In this study, the authors propose a secure cooperative spectrum sensing algorithm that is based on compressive sampling theory and employed in wide-band cognitive radio network. The proposed algorithm seeks to reduce the hardware complexity of the spectrum sensing node by reducing the reported data from this node to the fusion centre and/or other sensing nodes. Due to the spatial correlation between the received primary users' signals at the sensing nodes, the difference between the measurement vectors of any two sensing nodes is expected to be very small when it is compared with the value of the measurement vector itself. The expected reduction in the dynamic range of the difference measurement vector motivates to use the 1-bit quantiser where only 10bit per measurement is retained, representing its sign. Moreover, the proposed algorithm is impregnable against spectrum sensing data falsification attacks. Both the fusion centre and sensing nodes utilise the proposed authentication algorithm to pick out data from the trustful nodes only to estimate its output data. According to the simulation results, the proposed system guarantees more safeguard to the license primary user while preserves the unlicensed secondary user throughput.

Compensating for the considerable propagation loss, millimetre-wave communication systems adopt large antenna arrays and beamforming technologies to obtain high antenna gains. The beamforming training is rather time-consuming especially in multi-user cases. To reduce the training overhead, a new fast multi-user training scheme based on Compressed Sensing theory is proposed. This scheme includes a multi-user training algorithm and a corresponding semi-fixed semi-random codebook design strategy. The base station (BS) simultaneously broadcasts the training pilots to all user equipments (UEs). Then all UEs independently conduct the proposed training algorithm from channel responses. Finally, all UEs send back the training results to the BS. Compared to the exhaustive search algorithm's training overhead , the cost of the proposed scheme is only , where and denote the number of beam patterns in the receiver and the transmitter. Simulation results show that the proposed scheme achieves excellent performance in high SNR (signal-to-noise ratio) cases with only performance difference from the theoretical bound. And in contrast with other Compressed Sensing schemes with random codebooks, the proposed scheme reduces the sensitivity to transmission SNR and improves approximately 3 dB performance in low SNR cases.

In this study, the authors consider a two-way relaying (TWR) system with source terminals and and a relay terminal . They analyse the performance of a fixed-gain amplify-and-forward-based TWR system over Rayleigh fading channels with co-channel interference at all the terminals. Expressions are derived for the outage probability of the system at a medium-to-high signal-to-interference-plus-noise ratio (SINR) range. They also obtain the expression for the value of outage floor and use this to optimise relay location and power allocation. Simulation results demonstrate accuracy of the derived expressions in different SINR ranges.

In this study, a new greedy-based algorithm for sparse channel estimation in frequency-division duplexing massive multiple-input multiple-output (MIMO) systems is introduced. The proposed algorithm is able to acquire the channel with no information about the channel model such as the sparsity order, statistical bound on sparsity support, and special features of the channel. In other words, the authors assume that the massive channel is totally unknown and then exploit the inherent property of correlation between measurements and the sensing matrix to estimate the channel, which is available at the user side. By utilising this property, a halting parameter is defined as the halting threshold instead of known prior information assumed in the conventional greedy algorithms. Furthermore, the lower and upper bounds of the halting parameter are obtained that helps the algorithm to take the suitable values of this parameter and by considering the lower bound as the values of the halting parameter, the algorithm can prevent from missing the original channel bins. Simulation results demonstrate that the proposed algorithm outperforms its counterparts in terms of normalised mean square error while it faces a completely unknown massive MIMO channel.

The design problem associated with robust downlink beamforming in multicast, multigroup, multicell wireless systems is addressed. The channel state information (CSI) of users is assumed to be imperfect and the uncertainty of CSI is modelled using the Frobenius norm. The objective is to optimise the signal-to-interference-plus-noise ratio over all users with a constraint on the maximum total transmitted power. This was achieved through a robust solution using the successive convex approximation (SCA) method. The beamforming problem is treated as a bi-convex problem, which is solved using the iterate-alternative convex technique. Here, the CSI uncertainty is addressed using a convex package through the non-monotone spectral projected gradient method and the beamforming vector is extracted using the SCA method. Also, the authors offer the required condition to extract the beamform vector using the SCA method through a suboptimal solution that always addressed before using different beamforming methods. Their simulation results examine all proposed system parameters in order to show convergence and feasibility of the solution. They also compare the solution with a suboptimal solution and the quality of service method for imperfect CSI in downlink beamforming. Numerical results show that the robust solution achieves the best power efficiency for practical solutions.

