In this study, the authors study a sustainable resource allocation scheme for delay-sensitive applications in an energy harvesting (EH)-cloud radio access network (CRAN). The authors formulate an optimisation problem to maximise the user equipment (UE) utility and provide them with strong delay-guarantee by jointly considering the stochastic EH process, dynamic wireless channel state. By using the Lyapunov stochastic network optimisation technique combined with virtual queues, the authors decompose the formulated problem into four sub-problems, including channel allocation, data dropping, UE request scheduling and energy management. Based on the solutions of these sub-problems, a UE optimal resource allocation algorithm is proposed to maximise UE utility while guaranteeing the delay bound and the sustainability of remote radio heads. Furthermore, this algorithm does not require any prior statistical information of the system, e.g. EH process and channel state. Both theoretical analyses and simulation results demonstrate that the proposed algorithm can achieve close-to-optimal UE utility, bounded data buffer, delay-guarantee, and required battery capacity for the operation of the CRAN.

This study investigates a problem of resource allocation for an uplink multi-carrier non-orthogonal multiple access (NOMA) system. To provide a general resource allocation problem, the order of successive interference cancellation (SIC), subcarrier assignment and power allocation are all considered as the optimisation variables of interest, with the objective of maximising the weighted sum rate under the transmit power constraint of each user equipment (UE). Firstly, a novel optimal SIC order is proposed based on the inherent structure of the uplink NOMA system. Then, with the optimal SIC order, the Lagrange dual method is employed to solve the joint subcarrier assignment and power allocation problem in an asymptotically optimal manner. In addition, an optimal solution of power allocation with a fixed subcarrier assignment is presented. In light of the optimal power allocation, a tight upper bound of the uplink NOMA system is developed by relaxing the number of multiplexed UEs on each subcarrier. Simulation results show that the proposed algorithm outperforms conventional orthogonal multiple access schemes and other static NOMA schemes, and as a benchmark, the upper bound reveals that multiplexing at most two UEs on each subcarrier is sufficient for the performance improvement.

Integrating Kirchhoff approximation (KA) and a ray-tracing (RT) algorithm, this study develops a new directional three-dimensional channel model for urban millimetre-wave small cells. The authors study the path loss, spatial correlation, coverage distance, and coherence length for line-of-sight (LOS), obstructed LOS, and non-LOS (NLOS) scenarios in urban areas. Exploiting physical optics and geometric optics solutions, closed-form expressions for spatial correlation are derived. It is deduced that LOS availability, frequency, and surface roughness scale highly impact spatial diversity. In addition, using antenna arrays of moderate gain at both sides of the link, even under NLOS conditions, a typical urban cell size of 200 m is achievable.

In this study, the authors consider the physical-layer security problem in the relay networks. The relay nodes are employed not only to aid the information transmission but also to improve the network security in the physical layer by sending artificial noise to resist the potential malicious eavesdropper. By allowing shared randomness between the jamming nodes, it is shown that the maximum degrees of freedom (DoF) of the considered network is almost surely. The necessary and sufficient conditions for the optimal DoF setup are established. Moreover, a simple DoF-optimal collaborative beamforming algorithm is proposed, and it works very well in the high signal-to-noise ratio regime, which is verified by computer simulations.

To enable sustainable wireless networks, though new technologies have been proposed to improve the system spectrum efficiency, the energy efficiency (EE) is also of vital importance due to the increasing users and devices. Active array system (AAS) and heterogeneous networks (HetNets) have been reckoned as an enormous enhancement in spectrum efficiency and EE. In this study, the energy efficient user association and resource allocation problem for preference-aware multicast service in AAS aided HetNets is investigated, formulated as a mixed-integer non-linear fractional programming. By generalised fractional programming theory and Lagrangian dual decomposition, an iterative algorithm is devised to determine user association and resource allocation. Further, an efficient solution is proposed to perform quality of service-guaranteed user association and resource allocation to maximise the EE. Simulation results demonstrate the convergence performance and potential gain of the proposed algorithms in terms of EE.

