In this study, the authors address the problem of joint resource block and power allocation in ultra-dense device-to-device (D2D) networks underlaying cellular networks. They propose a fully distributed scalable scheme that ensures quality-of-service (QoS) of the cellular user equipments (CUEs) while maximising the sum rate of the D2D tier. The resource allocation problem is modelled as a Stackelberg game with pricing. The base station as the leader decides prices to be paid by the D2D users for reusing the resources of the CUEs, based on the QoS requirements of the CUEs, and broadcasts the prices. D2D pairs as followers use the pricing information and a completely uncoupled learning algorithm that guarantees Pareto optimal solution. Analytical proof is provided to establish the convergence of the learning algorithm. Simulation results show superior performance compared to two other existing schemes.

Periodic broadcast of cooperative awareness messages (CAMs) is of great importance considering safety-related applications, for a network like VANET. This study proposes a vehicle-identifier (ID)-based MAC scheme for the periodic broadcast of CAMs in a vehicular network. Each CAM generated by a vehicle is associated with a unique ID. This study uses this attribute of CAM messages while participating in the channel assessment procedure. Each vehicle weighs the random back-off number with the unique ID incorporated in their respective CAM. This eventually leads to the selection of a vehicle-ID-based random back-off number, mitigating all possible probabilities of collision due to same back-off number selection. The simulation is performed considering saturated traffic conditions, to analyse its behaviour under most critical situations. The proposed model eliminates the chances of selecting zero as the initial back-off number, eliminating any chances of consecutive freeze process. The proposed one-dimensional Markovian model is validated by MATLAB. The proposed model provides a clear depiction that it performs better than the traditional IEEE 802.11OCB used for VANET. Also, it is worth noting that the achieved results outperform the existing work in terms of average packet delay since nearly one-fourth of the contention window size is utilised throughout the simulation.

In this study, the authors examine the performance of an uplink non-orthogonal multiple access (NOMA) system with cooperative full-duplex relaying (CFR-NOMA), where the user closer to the base station (BS) is considered as a full-duplex relay to aid the transmission from the other user to the BS. The closer user first decodes the signals transmitted from the far user and then forwards them using superposition coding to the BS on top of transmitting its own information signals to the BS. First, they analyse the performance of the CFR-NOMA system in terms of the outage probability and average sum rate. Then, they analytically obtain the optimal power allocation coefficients that minimise the outage probability. They also study the optimal power allocation to maximise the average sum rate under specified constraints. Their examination demonstrates that the CFR-NOMA system can significantly outperform the uplink conventional orthogonal multiple access and uplink NOMA with half-duplex relaying system in terms of achieving a lower outage probability or a higher average sum rate.

When oriented to the needs of the future fifth generation (5G) networks, orthogonal frequency division multiplexing (OFDM), as a modulation scheme, has some drawbacks: high out-of-band emission (OOBE) of power, relatively low spectrum efficiency, and poor flexibility for allocating resources. In this study, a subband superposed OFDM (OFDM) scheme, based on a variable granularity spectrum allocation, is proposed to divide the transmission channel into several subbands considering the compromises between single-carrier and multicarrier spectrum utilisation. For accommodating the diverse 5G scenarios, appropriate signalling parameters can be independently configured among the subbands. A multistage polyphase interpolator is developed in the transmitter to reduce the implementation cost of time-domain filter depressing the OOBE. Extremely narrow frequency guard intervals between subbands are realised by filtering to maximise the spectrum utilisation. At the receiver, a subband decision feedback and feedforward equaliser, relying on the subband's oversampling architecture, is designed to utilise the diversity gains in both the Doppler and the multipath delay domains. Simulation results indicate that the spectral efficiency, in terms of the spectrum utilisation rate, is increased up to and that the bit-error-rate performance is significantly improved for the subbands experiencing high-speed mobile channels while preserving a relatively low computational complexity.

