In 2008, the Federal Communications Commission issued a ruling permitting the unlicensed usage of TV white spaces (TVWS), i.e. locally vacant TV channels. Due to its low-frequency range (50–698 MHz), the TV spectrum has much better propagation characteristic and higher-spectral efficiency, resulting in a wide range of potentially important applications. However, unlike typical cellular and industrial scientific medical bands, TVWS are subjected to high-spatial variation, temporal variation, and fragmentation, resulting in new challenges in TVWS identification and in implementing a wireless network in this band. Identification and network design are the two key issues required to be addressed while investigating TVWS. These two problems have been widely discussed in several existing literature. Applications in TVWS are also an important topic, which has not been adequately explored. This study provides an up-to-date survey of TVWS and its applications in future wireless networks and communication. Various problems and challenges associated with each use case as well as the possible enabling methods to address these challenges are also presented.

Atmospheric turbulence causes severe impairment of FSO communication link. Existing model underestimates the beam wander effect in high turbulence regime. In this paper, we model each turbulent eddy as a thin dielectric lens with Gaussian shaped refractive index profile and assume there are several sheets of eddies throughout the propagation path. We consider uniformly distributed eddy positions in a laminar sheet with Gamma distributed eddy sizes and refractive index fluctuations. We calculate mean beam wander and link availability for a given aperture size in high turbulence regime. Our simulation results show good concordance with the analytical results.

Multi-hop relaying is used to extend the reach of wireless communication systems whereas cooperative relaying is used to improve the performance gain by exploiting the spatial diversity. In this study, the authors combine these two techniques to improve the range as well as the performance gain of cognitive radio networks (CRNs). Selective decode-and-forward relays are considered and two relay selection schemes are used to study the performance of multi-hop CRNs over Rayleigh fading channels. The exact outage probability and throughput of the considered system are derived for both the schemes by considering the effect of both peak-power and peak-interference constraints. By using the derived outage probability, the diversity gains for both considered schemes are determined. Numerical results show that the outage probability monotonically improves, whereas the throughput has concave behaviour with respect to increasing number of relaying hops.

Achieving large confidential capacity under the wiretap channel model is a challenge due to the narrow modulation bandwidth and total transmission power constraints. The confidential capacity of a system can be improved through a non-orthogonal multiple access technique that can obtain the highest transmission power in a downlink network. A clustering method is applied to network users who require data with similar contents. Based on the channel gain of each user, cluster heads are selected as agents for the corresponding clusters; then, the total transmission power is shared among the cluster heads. Before the power allocation process, the signal-to-interference-plus-noise ratio of the cluster heads is derived by considering clipping noise to ensure fairness. On this basis, an optimal power allocation scheme is proposed using Lagrangian dual theory. A case is presented to validate the performance of the proposed power allocation scheme. The comparison of the numerical results with those of other schemes shows that the proposed method achieves better performance regarding both secrecy sum capacity and outage probability.

Physical-layer security is usually ensured by the injection of artificial noise (AN) at the legitimate source or destination when relays are cooperative but untrusted. In this work, in order to avoid the power-consuming AN at the legitimate user pairs, the authors investigate multi-pair two-way relaying as a solution for secure transmission in wireless relay networks with untrusted relays. They formulate a generalised problem for the joint design of cooperative beamforming (CB) and AN at relays to maximise the secrecy sum-rate in wireless networks with multi-pair legal users, multiple untrusted relays as well as multiple non-colluding eavesdroppers. Further, they reformulate, approximate and relax the original non-convex problem into a sequence of convex sub-problems based on semi-definite relaxation (SDR) and Taylor series approximation. Particularly, for the reformulated problem they prove that the SDR is in fact tight, and hence propose an iterative algorithm for CB and AN design at the relays. In the simulations, they demonstrate the fast convergence and high achievable secrecy sum-rate of the proposed algorithm. Also, they simulate and discuss the impact of the number of user pairs on the secrecy sum-rate, and reveal the change of performance gain with the number of multiple user pairs.

