The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on visible light communication (VLC) systems. Although VLC systems provide lighting and communications simultaneously from light emitting diodes (LEDs), LEDs, the uplink channel design in such a system is a challenging task. In this study, the authors propose a solution in which the uplink challenge in indoor VLC is resolved by the use of an infrared (IR) link. The authors introduce a novel fast adaptive beam steering IR system (FABS-IR) to improve the uplink performance at high data rates while providing security for applications. The goal of the authors’ proposed system is to enhance the received optical power signal, speed up the adaptation process and mitigate the channel delay spread when the system operates at a high transmission rate. The channel delay spread is minimised from 0.22 ns given by hybrid diffuse IR link to almost 0.07 ns. At 2.5 Gb/s, the authors’ results show that the imaging FABS-IR system accomplished about 11.7 dB signal to noise ratio in the presence of multipath dispersion, receiver noise and transmitter mobility.

Over last 4–5 years, there has been an exponential increase in the amount of traffic transmitted over cellular network. Importantly, with humongous increase in the Wi-Fi hotspots across many places, subscribers tend to manually switch from cellular to Wi-Fi network. However, in this process, the operator loses the visibility of subscribers, and is not able to control the congestion in network, and importantly, is not able to provide a guaranteed quality of experience (QoE) to the subscribers. In this study, a network-centric near-real-time mechanism is proposed for maintaining QoE among the subscribers but is found to be a non-deterministic problem. Importantly, an adaptive dichotomic classification based mechanism is proposed and investigated for offloading the cellular subscribers to Wi-Fi network, while keeping the computational complexity to less than O(log(n)), where n is the number of nodes in a binary tree. Further, an algorithm is proposed for intelligent selection of subscriber profile that would enable faster completion of the offloading process. An extensive simulation of the proposed algorithm and comparison with state-of-the-art mechanisms reveal up to seven time reduction in computational time; with additional performance increase occurring with increasing number of subscribers.

In this study, the authors address the downlink resource (subchannels and power) allocation problem for device-to-device communication with wireless power transfer technique in a cellular network to improve the energy efficiency (EE). The considered problem is formulated as maximising the weighted EE and is solved by leveraging a game-theoretic learning approach. Specifically, they first prove that an exact potential game applies to the resource allocation problem and there exists the best Nash equilibrium (NE) which is the optimal solution of the optimisation problem. Then, aiming to this optimisation problem with imperfect information, a robust and distributed learning algorithm is proposed and is proved that it can converge to the best NE. Finally, numerical results verify the effectiveness of the proposed scheme.

This study investigates the physical-layer security in random cognitive radio network (CRN) consisting of randomly distributed primary nodes, secondary nodes, relay nodes and eavesdroppers, where the secondary nodes share the spectrum of the primary nodes and the eavesdroppers attempt to intercept the secondary transmissions. The authors develop a framework to analysis the reliability–reliability tradeoff (RRT) and security–reliability tradeoff (SRT) in the random CRNs, where the security and reliability are quantified in terms of secrecy outage probability and connection outage probability. The RRT evaluates performance tradeoff between the primary and the secondary networks and the SRT evaluates the performance tradeoff inside the secondary network. Furthermore, they propose an opportunistic relay selection (ORS) scheme to enhance the secondary confidential transmission. It is demonstrated that the ORS scheme significantly improves the RRT and SRT as the density of relays increases, and outperforms the conventional direct transmission when the density of relays is larger than a certain value. This actually promotes the understandings of the performance tradeoffs and provides direct insights on system design for the practical CRNs.

