In this study, the authors investigate the energy-efficient resource allocation in a multiuser downlink multiple-input multiple-output (MIMO) orthogonal frequency-division multiple access system with block diagonalisation. Unlike the existing works in which one subcarrier is exclusively used, they consider the multiple user MIMO case on each subcarrier. An optimisation problem involving user selection, receive-signal subspace selection and power allocation is formulated to maximise the system energy efficiency (EE). As optimising the orientation of the receive-signal subspace is difficult, they considered two simpler resource allocation schemes, subspace selection scheme and user selection scheme. The two optimisation problems for the subspace and user selection schemes can be rewritten as a unified problem involving set selection and power allocation. By relaxing the combinatorial variables, they obtain an optimal joint set selection and power allocation solution, which can be directly applied to the original problem in most cases. To further reduce the complexity of the algorithm, they also develop a preselection technique for the user and received-signal subspace on each subcarrier. Through simulations, they discuss the impact of different parameters on the EE for the two schemes and show that the proposed suboptimal algorithm can achieve a close performance to the optimal algorithm.

In this paper, the authors show that using physical layer network coding (PNC) in wireless relay systems does not always increase throughput performance, and to achieve maximum throughput, PNC should be exploited intelligently regarding to the channel conditions. In this study, they propose a selective PNC (SPNC) scheme in bidirectional relay systems for binary phase shift keying. In the proposed scheme, the relay chooses either to detect network-coded data from superimposed signal by PNC scheme or single source data by a so-called single node detection (SND) scheme, based on which offers more end-to-end throughput for current channel realisation. They analytically determine the region of channel state plane in which SPNC selects SND scheme. Also, they obtain expressions for instantaneous bit error rates (BERs) of PNC and SND protocols. Moreover, they derive upper bounds in closed-form for average BERs of PNC and SND schemes during multiple access phase at the relay. Then, they investigate SPNC with high-order modulations. Simulations and analytical results confirm that SPNC achieves considerable throughput gain over PNC in Rayleigh fading channels.

The broadcast nature of communication systems opens the possibility for attackers to eavesdrop the data and compromise data confidentiality. This study takes the information theoretic security at the physical layer of single-input single-output orthogonal frequency division multiplexing (SISO-OFDM) wiretap system into account, in which, different signal-to-noise ratio (SNR) values on the legitimate and eavesdropper's receivers are assumed. The optimisation problem for secure resource allocation is formulated. Then, the secrecy rate of the system is used as the objective function for resource allocation. Finally, a power allocation strategy is obtained. The upper bound of the secrecy capacity of the single-user system is proposed as a linear function of legitimate receiver's SNR (dB), based on the mentioned strategy. In addition, an iterative power allocation algorithm is proposed for two-user SISO-OFDM wiretap channel. Results showed that the proposed algorithm is fast and converges to the optimal value in the second iteration. The upper bound linear model is valid in a two-user case when there is a relatively large difference between Bob and Eve SNRs.

Deploying a networked set of robots is an effective way to serve applications in environments where human intervention is impossible or possess risks. For example, a team of robots can assist rescuers to map, navigate indoor hazardous areas in rescue operation. Collaboration among the robots is very essential in these applications in order to efficiently achieve the aimed goals in a timely manner. Realising such a collaborative operation autonomously in the absence of GPS services is a challenge. This study tackles this challenge assuming sensors/landmarks are present in the deployment area. Each sensor/landmark requires a specific number of robots to perform certain tasks. A spatial–temporal coverage solution is pursued to maintain connectivity and overcome the shortage of available robots. Dynamic coverage problem is formulated as potential fields where landmarks and nodes exert virtual forces among each other based on coverage demand and overlapped area. The proposed approach has been validated through extensive simulation using NS3 simulator and real experimentation using EV3 robots. The proposed approached has shown maximal task satisfaction compared with random waypoint and very close behaviour compared with a centralised approach (Hungarian method).

Energy efficiency (EE) is an important criterion in devising emerging mobile networks. One of the techniques that has been proposed to reduce energy consumption of base stations (BSs) in cellular networks is BS sleep mode. In this work, the effect of sleep mode on throughput, coverage and EE of relay assisted heterogeneous cellular networks is analysed. A cooperative relay-BS sleep mode-based algorithm for heterogeneous networks is proposed and its performance analytically evaluated. It is shown that the proposed algorithm has a considerably higher EE compared with a homogeneous network without sleep mode or a heterogeneous network with relay-only sleep mode.

