In this study, the authors address a brief survey on the half-duplex (HD) and full duplex (FD) relay based cooperative communications. Some nodes in wireless communication acting as relays can share their resource with other nodes by exploiting relaying technologies to achieve cooperative communications. Generally, the buffer-less HD relaying (HDR) limits the performance of a wireless system when the worst condition of transmitting and receiving channels of the relay occurs. The HDR is affected by pre-log factor one-half that reduces the spectral-efficiency of the wireless system. Significantly, advanced technologies in self-interference cancellation enable the FD relaying (FDR) in the cooperative wireless system to achieve high spectral efficiency. Recently, the buffer-aided FDR provides significant performance gains by exploring the concepts of Markov chain of queuing theory at relay as compared to either buffer-aided or buffer-less HDR. Finally, they outline several research challenges associated with small size, interference management, and fading channel for FDR. In addition, some research challenges remain for further investigation that is related to physical-layer security, FDR with a cross-layer approach and two-way buffer-aided FDR.

In this study, two novel multi-hop relay-assisted hybrid FSO/RF communication systems are presented and compared. In these structures, RF and FSO links, at each hop, are parallel and send data simultaneously. This is the first time that in a multi-hop hybrid FSO/RF structure, detect and forward protocol is used. In the first structure, at each hop, received signals with a higher signal-to-noise ratio are selected. However, in the second structure, at each hop, received FSO and RF signals are separately detected and forwarded and selection is done only at the last hop. Considering FSO link in negative exponential atmospheric turbulence and RF link in Rayleigh fading, for the first time, closed-form expressions are derived for outage probability () and bit error rate of the proposed structures. MATLAB simulations are provided to verify derived expressions. Results indicate that the structure with the selection at each hop has better performance than the structure with a selection at the last hop.

In this study, the authors consider multi-user millimetre wave (mmWave) multiple-input multiple-output (MIMO) downlink communications for multi-carrier scenarios, e.g. orthogonal frequency-division multiplexing (OFDM) a common analogue precoder and combiner for the transmitter and receiver to maximise spectral efficiency is the main challenge for multi-carrier MIMO systems, they propose two methods to solve this problem. The first method designs the analogue precoder and combiner based on the channel average of all subcarriers, which helps reduce computational complexity. Moreover, the channels of all subcarriers can be viewed as a third-order tensor, and the second method is based on tensor unfolding, which makes full use of the channel information of all subcarriers. When the common analogue precoder and combiner are fixed, they consider designing a digital precoder to maximise the signal-to-leakage-plus-noise ratio of each user in every subcarrier, which leads to closed-form solutions compared with the block diagonal method. Simulation results demonstrate that the performance of the proposed methods is close to that of the fully digital precoding method, and increasing the number of RF transceiver chains helps improve the performance of the proposed methods.

In this study, a new non-iterative adaptive beamforming (ABF) algorithm for the signal-to-interference and noise ratio (SINR) enhancement is proposed. It is based on a combination between the direction of arrival (DOA) estimation and the method of moments (MoM). The proposed algorithm is denoted as DM/ABF which stands for DOA and MoM-based ABF. The DOA is used to provide accurate estimates for the directions of the desired and interfering signals. On the basis of the estimated DOAs, a dedicated shaped pattern version of the ordinary pattern is created and applied as the desired input to the MoM algorithm. The MoM is used for shaped pattern synthesis to estimate the weights vector required to provide deep nulls toward the interfering signals and directs the main beam toward the desired signal. In this case, the weights vector does not update iteratively at each received signal sample as in case of least mean square (LMS) and recursive least squares (RLSs) algorithms, but it is updated only when the estimated DOAs of the desired and interfering signals are changed. Furthermore, a large number of close nulls can be produced without the need for additional antenna elements compared with other algorithms.

We propose and experimentally demonstrate a bidirectional Community Antenna Television/radio-over-fibre (RoF) hybrid transmission system based on incoherent light injection and RF amplifier pre-distortion to reduce third-order non-linearity. At downlink, 10-Gbps/30-GHz data and 79 CATV channels are transmitted over 50 km single-mode fibre (SMF), and at uplink 5-Gbps/15-GHz data and CATV signals are successfully transmitted concurrently over 50 km through the same SMF. The authors have found low bit-error rate (BER) and clear eye diagrams for the RoF data signals, and obtained outstanding transmission performance in terms of carrier-to-noise ratio, composite second order, and composite triple-beat for the CATV signals in downlink and uplink transmission.