A new beamforming scheme is proposed for multi-input multi-output (MIMO) non-regenerative relays in an overloaded synchronous direct sequence code division multiple access (DS-CDMA) network in which the number of users is larger than the processing gain. In this scheme, several transmitters multicast their data to their groups of receivers through MIMO relays and DS-CDMA technique is utilised to decrease the level of multiple access interference (MAI) at the relays and the receivers. At the relays, the data of transmitters are despread, beamformed and re-spread. The aim of the beamformer is to minimise the total relays transmission power subject to the signal to interference and noise ratio (SINR) constraints at the receivers. This optimisation problem is an indefinite quadratic (non-convex) programming. Semi-definite programming (SDP) and second-order cone programming (SOCP) are two existing methods to solve the problem. However, they, respectively, suffer from high computational complexity and performance degradation when the number of antennas or users increase. To effectively mitigate these deficiencies, we propose a novel DC (difference of two convex functions) programming method. Our simulation results demonstrate the computational advantage of the proposed DC programming over SDP, while a better performance over SOCP is achieved. Moreover, the superiority of the proposed MIMO-CDMA scheme over other multiplexing schemes is shown by several scenarios.

In this study, the channel estimation problem for the uplink massive multi-input multi-output (MIMO) system is considered. Motivated by the observations that the channels in massive MIMO systems may exhibit sparsity and the channel support changes slowly over time, the authors propose one efficient channel estimation method under the framework of compressive sensing (CS). By exploiting the channel impulse response (CIR) estimated from the previous orthogonal frequency division multiplexing symbol, they firstly estimate the probabilities that the elements in the current CIR are non-zero. Then, they propose the probability-weighted subspace pursuit algorithm exploiting these probability information to efficiently reconstruct the uplink massive MIMO channel. Moreover, noting that the massive MIMO systems also share a common support within one channel matrix due to the shared local scatterers in the physical propagation environment, an antenna collaborating method is exploited for the proposed method to further enhance the channel estimation performance. Simulation results show that compared to the existing CS methods, the proposed methods could achieve higher spectral efficiency as well as more reliable performance over time-varying channel.

To reduce multiple-failure repair traffic in erasure coded storage systems, Patrick Lee et al. introduce concurrent framework-based minimal-storage regenerating codes (RGCs). The approach is simpler and more practical than the cooperative mechanism in non-fully distributed environment. This study unifies such class of codes as concurrent RGC and further studies the characteristics by analysing the cut-based information flow graph. The authors present a general storage–bandwidth tradeoff and give closed-form expressions for the points on the curve including the minimal-bandwidth point. They show that the concurrent RGC can be constructed by reforming the existing single-node RGC or multiple-node cooperative RGC. Moreover, a connection to strong-maximum distance separable is also analysed.

Almost blank subframe (ABS) techniques emerge as inter-cell interference mitigation techniques in time region. One of the conventional ABS techniques is dynamic ABS assignment, which is able to adapt to interference state to protect the outage users more. However, the number of ABS assignments increases to protect a lot of outage users in the dense BS deployment. Therefore, the resource utilisation of base stations (BSs) decreases. Moreover, the convergence time of subframe assignment should be short enough to adapt to the change of environments. In this study, the authors propose a dynamic ABS assignment method to improve the resource utilisation of BSs and the convergence time of subframe assignment. Each BS receives feedback from surrounding BSs and users, and selects its subframe assignment based on the received feedback. Simulation results show that the proposed method improves the resource utilisation of BSs and the convergence time of subframe assignment compared with the conventional dynamic ABS assignment one, while achieving a similar user outage ratio.

In this study, the authors propose a secure transmission scheme using polar codes and artificial noise (AN) for the wiretap system without assuming the channel quality advantage of main channel over wiretap channel. They first derive lower and upper bounds on the symmetric capacity of the polarised bit-channels, which depend on the signal-to-noise ratio of each use of physical channel. According to the bounds, they prove existence of the bit-channels that are beneficial to the signal reception of the main channels but hostile to the wiretap channel, and a method based on injecting the AN at the transmitter is introduced to achieve those bit-channels. Through theoretical analysis, the security of the proposed AN method is proven. Thereafter, they elaborate two AN power allocation schemes denoted by AN-PA-I and AN-PA-II for each use of physical channel. The former proves the existence of the minimum AN power to achieve the secrecy rate that is equal to the capacity of the main channel, referred to as the maximum secrecy rate, and the latter introduces how to obtain it with an optimisation method. Numerical results show that both the two schemes can achieve the maximum secrecy rate.