In mobile communication networks, the handover procedure enables a continuous communication service for users on the move. However, handovers, handover failures, and ping-pong handovers increase the signalling load in the network, resulting in the use of network resources and a reduction of the system throughput. They also add delay to the transmitted data and even the risk of disconnection in detriment to the quality of experience of the user. Therefore, reducing the handover processes and their errors is an important issue, particularly, in heterogeneous networks that are more prone to trigger handovers due to their configuration with overlapped cells of different sizes. Additionally, heterogeneous networks present a higher percentage of handover errors in comparison with networks only formed by macro-cells. In this work, the authors present a method to adapt the start of the handover based on a prediction of the signal-to-interference-plus-noise ratio. Their proposal reduces handover failures and the probability of ping-pong handovers simultaneously, by determining the appropriate time to safely perform the handover.

The authors study the optimal design of simultaneous wireless information and power transfer relaying in bidirectional non-regenerative relay networks. They consider both power splitting relaying and time switching relaying. Since there are two opposite traffic flows between two sources, they characterise the transmission rate performance by the minimum rate of two opposite traffic flows. Specifically, they first obtain closed-form expressions for the optimum power splitting and time switching coefficients to maximise the minimum transmission rate of bidirectional non-regenerative relaying. They also derive the resulting maximum transmission rate expressions. Furthermore, they consider a minimum input radio frequency (RF) power level to turn on diodes, and derive the turn-on probability of the RF energy harvesting circuit when two channels experience independent Rayleigh fading. Numerical results confirm that the authors' analyses exactly match with simulation results and that the two relaying strategies with optimum coefficients give almost the same transmission rate performance.

The caching in fifth generation (5G) networks has been considered as a promising technique to reduce the duplicate traffic transmission and improve the users' quality of experience (QoE). Although many works have been done for caching in 5G networks, most of them focus on the content caching policy design to optimise the users' QoE, the issue to realise the energy efficiency of the whole network is not fully considered. Therefore, in this study, by introducing the hierarchical cooperative caching property, i.e. the core gateway and the base stations can cooperative cache the content, the authors study the problem of the hierarchical cooperative caching policy to realise the energy efficiency. They then formulate the hierarchical cooperative content placement problem as an integer programming problem to minimise the total energy consumption. Also, to reduce the computation complexity, the optimisation algorithm based on the idea of quantum-inspired evolutionary is proposed, which has the fast convergence and approximate to the optimal solution. Finally, extensive simulation results are illustrated to demonstrate the performance of the proposed scheme.

This study focuses on spectrum sensing under Laplacian noise. To mitigate the negative effects caused by the heavy-tailed behaviour of Laplacian noise, the fractional lower order moments (FLOM) technology is employed to pre-process the received samples before spectrum sensing. Through exploiting the asymmetrical difference between the distribution for the FLOM of received samples in the absence and presence of primary users, the authors formulate the spectrum sensing problem under Laplacian noise as a unilateral goodness-of-fit (GoF) test problem. Based on this test problem, they propose a new GoF-based detector, which is called a unilateral left-tail Anderson Darling (ULAD) detector. The analytical expressions for the theoretical performance, in terms of false-alarm and detection probabilities, of the ULAD are derived. Moreover, a closed-form expression for the optimal detection threshold is also derived to minimise the total error rate. Simulation results are provided to validate the theoretical analyses and to demonstrate the superior performance of the proposed detector than others.

Spectrum handoff has a negative impact on the performance of cognitive users (CUs) in terms of handoff delay in cognitive radio (CR) networks. In this study, a pre-emptive resume priority (PRP) M/G/1/K queuing network model is proposed with a finite number of allowable interruptions for proactive decision spectrum handoff scheme in order to minimise the cumulative handoff delay (CHD) and total service time (TST) for CUs. The CHD and TST for different proactive decision handoff schemes: non-switching spectrum handoff, switching spectrum handoff, and random spectrum handoff are modeled under the proposed PRP M/G/1/K queuing network model. Comprehensive results of CHD and TST are obtained to compare the performances of the proactive decision handoff schemes under the proposed PRP M/G/1/K queuing network model. This study also presents an analytical framework to examine the effect of primary users activity and buffer size on spectrum handoff delay performance with a finite number of allowable interruptions in a CR network. Thereafter, the optimal buffer size (K) is estimated for the proposed PRP M/G/1/K queuing network model, which gives performance similar to the infinite buffer size PRP M/G/1 queuing model with negligible (<1%) error.

In cognitive radio (CR) systems, secondary users (SUs) equipped with a single transceiver are unable to sense and transmit simultaneously. Due to this limitation, most of the models intended to describe spectrum sensing focus on pre-transmission sensing and consider that primary users (PUs) only change their activity state in the beginning of each SU's operation cycle. This study characterises the more practical scenario which considers the reappearing PU during ongoing SU communication. The authors study a quickest detection scheme that uses an error vector magnitude (EVM) of the received signal. They consider two models of PUs namely an unknown deterministic signal and a Gaussian random signal with additive white Gaussian noise. The probability density function of the EVM test statistic is derived for both cases. The authors develop an exact quickest detection scheme by using a traditional cumulative sum (CUSUM) test. They show that CUSUM EVM outperforms CUSUM ED using theoretical analysis and numerical simulations.

