In this study, the authors take into account the imperfect channel state information for beamforming (BF) scheme in a dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay network. Since the overall performance has been decided by the signal-to-interference-plus-noise ratio (SINR) at the destination, the authors derive the optimal BF weights that maximise the SINR at the desination. To evaluate the performance of the relay network, the authors also derive closed-form expressions for the outage probability and probability density function of the received SINR. Computer simulations are carried out, which show the superiority of the designed optimal BF scheme, the impacts of channel errors and antenna configurations on the performance of the MIMO AF relay systems, and the validity of the analytical expressions. It is shown that due to the channel errors, the performance of the relay network is bounded no matter how much power is injected into the system.

In this study, a new beamforming and power allocation method for cooperative cognitive radio (CR) networks is proposed. The proposed method can be deployed in systems with one primary user (PU) and arbitrary number of secondary users (SUs). By using transmit beamforming in both PU and SUs, multiple transmission with limited interference effect in the receivers can be attained. SUs get permission to use the licenced spectrum in the price of enhancing the data rate of the PU. The problem investigated in this study is to maximise the weighted sum rate in the multiple-input single-output (MISO) cooperative CR networks. Transmit powers and interference temperature in the receivers are the constraints that must be satisfied. By the virtue of cooperation with SUs, data rate of the PU is another constraint that must not be less than a predefined value. Transmit/receive duality in MISO and single-input multiple-output systems are used to obtain the beamforming weights in the transmit antennas. By defining a specific optimisation problem, power portion of each SU in cooperative transmission will be found in the way that constraint on the data rate of the PU is fulfilled. Simulation results show that by using the cooperative method presented in this study, data rate of the PU is enhanced.

In this work, a reliable topology construction protocol (RTCP) called Dual-Ring Tree scatternet with a self-routing algorithm is proposed for hybrid single-hop/multi-hop situations. To benefit from the advantages of the hybrid scenarios, a dual-ring subnet is presented as a single-hop solution for one dense area, while a tree-shaped subnet is designed as a multi-hop solution for other sparse areas. To the best of the author's knowledge, this is the first time that such an algorithm has been presented to deal with the hybrid scenarios. Since the dual-ring structure serves as the core network design, the resulting architecture demonstrates better fault tolerance capability than the conventional single ring networks do. In addition, a self-routing protocol is introduced to efficiently deliver packets over the scatternet. Simulation results suggest that the RTCP scheme outperforms conventional Bluetooth hybrid ring tree (BlueHRT) and Bluetree methods in terms of routing performance and network survivability for Bluetooth ad hoc networks.

In conventional schedule-based wireless transmission system, frequent interactions between devices and access networks lead to significant signalling overhead, and thus limit the development of low-latency applications. Contention-based data transmission (CBDT) is widely used as a promising solution to address the above issues. In this study, the authors propose a detection-based retransmission scheme for CBDT to further reduce the delay-outage probability which cannot be avoided due to collision. In this scheme, each device simultaneously monitors the occupied resource blocks during data transmission. When a collision event is detected, the retransmission for this packet is determined without waiting for the acknowledgment message from the receiver. The reliability performance is significantly improved for low-latency applications, since the possible retransmission times for each packet is increased within the limited transmission period. In addition, the impacts of imperfect detection on extra transmission load and packet loss are analysed in detail. The simulation and analytical results demonstrate that the detection-based scheme significantly improves the reliability of CBDT.

This study focuses on robust Tomlinson–Harashima precoding transceiver design for multi-cell multiple-input–multiple-output interference channel with statistical channel state information error. The objective is formulated to minimise the maximum per-user mean square error (MSE) with per-transmitter power constraint. Since the problem is not jointly convex, an approximated method is proposed. The authors optimise the receiver matrix to be minimum MSE form as well as derive the optimisation problems of transmitter matrix and feedback matrix to be second-order cone programming, respectively. By use of the results, the three matrices are updated iteratively. The convergence of the proposed method is also proved. Simulation results show that the proposed scheme outperforms the robust linear transceiver in both MSE and bit error ratio.

