Showing papers in "Iet Communications in 2015"

Performance analysis of non-orthogonal multiple access in downlink cooperative network

Abstract: Non-orthogonal multiple access (NOMA), an emerging technology to improve system capacity and spectrum efficiency, has attracted significant attention. In this study, the authors propose a NOMA-based downlink cooperative cellular system, where the base station communicates with two paired mobile users simultaneously through the help of a half-duplex amplify-and-forward relay. The outage performance of the system is investigated and closed-form expressions for their respective exact and asymptotic outage scheme are derived. Furthermore, they study the ergodic sum rate of the two paired users and the upper bound of the ergodic sum rate is obtained. By comparing the NOMA with conventional multiple access (MA) via numerical simulations, they have shown that NOMA can obtain the same diversity order with conventional MA, and achieve nearly the same sum rate with conventional MA. Furthermore, NOMA can offer better spectral efficiency and user fairness since more users are served at the same time, frequency, and spreading code.

Game-theoretic approach to energy-efficient resource allocation in device-to-device underlay communications

Abstract: Despite the numerous benefits brought by device-to-device (D2D) communications, the introduction of D2D into cellular networks poses many new challenges in the resource allocation design because of the co-channel interference caused by spectrum reuse and limited battery life of user equipment's (UEs). Most of the previous studies mainly focus on how to maximise the spectral efficiency and ignore the energy consumption of UEs. In this study, the authors study how to maximise each UE's Energy Efficiency (EE) in an interference-limited environment subject to its specific quality of service and maximum transmission power constraints. The authors model the resource allocation problem as a non-cooperative game, in which each player is self-interested and wants to maximise its own EE. A distributed interference-aware energy-efficient resource allocation algorithm is proposed by exploiting the properties of the nonlinear fractional programming. The authors prove that the optimal solution obtained by the proposed algorithm is the Nash equilibrium of the non-cooperative game. The authors also analyse the tradeoff between EE and SE and derive closed-form expressions for EE and SE gaps.

Cumulants-based modulation classification technique in multipath fading channels

Abstract: Automatic modulation classification (AMC) is a classical topic in the signal classification field and is often performed when the modulation type is adaptive. For typical modulation types such as M-PSK and M-QAM, the fourth-order cumulant statistics are usually used for modulation classification. Besides, it is also known that the AMC performance can be seriously degraded by the effects of multipath fading in wireless channels when compared with the ideal white Gaussian noise channel. In this study, a new modulation classification method is proposed, exploring different features of normalised fourth-order cumulant statistics for a modified blind channel estimation method in the multipath fading channel. The relationship between the cumulants of the received signal and the multipath fading effects is established to cope with the channel impulse response in the new algorithm. Simulation results show that the performance of the proposed AMC method is much improved than that of previously proposed ones in terms of the probability of correct classification.

Analysis of earth-to-satellite free-space optical link performance in the presence of turbulence, beam-wander induced pointing error and weather conditions for different intensity modulation schemes

Abstract: In this study, the authors evaluate the performance of an earth-to-satellite free-space optical link in terms of bit error rate (BER) for three intensity modulation (IM) schemes [on–off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM)] and direct detection receiver. The performance is analysed in the presence of atmospheric turbulence, beam-wander induced pointing error and weather conditions. Turbulence with beam wander effect is modelled using gamma-gamma distribution and the weather effects are incorporated using the Beer-Lambert law. They obtain closed form BER expressions for the above IM schemes using combined channel state probability density functions. They show that for the same average power, M-PPM offers the best performance, followed by M-DPPM and OOK schemes. Link performance degrades for all IM schemes with increase in the value of ground level refractive index structure parameter and bit rate. Presence of weather conditions like moderate, light and thin fog increase signal attenuation and this increase may be very high in case of thick and dense fog or clouds and can lead to link failure.

