To realise load optimisation in cellular and public wireless local area network (WLAN) interworking network, a fairness preferred throughput maximisation (FPTM) optimisation model and a particular algorithm for it named joint UE-AN association and resource allocation optimisation based on generalised benders decomposition are proposed in the study. The derived solution will give guidance on UE's access selection and resource allocation in cellular network to optimise the overall performance of the interworking network. Simulation results validate the performance on optimising access load in the interworking networks of FPTM model, which can practically enhance the effect of offloading from cellular network to WLAN and improve the total throughput.

In this study, the authors propose a novel dynamic channel assignment scheme called graph colouring based fractional frequency reuse (GC-FFR) to improve system performance for the downlink of enterprise femtocell networks based on orthogonal frequency division multiple access with frequency division duplex. In order to mitigate co-tier interference from neighbour femtocell access points, the proposed GC-FFR scheme uses a heuristic method that consists of two steps: multiple femtocell user equipment (FUE) clustering step and dynamic subchannel assignment step. Simulation results show that the proposed GC-FFR scheme outperforms other schemes in terms of the mean FUE capacity and unsatisfied FUE probability.

QR decomposition is an essential operation in various detection algorithms utilised in multiple-input multiple-output (MIMO) wireless communication systems. This study presents a Givens rotation-based QR decomposition for MIMO systems. Instead of performing QR decomposition by coordinate rotation digital computer (CORDIC) algorithms, LUT compression algorithms are employed to rapidly evaluate the trigonometric functions. The proposed approach also provides greater accuracy compared with the CORDIC algorithms. QR decomposition is performed by complex Givens rotations cascaded with real Givens rotations. In complex Givens rotations, a modified triangular systolic array is adopted to reduce the delay units of the design and hence, reducing the hardware complexity. The proposed QR decomposition algorithm is implemented in TSMC CMOS technology. It achieves the throughput of 53.5 million QR decompositions per second when operating at 214 MHz.

In this study, the authors study an energy harvesting relaying system with multiuser, in which the relay node is capable of harvesting radio-frequency energy and retransmitting data with harvested energy by employing the power splitting strategy. The joint impact of direct and relaying links is taken into account in the process of user selection, and furthermore exploited for data transmission by using the selection combing receiver. To evaluate the system performance, analytical outage probabilities regarding both amplify-and-forward (AF) and decode-and-forward (DF) relaying have been derived under Rayleigh fading channel. Furthermore, they calculate the asymptotic expressions of outage probability, and they confirm that AF relaying as well as DF relaying approaches the system diversity order of , where N denotes the user number. Numerical results are demonstrated to validate the proposed analysis as well.

This study gives a general bit-error rate expression, using Gil-Palaez lemma-based approach, of a M branch equal gain combining (EGC) receiver over two-wave diffused power (TWDP) fading channels. The expressions obtained are evaluated numerically and the results are verified using Monte Carlo simulation. Also the impact of the fading parameters δ and K on the performance of M branch-EGC has been analysed.

A cooperative cognitive radio (CR) network with multiple secondary users (or CRs) is considered. Each CR consists of an arbitrary M number of antennas. For spectrum sensing, at each CR, an improved energy detector with selection combining mechanism is assumed. Moreover, the impact of secondary user mobility on the performance of spectrum sensing is analysed. Specifically, the expression for received signal at destination is derived considering the imperfect channel state information in Rayleigh fading environment. The authors derive the expression for probability of false alarm and miss detection using arbitrary power p-based improved energy detector and analyse the error performance of the system. The area under receiver operating characteristics curve is also obtained. Simulation results are provided to verify the analysis presented in this study.

In cloud radio access network, a baseband unit (BBU) performs the baseband processing for a cluster of low-power low-cost remote radio heads (RRHs) that are connected to the BBU through low-latency fronthaul links. In this study, the authors study the optimisation of two energy-efficient compression and precoding strategies which take transmit power constraint, fronthaul capacity constraint and user specific rate constraint into account. To overcome the non-convexity nature of the original problem, they first transform the objective of the original problem into a parameterised subtractive form and obtain an approximate convex problem via the successive convex approximation. Then, an effective optimisation algorithm with provable convergence is designed to solve the effective problem. Numerical results reveal that the proposed scheme outperforms the conventional maximum sum rate and minimum total power consumption schemes in terms of the energy-efficiency criterion. In particular, compression after precoding strategy outperforms compression before precoding strategy when both of their RRHs perform the same user scheduling, while the opposite conclusion can be drawn otherwise.

In this study, a wireless powered dual-hop relay system, which consists of a source, a destination and a relay that is equipped with () receiving antennas and finite energy storage, is considered. Antenna selection scheme is employed for the relay to harvest energy from the received signals, under which the () strongest received signals are combined for information processing and the other copies of signals are used for energy harvesting. Considering Nakagami-m fading scenarios, the authors first derive the closed-form expressions for the probability density function and the cumulative distribution function of the signal-to-noise ratio with generalised selection combining (GSC), and then the exact and asymptotic analytical expressions for outage probability are derived, respectively. Finally, simulation results are presented to verify the proposed analysis model.