In this study, the authors investigate average capacity of free space optics communication over Málaga atmospheric turbulence channel with pointing errors and path loss, for intensity modulated/direct detection (IM/DD) and heterodyne detection. Various algorithms which use adaptive transmission with both types of detection are considered, such as: optimal rate adaption (ORA), optimal power and rate adaption (OPRA), channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR). Analytical closed-form expressions for channel capacities of ORA, OPRA and TIFR adaptive transmission are presented, and the authors prove that CIFR transmission is not feasible in the strict sense for the conditions considered. Obtained analytical results are numerically evaluated and graphically presented for different strengths of atmospheric turbulence (in weak, moderate and strong turbulence regime) for both types of detection (IM/DD and heterodyne), and for considered algorithms of adaptive transmission (ORA, OPRA and TIFR). The authors have developed expressions suitable for approximating high signal-to-noise ratio channel capacity, and they graphically present and compare the asymptotic approximations with the obtained analytical results for different strengths of turbulence for both types of detection. Also, obtained analytical results were confirmed by Monte-Carlo simulations, and graphically compared for different strengths of turbulence regimes.

In this study, the authors study the effect of non-identical channel estimation error and feedback delay on the performance of an opportunistic beamforming system. This study derives the exact system performance (i.e. outage probability, symbol-error rate (SER), and ergodic capacity) of the proposed system using moment generating function in an imperfect channel environment. This study also uses an asymptotic analysis to quantify the diversity order of SER and outage probability to analyse which system variables affect system performance. From the results of an asymptotic analysis, it is shown that by channel estimation error and feedback delay, spatial diversity is eliminated, but the benefits of multiuser diversity still exist. Therefore, the diversity order of the SER and the outage probability of the proposed system are proportional to the number of user terminals, but the conventional system is limited to 1 by channel estimation error and feedback delay.

This study presents a smart-phone-based hybrid indoor localisation system (HILS), which integrates two different localisation approaches, i.e., pedestrian dead reckoning (PDR) and Wi-Fi-based localisation to compensate the limits of each other. In PDR, the localisation accuracy degrades continuously when the moving distance increases from the starting reference point. However, Wi-Fi-based trilateration method requires the Wi-Fi signals from at least three access points (APs). In this study, the authors propose a more efficient novel Heron-bilateration-based position determination (HBPD) technique, which requires the Wi-Fi signals from only two APs to locate the mobile device. The proposed HILS utilises the HBPD technique to reset the bias drift errors involved with inertial sensors, and compensate the unavailability of strong Wi-Fi signals from APs using the PDR method. In this work, an experimental testbed is developed to collect the Wi-Fi signals and evaluate the proposed method. The proposed HILS is also compared with five other benchmark methods for two different trajectories and the experimental results show that the mean localisation error is decreased up to 1.68 and 1.96 m, which indicate the improvement by 16.83 and 20.97% for both the trajectories, respectively, in comparison with the best performing method among the benchmark methods.

Femtocell network is regarded as the potential and effective technique to improve the capacity and coverage of traditional cellular networks. One of the challenges is how to access the network and manage the interference among different users. Compared with other access strategies, hybrid access strategy allows femtocell base stations (FBSs) to provide preferential access to femtocell users (FUEs) while other users can access nearby FBS with specific restrictions. In this paper, a robust downlink power control scheme is studied in two-tier femtocell networks, where femtocells share the same frequency with macrocell. A hierarchical game framework that takes the different users' requirements into consideration is constructed. In addition, as the link gains are actually uncertain in dynamic environment, probabilistic constraints are used to describe the uncertainty. Then two sub-problems are obtained to maximise the sum rate of macrocell and femtocells, respectively and guarantee the quality of service (QoS) of different users. To tackle the nonlinear and nonconvex optimization problem, successive convex approximation is introduced. And the practical iterative power allocation algorithm is provided. Finally, numerical results show that the proposed scheme is effective in aspect of energy saving and QoS guarantee under dynamic environment.

Recently, a class of low-density parity-check (LDPC) codes from affine permutation matrices, called APM-LDPC codes, have attracted because of some advantages rather than QC-LDPC codes in minimum-distance, girth, cycle distribution and error-rate performance. In this study, a new class of LDPC codes based on Mobius transformations, called MT-LDPC codes, are presented as a generalisation of APM-LDPC codes which have some new achievements rather than QC and APM LDPC codes in the terms of length, cycle distribution and error-rate performance. Moreover, each Mobius transformation is represented by a square matrix which is helpful to pursuing the cycles in the Tanner graph of an MT-LDPC code by the product of some square matrices. In continue, for a given base matrix, the authors propose a deterministic algorithm which efficiently produces MT-LDPC codes with the desired girth. Simulation results show that the binary and non-binary constructed MT-LDPC codes outperform APM, QC, PEG, random-like and some algebraic LDPC codes with the same rates and lengths.