Non-orthogonal multiple access has recently emerged as a promising multiple access technique for future wireless technology. In this study, the authors investigate superposition coding in a downlink cooperative cellular system based on the orthogonal frequency division multiplexing (OFDM) modulation in the presence of frequency selective multipath fading channels, a setup that has not been studied before. Specifically, the base station communicates with two paired mobile users simultaneously via the OFDM modulation with the help of a half-duplex relay under either the decode-and-forward (DF) or amplify-and-forward (AF) scheme, where the power allocation between two mobile users depends on the statistical channel state information (CSI) rather than perfect CSI. They derive the ergodic rate regions under Rayleigh fading channels and present an ad-hoc approach to determine the power splitting parameters when the target data rates are given. Simulation results based on the outage probabilities show that superposition coding consistently outperforms frequency division, however, the relative advantage of the DF and AF schemes in a superposition-coded OFDM relay system depends on the system geometry.

In this study, they authors introduce a suboptimal training sequence for burst-mode continuous phase modulation. The optimum training sequence has been prove to be optimal for the estimates of carrier frequency offset, carrier phase error and timing error. However, the optimum sequence brings high side-lobe of the log-likelihood function (LLF), that is not benefit for detecting the start of the sequence (SOS). Thus, the suboptimal sequence is designed to improve the SOS performance through decreasing the side-log effect of the LLF. Meanwhile, the proposed sequence can minimise the Cramer-Rao bound for the joint estimation of carrier frequency offset, carrier phase error and symbol timing error. The data-aided maximum likelihood algorithms for timing error and phase error estimation are derived for evaluating the performance of the proposed sequence. The simulation results demonstrate that the new sequence provides better performance on start detection of the sequence than the optimal one. The performance of timing and carrier phase recovery is also close to the ideal synchronisation performance.

Zero correlation zone (ZCZ) sequences have received much research attention in many practical applications, such as quasi-synchronous code-division multiple-access systems and MIMO systems. In this study, three constructions of multiple polyphase ZCZ sequence sets with low inter-set cross-correlation property are proposed. The resultant periodic ZCZ sequence sets are optimal with respect to the theoretical bound and have new parameters uncovered in the literature. Consequently, a great deal of flexibility may be provided in the choice of periodic optimal ZCZ sequence sets with good inter-set cross-correlation property for their applications.

In this study, the authors consider the sensors' connection model design and energy optimisation of routing protocol in wireless sensor networks based on the Gaussian network connection model. Accordingly, by the node-symmetric and four different directions to four adjacent nodes of each node in the Gaussian network model, the study recommends a new wireless sensor network connection model, on which the network area will be divided into some virtual square grids. In the new wireless sensor network connection model, they describe each virtual square grid as a node in the Gaussian network, therefrom, they propose a routing method, which is a combination of the shortest path routing protocol in the Gaussian network and clustering protocol to improve the routing efficiency of the wireless sensor network. Some simulations were implemented in NS2, the results show that the proposed routing is very good.

In this study, the authors propose a class of exclusive OR (XOR)-based maximum distance separable (MDS) array codes, referred to as horizontal–vertical–diagonal (HVD) codes, which can tolerate triple disk failures with optimal update complexity. The HVD code has a similar data/parity layout to the horizontal–vertical (HV) code and has many figures of merits as the HV code. Also, an efficient recovery algorithm is proposed, which can be implemented to accelerate the recovery process of double disk failures by making full use of all kinds of parities in the HVD code. The authors evaluate the encoding/decoding efficiency of the HVD code by comparing the number of XORs and the number of disk reads with other MDS array codes. Results show that the HVD code inherits most of the merits of the HV code and requires less number of disk reads when recovering single disk failure.

Cluster based cooperative spectrum sensing (CSS) in cognitive radio networks provides for reduced sensing error, reporting delays and improved energy efficiency, in a practical network. However, achieving these advantages depend on suitably selecting a cluster head and adopting an appropriate fusion rule. This work investigates a new hard decision fusion rule, which makes the cluster heads non-cooperative sensing result a necessary condition for cooperative decision making. The study also presents a comparative numerical study of three existing cluster head selection schemes with respect to their performance in CSS, under varying detection thresholds and cluster's heterogeneity. A robust and generalised cluster head selection scheme that overcomes the limitations of the existing schemes is thereafter proposed. The performance of the existing cluster head selection schemes depends on the distribution of secondary users relative to the primary user's position, and the detection threshold. Simulation results show that the proposed cluster head selection scheme can overcome the limitations of existing schemes. Furthermore, the hard decision fusion rule being proposed indicates improved performance compared with the OR rule in minimising the total error rate over Rayleigh fading channels.

