A ‘fibre-switch block’ is a switch with delay lines that feedback from some outputs to inputs. In every unit time, it receives and transmits a packet concurrently. A ‘fibre memory’ means a multi-block serial connection. Its performance of time-multiplexed operation is often said to ‘emulate’ a multistage interconnection network. This study formulates this concept of emulation. The formalised concept is useful in the design and validation of various switching functionalities, including timeslot interchanging, sorting, merging and concentration. For illustration, ‘banyan-type networks’, ‘Clos network’ and several familiar multi-stage sorting networks are all efficiently emulated.

In this study, the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number, location and power delay profile of significant taps, as well as environmental parameters such as distance, temperature, salinity, pressure and depth. Then, the authors use this expression to determine the optimal carrier frequency, input signalling and bandwidth for capacity maximisation.

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.

Interference alignment (IA) is a data transmission scheme that achieves maximum multiplexing gains in interference channel. This study investigates the theoretical sum rate for IA. By analysing both the asymptotic eigenvalues distribution and the magnitude of the effective channel after interference cancellation in IA, a closed-form of sum rate expression is derived for Gaussian interference channel. Numerical results show that the closed-form results nearly coincide with that derived from numerical results of IA.

Efficient partial relay selection (EPRS) is an advanced technique to improve the performance of partial relay selection (PRS) at the cost of a small additional feedback overhead. However, EPRS has the worst performance but lower feedback overhead when compared with best relay selection. In this study, the authors present a bit error probability (BEP) analysis of EPRS in decode-and-forward relaying systems over independent and non-identical Rayleigh fading channels, where the direct link between the source and the destination is available. In particular, they provide an exact and closed-form expression of the BEP of M-ary square quadrature amplitude modulation for EPRS. The BEP analysis is verified through simulations. The numerical results show that EPRS significantly outperforms PRS for a large gap between the average channel powers for the first and the second hops except when all the average channel powers for the first hop are smaller than those for the second hop.

In this work, the impact of outdated channel state information because of feedback delay is evaluated for the performances of several generalised relay selection schemes. Multi-hop amplify-and-forward relaying is considered over Rayleigh fading channels. Numerical results show that different relay selection schemes suffer from different performance degradations when the hop index increases. Interestingly, for generalised relay selection, numerical results also show that selecting more relays does not necessarily lead to better power outage probability and bit error rate performances. These observations provide useful guidance on relaying system designs.

Rectenna can be used for remotely charging the rechargeable batteries, commonly used for powering wireless sensors in buildings, with the help of a dedicated RF source. However, in such a process, the effective path loss reduces the RF power level on rectenna which lowers the RF-to-DC conversion efficiency of the system. This study therefore focuses on the design and analysis of an efficient integrated rectifier-antenna (rectennas) for indoor applications. In this proposed study, first a pentagonal antenna is designed at 5 GHz using Ansoft HFSS simulation. The obtained results show that the antenna resonates at two more frequencies, 10.7 and 14.2 GHz, other than the designed frequency. In order to eliminate the signals received by the antenna at these frequencies, a low-pass filter cornered around 5 GHz is designed and integrated with the antenna. As a result, the integrated structure reveals a return loss of around 15 dB at 5 GHz. Next for rectification purpose, a Schottky diode is characterised at 5 GHz. The proposed antenna structure is then matched to the optimal complex impedance of the diode circuit. Consequently the RF–DC conversion efficiency of the rectenna is found to be 46%.

Increasing the number of transmit antennas can improve the diversity gain of the system, and accordingly reduce the transmit power dissipation. However, the high circuit power dissipation incurred cannot be ignored. Generalised selection combining, which could provide a certain spatial diversity in the transmit diversity systems, performs a good balance between system performance and practical implementation cost. In this study, the authors propose an energy efficient generalised selection combining (EE-GSC) scheme which obtains improved transmitter energy efficiency (EE) by providing a best tradeoff between the diversity gain and the circuit power dissipation of multiple antennas. Based on the classical results of order statistics, a theoretical analysis of EE-GSC performance is carried out in detail over Rayleigh fading channels. Based on this analysis, the average number of active branches as well as the average power dissipation of the proposed scheme is also derived. Numerical results are also given to further illustrate the EE performance of the proposed scheme.

The receiver with message propagation (MP) decoder algorithm realises the decoding of traditional Luby transform (LT) encoded packages when there is only one unknown packet adjacent to the encoded package. Error packets can be recovered by decoding with jointing product code composed of shifted Luby transform (SLT)-encoded package and error packets. In this study, error correction scheme based on single feedback of SLT-encoded package was adopted for the recovery of received partial error packets over the erasure channel. The scheme of an MP decoder with an error correction code was proposed, and expand shifted robust soliton distribution (ESRSD) appropriate for the scheme feature was designed. Experimental results indicate that the scheme effectively improves the efficiency of the decoder. Compared with the traditional shifted robust soliton distribution, the ESRSD has better decoding performance for the LT code.

