out STBC decoding, while mitigating the Multiuser Interference (MUI) and generating the Log-Likelihood Ratios (LLR) for facilitating the iterative exchange of extrinsic information between the URC and RSC decoders of each user. With aid of the above mentioned state-of-the-art techniques, the proposed system becomes capable of approaching the performance of the single-user system within about 0.5dB, when K = 32 users are supported with the aid of 31-chip Gold-codes.

This paper presents a novel multi-functional MultipleInput Multiple-Output (MIMO) scheme that combines the benefits of the Vertical Bell Labs Layered Space-Time (V-BLAST) scheme, of SpaceTime Codes (STC) as well as of beamforming. To further enhance the attainable system performance and to maximise the coding advantage of the proposed transmission scheme, the system is also combined with multi-dimensional Sphere Packing (SP) modulation. Additionally, further system performance improvements can be attained by serially concatenated convolutional coding combined with a Unity-Rate Code (URC) employed as an inner code. Then, at the receiver side, iterative decoding is invoked by exchanging extrinsic information between the three constituent decoders, i.e. the outer convolutional code's decoder, the inner URC's decoder as well as the SP demapper. Moreover, the convergence behaviour of the proposed scheme is evaluated with the aid of both three-dimensional (3D) and two-dimensional (2D) Extrinsic Information Transfer (EXIT) charts. Finally, we quantify the maximum achievable rate of the system based on EXIT charts and demonstrate that the iterative-detection-aided system is capable of operating within 0.6 dB from the maximum achievable rate limit. Explicitly, the proposed iteratively detected three-stage LSSTC-SP scheme is capable of attaining at least 4.8 dB gain at a BER of 10-5over the conventional iterativedetection aided two-stage scheme, where the extrinsic information is limited to the SP demapper and the outer code's decoder.

In this paper we considered jointly optimised source and channel decoding, while employing serially concatenated and iteratively decoded Short Block Codes (SBC) combined with a Unity Rate Code (URC) and multi-dimensional Sphere Packing (SP) modulation. The resultant coded signal is transmitted over non-coherently detected Multiple-Input Multiple-Output (MIMO) Differential Space-Time Spreading (DSTS) designed for near capacity joint source-channel decoding (JSCD). The performance of the system was evaluated by considering interactive video telephony using the H.264/AVC source codec. The source coded parameters generated by the state-of-the-art H.264/AVC video codec typically contain limited natural residual redundancy. Therefore, to improve the error robustness of iterative sourcechannel decoding (ISCD), SBCs are incorporated to impose artificial redundancy on the source coded parameters. The natural residual redundancy after source coding and the artificial redundancy due to SBC coding is iteratively exploited in a turbo process to improve the overall Bit Error Ratio (BER) and objective video quality performance quantified in terms of the Peak Signal to Noise Ratio (PSNR). The convergence behaviour of the advocated MIMO transceiver is investigated with the aid of Extrinsic Information Transfer (EXIT) charts. The proposed system exhibits an Eb/N0gain of about 22 dB at the PSNR degradation point of 2 dB in comparison to the benchmarker scheme carrying out DSTS aided SP-demodulation as well as iterative source and channel decoding, when using Isystem= 5 system iterations, while communicating over correlated narrowband Rayleigh fading channels.

We present a novel tri-functional multiple-input multiple-output (MIMO) scheme that intrinsically amalgamates space-time spreading (STS), the Vertical Bell Labs Layered Space-Time (V-BLAST) scheme and beamforming with generalised multicarrier direct sequence code division multiple access (MC DS-CDMA). Further system performance improvements can be attained by employing channel coding, where the source bits are serial-to-parallel converted to two layers, each constituted by a serial concatenation of an outer code amalgamated with a unity-rate code for the sake of improving the convergence behaviour of the proposed system. Additionally, the convergence behaviour of the iteratively detected scheme is evaluated with the aid of extrinsic information transfer (EXIT) charts. We also propose a novel logarithmic likelihood ratio (LLR) postprocessing technique for improving the iteratively detected system's performance. Explicitly, after I = 10 decoding iterations and employing an interleaver depth of Dint= 160,000 bits, the proposed system supporting K = 4 users attains a BER below 10-5for Eb/Novalues in excess of -2.8 dB.