Luby transform (LT) codes have received less attention in larger non-binary fields. Robust soliton distribution (RSD) was designed to provide universal optimality over the binary erasure channel in terms of minimising the overhead. In this study, the authors introduce a fundamental degree distribution (FDD), which when used with non-binary LT codes, outperforms their binary counterparts using the RSD in terms of error rate and realised code rate. For instance, over an additive white Gaussian noise (AWGN) channel at of 12 dB and a rateless criteria (zero error probability), a non-systematic 4-ary LT code using the FDD can achieve a code rate of 0.75, compared to its binary counterpart which only achieves a code rate of 0.7.

This study investigates the unified performance of a free space optical link with a finite-sized receiver over an exponentiated Weibull distributed atmospheric turbulence in the presence of a misalignment error (ME). The unification is done for two detection techniques namely heterodyne and intensity modulation/direct detection. First, the unified expressions for probability density function, cumulative distribution function, moment generating function, and moments of instantaneously received signal-to-noise ratios (SNRs) at the receiver, have been derived. By utilising the derived statistics, the unified novel expressions for outage probability, average error probability (AEP), and ergodic capacity are obtained. Furthermore, the AEP performance is examined at a high SNR in order to obtain the diversity order and coding gain, analytically. The derived results clearly demonstrate the impact of severe atmospheric conditions, ME, aperture size, and type of detection scheme on the system performance. The derived analytical results are verified through simulations.

In the software defined network (SDN) environment, network function virtualisation enables the virtual machine migration. Owing to the fact that transferring large amount of data will impede competing workflows, virtual network function (VNF) migration has brought a new perspective. Many optimised algorithms focusing on limiting migration time and migration cost have been proposed. In this study, the authors address the problem from a different perspective. They view the network topology from a global perspective and focus on the network effect of the whole network caused by VNF migration in the context of SDN. They introduce a parameter delay to formulate the network effect and an effect model is proposed to evaluate the migration effect of the network. In addition, a heuristic algorithm is proposed to minimise network effect while balancing network load and improving the service considering the migration cost and resources limit at the same time. The practicability and efficiency of the proposed model and algorithm are validated by simulation evaluation. By comparing their proposed algorithm with traditional benchmarks and closely related benchmarks, the experimental results show that their proposed algorithm largely reduces the network effect, while at the same time limiting the run time.

Deep clipping is beneficial for the optical orthogonal frequency division multiplexing (O-OFDM) system, since it can lower the peak-to-average power ratio, reduce the direct current requirement in light emitting diodes (LEDs), and relax the bit-resolution requirement in digital-to-analogue converters (DACs). However, it is accompanied by more signal distortions. In this study, a deep clipping noise mitigation scheme using iterative shrinkage/thresholding algorithm (ISTA) with three steps is proposed to improve bit error rate (BER) performance of the LED-based DCO-OFDM systems. In the first step, the estimated observation interference is eliminated from the received symbols to minimise the negative effect of channel noise. In the second step, two strategies are presented to generate the specified observations thus reduce the component of measurement noise in the whole observation vector. In the last step, combining the generalised cross validation and the estimation of observation interference, the appropriate regularisation parameter are calculated for ISTA to improve the robustness of the sparse recovery performance. They use simulations to show that the proposed scheme can correct the deep clipping noise with favourable reconstruction quality, which significantly improves the BER performance and therefore assist the LED non-linearity mitigation.

In this study, the authors consider a two-way amplify-and-forward communication system over Nakagami-m fading environments, where an intermediate relay node harvests energy from its surrounding radio frequency environment using an energy harvesting technique. They propose a novel derivation approach to obtain exact expressions for user outage probability, system outage probability, and upper bound on system ergodic capacity per unit bandwidth over Nakagami-m fading channels. Monte–Carlo simulation results under Matlab software packages match the proposed analytical analyses confirming the correctness of the proposed derivation approach and the advantage of the system under consideration.