Pilot scheduling schemes for multi-cell massive multiple-input–multiple-output transmission

Abstract: This study addresses the pilot scheduling problem in multiuser multi-cell massive multiple-input–multiple-output (MIMO) systems, aiming at mitigating the inter-cell interference (pilot contamination), which constitutes a bottleneck of the system performance. First, the authors investigate the pilot reuse and scheduling problem in cellular systems with unlimited number of base station antennas, only considering the large fading coefficients. Three low-complexity pilot scheduling schemes are then proposed by maximising the system achievable sum rate, including the greedy algorithm, the tabu search (TS) algorithm and the greedy TS algorithm. Second, they investigate the pilot reuse problem among the inter-cell user terminals (UTs) under spatially correlated channels for massive MIMO transmission, trying to distinguish UTs sharing the same time-frequency resources from the spatial domain. A closed-form expression of the non-asymptotic downlink achievable rate is derived by exploiting the second-order channel statistical information. On the basis of the degree of the UTs’ covariance matrices overlap with each other, they further propose a spatial orthogonality-based greedy pilot scheduling algorithm. The proposed approaches can provide much better performance in the presence of pilot contamination. Theoretical analysis and numerical results both verify the effectiveness of the proposed algorithms.

Robust secrecy rate optimisations for multiuser multiple-input-single-output channel with device-to-device communications

Abstract: In the present study, the authors investigate robust secrecy rate optimisation problems for a multiple-inputsingle-output secrecy channel with multiple device-to-device (D2D) communications. The D2D communication nodes access this secrecy channel by sharing the same spectrum, and help to improve the secrecy communications by confusing the eavesdroppers. In return, the legitimate transmitter ensures that the D2D communication nodes achieve their required rates. In addition, it is assumed that the legitimate transmitter has imperfect channel state information of different nodes. For this secrecy network, the authors solve two robust secrecy rate optimisation problems: (a) robust power minimisation problem, subject to the probability based secrecy rate and the D2D transmission rate constraints; (b) robust secrecy rate maximisation problem with the transmit power, the probabilistic based secrecy rate and the D2D transmission rate constraints. Owing to the non-convexity of robust beamforming design based on two statistical channel uncertainty models, the authors present two conservative approximation approaches based on 'Bernsteintype' inequality and 'S-Procedure' to solve these robust optimisation problems. Simulation results are provided to validate the performance of these two conservative approximation methods, where it is shown that 'Bernstein-type' inequality based approach outperforms the 'S-Procedure' approach in terms of achievable secrecy rates.

Device-to-device channel measurements and models: a survey

Abstract: Channel measurements and modelling have been long considered as the foundation for effective and efficient wireless communication system designs. Recently, there has been an explosive growth of research work dedicated to the so-called device-to-device (D2D) communications. In the mean time, however, measurements and modelling of D2D channels seem to somewhat fall behind. To promote research on these aspects, in this study, the authors provide a critical overview of the current state of research on D2D channels, and comprehensively discuss future trends and research directions.

Performance analysis of a multi-hop power line communication system over log-normal fading in presence of impulsive noise

Abstract: The authors present a study on the end-to-end average bit error rate (BER), the average channel capacity and the outage performance of a multi-hop power line communication (PLC) system equipped with decode-and-forward (DF) relays. To combat the issue of distance dependent signal attenuation, multi-hop data transmission has recently been introduced for PLC systems. However, apart from the distance dependent signal attenuation, PLC systems also suffer from (i) the variation in signal amplitude (fading) because of reflections and (ii) impulsive noise. Thus, in this study, the channel for each hop of the multi-hop PLC system is modelled by a log-normal fading amplitude, which is clubbed to a distance dependent signal attenuation factor. To consider the effect of the impulsive noise along with the background noise, the additive noise at each node is modelled by a Bernoulli-Gaussian process. Analytical expressions for the end-to-end average BER for binary phase-shift keying, the average channel capacity and the outage probability are obtained. The merit of the multi-hop PLC system over a conventional direct transmission PLC system for fixed transmission power is shown through numerical results. The authors' results show that with increasing number of DF relays, the end-to-end average BER, the average channel capacity and the outage performance improve.