The potential of millimetre wave frequencies band has motivated the study of large-scale antenna arrays to improve the spectrum efficiency of massive multiple-input multiple-output wireless communications systems. However, conventional fully digital precoding schemes, which require one radio frequency (RF) chain for each antenna, are cost prohibitive and have high-power consumption. To address these hardware limitations, this study considers a hybrid precoding scheme that provides high performance in terms of spectrum efficiency. By deducing the derivative of the spectrum efficiency function with respect to the phase matrix variable of the RF precoder, an efficient RF precoding scheme based on the normalised matrix adaptive method (NMAM) is proposed. Numerical simulations show that the NMAM achieves excellent performance approaching that of fully digital precoding, with relatively low computational complexity.

The decode-and-forward multi-relay system with the presence of an eavesdropper is researched in this study. Two widely used transmission schemes are considered, namely, the best-relay selection scheme and the all-relay-based beamforming scheme. To be specific, the former scheme adopts only the single best relay among all the candidate relays that have succeeded in decoding the source signal to assist the transmission, whereas the all-relay-based beamforming scheme allows all the candidates to assist the source simultaneously in a beamforming manner. The authors reveal that in both schemes, if the total transmit power of the two hops is constrained, contradiction exists between the two means of improving physical-layer security: (i) letting more relays succeed in decoding the source signal; (ii) increasing the transmit power of the selected relay(s). The authors thus analyse the secrecy outage behaviour of the two schemes and derive expressions of secrecy outage probability (SOP), based on which, the optimal power allocation solutions are obtained. It is demonstrated that in both schemes, the analysis results match well with the simulation results. Moreover, the proposed power allocation solutions surpass the conventional average power solution in SOP in both schemes.

In wireless sensor and actuator networks, none of the existed events ordering algorithms addressed the network delay and failure link jointly. In ordering by double confirmation (OBDC), the process of events ordering cannot be completed, if the failure link existed in network. In temporal event ordering with fault tolerance (TEOFT), the rate of correct events ordering decreased dramatically if the network delay existed. However, both the network delay and failure link were all prone to happen over the wireless communication medium. Network delay usually varied over time in wireless network. To address this issue, the authors proposed a fault tolerance events ordering by aging learning (FTEOAL), in this study. FTEOAL defined the non-determined aging waiting time (AW) and aging learning time to order events without broadcasting any confirmation message. Thus FTEOAL could work while the network delay and failure link existed jointly. By aging learning, the AW and aging learning time were adjusted dynamically. The rate of correct events ordering (R) in FTEOAL thus could be converged to the expected R system required. The simulation results demonstrated that R in FTEOAL could be up to the expected R being 90% but R in TEOFT and OBDC was 10% and 0%.

Sharing a relay in cognitive radio (CR) networks in order to enhance the secondary user's (SU's) performance in an interference-limited scheme is investigated. It is assumed, by utilising hierarchical modulation, a shared relay is used simultaneously between both primary user (PU) and SU. The proposed scheme relies on both power adaptation and rate scheduling. Based on channel side information and tolerable interference limitation at the PU, the SU adapts its power and the transmission data rates are regulated by the PU's status and channels condition. Theoretical analyses and simulation results are provided to evaluate the performance of the proposed dynamic spectrum sharing scheme. It is shown that rate adaptation leads to significant improvement of the throughput of the SU, at the cost of negligible degradation in performance of the PU. The results also demonstrate that sharing CR relay with the PU can compensate the side effects of spectrum sharing and interference caused by the SU, which for instance is equivalent to ∼8 dB (low signal-to-noise ratio (low-SNR) regime) and to 15 dB (high-SNR regime) SNR improvement.

The iterative header recovery algorithm holds the potential of improving the performance of wireless communication, yet it has to face the challenge of reducing the high complexity. In this study, a method of constructing a candidate set around the observation sequence is proposed to approximate the original code space, by exploiting the channel measurement information. This approximation method narrows the decoding processing scope resulting in an effective estimation of the extrinsic information and a significant reduction of the computational complexity. The extrinsic information in soft form is derived to exploit the soft input and promote header recovery performance. Simulation results and analysis show that the approximation method not only has a comparable performance, but also decreases the computational complexity and the storage consumption, which are of great importance of practical application.

A method for predicting radio signal strength using echo state networks (ESNs) is proposed and applied to three different locations in Northern Namibia. This method aims at providing a better way for radio signal strength prediction, which leads to improvements in wireless communication planning, design and analysis. Its performance is compared with the support vector regression (SVR) method optimised for radio propagation modelling. Simulations are conducted in Python using propagation data measured from the three locations based on the following four performance measures: goodness of fit criteria; error measures; computation complexities; and F-test for statistical model comparison. Simulation results show that the ESN method gives a better prediction accuracy in terms of the goodness of fit criteria and the error measures; however, it is inferior to the SVR method in terms of computation complexities. In addition, results from the F-test also indicate that the ESN method provides a significantly better fit than the SVR method.