The emerging non-orthogonal multiple access (NOMA) has been considered as a promising scheme to reach the goals of 5G cellular systems. By enabling a group of mobile users (MUs) to share a same frequency channel and adopting the successive interference cancellation to mitigate the co-channel interference, NOMA can improve the spectrum efficiency compared with the orthogonal multiple access (OMA). This study proposes a joint optimisation scheme of the channel bandwidth and the transmit-power allocations for the NOMA downlink transmission, which aims at minimising the overall resource consumption cost including both the spectrum consumption and the power consumption, while satisfying the MUs' traffic requirements. In spite of the non-convexity nature of the joint optimisation problem, this study characterises the connection between the channel bandwidth and the associated transmit powers for the MUs. Based on this connection, this study transforms the joint optimisation problem into an equivalent bandwidth optimisation problem, and further proposes an efficient algorithm to compute the optimal bandwidth allocation (which enables us to derive the corresponding transmit powers for the MUs). Extensive numerical results are provided to validate the proposed algorithm and the advantage of the proposed joint channel bandwidth and power allocations for the NOMA transmission.

Non-orthogonal multiple access (NOMA) has been proposed as a promising technique for the fifth generation wireless networks. In this study, the authors investigate the performance of a cooperative relaying scheme using NOMA (termed NOMA-AF-CRS), where two sources communicate with their corresponding destinations over the same frequency simultaneously through a shared amplify-and-forward (AF) relay. First, the closed-form approximations are derived for the outage probability. The analytical results are further evaluated in the high signal-to-noise ratio region to characterise the diversity order achieved by the system. Then, the ergodic sum capacity of NOMA-AF-CRS is analysed and an upper bound to the ergodic sum capacity is derived. Finally, simulation results are presented to verify the proposed analysis and demonstrate the advantages of NOMA-AF-CRS over the conventional orthogonal multiple access techniques.

The long term evolution (LTE) cellular network, primitively designed for human-to-human communications, is attracting more and more attention in machine-to-machine communication scenarios. However, when a massive number of machine-type communication (MTC) devices require access to the network simultaneously, the existing random access mechanism in LTE networks will inevitably suffer from severe congestion. In order to address this problem for stationary MTC devices, the authors propose a novel random access scheme. In the proposed scheme, an alleviating-collision based timing-advance selection (ACTS) algorithm is designed where, aided by a special preamble placement method, the eNodeB (eNB) can estimate the number of contenders with different timing advance (T) indices. According to the estimated results, the eNB can choose the T index to be contained in the random access response information. In addition, they further analyse the number of MTC devices which could successfully access the network in each random access slot. The simulation results prove the accuracy of the throughput analysis as well as the remarkable performance of the proposed random access scheme in terms of the number of required slots to serve all the devices.

This study investigates multi-layer coding over a dirty-paper channel. First, it is demonstrated that superposition coding in such channel still achieves the capacity of interference-free additive white Gaussian noise channel when the transmitter is non-causally aware of interference signal. Then, the problem is extended to the dirty-paper block fading channel, where it is shown that in the lack of channel information at the transmitter, the so-called broadcast approach maximises the average achievable rate of such channel.

Traditional cyclic prefix-orthogonal frequency division multiplexing is a popular multicarrier modulation (MCM) scheme, which provides advantages of good bandwidth utilisation and simplicity in transceiver design. However, the waveform suffers from poor spectral utilisation due to the utilisation of rectangular window and lack of flexibility. Hence, an alternative MCM scheme based on wavelet filter-bank architecture is considered in this study for fifth-generation wireless access systems. Cyclostationarity-based joint sensing and channel equalisation is applied at the receiver side, which demonstrates improved signal detection performance. Adaptive line enhancement adaptive line enhancement (ALE)-based noise cancellation is explored to improve the sensing performance. The combined noise cancellation and sensing scheme improve the cyclostationarity-based equalisation and demodulation performance.

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.

In order to make efficient use of the benefits of smart grid, meeting the security objectives of the network seems an essential requirement. Implementation of authentication protocols on the communication among the nodes of the network plays an important role in achieving the security objectives. In this study, a lightweight authentication scheme is presented for the connection between the neighbourhood area network gateway and the control centre in the smart grid. In the proposed scheme, a lossless compression algorithm, as well as Merkel hash tree, is used to compress the data prior to cryptography. Due to the fact that large amounts of data are compressed in the compression process and then Merkel tree is applied on them, confidentiality of the data against cryptanalysis attacks has increased considerably. Security analysis of the proposed scheme indicates that the objectives of confidentiality, data integrity, and availability have been fully achieved, and the process of authentication and counteraction to the replay attack has been successfully applied. In addition, making use of the compression algorithm, as well as one time pad cryptography system, tends to reduce the computational, communication, and storage costs of the proposed scheme compared to previous scheme.