Joint optimal power allocation and relay selection scheme in energy harvesting asymmetric two-way relaying system

Abstract: Energy harvesting, which is an emerging technology to prolong the lifetime of energy-constrained wireless networks, has received significant attention In this study, the authors consider an amplify-and-forward-based asymmetric two-way relaying system, where two source nodes exchange information through an energy-constrained relay node The relay node scavenges energy from the received signals and uses the harvested energy to forward the received signals to the two terminal nodes The signal power splitting ratio, depicting the trade-off between the harvesting energy and the forward signals’ power, is a crucial factor for the system outage probability Therefore, an optimal power allocation (OPA) scheme, which jointly takes into consideration the optimisation of signal power splitting ratio and the transmission power allocation, is proposed to minimise the outage probability In addition, a close-form solution for the OPA scheme is obtained Finally, a joint OPA and relay selection schemes are presented to further improve the system performance Simulation results highlight the superiority of the author's proposed scheme

Secrecy performance analysis with relay selection methods under impact of co-channel interference

Abstract: In this study, the authors evaluate secrecy performance of cooperative protocols with relay selection methods under impact of co-channel interference. In particular, the authors propose an optimal selection scheme to maximise the secrecy capacity obtained at the cooperative phase. In addition, the authors also consider suboptimal and random selection schemes which reduce the complexity of implementation, when compared with the optimal one. For performance evaluation, the authors derive exact and asymptotic closed-form expressions of secrecy outage probability and probability of non-zero secrecy capacity for the considered schemes over Rayleigh fading channels. Monte Carlo simulations are performed to validate the derivations.

Sociality-aware resource allocation for device-to-device communications in cellular networks

Abstract: Exploiting direct transmissions between geographically close mobile users without passing through the base stations, device-to-device (D2D) communications contribute significant improvement to the spectral efficiency of cellular networks. In D2D-assisted cellular networks, the social interaction of mobile users is an important property that will affect the practical performance and should be seriously accounted in the network resource allocation, which is yet to be fully explored. In this study, the authors investigate the social interactions for D2D transmissions and develop a contact time model to characterise the D2D links. A D2D link can be considered for resource allocation only when the two users encounter and their contact time is enough long to complete a meaningful transmission. They formulate and compare both sociality-blind and sociality-aware optimisation problems for resource allocation in D2D-assisted cellular networks. Extensive numerical results are presented, validating that the sociality-aware resource allocation can achieve higher performance than that of the sociality-blind approach.

Modelling and performance analysis of dynamic contention window scheme for periodic broadcast in vehicular ad hoc networks

Abstract: This study proposes an analytical model and an effective scheme for the periodic broadcast on the control channel in vehicular ad hoc networks (VANETs). An improved Markov model for analysing the performance of the periodic broadcast in VANETs is established. Compared with the traditional two-dimensional Markov chain models, the improvement of our proposed model is achieved by the considerations of the unsaturated traffic conditions with the deterministic message generation at each node, modelled by a discrete-time D/M/1 queue and the control mechanism of freezing the backoff-time counter. In adapting to the change of the vehicle densities, the authors propose to use the dynamic contention window (DCW), instead of the fixed contention window (CW), for the broadcast in the IEEE 802.11p medium access control in VANETs. For a certain vehicle density, a best CW size is chosen to achieve a more effective broadcast. Simulation results show that the proposed DCW-based broadcast performs better than the traditional fixed-CW-size broadcast in terms of the packet collision probability. The results also validate our proposed Markov model and its performance improvement than the scheme without the consideration of freezing the backoff-time counter.

Performance analysis of free space optical links using multi-input multi-output and aperture averaging in presence of turbulence and various weather conditions

Abstract: The authors study the effect of multi-input multi-output (MIMO) spatial diversity schemes when used in a free space optical (FSO) communication link in the presence of turbulence and varied weather conditions such as very clear air, drizzle, haze, fog etc. The performance is evaluated in terms of the bit error rate (BER) and outage probability P out. We show that MIMO schemes cause a decrease in the BER and P out which, at low signal-to-noise ratios, is more significant in presence of very clear air and clear air as compared with haze and fog weather conditions. The diversity gain at a BER of 10−6 is evaluated and observed to increase as the number of transmit/receive apertures increase. However, it remains almost constant over all the weather conditions for a given MIMO scheme and turbulence strength. The performance of FSO link with MIMO schemes is compared with a FSO link using aperture averaging. Owing to constraint on the receiver aperture diameter, the aperture averaging technique fails to give the same kind of performance as provided by the higher order MIMO schemes.