The authors study the opportunistic spectrum access techniques for hybrid overlay–underlay cognitive radio networks. A secondary user (SU) chooses a channel, transmission mode and adjusts its power so that the interference limit is not crossed and its throughput is maximised. The authors assume that multiple primary user (PU) channels are available and the SU conducts spectrum sensing to access the channels. The objective is to maximise the throughput by switching between the overlay and underlay transmission modes. Using finite-horizon partially observable Markov decision process framework, the authors first study the optimal policies, where the PU is assumed to be in busy, concurrent or idle state, and the SU either stays idle or transmits with any of the two designed power levels. Although the PU's states are hidden, their activity statistics, transmission ranges and interference thresholds are assumed to be known. Via Monte Carlo simulation, the authors evaluate the performance of physical layer optimal policy (PLOP) and cross-layer policy (CLAP) and compare them with a fully observable optimal policy. The beliefs in each slot for both policies are updated using the forward algorithm based technique. Simulation results show that the proposed CLAP is more throughput efficient than the conventional PLOP.

In overlay-based applications, multiple overlay networks are deployed to fulfill different service requirements. A multi-overlay environment may exist in which a number of nodes simultaneously participate in the networks. When there are multiple overlay-based applications running over a set of nodes, some of the nodes take extra effort to maintain multi-overlay networks. Therefore, maintaining these co-existing overlays incurs redundant maintenance overhead. This research presents a cooperative strategy for exploiting a master–slave model to handle the common overlay-maintenance. The purpose is to eliminate the redundant maintenance overhead. To evaluate system performance, this study not only analyses various combinations of multiple overlays but also considers the effectiveness of the master selection approach. Experimental results demonstrated that the proposed cooperative strategy significantly decreases the redundant overlay-maintenance overhead. In some cases, the overall reduction ratio of maintaining multiple overlays is as high as 60%.

The downlink throughput of opportunistic-feedback multiuser wireless systems with capture effects employing maximal ratio transmission (MRT) in a Rayleigh fading environment is studied. To the best of the authors’ knowledge, MRT has not been employed to improve multiuser system throughput with capture effects. Employing MRT means that the channel fading gains between the base station (BS) and users are a chi-square distribution with 2L degrees of freedom, where L is the diversity order, as opposed to Rayleigh distribution which has been examined in detail in the literature. Thus, the main challenge is to obtain a new and compact channel capacity expression for the system in which the roles of BS and users are reversed to make it practically sound. The new downlink throughput expression is derived as a function of L, fading-gain threshold η, capture ratio z and other parameters. For large η, the capture effects are not as effective as when η is small. Effects of the capture ratio z on system throughput are also obtained. The new findings are validated using available results in the open literature.

A novel iterative receiver is proposed for relay-assisted multiuser communications in which multiple users transmit to a destination with the help of a relay and using fast frequency-hopping modulation. Each user employs a channel encoder to protect its information and facilitate interference cancellation at the receiver. The signal received at the relay is either amplified, or partially decoded with a simple energy detector, before being forwarded to the destination. The proposed iterative receiver exploits the soft outputs of a channel decoder to successively extract the maximum-likelihood symbols of the users and perform interference cancellation. Under the same spectral efficiency, simulation results demonstrate superior performance of the proposed receiver when compared to the performance of an interference cancellation scheme that was previously proposed for multiuser communications and is extended to multiuser amplify-and-forward relaying considered in this study, as well as performance of the maximum-likelihood multiuser detection for uncoded transmission.

In this study, activation cycle of turbo detection system is investigated using three-dimensional extrinsic information transfer charts. Turbo detection typically employs an iterative process of information transfer with a fixed activation schedule. In the proposed work, the activation cycle of different component decoders is adapted for each signal-to-noise ratio value using information obtained from extrinsic information transfer charts. The objective is to reach the desired reliability of estimates at a lower complexity and for that purpose an exhaustive tree search-based message passing algorithm has been adopted. The results are validated by showing that the optimum activation cycles are similar to that of fixed scheduler with matched component decoders. The resulting bit error rate curves closely approach and in some cases excel the results obtained for the fixed activation while operating at only a fraction of their complexity.

A relay communication system where its nodes are equipped with multiple antennas is considered. The relay applies a transformation matrix on its received signal and forwards it to the destination. The authors show that, given a limited relay transmit power, the transformation matrix which maximises the signal-to-noise power ratio (SNR) is almost surely a rank-one matrix. Such a singular transformation matrix prevents accurate channel estimation. As a remedy, they impose a constraint on the condition number (CN) of the relay transformation matrix. They prove that the optimal relay matrix under this new constraint has up to two distinct singular values. Thus, the relay transmits some power in all directions, and this small energy allows better channel estimation. The author's simulation results show that imposing the CN constraint on the relay matrix results in some small loss in the SNR which is quantified in this study; however, the optimal relay matrix enables the receivers to track the channel state information.