This study presents a new machine learning (support vector machine (SVM))-based cooperative spectrum sensing (CSS) model, which utilises the methods of user grouping, to reduce cooperation overhead and effectively improve detection performance. Cognitive radio users were properly grouped before the cooperative sensing process using energy data samples and an SVM model. The resulting user group which participates in cooperative sensing procedures is safe, less redundant, or the optimised user group. Three grouping algorithms are presented in this study. The first grouping algorithm divides normal and abnormal users (malicious and severely fading users) into two groups. The second grouping algorithm distinguishes redundant and non-redundant users. The third grouping algorithm establishes an optimisation model with the objective of minimising average correlation within subsets. All users are then divided into a specific number of optimised groups, only one of which is required for cooperative sensing in each time. The performances of the three algorithms were quantified in terms of the average training time, classification speed and classification accuracy. Experimental results showed the proposed algorithms achieved their intended function and outperformed a conventional machine learning-based CSS model (proposed by Karaputugala et al.) in terms of security, energy consumption, and sensing efficiency.

The upcoming 5G system is expected to utilise large-scale antenna arrays to increase the users’ data rate and system capacity. With a large number of antennas, channel estimation becomes a very critical design issue due to the adverse effects of pilot contamination. Some problems in the existing channel estimation methods studied in the literature include: (i) the complexity of signal processing on the spatial domain is very high. (ii) Channels are quite frequency selective in the spatial domain. (iii) It is not easy to obtain the second-order statistics of channels. In this study, the channel estimation issue is investigated using the signal processing in the beam domain. It is due to the salient channel sparsity at millimetre-wave frequencies that only a few beam channels need to be estimated. The authors exploit these beam channels to propose some pilot decontamination techniques: basic pilot allocation, beam-set non-overlapping allocation, intra-cell interference mitigation allocation and maximum beam power based allocation (MBPBA). Both large pilot reuse factor and beam-domain power control are also presented to supplement the proposed techniques. Simulation results show that the best method is MBPBA in terms of overhead and normalised square error.

A techno-economic analysis of the 5G enhanced mobile broadband scenario in dense urban areas has been accomplished by radio capacity modelling of probable 5G technologies within a 1 km² grid representing central London. Different density networks were modelled at 700 MHz (macro network), 3.5 GHz (micro network) and 24–27.5 GHz (hot spots) – together with 802.11ac access points. Using published data on network costs various deployment options have been evaluated for capacity, headline rate and capital expenditure/operating expense. It has been shown that reaching headline rates of 64–100 Mbps everywhere is possible with a number of different technology options. Massive increases in capacity (in excess of 100 Gbps/km²), however, can only be realistically achieved with a millimetre wave (outdoor) and 802.11ac (internally). The cost of deploying such capacity, however, will be several times that of LTE – the authors estimate a 4–5 times increase in costs for a 100 Mbps everywhere network that has ×100 capacity increase over existing LTE networks. The cost of rolling out 5G is becoming an important issue and this work provides one of the few published estimates of the economics of ultra-high capacity networks.

Cognitive radio (CR) technology enables adaptation of transmission parameters according to the operating environment and different quality of service (QoS) requirements. This feature can be applied to realise green radios as recent research trends are focused on improving the energy efficiency of wireless communication systems. A power amplifier (PA) is found to consume a major portion of energy in radio-frequency circuits for medium- and long-range transmissions. Thus, minimising PA power consumption is one of the major challenges to realise green radios. In this study, mathematical formulation of total system power consumption at CR transmitter with Class B PA is shown and its optimisation is done by parameter reconfiguration for data transmission scenario employing recently proposed nature-inspired optimisation techniques. Performance of ant lion optimiser, grasshopper optimisation algorithm, Grey wolf optimiser, Moth-flame optimisation and Whale optimisation algorithm (WOA) is compared for solving this problem in terms of different performance metrics. Simulation results show the effectiveness of WOA in minimising the system power consumption by parameter adaptation in multicarrier CR system while satisfying different QoS constraints.