Adaptive power control algorithm in cognitive radio based on game theory

Abstract: Cognitive radio (CR) has achieved increasing attention to improve the spectrum utilisation by allowing the coexistence of primary users (PUs) and cognitive users (CUs) in the same frequency band. As the spectrum of interest is licenced to primary network, power control must be carried out within the CR system so that no excessive interference is caused to PUs. In this study, the problem of power control is investigated in CR systems based on game theory subject to interference power constraint at PU and the signal-to-interference-plus-noise ratio (SINR) constraint of each CU. The objective is to reduce the power consumption caused by some CUs’ SINR over the target value. First, a non-cooperation power control game is formulated, and then an adaptive power control algorithm based on feedback function is proposed. Moreover, the existence and uniqueness of Nash equilibrium are proved. Simulation results show that, compared with other distributed algorithms, the proposed algorithm can reduce the power consumption and overcome the near-far effect.

Optimal user-centric relay assisted device-to-device communications: an auction approach

Abstract: Device-to-device (D2D) communication has recently attracted much research attention because of its potential to increase the capacity of cellular networks. Most existing works aim to maximise the overall system throughput (system-centric), which ignores the actual traffic demands of D2D users. In this study, the authors consider user-centric relay assisted D2D communications where D2D users have different evaluations for the significance of every unit of increased data rate. By considering the traffic demands of D2D users, the authors propose a Vickrey–Clarke–Groves auction based relay allocation mechanism (ARM) in which every D2D user submits a bid to the basestation (BS). The submitted bids indicate D2D users’ valuation on every unit of the increased data rate. The BS then allocates relays to D2D users by maximising the social welfare of D2D users while maintaining a predefined data rate requirement for cellular users. A payment scheme to charge D2D users for using relays is designed, and the authors show that the auction is truthful. The authors also extend the results to a general case and provide a general ARM accordingly. Extensive simulation results are provided to demonstrate the performance of the proposed mechanisms.

Multi-hop delay reduction for safety-related message broadcasting in vehicle-to-vehicle communications

Abstract: In vehicle-to-vehicle (V2V) communications, low delay and long propagation distance are very important for multi-hop safety-related message broadcasting. Most earlier studies focused on one-hop broadcasting while little attention has been paid to multi-hop delay and propagation distance. In this study, a new model for analysing the connectivity probability, average hop count and one-hop delay of multi-hop safety-related message broadcasting in V2V communications is built, taking into account the following factors: propagation distance, one-hop transmission range, distribution of vehicles, vehicle density, average length of vehicles and minimum safe distance between vehicles. Simulation results demonstrate that the proposed model can provide better performance in terms of multi-hop delay and there exists an optimal one-hop transmission range to minimise the multi-hop delay. After that, A new scheme is proposed to track the optimal one-hop transmission range by using a Genetic Algorithm. With this scheme, vehicles are allowed to adjust the one-hop transmission range based on vehicle density to reduce the multi-hop delay. The proposed scheme is validated by simulations using realistic vehicular traces.

Energy detection of unknown signals in Gamma-shadowed Rician fading environments with diversity reception

Abstract: This study presents a comprehensive performance analysis of an energy detector over Gamma-shadowed Rician fading channels, namely Rician fading channels with the fluctuating line-of-sight components following the Gamma distribution. This composite multi-path/shadowing model has been shown to provide a remarkably accurate fading characterisation while leading to closed-form expressions for important channel statistics. Rapidly convergent infinite series representations are firstly derived for the average probability of detection and the area under the receiver operating characteristic curve for the no-diversity reception case. These results are then extended to the case of maximal ratio, equal gain and selection diversity. To this end, novel analytical expressions for the statistics of the end-to-end signal-to-noise ratio of equal gain and selection diversity receivers, operating over Gamma-shadowed Rician fading channels are derived. Analytical results are substantiated by Monte Carlo simulation, as well as by extensive numerically evaluated results.

Enhancing the bit error rate of indoor visible light communication systems using adaptive channel estimation algorithm

Abstract: In this study, the authors propose an adaptive channel estimation algorithm for asymmetrically clipped optical orthogonal frequency-division multiplexing visible light communication (VLC) systems and analyse its optimal signal-to-noise ratio (SNR) threshold through the simulation experiments. The novel estimation scheme combines the advantages of orthogonal matching pursuit algorithm and least-square discrete Fourier transform algorithm. It is robust to the changes in channel distribution and SNR range. The performance for a VLC system using 16-quadrature amplitude modulation is presented in terms of mean square error (MSE) and uncoded bit error rate. In the high SNR range, the proposed scheme improves the MSE up to more than 10 dB.