In wireless sensor network (WSN), during fault detection and recovery, average energy loss, and message loss occurs including the link failure. Also, the number of faulty nodes and the traffic overhead is increased with the size of WSN. In order to overcome this issue, in this study, a cluster-based fault tolerance technique using genetic algorithm is proposed. Here the network is clustered according to energy-efficient distance-based clustering algorithm. For each cluster head, a set of backup nodes are selected using genetic algorithm based on the sponsored coverage and residual energy parameters. This helps in detecting the faults occurring in cluster members and cluster heads. Simulation results show that the proposed technique minimises the energy loss and overhead.

In wireless sensor networks, an energy-efficient routing protocol plays a crucial role in extending the lifetime of the network. In order to realise this, an optimal coverage-preserving scheme (OCoPS) has been proposed by Boukerche et al. in 2005 as an add-on to the Low-energy Adaptive Clustering Hierarchy (LEACH) protocol. This scheme operates alongside another coverage-preserving scheme that excludes redundant nodes if their on-duty neighbours fully overlap in terms of their sensing ranges, hence saving energy. In this study, the authors propose a central angle decision algorithm that ensures that it does not introduce any coverage hole after applying the coverage-preserving scheme. They also propose a base station (BS)-aided clustering routing protocol with a coverage-preserving scheme (BCoPS) to assess the applicability of the authors’ proposed algorithm to routing protocols and verify the performance gains. In BCoPS, energy-intensive tasks for deployed sensor nodes are substituted by the BS to ensure longer network lifetime. The performance of the BCoPS was compared to that of LEACH and OCoPS. The results of simulations carried out in considered scenarios showed that BCoPS outperformed OCoPS by >20% in terms of network lifetime in general, and by >30% when the coverage rate was higher than 80%.

Multicarrier transmission in the form of orthogonal frequency division multiplexing (OFDM) is an efficient method to handle inter-symbol interference resulting from the frequency selectivity of the underwater acoustic (UWA) channels. OFDM can be further combined with cooperative transmission to benefit from the spatial diversity advantages and improve the performance over conventional point-to-point UWA communication systems. In this study, the authors consider a cooperative OFDM UWA communication system and investigate the outage performance for both amplify-and-forward relaying and decode-and-forward (DF) relaying. They derive expressions for bounds on outage probability and outage capacity. Monte Carlo simulations corroborate and quantify the enhanced performance of cooperative OFDM UWA communication compared with direct transmission systems. Through numerical simulations, they investigate the impact of geometry on outage probability and signal-to-noise ratio requirements in cooperative OFDM UWA communication with DF relaying. Furthermore, the authors analyse the effects of relay location and carrier frequency on the outage probability for both relaying schemes.

In this study, the authors consider the power optimisation based on the MOS (mean of score) models of different services over multi-user femtocell systems. They first formulate a mathematic model to minimise the total power consumption, subject to the MOS requirements and the network resource constraint. To solve the formulated problem, they first propose an optimal power allocation (OPA) scheme, in which the optimal power allocation and RB (resource block) assignment can be obtained by employing the Lagrange dual decomposition method. However, iterative update of the Lagrange variables leads to high complexity. To deal with this, they further propose a utility-based suboptimal power optimisation algorithm (SPA). The utility of assigning each RB to each user is defined as the power consumption difference caused by adding the RB to the set of the RBs already assigned to the user. To calculate the utility, they develop a low-complexity optimal power allocation scheme. Based on the calculated utility, each RB is assigned to the user with the maximum utility. Experimental results demonstrate that OPA can indeed acquire an upper bound of the system performance. SPA can improve the MOS of the users with acceptable complexity compared with other existing algorithms.

This study investigates the secrecy outage performance of a single-input multiple-output underlay cognitive radio network (CRN) with outdated channel state information (CSI). The confidential messages are transmitted from transmitter to the destination, while a multi-antenna eavesdropper exists. The maximal ratio combining and selection combining schemes are utilised at the receivers to improve the quality of the received signal-to-noise ratio. The exact and asymptotic closed-form expressions of secrecy outage probability are derived, and simulation results are provided to verify the authors' proposed analytical results. The results reveal that imperfect CSI of main channels deteriorates the secrecy outage performance while that of eavesdropping and interfering channels has contrary effect, and only a unity diversity order can be obtained in underlay CRNs with imperfect CSI.

As opposed to chaotic communication systems where a message signal directly modulates a broadband chaotic signal, it is also possible to indirectly utilise a chaotic signal to form a chaos-based communication system. This study proposes a class of novel broadband chaos-based coherent communication systems and demonstrates that their theoretical probability of error expressions match those of their counterpart conventional narrowband systems in the additive white Gaussian noise and the Rayleigh flat fading channel. The results are confirmed with the corresponding empirical bit error rate (BER) simulations. It is demonstrated that the chaos-based quadrature phase shift keying system offers an overall best performance while the chaos-based amplitude shift keying and frequency shift keying equivalent systems offer a possibility of performance optimisation. Most importantly, it is shown that the proposed systems outperform the chaotic communication systems in terms of BER while also being more practicable. The proposed systems thus hold high promise as the chaotic communication systems pose implementation difficulties, lack robust synchronisation techniques and are generally considered of academic interest only.