We propose a distributed turbo coding (DTC) scheme, where two users cooperate in a two-phase cooperation scenario constituted by the exchange of data between the users in the first phase followed by the uplink transmission of the two users' data in the second phase of cooperation. Following the information exchange phase, the data transmitted from the second user's transmitter during the second phase is an interleaved version of the first user's data. Each user's transmitter is equipped with a recursive systematic convolutional (RSC) code, an interleaver and a sphere packing (SP) mapper. At the receiver side, interference cancellation is employed, which outputs two branches of decoded data corresponding to the data transmitted from the two users' transmitters. Iterative detection is employed by exchanging extrinsic information between the RSC decoder and the SP demapper in each decoding branch, as well as between the RSC decoders in the two branches. The proposed DTC scheme is benchmarked against another cooperative scheme, where the two users do not exchange their data, they rather transmit their data simultaneously. At the receiver of the benchmark scheme, iterative detection is carried out by exchanging extrinsic information between the SP demapper and the RSC decoder of each user, but no iterations are invoked between the RSC decoders in the two branches. The proposed scheme attains an Eb/Nogain of about 25 dB at BER of 10-5, when compared to the benchmark scheme, while considering a perfect inter-user channel (IUC) and employing Isys=5 system iterations in conjunction with an interleaver depth of Dint=80, 000 bits. Additionally, we study the effects of both Gaussian as well as Ricean IUC on the achievable BER performance of the uplink DTC scheme.

A jointly optimised iterative source and channel decoding (ISCD) scheme invoking the Adaptive Multi Rate Wideband (AMR-WB) speech codec is proposed. More explicitly, the transceiver investigated consists of serially concatenated Recursive Convolutional (RSC) codes, a Unity Rate Code (URC) referred to as a precoder and the AMRWB speech codec, where the resultant bitstream is transmitted using Differential Space-Time Spreading (DSTS) and Sphere Packing (SP) modulation over narrowband temporally correlated Rayleigh fading channels. The convergence behaviour of the advocated scheme is investigated with the aid of Extrinsic Information Transfer (EXIT) charts, which suggests that potential performance improvements can be achieved by combining a serially concatenated precoder with the AMR-WB speech codec. The proposed system exhibits an Ef,/No gain of about 1.5 dB in comparison to the benchmark scheme carrying out iterative sourceand channel-decoding as well as DSTS aided SP-demodulation, but dispensing with the precoder, when using Isystem= 4 system iterations.

We present a novel multi-functional multiple-input multiple-output (MIMO) scheme, that combines the benefits of space-time codes (STC), of vertical Bell Labs layered space-time (V-BLAST) scheme as well as of beamforming. To further enhance the attainable system performance and to maximise the coding advantage of the proposed transmission scheme, the system is also combined with multi-dimensional sphere packing (SP) modulation. Additionally, we quantify the capacity of the proposed multi-functional MIMO aided multi-dimensional SP arrangement and propose a novel technique of computing an upper limit on the achievable bandwidth efficiency of the system based on extrinsic information transfer (EXIT) charts. Further system performance improvements can be attained by serially concatenating our proposed scheme with an outer code together with a unity-rate code (URC), where three different receiver structures are created by varying the iterative detection configuration of the constituent decoders/demappers. Moreover, the convergence behaviour of the proposed schemes is evaluated with the aid of EXIT charts. Explicitly, the three proposed systems are capable of operating within 0.9 dB, 0.6 dB and 0.4 dB of the maximum achievable rate limit. Additionally, the three stage assisted SP aided scheme is capable of outperforming its counterpart employing QPSK by 1 dB at a BER of 10-6.

Systematic Luby Transform (SLT) codes have shown good performance for single antenna aided systems for transmission over AWGN and uncorrelated Rayleigh fading channels. For the sake of improving both the Bit Error Ratio (BER) performance and the diversity gain of Vertical Bell Laboratories Layered Space Time (V-BLAST) schemes, in this paper we propose a SLT coded V-BLAST system having four transmit and four receive antennas. As a benefit of iteratively exchanging the Log-Likelihood Ratios (LLRs) between the QPSK demapper and the SLT decoder of each antenna-specific stream of the V-BLAST system, the system exhibits an infinitesimally low BER for Eb/N0values in excess of 6.5 dB, when using an interleaver length of L = 1, 200 bits. Additionally, the SLT coded system provides an Eb/N0gain of 5 dB at a BER of 10 6 over its benchmark scheme employing iterative extrinsic information exchange between a Recursive Systematic Convolution (RSC) code and a unity-rate code, having an interleaver length of L= 1,200 bits.