In cognitive radio networks, spectrum sensing is critical to the discovery of spectrum opportunities for secondary systems. To enhance the accuracy of spectrum sensing, cooperative sensing has been considered, but it incurs communication overhead as well as more energy consumption of secondary users. To alleviate these problems while taking advantage of cooperative sensing, the authors propose a two-step spectrum sensing scheme, where only one or a few selected sensors are involved in the first step, but the second step occurs for cooperative sensing when the outcome of the first step is uncertain to make a decision in the presence of primary users. For this, there are two thresholds for measured energy in the first step; if the sensed energy by the designated sensor in the first step is between these thresholds, the second step incurs cooperative sensing of all the other sensors; otherwise, the second step is not triggered. This way, they can enhance the probability of detection and reduce consumed energy as well as communication overhead while maintaining a reasonable sensing time. The authors’ analysis and simulation results confirm that their proposed selectively triggered cooperative sensing with two steps outperforms the conventional schemes.

Owing to the ability of improving spectrum utilisation and quality-of-service (QoS) in wireless communications, multiple-input–multiple-output (MIMO) cognitive radio (CR) network has been identified as an excellent choice for the next generation communication. To protect primary users (PUs) from excessive interference while ensuring a meaningful QoS of secondary users (SUs), one key challenge of such system is the joint design of transceiver beamforming for SUs. In this study, the authors investigate the beamforming in MIMO CR network, and two optimisation problems in terms of the minimisation of the total transmission power and the maximisation of the smallest received signal-to-interference-plus-noise ratio (SINR) are considered. The problems can be formulated as indefinite quadratic optimisation programs which are known to be non-convex NP-hard. Hence, a distributed algorithm based on semi-definite programming and minimum-mean-squared-error is proposed to achieve the optimal beamforming weight vector. The findings of this study demonstrated that the proposed algorithm outperforms the existing ones with respect to the total transmitted power and SUs SINR.

In this study, a network acknowledgement-based and error-propagation-aware (NEPA) importance model for H.264/AVC video packet is proposed. Unlike those existing models, the network acknowledgement information is firstly studied to predict the video importance in the author's NEPA model. As a result, the authors can dynamically predict the importance of the current video packet, when its referenced frames are lost. Moreover, by means of analysing the reference relationships among the macro-blocks (MBs), an error propagation/conceal map is drawn to accurately estimate the error propagation effect. The simulation results demonstrate that their NEPA model could achieve an acceptable accuracy for any video sequence as long as its group of pictures (GoP) size is not too large. Furthermore, an application example which adopts the NEPA model in High Speed Downlink Packet Access scheduling system demonstrates the effectiveness of the NEPA model.

Increase in number of mobile users, generates unbalanced load traffic in wireless network. In this study, a load-balancing solution is investigated in order to optimise quality of service. An intelligent distributed antenna system (IDAS) fed by a base transceiver station (BTS) has the ability to distribute the cellular capacity over a given geographic area depending on the time-varying traffic. A virtual cell network is an IDAS with capacity routing capability. To enable load balancing among distributed antenna modules, the authors dynamically allocate the remote antenna modules to the BTS sectors. A self-organised network of virtual cells is formulated as an optimisation problem, which attempts to balance traffic load and minimises the hand-offs as two important cost factors in the network. Two evolutionary algorithms are proposed for optimisation: genetic algorithm and estimation distribution algorithm. Computational results of different traffic scenarios after performing the algorithms, demonstrate that the two algorithms attain excellent key performance indicators for small-scale networks.

In this study, a dual-hop multiple-input–multiple-output relay network with the Nth-best relay selection scheme in the presence of co-channel interference is studied. Specifically, the Nth-best relay is selected based on the channel state information (CSI) of the first hop. The authors first consider the CSI is perfect feedback and derive exact as well as asymptotic closed-form expressions for the outage probability. Results reveal that the diversity order of N _R × min{N _S(K − N + 1), N _D} is achieved when there is no feedback delay, where N _S, N _R and N _D represent the number of antennas at the source, the relays and the destination, respectively, K is the number of the relays and N (1 ≤ N ≤ K) represents the rank of relay chosen. Then, they investigate the outage performance of the system with feedback delay, and exact and asymptotic outage probability expressions are also obtained. Results illustrate that outdated CSI degrades the diversity order of the system to min{N _R, N _D}, which is independent of the number of antennas at the source, the number of relays and the rank of the relay chosen. The findings of the study provide valuable insights into the practical system design.