Antenna beamforming is a key enabler for the deployment of reliable millimetre wave communication systems. Indoor millimetre wave network standards have adopted a multi-stage codebook-based beam training protocol with an objective to reduce the number of preamble transmissions required to identify the optimum transmit–receive beam pair. Multi-stage beam training schemes entail moderate search complexity; however certain implementation level challenges have an adverse impact on the search success efficiency. Moreover, it is desirable to reduce the complexity further in a dynamic environment with limited mobility where beam training needs to be repeated often. In this tudy, he authors develop a low-complexity algorithm for millimetre wave beam training within a heuristic numerical optimisation framework. Based on the classical Rosenbrock direct search method, he authors propose a threshold acceptance feature augmented with a divide-and-conquer strategy and direction of arrival aided initialisation, specifically to provide resilience to link blockage and enhance the search success performance, respectively. The method facilitates ease of implementation, and is applicable to generic phased array architectures irrespective of array geometry. he authors further evaluate the system bit error rate to benchmark the performance of the proposed scheme vis-a-vis optimal beamforming schemes.

Millimetre wave (mmWave) transmission is considered as one of the potential technologies in fifth generation (5G) cellular networks that could allocate more bandwidth to support the rapid growth of mobile data services. However, mmWave signals experience large path loss which can overcome by employing directional beamforming with high-dimensional antenna arrays. In this study, a downlink multiuser multiple-input multiple-output beamforming optimisation problem is considered for maximising the system utility subject to per-user quality-of-service constraint as well as per-antenna and base station transmit power constraints. The difficulty of this problem lies in its non-convex nature. To address this challenge, a weighted minimum mean square error (WMMSE)-based solution is proposed to reformulate the non-convex problem into equivalent convex one. Then, the block coordinate descent method is used to determine beamforming vectors. Moreover, the different antenna array geometries either two-dimensional (2D) such as planar array and circular array (CiA), or 3D such as conformal array and conical array (CoA) are designed at the base station and their effect on the system performance is exploited. Extensive simulations show that the performance of the proposed WMMSE-based solution with CiA and CoA geometries outperforms the comparable algorithms in terms of system throughput, system power consumption and access rate.

A non-orthogonal multiple access (NOMA) system is now considered as a promising radio access technique for next-generation networks owing to its benefits, e.g. spectral efficiency improvement. Due to the successive interference cancellation order at receivers, fairness among users in NOMA may not be guaranteed. In this study, the authors focus on -fair resource allocation in NOMA. The complexity of the considered problem is then analysed. In particular, the problem is shown to be convex when and , non-deterministic polynomial-time (NP)-hard when , and polynomial-time solvable when . Finally, simulation results are provided to examine the effects of the fairness degree on the system performance and verify the effectiveness of the proposed algorithms.

This work targets a comprehensive understanding of the impact of the serial-relaying and multiple-input-multiple-output (MIMO) fading mitigation techniques on the performance of indoor power line communication (PLC) systems. While these techniques were studied extensively under additive Gaussian noise, we aim at highlighting the implications of Nakagami-like noise on the achievable performance levels. The author derive approximate closed-form expressions for the bit error rate (BER) under Rayleigh fading and Nakagami-m background noise where the obtained approximations are very close to the exact BERs. The derived expressions are useful for evaluating the achievable diversity orders and for relating the BER to the main parameters of the PLC system in a direct and intuitive way. In this context, we analytically prove that MIMO doubles the diversity order with different combining schemes while the diversity order of a system under Nakagami-like noise is only half the diversity order that would have been obtained under Gaussian noise. The author also shows that multi-hop relaying does not enhance the diversity order.