The spatial degrees of freedom will be sacrificed to perform the precoding-based interference management (IM) for the cell-edge user (CEU) in a massive multiple-input and multiple-output enabled irregular network. It is desired to evaluate the impact of the precoding-based IM on the performance of both the cell-centre user (CCU) and CEU, which leads to a consideration of the balance between the CEU performance enhancement and the CCU tolerable performance degradation. Thus the separate analysis of CEU and CCU performance under the precoding-based IM is imperative. To facilitate the analysis, the authors propose an approximate distribution of the CEU numbers with a flexible CEU definition in a single-tier irregular network. With this distribution, the upper bound of the success probability of the typical CEU using the precoding-based IM is analysed. Also, a lower bound of the success probability of the typical CCU is given. Moreover, the impact of the cell-edge area on the success probability of both the CCU and CEU is discussed. It is found that the success probability of both the CCU and CEU decreases with the enlarged cell-edge area in the case of the high density of users and small density of base stations. Nevertheless, the tendency of the success probability versus the cell-edge area becomes diverse in the dense network or sparse user scenario.

The coexistence of a primary user (PU) with a secondary user (SU) is studied in an overlay cognitive radio network (CRN) which is proposed as an efficient technique to treat with the problem of spectrum underutilisation. A cooperative spectrum leasing process under the decode and forward protocol is considered among the PU and SU. Assuming users' specific Quality of Service requirements, a joint power and time allocation scheme for maximising the PU's cooperative effective capacity subject to minimum SU's and PU's effective capacities and maximum SU's instantaneous power transmission constraints is proposed. Its performance is close to the optimal one, that is computed using the exhaustive search scheme. A two-step solution is applied considering the fundamentals of convex optimisation theory and closed-form power and time expressions are extracted. As simulation results prove, the proposed scheme outperforms a less sophisticated scheme considering power allocation under constant time. Finally, the proposed algorithm is incorporated in a multi-user CRN scenario where efficient matchings among the PUs and the SUs are investigated targeting to the increase of PUs' cooperative performance applying the matching theory.

This study is concerned with coded multiple-input multiple-output (MIMO) visible light communication (VLC) system, where unipolar M-level pulse amplitude modulation is assumed along with MIMO transmission techniques, including repetition coding, spatial multiplexing and spatial modulation. In order to evaluate the performance of MIMO-VLC system, the authors analyse the mutual information of the MIMO techniques, based on which the block Markov superposition transmission (BMST) codes are constructed to improve the bit-error rate (BER) performance of the system. In addition, they present a genie-aided lower bound to predict the performance of the BMST-VLC system in the low-BER region. Simulation results demonstrate that the proposed scheme can achieve significant coding gain compared with Reed-Solomon-coded MIMO-VLC system adopted in IEEE standard 802.15.7.

With pervasive of mobile computing and wireless communication, the vehicular ad-hoc network has become a key technology in modern day's information exchange. Due to the fast growing number of vehicles and saturation of the transport infrastructure, it is inhabitable to come out with better solution considering the available resources. In this study, thorough traffic analysis has been carried out to suggest a better model. Further, an attempt has been made to propose an admission control algorithm based-on the parameters evolve from the mathematical analysis. Moreover, the performance analysis has been shown to establish the efficacy of the algorithm.

Exploiting physical layer in achieving different security aspects in wireless communications has been widely encouraged. In this work, the authors propose an entity authentication scheme for mobile devices with multiple antennas, which is purely based on physical layer parameters. According to the proposed scheme, in order to authenticate a device, a number of predefined authentication signals should be detected at the receive antennas on the authenticator side. The transmitted signals are designed based on the instantaneous channel responses in order to deliver the authentication signals to the receiver. The proposed scheme works efficiently even for mobile users, which is considered a significant improvement over previous related works. Mathematical analysis of the different involved factors along with sufficient simulations show the high performance of the proposed authentication scheme.