Compared with a traditional fixed sensor network, mobile crowdsensing provides an efficient way to collect sensing data. However, conducting sensing tasks consumes the resources of mobile users (e.g. battery, storage memory, time). Therefore, incentive mechanism design plays a key role in efficiently collecting the sensing data in a mobile crowdsensing system. Most of existing works about the incentive mechanism design simply use a constant to describe the data quality. In this study, the authors focus on the collection of video clips and introduce multiple parameters to evaluate the quality of the collected data. By jointly considering the social relationship of mobile users, they propose a social-aware incentive mechanism to achieve the full-view coverage for a target by efficiently collecting video clips. The proposed mechanism satisfies the properties of individual rationality, truthful and computational efficiency. Simulation results show better performance of the proposed mechanism compared with random selection and aspect based selection. In specific, with the number of users , the proposed mechanism can improve the data collector's utility by 485% and 33% compared with random selection and aspect based selection, respectively.

In underlay cognitive radio networks (CRNs), secondary users (SUs) are allowed to co-exist with the primary users at the cost of reduced transmit power in order to satisfy the stringent interference constraint. This obligation reduces the coverage area of the SUs and they have to involve relaying services for assistance. However, selecting the best combination of relays from the available options is more challenging in an energy-constrained environment, since it is affected not only by the interference constraint, but also the selected subset of relays must guarantee some quality-of-service (QoS) at the secondary destination also. This study is focused on an amplify-and-forward-based relay-assisted CRN operating in an underlay scenario and studies three relay subset selection or multiple relay selection schemes taking into consideration outgoing secondary and primary link qualities of each candidate relay. For each scheme, the closed-form expression for probability density function of signal-to-noise ratio at the secondary destination is derived followed by detailed analysis of two QoS metrics, i.e. outage probability and bit error rate. Finally, simulations have been performed to validate the analytical results.

Non-coherent impulse-radio ultra-wideband (IR-UWB) transceivers are attractive candidates for applications where the silicon area and power consumption are relatively limited. This study presents the compact digital architecture design and implementation of a non-coherent IR-UWB transmitter and receiver based on the energy detection scheme, including the synchroniser module. The software models of the designed transceiver are simulated and verified in both floating-point and fixed-point numerical representations. The synthesisable Verilog description of the transmitter and receiver architectures is simulated and verified against their fixed-point simulation model. The transmitter and receiver are implemented in the authors custom-developed field-programmable gate array (FPGA) board. The bit error rate performance of the transmitter and receiver is measured in real-time on the FPGA, utilising an accurate on-chip Gaussian noise generator. The characteristics and implementation results of the transmitter and receiver architecture on the FPGA are presented. An application-specific integrated circuit (ASIC) architecture of the IR-UWB transceiver is estimated to occupy 0.0227 mm² and dissipate 760 mW from a 1.0 V supply while operating at 82 MHz in a standard 32 nm complementary metal–oxide–semiconductor technology.

In this study, the authors propose a novel intra-data centre network (DCN) architecture based on cascaded micro-electro-mechanical system switches for dynamic DCN connectivity provisioning. Through combining the single-carrier frequency-division-multiplexed with the proposed architecture, this structure can achieve unprecedented flexibility in dealing with both mice and elephant flow in the DCN. Multiple-input multiple-output switching is experimentally demonstrated through intra- and inter-data centre switching scenarios. A numerical investigation is also performed to evaluate the performance of the fixed-grid transceivers, flex-grid transceivers and mixed-fixed/flex grid transceivers in the same switching scenario. The results show that the flex-grid transceivers significantly reduced the service latency and blocking probability compared to the fixed-grid transceivers. The proposed architecture would be better applied in the field of all-optical DCNs.

The Virtual Network Function (VNF) embedding problem is important for service provision in the context of Network Function Virtualisation (NFV). However, this problem is proved to be NP-hard and challenging, and requires to be explored further. In this study, the authors first formulate it as an Integer Linear Programming (ILP) model for optimal solutions. Then, to compensate for the high running time of solving the ILP model, they propose a heuristic approach which fulfils the embedding process by jointly taking the global network connectivity and the local substrate node capacity into consideration. The simulation on real-world network topologies demonstrates that the proposed approach can provide solutions within 1.7 times of the optimal solution offered by ILP. In addition, the experiments also suggest that the proposed approach can provide up to 2.75 times reduction in the overall cost than the other benchmarks.