Based on the original Jakes model, the authors have proposed a new design for an inexpensive fading channel simulator that can be easily actualised with fewer low-frequency oscillators than that used in existing structures. The major modifications from the original Jakes model include the generation of path gains under an improved distribution, and presetting the arrival angles and initial phases to be zero. These modifications not only reduce the hardware cost of the channel simulator, but also provide better statistic properties than the model proposed by Zheng and Xiao. Specifically, the improved Jakes fading channel model presented in this study needs only eight low-frequency oscillators. Simulation results have demonstrated that the proposed design exhibits improved first-order and second-order statistical properties.

The inherent broadcast characteristics of wireless medium make wireless data transmission difficult to be shielded from unintended recipients. As such, secure communication over wireless channels becomes a critical issue in the design of wireless networks. In this study, the authors study cooperative jamming and power optimisation in untrusted relay networks to improve physical layer security. By exploiting the direct link, a source-based jamming (SBJ) scheme is proposed to hinder the untrusted relay from intercepting the confidential message. Considering the total power budget, a power allocation strategy is also proposed to optimally determine the power of source and untrusted relay as well as the power of information and jamming signals. Furthermore, to evaluate the secrecy performance of the proposed SBJ scheme with the power allocation strategy, tight lower bound of ergodic secrecy capacity and asymptotic secrecy outage probability are derived in closed form. Simulation verifies the advantages of the proposed SBJ scheme and the power allocation strategy.

In this study, the author investigates the practical limitation of the recently proposed embedded cryptographic signature authentication scheme at the physical layer. By employing the log-likelihood ratio of a tag bit and its approximation, the author shows that the equivalent authentication channel observed by the secondary receiver can be viewed as a binary-input additive white Gaussian noise channel. Then, the sphere-packing lower bound can be employed to show the transmission capability for practical finite-length authentication tags. To achieve the same effective coverage area for both the primary and secondary receivers, it essentially requires efficient low-rate channel coding schemes with near sphere-packing-bound performance at the secondary receiver, which contrasts sharply with the pessimistic conclusion of Jiang et al.

In this study, the authors evaluate the bit error rate (BER) performance of multichannel power line communication (PLC) systems under lognormal fading and Nakagami-m background noise. The information signal propagates over two parallel, but correlated channels while maximum ratio combining and equal gain combining are implemented at the receiver side. By appropriately approximating the tail of the probability density function of a single Nakagami-m noise term and of the weighted sum of two Nakagami-m noise terms, they derive accurate expressions of the BER. They prove that single-channel and multichannel PLC systems both benefit from an infinite diversity order and that this quantity increases logarithmically with the signal-to-noise ratio. In this case, the advantage of the diversity combining techniques resides in their impact on the average energy of the fading gain; a quantity that they derive analytically by applying the lognormal-sum approximation.

Time allocation optimisation for a multi-antenna wireless energy and information transfer system is studied in this study. The terminal first harvests the wireless energy from the base station (BS) during phase I, and then uses the harvested energy to power its information transmission during phase II. Realistic channel state information (CSI) assumptions are made where the CSI at the BS is obtained via training and feedback and is subject to channel estimation error and quantisation error. Therefore, in addition to the tradeoff between information and power transfer, there is also a tradeoff in determining the overheads of training and feedback. To gain insight into this problem, the authors characterise the asymptotic behaviour of the parameters in the large system limit where the number of transmit antennas N _t and transmission block length L _tot tend to infinity with fixed ratio L _tot/N _t. The optimal overheads of training and feedback within each phase are first derived to maximise the harvested power and the information transmission rate, respectively. The optimised time allocation between phase I and phase II is then obtained by maximising the bounds of the effective average information transmission rate. Finally, numerical results are presented to verify the proposed theorems.