Massive multiple-input–multiple-output (MIMO) is acknowledged as a key technology for the fifth generation of wireless communication systems, theoretically proved to be of higher throughput, better robustness, superior spectrum- and energy-efficiency with a general presumption that the channels tend to pairwise orthogonal with the increasing of the asymmetrical antenna pairs. Recently, more and more researches have cast light on massive MIMO system modelling. However, few investigations have been done on spatial characteristics of massive MIMO systems, especially the systems equipped with more than 100 antennas. This study focuses on the massive MIMO channel spatial characteristics based on indoor line-of-sight radio propagation measurement at 1.4725 GHz, and extracts spatial parameters such as angle of arrival, angle of departure and power azimuth spectrum from experimental data. The angles of departure (AODs) show a linear decrease along the linear antenna array, which are in agreement with the simulation of the ray tracing. On the basis of the realistic results of angular spread and the Gaussian density model, the investigation proves that antenna elements are deeply correlated and the envelope correlation coefficients show negative exponential down-trend with the increasing of antenna spacing in massive MIMO systems.

To meet the spectrum requirement in the future wireless communication system, the m-ary phase position shift keying as a type of the spectrally efficient modulation has been considered in this study. However, the inter-symbol interference (ISI), the waveform distortion and the non-white noise are introduced by the band-pass infinite impulse response filters, which is adopted to limit the signal bandwidth and eliminate the out-band interference. The traditional demodulation methods based on impacting filter or matched filter cannot work well in these scenarios. Therefore, a neural network (NN)-based demodulator is proposed to solve the problem of waveform distortion. Additionally, a novel NN-based iterative decision feedback (IDF) demodulator is also proposed to further reduce the ISI iteratively by using the previous estimated symbol information. Simulation results show that both the NN-based demodulator and the NN-based IDF demodulator can greatly outperform the traditional demodulation methods in the band-limited communication system, and the NN-based IDF demodulator achieves better performance than the normal NN-based demodulator.

The common outage performance of an amplify-and-forward two-hop two-user channel is studied in the presence of multiple independent interferers at the destination. First, the exact integral form expression of the common outage probability is derived. Then, in order to decrease the computation complexity, a closed-form approximation of the common outage probability is derived. Finally, the asymptotic analysis is performed based on the approximation expression. Numerical results demonstrate that the integral form of the common outage probability, the corresponding approximation and the asymptotic results match well with the Monte Carlo simulations.

For a joint source–channel coding system based on double protograph low-density parity-check codes, the exchange of extrinsic information through edge connection between the source code and channel code is essential for good performance. In this study, the relationship between the performance and edge connection in the tanner graph is analysed and it has never been seen in the literature to the authors' knowledge. Both the joint protograph extrinsic information transfer and simulation results indicate that the edge connection should be optimised in practical applications since it plays an important role in the bit error rate performance and an optimisation scheme for the edge connection is put forward to enhance performance.

Cognitive radio and full duplex transmissions are regarded as two effective techniques to improve the spectral efficiency. By combining the two promising techniques, the problem of power allocation for bi-directional full duplex underlay cognitive spectrum sharing is studied. To protect the primary transmission, consider both the instantaneous and statistical channel state information to adjust the transmit powers of secondary users to avoid causing intolerable interference to the primary users. The corresponding quality-of-service (QoS) constraints are determined for the primary system. On this basis, propose optimal power allocation schemes to facilitate the secondary transmission while guaranteeing the primary QoS constraint. Simulation results are provided to verify the efficiency of proposed schemes in improving the system capacity.

Power-line communications (PLCs) endure a severe transmission channel distortion due to Gaussian noise, impulsive noise, and multipath self-interference. Conventional transmission models with white Gaussian noise would be very inappropriate and impair the necessary channel estimation drastically to the PLC receivers. In this study, a statistical model for impulsive noise, namely Middleton Class A model, is employed for Gaussian information sources. Robust channel estimation algorithms based on a novel parameter estimation scheme are established thereby. Superior to the conventional robust-least-square estimation algorithms, the authors' proposed new adaptive robust-least-square estimation methods can take advantage of the statistical parameter estimation for impulsive noise. The studies on the theoretical and practical aspects of their proposed new parameter estimator are also presented.