In this paper we propose an iteratively detected Sphere Packing (SP) aided Differential Space-Time Spreading (DSTS) scheme using a Recursive Systematic Convolutional (RSC) code, for protecting the soft-bit assisted Adaptive Multi Rate Wideband (AMR-WB) decoder's bitstream, which is also protected by a novel over-complete source-mapping scheme. The convergence behaviour of the Multiple-Input Multiple-Output (MIMO) transceiver advocated is investigated with the aid of both three- dimensional (3D) and two-dimensional (2D) Extrinsic Information Transfer (EXIT) charts. The proposed system exhibits an Eb/Nogain of about 2.5 dB in comparison to the benchmark scheme carrying out iterative source- and channel-decoding as well as DSTS aided SP-demodulation, but dispensing with the over-complete source-mapping, when using Isystem= 3 system iterations.

A novel iteratively detected Sphere Packing (SP) modulation aided Orthogonal Frequency Division Multiplexing (OFDM) scheme is proposed, which we refer to as the SP- OFDM arrangement. The advocated SP-OFDM system outperforms conventional OFDM dispensing with SP. As its upper- bound performance limit, the Discrete Input Continuous Output Memoryless Channel (DCMC) capacity of this system is formulated. In order to maximize the DCMC channel capacity, a SP-to- OFDM-sub-carrier mapper (SPTSCM) is contrived, which is capable of providing an approximately 0.3 bit/s/Hz DCMC capacity benefit, by employing a variety of different SPTSCM arrangements. Additionally, the proposed SP-OFDM scheme exhibits a DCMC capacity advantage of 0.8 bit/s/Hz over the conventional equivalent-throughput Gray Mapping (GM) and Anti-Gray Mapping (AGM) based QPSK-OFDM schemes. Furthermore, the performance of the SP-OFDM system can be improved by serially concatenated convolutional coding relying on iterative extrinsic information exchange between the SP-symbol-to-bit demapper and the channel decoder. Explicitly, the proposed turbo-detected SP-OFDM scheme exhibits an approximately Eb/N0= 3 dB and Eb/N0= 4.5 dB gain at a Bit Error Ratio (BER) of 10-4over the equivalent- throughput turbo-detected GM based QPSK-OFDM scheme and AGM QPSK-OFDM scheme, respectively. EXtrinsic Information Transfer (EXIT) charts are employed for analyzing the achievable convergence behaviour.

In this paper we evaluate the performance of data-partitioned H.264 video transmission using Unequal Error Protection (UEP) Recursive Systematic Convolutional Codes (RSC). Sphere Packing modulation aided Differential Space Time Spreading is used to improve the overall BER performance and to enhance the objective quality of the transmitted video sequence expressed in terms of Peak Signal-to-Noise Ratio (PSNR). The effect of different error protection schemes on the attainable system performance is demonstrated, when using iterative Soft-Bit Source Decoding (SBSD) and channel decoding, while keeping the overall bit-rate budget constant. Additional system performance improvements are achieved by intentionally increasing the redundancy of the source coded bit-stream using Over-Complete Mapping (OCM). This is achieved by appropriately partitioning the total available bit rate budget between the source and channel codecs. EXIT Charts were used for analysing the attainable system performance. Explicitly, our experimental results show that the proposed UEP scheme outperforms its Equal Error Protection (EEP) counterpart by about 1 dB Eb/NOat the PSNR degradation point of 1 dB. Additionally, an Eb/NOgain of 12 dB is attained using iterative soft-bit source and channel decoding with the aid of rate 3/4 OCM.

This paper presents a novel ultrawideband (UWB), direct sequence code division multiple access (DS-CDMA) aided system designed for the IEEE 802.15.3a UWB channel specifications. Substantial performance improvements can be attained by serially concatenated channel encoding combined with a unity rate code (URC). We compare the performance of the iterative aided decoding correlation (Corr) and minimum mean square error (MMSE) detectors exchanging extrinsic information between the URC's decoder as well as the outer recursive systematic convolutional (RSC) code's decoder. Moreover, the iterative decoding convergence analysis of the proposed system is carried out with the aid of extrinsic information transfer (EXIT) charts. As expected, the iteratively decoded fully-loaded system employing MMSE detection outperforms its counterpart employing the equivalent Corr detection. Explicitly, UWB DS-CDMA using the MMSE detector attains a BER of 10-5at Eb/No=2 dB when supporting U=32 users employing i=12 decoding iterations, while the same system using the Corr detector operates at BER-10-1.