In this study, the performance analyses of the proposed turbo-coded orthogonal frequency division multiplexing (T-COFDM) are investigated over the power-line communication with lognormal channel gain based on derived effective complex-valued ratio distributions of the individual and combined noise samples at the zero-forcing equaliser output. The effective noise samples are derived in the presence of Nakagami-m background interference (BI) noise, Middleton class A impulsive noise (MCAIN) and their combination. The performance of the turbo code has been improved by computing the exact log-likelihood ratio using derived distributions, with the derivation of pairwise error probability and the average upper-bounds (AUBs). Moreover, the bit error rate (BER) degradation in the conventional T-COFDM system has been improved by deriving two clipping thresholds to combat the effect of the non-Gaussian noise, the first one has been derived in the presence of the impulsive noise only modelled by MCAIN model and the second one in the presence of combined Nakagami-m BI noise and MCAIN model. Monte Carlo simulations demonstrate the significant BER improvements of the proposed T-COFDM system compared to the improved conventional T-COFDM system with a close agreement to the AUBs derivation and analytical BER expression.

The downlink communication of a single-cell millimetre wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) system with hybrid beamforming (HBF) is studied. The authors consider the system with in-phase and quadrature-phase imbalance (IQI) at the radio-frequency (RF) chains. Firstly, they provide the HBF designs based on the complex-valued effective channel and augmented real-valued equivalent channel, respectively. Then, they study the impact of IQI on the achievable downlink sum rate and derive the approximation of the achievable sum rate on various HBF schemes. Results show that the sum rate of the receiver designed based on real-valued equivalent channel increases without bound, but the performance of the receiver designed based on complex-valued presentation exhibits a finite ceiling, as the number of BS antennas increases. Furthermore, both receivers limit to finite ceiling rates due to IQI as the transmit power goes to infinity. Moreover, the HBF system reaches a peak sum rate at a certain value of the number of users, and IQI has an ignorable impact on the value. Meanwhile, the impact of the amplitude imbalance is more significant on the performance degradation of the HBF system than that of the phase imbalance.

In this study, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the impact of Doppler frequency shift on minimum mean square error receiver is derived for Walsh Hadamard (WH) and polyphase carrier interferometry (CI) code based multicarrier spread orthogonal frequency division multiplexing (SOFDM) transmission scheme over integrated satellite–terrestrial broadcast system. Additionally, bit error rate and spectral efficiency are analysed based on the obtained SINR expression. To examine that, three-state Fontan land mobile satellite, and six-path typical urban and rural area terrestrial channel models are employed. This analysis is performed to substantiate variable bit rate (VBR) quality of service at the physical layer of digital video broadcast satellite handheld (DVB-SH)-A architecture, the provision of which is absent in DVB-SH standard. VBR is assumed for SOFDM. The results illustrate that WH-SOFDM outperforms CI-SOFDM under both performance measures in all the three channel environments. Further, pilot-based channel estimation technique is performed and the estimated error variance is evaluated for VBR WH/CI-SOFDM. Later, block-wise system computational complexity of WH/CI-SOFDM schemes is evaluated. It is shown that, CI-SOFDM is a relatively more complex system than WH-SOFDM. Thus, a trade-off is present between the achieved performance gain and system complexity.

Impulsive noises severely degrade the performance of a communication system. This study deals with the performance of the soft decision decoder for low-density parity-check codes over impulsive noise channels. To simplify the calculation of log likelihood ratio (LLR) and cooperate with the soft decision decoder, a new non-linear approximation named inverse demapper of LLR over the impulsive noise is proposed. Without carrying the noise statistics, the inverse demapper performs close to the optimal demapper. In addition, the density evolution is employed to obtain optimal parameters of the inverse demapper. Then, the extrinsic information transfer chart analysis and simulation results are presented to verify the effectiveness of the authors' proposed demapper.

Aggregating a lot of subcarriers will generate high peak-to-average power ratio (PAPR) which makes the overall system performance degradation. Among the existing PAPR reduction methods for orthogonal frequency-division multiplexing (OFDM)-based systems, iterative clipping and filtering (ICF) may be easy to implement, but ICF may cause signal distortion, so that the system cannot approximate the processed signals to the original signals which degrades error rates at receivers. Here, the authors proposed a new method based on ICF with smoothed clipping signals, and find the optimised filter to achieve the minimum error vector magnitude and efficiently reduce PAPR. Owing to the lack of a wide range of continuous bandwidth, the Third Generation Partnership Project proposed carrier aggregation (CA) technology in LTE-advanced systems. CA can aggregate many contiguous or non-contiguous fragment spectrums for supporting larger bandwidth and higher peak data rate. Here, the authors also evaluate the developed PAPR reduction scheme for the use in CA scenarios. The efficacy of the proposed scheme is demonstrated in the simulation results.