Full-duplex relay-assisted device-to-device (D2D) communication underlaying fifth generation cellular networks allow devices to exchange information directly and extend coverage via relay strategy. In this study, the authors consider such a scenario, where the D2D communications assisted by fixed-location full-duplex relays in interference existing circumstance. Different from previous works, they assume that there are two types of users, cellular users and D2D users. They investigate power control problem and coverage probability performance in the previously assumed situation. Therefore, an effective power control scheme is of great importance to suppress interference between D2D and cellular communications, which can improve the total system throughput and spectral efficiency. To describe it, they formulate a power control optimisation problem for cellular communication and propose a simple on–off power control algorithm for D2D communication. They also obtain an analytic expression for the coverage probability of the cellular link using stochastic geometry according to the proposed algorithm. Simulation results follow to show the rates of both cellular and D2D links in the various numbers of D2D transceivers.

In this study, a joint detection and generalised sum-product decoding algorithm for a two-way relay physical-layer network coding (PLNC) system in power line communication is proposed. Distinct from the existing works which mainly focused on separate or iterative PLNC detection and decoding, the proposed algorithm is a belief propagation-based joint PLNC detection and decoding algorithm, which integrates the PLNC, symbol detector and channel decoder together. The proposed algorithm is described by a joint factor graph, in which the detection nodes are connected to the factor graph of a generalised sum-product decoder. The PLNC demodulation is redesigned to make sure that the degree of each detection node in the joint factor graph is more than one. A low computational complexity solution of the proposed joint decoding algorithm based on the majority-logic algorithm is also proposed. The simulation results reveal the validity of the proposed algorithms.

Up to now, some related results on the upper bounds of error probability have been concluded for some linear modulations with orthogonal space–time block codes in multiple-input and multiple-output (MIMO) systems. For instance, the performance of MIMO systems with antenna selection (AS) has been investigated widely, whereas in non-linear modulations, i.e. continuous phase modulation (CPM), there are few relevant literatures found to this date. With this motivation, this study derives upper bound of the error probability of Alamouti scheme with transmit AS (TAS) in CPM-MIMO systems. First, a new form of signal matrix for CPM-MIMO system is given. Then, the pair wise probability conditioned on fading channel statistics is written availably by computing the difference of signal matrix. Moreover, the probability distribution function is obtained by employing order statistics theory. Furthermore, the tight upper bounds of the frame error rate are derived. Finally, simulated results verify the accuracy of the theoretical analysis.

In this study, the physical layer resource allocation in orthogonal frequency-division multiple access (OFDMA) systems is studied by considering the non-linear effects of power amplifier (PA). The non-linearity produces cross-correlation among the subcarriers and results in deteriorating the OFDMA subcarriers orthogonality. Hence, the signal-to-interference ratio (SIR) of the output signal of PA for OFDMA signal with different power scaling factors for subcarriers is derived. Then, the theoretical SIR is verified by simulation result. Next, the optimisation problem is designed to maximise the total achievable downlink rate of all users by assigning subcarriers and power scaling factors. This non-convex problem is solved by comprehensive learning particle swarm optimisation. The simulation results show that when PA is non-linear, better total rate is achieved by considering non-linearity in resource allocation compared with the conventional resource allocation techniques.

Point-to-point communication channels with phase noise have been studied extensively. To the best of the authors’ knowledge, the broadcast channel (BC) with phase noise has not been studied yet. In this study, having reviewed definitions of the channels with phase noise, the authors analyse capacity region of the BC impaired by Wiener phase noise and additive white Gaussian noise and obtain an outer bound for the capacity region. Also, its high signal-to-noise ratio analysis is presented. Their outer bound includes the known outer bound for the point-to-point phase noise channel as its special case. Mathematical findings are explained more by simulation results.