This paper presents a novel analysis on the decoding convergence of Time Hopping (TH) and Direct Sequence (DS) Code-Division Multiple-Access (CDMA) Ultrawide Bandwidth (UWB) systems when communicating over multipath Nakagami channels. The analysis is based on the Extrinsic Information Transfer (EXIT) chart where the UWB systems are serially concatenated pulse-position modulated TH and code-synchronous DS-CDMA. It is shown from an EXIT chart analysis that the multipath diversity can yield a larger area under the EXIT curve of the inner detector. This area is related to the achievable rate of the system and it can be exploited with the aid of iterative detection. Simulation results of the iteratively detected TH and DS-CDMA UWB schemes verify the EXIT chart analysis.

This paper presents a novel amalgam of steered space-time spreading (SSTS) and orthogonal frequency division multiple access (OFDMA) designed for attaining both spatial diversity gain and beamforming gain for transmission over OFDM-symbol-invariant frequency selective channels. We propose a flexible technique for increasing the number of users beyond the number of chips in the spreading sequence employed by the SSTS scheme with the aid of the multiple carriers of OFDMA, which requires an extended bandwidth. However, employing a separate low-complexity SSTS detector combined with another separate OFDMA detector is potentially less complex than a single detector designed for detecting all the users supported in a single domain, regardless whether the single- domain Multi-User Detector (MUD) is an SSTS or OFDMA MUD. This is because the MUD's complexity tends to increase exponentially with the number of users detected. The SSTS-OFDMA system is benchmarked against its counterpart using S-depth Frequency Domain (FD) repetition, which increases the FD diversity order at the cost of reducing the overall throughput by a factor of S. Fortunately, a similar FD diversity gain may be achieved without a factor-S reduction in the throughput, when using FD spreading and assigning all the superimposed FD spreading codes to the same user.

This paper presents a novel turbo-detected multidimensional sphere packing (SP) modulation scheme using four transmit antennas combined with differentially encoded space-time spreading (DSTS). The DSTS scheme can be readily combined with PSK, QAM as well as SP modulation schemes. The SP-aided DSTS system advocated has low-complexity encoding and decoding algorithms that require no channel knowledge and it is capable of outperforming the DSTS system dispensing with sphere packing. Further system performance improvements can be attained by serially concatenated convolutional encoding combined with a unity-rate code (URC) referred to as a precoder. Then, at the receiver side, iterative decoding is invoked by exchanging extrinsic information between the precoder's decoder as well as the outer recursive systematic convolutional (RSC) code's decoder. Moreover, the convergence behaviour of the proposed system is evaluated with the aid of extrinsic information transfer (EXIT) charts. Explicitly, the turbo-detected precoded DSTS-SP system performs within 1.6 dB of the achievable multiple-input multiple output (MIMO) capacity. Finally, in contrast to an equivalent 0.5 bit/symbol throughput turbo- detected DSTS-SP scheme using no preceding, the turbo-detected precoded DSTS-SP scheme exhibits no error floor.

In this paper we consider serially concatenated and iteratively decoded irregular variable length coding (IrVLC) combined with preceded differential space-time spreading (DSTS) aided multidimensional sphere packing (SP) modulation designed for near-capacity joint source and channel coding. The IrVLC scheme comprises a number of component variable length coding (VLC) codebooks having different coding rates for the sake of encoding particular fractions of the input source symbol stream. The relative length of these source-stream fractions can be chosen with the aid of extrinsic information transfer (EXIT) charts in order to shape the EXIT curve of the IrVLC codec, so that an open EXIT chart tunnel may be created even at low Eb/N0values that are close to the capacity bound of the channel. These schemes are shown to be capable of operating within 0.9 dB of the DSTS-SP channel's capacity bound using an average interleaver length of 113,100 bits and an effective bandwidth efficiency of 1 bit/s/Hz, assuming ideal Nyquist filtering. By contrast, the equivalent-rate regular VLC-based bench- marker scheme was found to be capable of operating at 1.4 dB from the capacity bound, which is about 1.56 times the corresponding discrepancy of the proposed IrVLC-aided scheme.

This paper presents a novel generalised Multi-Carrier Direct Sequence Code Division Multiple Access (MC DS-CDMA) system invoking smart antennas for improving the achievable performance in the downlink, as well as employing multi-dimensional Sphere Packing (SP) modulation for increasing the achievable diversity product. In this contribution, the MC DS-CDMA transmitter considered employs multiple Antenna Arrays (AA) and each of the AAs consists of several antenna elements. Furthermore, the proposed system employs both time- and frequency- (TF) domain spreading for extending the achievable capacity, when combined with a novel user-grouping technique for reducing the effects of Multiuser Interference (MUI). Moreover, in order to further enhance the system's performance, we invoke a MultiLevel Coding (MLC) scheme, whose component codes are determined using the so-called equivalent capacity based constituent-code rate-calculation procedure invoking a 4-dimensional bit-to-SP-symbol mapping scheme. Our results demonstrate an approximately 3.8 dB Eb/N0gain over an identical throughput scheme dispensing with SP modulation at a BER of 10-5.