In this study, the performance of multiple-input multiple-output (MIMO) systems based on the fractional Fourier transform (FRFT) and the fast Fourier transform (FFT) in underwater acoustic (UWA) communication channels is evaluated and compared for various conditions including the number of subcarriers, modulation schemes, the number of paths between the transmitter and the receiver, Doppler frequencies, and MIMO modes including diversity and multiplexing. The study demonstrates while the computational complexity of the FRFT is in the order of the FFT, the performance of the FRFT-based UWA system is superior to that of the FFT-based system for all multipath scenarios, and for the flat fading channel, they achieve the same performance.

The authors study the performance of an amplify-and-forward dual-hop, switch-and-stay combining receiver, used in free space optical communications over non-identical fading channels. One path is characterised by the generalised Málaga (or M distribution), whereas the other is influenced by the combined effects of Gamma–Gamma distributed atmospheric turbulence, pointing error and path loss. Novel closed-form expressions for the end-to-end moment generating function, probability density function, and cumulative distribution function are derived in terms of Meijer's G function. Furthermore, the performance of the system is analysed, and closed-form expressions are presented for the end-to-end outage probability and channel capacity.

New precoder matrices are designed to estimate an unknown vector parameter considering stochastic channels for multiple-input multiple-output wireless sensor network (MIMO-WSN) with decentralised sources. Two types of WSNs are considered, with and without total power network limitations. Within this context, two closed-form relations are derived for the precoder matrices and mean square error (MSE) of the unknown vector parameter is obtained. To cancel any operations at a fusion centre to estimate the aforementioned parameter, a distortionless constraint is added. In simulation section, the authors compare the MSE performances of the proposed method in stochastic MIMO channels with those in deterministic MIMO channels. The simulation result indicates that the MSE performance in the stochastic channels is decreased by almost 1.3 dB at low signal-to-noise ratios. Therefore, the reliability of the unknown vector parameter estimation is enhanced using the MIMO model. Ultimately, effects of bandwidth and number of sensor nodes on the MSE criterion are also analysed.

With the development of the new generation satellite navigation and positioning systems utilise binary offset carrier (BOC) modulation to improve inter-operability. The main shortcoming of BOC modulation is its ambiguity of searching for a multi-peaked auto-correlation function (ACF). In this study, an improved unambiguous synchronisation algorithm based on compensated correlation reconstructed technique (CCRT) is proposed for the arbitrary-order BOC, which is a new modulation technique for navigation modernisation. The key technique used in this study is to generate local reference signals with different shape vectors. By recombining the piecewise correlation functions of the step-shape coded symbol, a reconstructed correlation function which has only one peak is obtained, and the energy loss is compensated by the ACF. In the proposed algorithm, different shape vectors are employed in different BOC modulation signals. The simulation results demonstrate that the ambiguity problem is completely eliminated. Compared with traditional synchronisation methods, the proposed algorithm shows outstanding detection and multipath mitigation performance. Moreover, the CCRT can be utilised for arbitrary stage BOC modulation signals.

People watching smartphones while walking causes a significant impact to their safety. Pedestrians staring at smartphone screens while walking along the sidewalk are generally more at risk than other pedestrians not engaged in smartphone usage. In this study, the authors propose Safe Walking, an Android smartphone-based system that detects the walking behaviour of pedestrians by leveraging the sensors and front camera on smartphones, improving the safety of pedestrians staring at smartphone screens. More specifically, Safe Walking first exploits a pedestrian speed calculation algorithm by sampling acceleration data via the accelerometer and calculating gravity components via the gravity sensor. Then, this system utilises a greyscale image detection algorithm to detect the face and eye movement modes based on OpenCV4Android to determine if pedestrians are staring at the screens. Finally, Safe Walking generates a vibration by a vibrator on smartphones to alert pedestrians to pay attention to road conditions. The authors implemented Safe Walking on an Android smartphone and evaluated pedestrian walking speed, the accuracy of eye movement, and system performance. The results show that Safe Walking can prevent the potential danger for pedestrians staring at smartphone screens with a true positive rate of .