Random codes based on quasigroups (RCBQ) are cryptcodes, i.e. they are error-correcting codes, which provide information security. Cut-Decoding and 4-Sets-Cut-Decoding algorithms for these codes are defined elsewhere. Also, the performance of these codes for the transmission of text messages is investigated elsewhere. In this study, the authors investigate the RCBQ's performance with Cut-Decoding and 4-Sets-Cut-Decoding algorithms for transmission of images and audio files through a Gaussian channel. They compare experimental results for both coding/decoding algorithms and for different values of signal-to-noise ratio. In all experiments, the differences between the transmitted and decoded image or audio file are considered. Experimentally obtained values for bit-error rate and packet error rate and the decoding speed of both algorithms are compared. Also, two filters for enhancing the quality of the images decoded using RCBQ are proposed.

In indoor environment, passive human detection and localisation are important enabling technologies for elder healthcare, emergence rescue and target tracking applications. Recently, the fine-grained channel state information (CSI) of Wi-Fi was adopted for indoor localisation due to the low-cost Wi-Fi network interface card and available firmware modifications for CSI extraction. However, due to multipath fading and spatial-temporal dynamics of wireless channel, stable CSI extraction is a challenging task to achieve reliable CSI fingerprint matching. In this study, the sensitivity of CSI is first analysed and stable CSI fingerprints can be obtained by reducing the variance from interference and white noise. The stable CSI fingerprints are then classified by quadratic discriminant analysis to achieve location matching. Extensive experiments have been conducted to justify the system performance. The results reveal that the proposed indoor passive localisation system outperforms passive CSI-MIMO system in terms of performance.

Millimetre wave (mmWave) multiple-input multiple-output (MIMO) systems have been proposed to enable Gbps communication for next-generation cellular systems and local area networks. To compensate for the severe propagation loss of the mmWave channel, a cost-effective hybrid precoding architecture, combining a digital precoder and an analogue precoder, is widely used in mmWave MIMO systems. In this study, two hybrid precoding algorithms based on particle swarm optimisation (PSO) algorithm will be proposed for two different hybrid precoding structures, i.e. the fully connected and partially connected structures. First, the authors use the phase of the analogue precoding variable to replace the corresponding variable with the constraints of the unit norm to solve the non-convex constraints skillfully. Then they design analogue precoding by using PSO algorithm and compute the digital precoding based on the least squares solution. Finally, the proposed algorithms are compared with the existing advanced algorithms. Simulation results demonstrate that the proposed algorithms can approach the optimal performance under the corresponding structure.

Cloud computing has several favourable characteristics for supporting Internet of things (IoT) applications and services. While provisioning support for heterogeneous devices adapting different semantics in IoT, cloud-based technology is highly used. In semantic model, attaching additional information to raw sensory data is accomplished with the help of ontology. However, the longer distance between the cloud and IoT devices becomes a bottleneck for critical IoT applications. In this study, the authors proposed a fog-based semantic model called semantic-fog to reduce this gap. The proposed model shifts some of the frequently used semantic services of the cloud to the edge of the sensor network. Additionally, it provides an efficient off-loading technique among fog–fog and fog–cloud devices to reduce task execution time and energy consumption of the fog nodes. Furthermore, an effective mapping method for converting raw sensory data into Resource Description Framework format is also presented in this work. A comparative analysis among the relevant cloud-based computing models and the proposed semantic-fog model is performed in terms of service delay, energy consumption, network usage, and the total cost of the system. Simulation results show that semantic-fog outperforms the cloud-based models almost in all the aspects considered.

This study presents an analysis for a cross-layer design of a combined adaptive modulation and coding (AMC) with a truncated automatic repeat request (T-ARQ) scheme in an underlay spectrum sharing cognitive radio employing an amplify-and-forward cooperative relaying system. The considered AMC employs a coded M-ary quadrature amplitude modulation scheme combined with a T-ARQ to improve the performance of the secondary user (SU) system in the considered cognitive radio. To establish the performance analysis, the cumulative distribution function (CDF) of the end-to-end signal-to-noise-ratio at the receiver side of the SU system is derived. Then, using the derived CDF, closed-form expressions are derived for three important performance metrics: the average spectral efficiency, the average packet-error-rate, and the outage probability. To evaluate the performance of the considered system, numerical results obtained from the derived closed-form formulas are presented and compared. In addition, to verify the validity of the analysis, Monte–Carlo simulation results are also provided.