In this paper we propose two adaptive schemes for improving the achievable bandwidth efficiency (BE) of cooperative diversity aided wireless networks. These schemes are capable of accommodating the channel signal-to-noise ratio (SNR) variation of wireless systems by near-instantaneously adapting the uplink transmission configuration. Explicitly, the first adaptive transmission scheme is constituted by a novel reconfigurable four-antenna-aided cooperative uplink space-time block coded (STBC) structure designed for communicating with a base station (BS) equipped with a single receive antenna. By contrast, the second adaptive scheme is constituted by a reconfigurable cooperative uplink vertical Bell Labs layered space time (V-BLAST)-like architecture constituted by single-antenna-aided mobiles communicating with a BS equipped with multiple receive antennas. Our results demonstrate that significant effective BE improvements can be achieved by both systems, while maintaining a target bit-error-ratio of 10-3. Explicitly, when neglecting the Nyquist excess bandwidth, the first system is capable of attaining an effective BE varying between 0.316 bits/sec/Hz and 2.18 bits/sec/Hz, while the second has a BE varying between 2 bits/sec/Hz and 8 bits/sec/Hz.

Jointly optimised iterative source- and channel-decoding is invoked for enhancing the error resilience of the adaptive multi rate wideband (AMR-WB) speech codec. The resultant AMR-WB coded speech signal is protected by recursive systematic convolutional (RSC) codes and transmitted using a sphere packing (SP) aided differential space-time spreading-/(DSTS) assisted transceiver. The performance of the proposed scheme is evaluated when communicating over correlated non-dispersive Rayleigh fading channels. The proposed system exhibits an Eb/N0gain of about 1 dB in comparison to the benchmark scheme carrying out joint channel decoding and DSTS aided SP-demodulation, but separate AMR-WB decoding, when using Iout= 4 external iterations.

In this contribution a novel adaptive differential space-time spreading assisted turbo detected sphere packing modulation scheme is proposed for improving the achievable throughput of code division multiple access (CDMA) systems. The scheme is capable of accommodating the channel signal-to-noise ratio (SNR) variation of wireless systems by adapting the system parameters. Explicitly, an adaptive transmission scheme constituted by a novel reconfigurable four transmit antenna aided arrangement using a variable spreading factor based differential space-time spreading scheme, as well as variable code rate recursive systematic convolutional codes is introduced. Our results demonstrate that significant effective throughput improvement can be achieved while maintaining a target bit-error-ratio of 10-4. Explicitly, when assuming an ideal Nyquist filter having a zero excess bandwidth, the system's effective throughput varies from 0.25 bits/sec/Hz to 16 bits/sec/Hz.

This paper presents a generalised multicarrier direct sequence code division multiple access (MC DS-CDMA) system invoking smart antennas for improving the achievable performance in the downlink. In this contribution, the MC DS-CDMA transmitter employs an antenna array (AA) and steered space-time spreading (SSTS). Furthermore, the proposed system employs both time and frequency (TF) domain spreading for extending the capacity of the system, which is combined with a user-grouping technique for reducing the effects of multi-user interference (MUI). Moreover, to eliminate the high- complexity multiple input multiple output (MIMO) channel estimation required for coherent detection, we also propose a Differential SSTS (DSSTS) scheme. More explicitly, for coherent SSTS detection MVNrnumber of channel estimates have to be generated, where M is the number of transmit AAs, V is the number of subcarriers and Nris the number of receive antennas. This is a challenging task, which renders the low-complexity DSSTS scheme attractive.

A novel differentially encoded space-time spreading (DSTS) scheme using two transmit antennas and Sphere Packing (SP) is proposed, which we refer to as the DSTS-SP arrangement. The advocated SP-aided system outperforms DSTS dispensing with SP and requires no channel knowledge. We also demonstrate that the performance of DSTS-SP systems can be further improved by serially concatenated convolutional coding and by performing SP-symbol-to-bit demapping as well as channel decoding iteratively. Explicitly, the proposed turbo-detected DSTS-SP scheme exhibits an Eb/Nogain of 17.0 dB at a bit error rate (BER) of 10-5over an uncoded identical-throughput system and an Eb/Nogain of 1.9 dB over the equivalent 2 bits/symbol effective throughput QPSK-modulated turbo-detected DSTS scheme