In this study, the authors propose a multi-round elimination contention-based multi-channel medium access control (VEC-MAC) scheme for vehicular ad hoc networks. In our proposed scheme, the control channel (CCH) interval is divided into three phases: roadside unit broadcast phase (BP), safety message BP (SBP) and service channel (SCH) reservation phase (RP). On the basis of this division, both the demand of safety-relevant applications and non-safety service applications can be satisfied. In addition, through the multi-round elimination contention in the SCH RP collision probability of transmissions significantly decreases and more successful reservations can be provided. Furthermore, the proposed multi-round elimination contention-based multi-channel MAC for VANETs (VEC-MAC) can adaptively adjust the length of the CCH interval (CCHI) and the value of the round number for the improvement of the system throughput. Theoretical analysis and simulation results exhibit the superiority of the proposed VEC-MAC in saturated throughput compared with the variable CCHI MAC and the wireless access in vehicular environment MAC.

The demands for vehicular Internet access are proliferating. To enable vehicular communications, roadside units (RSUs) can be deployed along the roadside to provide wireless coverage and network access for driving-thru vehicles and the performance of vehicle to RSU communications have been studied in multiple contexts. However, there is not still an efficient media access control (MAC) scheme specific for the sparse highway environment. In this study, the authors investigate the MAC scheme of drive-thru Internet in a sparse highway environment by a Markov chain encountering model. The analytical model incorporates the high-node mobility with the modelling of distributed coordination function (DCF) and unveils the impacts of mobility velocity and number of vehicles on the throughput. On the basis of the model, they develop a new MAC scheme and show that when vehicle number is small the proposed MAC scheme can obtain higher throughput and mitigate the impacts of vehicle mobility on the system throughput, which is desirable for the sparse highway environment. Using extensive simulations, they validate the accuracy of the analytical model and effectiveness of the proposed MAC scheme.

New transmit mutual coding for multiple input multiple output (MIMO) broadcasting is proposed. The proposed coding is based on wireless transmission over symbol multicasting to independent and uncoordinated terminals in the downlink. The motivation of proposing symbol-multicast is the fact that in digital communication the transmission is based on a finite alphabet set of symbols. Therefore, it would be possible to multicast symbols to receivers with multi-content broadcasting. In this technique, it has been shown that the required transmit power budget becomes independent of the number of served terminals in the downlink. In other words, any number of downlink terminals could be supported with finite power budget at the transmitter. Furthermore and under the same concept, a new system configuration for a single link (point-to-point) communication has been presented. With this configuration, it is possible to achieve any data rate under fixed transmit power budget.

A traffic-aware routing protocol (TARCO) that considers integrated real-time traffic conditions for constructing delivery paths over a vehicular environment is presented. This goal was achieved through three mechanisms: cooperative traffic information collection, lightweight real-time road scoring and adaptable data route construction. An accurate overall view of the real-time traffic conditions was obtained from the cooperation between information aggregators at junctions and information collectors on road segments. Each road segment was then assigned a weight according to the overall view of the traffic conditions and updated periodically to reflect traffic variations. Finally, the road segments providing efficient and reliable data routes were used to construct a routing path with guaranteed connectivity and a short delivery delay to the destination. Simulation results showed that the use of TARCO leads to high network performance in terms of the packet delivery ratio, end-to-end delay and communication overhead.

The combination of differential space–time block codes and orthogonal frequency-division multiplexing (OFDM) as differential space–frequency block coded (DSFBC)-OFDM system is a good candidate to achieve maximum diversity without the need to channel estimation. High peak-to-average-power ratio (PAPR) is a major drawback in these systems. The available PAPR reduction methods are not directly applicable in DSFBC-OFDM system. In this study, the proper application of selected mapping (SLM) method for reducing PAPR in Alamouti DSFBC-OFDM system is investigated and two different schemes are presented: conventional SLM (C-SLM) and blind differential SLM (BD-SLM). In C-SLM technique, the index of the selected phase sequence must be sent to the receiver side as the side information (SI). In the proposed BD-SLM method, specific phase mask vectors are generated with one-to-one correspondence with the different phase rotation sequences. Then at the receiver side, a differential minimum Hamming distance decoder is introduced to detect the index of optimum phase mask vectors without SI. Simulation results show that the proposed BD-SLM scheme (without the need to SI) provides good performances of both the bit error rate and PAPR reduction compared with C-SLM method.