This study considers an improved decode and forward (DF) protocol in an orthogonal frequency division multiplexing-based cooperative system, where the improved DF protocol implies that the source node is allowed to emit the same symbol in the second phase as that in the first phase, irrespective to whether the relay is idle or not. Because rate provision is one of the main design goals in wireless network, the authors construct an optimisation problem to improve the overall sum rate of the system and propose a joint power allocation and subcarrier pairing algorithm. Total power constraint and individual power constraints at the source node and the relay node will be treated differently. Both theoretical analysis and simulation results demonstrate that the authors' proposed joint algorithm for the improved DF protocol drastically harvests remarkable gains from the extra repeat transmission in the second phase and is superior to other existing methods.

The mobile communication system has become increasingly complicated with the dramatic growth of user's requirement in quality of service (QoS). The high fluctuation of traffic data makes conventional cell association schemes difficult to guarantee satisfactory service in accord with traffic demand. In this study, the authors propose a novel QoS-aware cell association scheme in a heterogeneous network. Utilising traffic prediction achieved by support vector regression, the user can decide the best cell according to the future traffic demand. The authors aim at maximising the total throughput with consideration of channel gains and blocking probability in different cells and formulate the cell association as a binary combinatorial optimisation problem. Since users are selfish for their own benefits without the global information, the authors turn this problem into a game theoretical framework. To obtain the Nash equilibrium with low computation complexity, a heuristic dynamic selection algorithm is proposed by updating selection probability which enables each user to associate with the best cell independently. Numerical simulation results show that the proposed algorithm achieves a remarkable throughput gain. The number of satisfied users increases substantially under the different density of users compared with conventional cell association schemes.

Heterogeneous cellular networks (HCNs) are usually modelled as a Poisson point process (PPP) due to mathematical tractability. However, in urban areas, small cells are more likely to cluster around hotspots rather than be uniformly distributed. Meanwhile, in reality, small cell locations are not completely independent of the macro base station (MBS) locations. To capture both features, the authors propose a new modelling method considering inter-tier dependence for a two-tier HCN, where MBSs follow a PPP, small cells follow a Matern cluster process and are not allowed to be deployed inside the MBS exclusion regions (i.e. within a prescribed distance from each MBS). Approximate expressions of the average coverage probability and the area spectral efficiency (ASE) are obtained, respectively. Simulation results confirm the accuracy of the derivations. It is observed that the model can achieve a good tradeoff between coverage and ASE, and if the small cell density in this model is kept identical to the HCN without inter-tier dependence, both coverage and ASE can benefit from involving the inter-tier dependence in the HCN.

Network slicing has been considered as one of the key technologies in the next generation mobile network (fifth generation – 5G), which can create virtual network and provide customised services on demand. Most of the current work on network slicing mainly focuses on virtualisation technology, especially in virtual resource allocation. However, caching as a significant approach to improve the content delivery and quality of experience for end-users has not been well considered in network slicing. In this study, the authors consider in-network caching combining with network slicing, and propose an efficient caching resource allocation scheme for network slicing in 5G core network. They first formulate the caching resource allocation issue as an integer linear programming model, and then propose a caching resource allocation scheme based on chemical reaction optimisation (CRO) algorithm, which can significantly improve the caching resource utilisation. The CRO algorithm is a population-based optimisation metaheuristic, which has advantages in searching optimal solution and computation complexity. Finally, extensive simulation results are presented to illustrate the performance of the proposed scheme.

Due to the high cost and power consumption, it is impractical to perform full-digital beamforming at baseband in millimetre-wave systems. Thus, as a cost-effective alternative, a hybrid beamforming (HBF) is introduced in this study. Since the HBF can be designed as a matrix factorisation problem, an effective greedy algorithm with low complexity for multiuser scenes is proposed to approach the full-digital matrix. Firstly, initialisation for partial columns of the analogue matrix is enabled by extracting the phases of the full-digital scheme. Then the singular value decomposition in low-dimension matrix can be used to obtain the rest columns of the analogue matrix. Finally, based on effective channel, the digital matrix can be easily designed. Therefore, the authors' proposed algorithm has low complexity and only needs fewer iterations. Furthermore, by handling the inter-user interference, the full-digital matrix needed for the initialisation in analogue domain can be approximated to an orthogonal matrix, which can further reduce computational complexity. Simulation results demonstrate that the proposed greedy algorithm performs very close to the optimal unconstrained solution and enjoys low complexity.