In this study, two iterative design algorithms for multiple-input multiple-output (MIMO) radars with co-located antennas with point targets are proposed. In these algorithms, by joint design of the receiver filter and transmit waveform using linear combination of orthogonal waveforms, the authors aim to maximise the signal-to-interference plus-noise ratio (SINR) in the presence of signal dependent interference. In the first proposed algorithm, in each iteration, transmit waveforms and receive filter are designed in closed form to decrease the computational complexity. In the second method, by adding constant envelope criteria, the final waveform would be a linear combination of orthogonal waveforms and because of using a constant envelope, combining coefficients have equal magnitudes and different phases. Therefore, it is more practical for hardware implementation in comparison to the first proposed method. Simulation results show that both proposed methods have better SINR performances compared with other methods proposed in MIMO radar literature. The outperformance of the second proposed method with respect to phased arrays shows that by only using phase shifted combination of orthogonal waveforms, better performance in comparison to phased array radars can be achieved.

In this work, the author investigate the performance of the hybrid free-space optical/radio frequency (FSO/RF) communication systems where RF links are subject to Nakagami-m distribution fading effects. The author derive the statistical characteristics of the hybrid FSO/RF systems in closed-form in terms of Meijer's G-function and the extended generalised bivariate Meijer's G-function. Then, the author rely on these new results to present the performance analysis of the selection combining diversity based on hybrid FSO/RF systems. Also, the author consider a Gamma–Gamma turbulence distribution under the impact of pointing errors and subject to both types of detection techniques (i.e. heterodyne detection and intensity modulation with direct detection (IM/DD)) in the FSO link. Computer-based Monte–Carlo simulations are proved the accuracy of the new analytical results.

This study proposes a technique for multipath data transmission in Wireless Sensor Network (WSN) by proposing a novel optimisation algorithm, named exponential cat swarm optimisation (ECSO), by integrating the exponential weighted moving average and CSO. Initially, the CH is selected by the penguin fuzzy-based ant colony optimisation (PFuzzyACO) technique, which is the integration of fuzzy, ACO and penguin search optimisation algorithm (PeSOA). After the selection of the optimal CH, the multipath transmission is done by the proposed ECSO algorithm. Here, an optimal path is selected for transmitting the routeing information from source to destination based on various parameters such as trust, energy, distance, delay, traffic density and link lifetime (LLT). Thus, the CHs with maximum trust, energy and LLT, and minimum distance, delay and traffic density are adapted for multipath data transmission using the proposed ECSO algorithm. The proposed ECSO algorithm shows 18.75, 2.99 and 29.87% improvements in terms of number of alive nodes, throughput and network energy, respectively, than the existing PFuzzyACO, which has high performance than the other comparative methods such as artificial bee colony, ACO, fractional artificial bee colony, Low-Energy Adaptive Clustering Hierarchy (LEACH), FuzzyACO and PeSOA.

In this study, the authors consider the utilisation of multicast technology in cellular networks given different arrival patterns for the content requests of mobile users. Traditionally, the performance evaluation of multicast in the literature usually depends on the adoption of temporal Poisson processes for content requests, which is not accurate any more according to many real data measurements. Therefore, to make use of the bursty nature of content requests, they propose a hybrid unicast/multicast strategy where the base station (BS) can perform the unicast or multicast procedure according to its serving status. By modelling the complete process into a circular Markov chain, they derive the average latency of content requests and the average power consumption of BSs under different arrival patterns and serving configurations in theoretical and/or simulative ways. Moreover, the multicast threshold introduced in their strategy can be dynamically adjusted to achieve a joint optimisation between average latency and power consumption when confronted with varied demands. Numerous results show that the proposed strategy can not only reduce the average latency of content requests but also decrease the average power consumption of BSs, especially under the bursty request arrival patterns.

In this study, a segment-selected mapping (SSLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) of the filter bank multi-carrier (FBMC) signal in satellite communications. The standard selected mapping (SLM) scheme is suggested to reduce the PAPR of the traditional multi-carrier signals. However, it cannot be directly applied to the FBMC signal due to the overlapping nature of the FBMC signal. In the proposed method, each symbol in the FBMC signal is divided into several segments to solve the overlapping problem. Each segment is regarded as an independent unit, and rotates a suitable phase to minimise the PAPR in the frequency domain. The authors simulated the FBMC signal in the satellite communications by introducing the influence of the high power amplifiers and the Doppler frequency shift. The simulation results from complementary cumulative distribution function of the PAPR show that the proposed scheme can achieve about 0.3 dB PAPR performance compared to the existing dispersive SLM scheme, with lower complexity.