Energy efficient relay selection and power allocation for cooperative cognitive radio networks

Abstract: Owing to environmental, financial and quality of service (QoS) considerations, energy efficient wireless communications have been paid increasing attention under the background of limited energy resource. This study considers a spectrum sharing cognitive radio network, where the primary system leases its radio spectrum to the secondary system for a fraction of time in exchange for secondary users served as relays to assist the transmission of the primary traffic. Based on the cooperative spectrum leasing protocol, the authors formulate a joint optimisation of relay selection and power allocation under QoS requirements to improve energy efficiency (EE). By employing a greedy spectrum sharing (GSS) algorithm, the optimal relay selection, power and sharing time allocation are readily obtained. Monte–Carlo simulations are performed to demonstrate that significant EE improvement is achieved by the proposed GSS algorithm, and that the network performance is enhanced.

Improved finite-length Luby-transform codes in the binary erasure channel

Abstract: Fountain codes were introduced to provide high reliability and scalability and low complexities for networks such as the Internet. Luby-transform (LT) codes, which are the first realisation of Fountain codes, achieve the capacity of the binary erasure channel (BEC) asymptotically and universally. Most previous work on single-layer Fountain coding targets the design via the right degree distribution. The left degree distribution of an LT code is left as a Poisson to protect the universality. For finite lengths, this is no longer an issue; thus, the author's focus is on designing better codes for the BEC at practical lengths. Their left degree shaping provides codes outperforming LT codes and all other competing schemes in the literature. At a bit error rate of 10−7 and packet length k = 256, their scheme provides a realised rate of 0.6 which is 23.5% higher than that of Sorensen et al.’s decreasing-ripple-size scheme.

Cooperative communication with energy-harvesting relays under physical layer security

Abstract: In this study, the authors propose a cooperative transmission scheme with energy-harvesting (EH) relays under wiretapping of an eavesdropper. In this scheme, the relays harvest energy from radio-frequency (RF) signals of a source through power-splitting receivers, and process arrived signals by amplify-and-forward (EH-AF protocol) and decode-and-forward (EH-DF protocol) technologies. In the proposed protocols, a best relay is selected at the destination so that the end-to-end achievable secrecy rates are maximal. Exact and asymptotic secrecy outage probability expressions are used to evaluate the EH-AF and EH-DF protocols, respectively, and are confirmed by Monte Carlo simulations. The simulation results show that (i) the EH-DF protocol outperforms the EH-AF protocol, and both proposed protocols are improved when the number of cooperative relays and the distances of the relay–eavesdropper links increase and the relays move toward the destination, (ii) the secrecy performance of the EH-AF and EH-DF protocols is the best at optimal power-splitting ratios, which are obtained by the golden section search method, (iii) the energy conversion efficiency and the noise at RF-to-baseband conversion units seriously affect the proposed protocols, and finally, (iv) the theoretical analysis results fit those of the Monte Carlo simulations.

Spectral efficiency analysis of large-scale distributed antenna system in a composite correlated Rayleigh fading channel

Abstract: In this study, the downlink spectral efficiency of multi-cell multi-user large-scale distributed antenna systems (DASs) with pilot contamination is studied in a composite correlated Rayleigh fading channel. Firstly, under a physical channel model, the equivalent channel model of large-scale DAS with pilot contamination is given. Secondly, based on the equivalent channel model, the closed-form expression is derived for the downlink achievable rate with maximum ratio transmission, and the ultimate rate is also given when the ratio of the total number of base station antennas to the number of users goes to infinity. Thirdly, the results are validated via numerical simulations. It is shown that the closed-form expression is very accurate, and the downlink achievable rate of the large-scale DAS is much larger than that of the co-located massive multiple-input multiple-output (MIMO) with the same antenna configuration.

Load-aware user association with quality of service support in heterogeneous cellular networks

Abstract: In this study, the authors propose a user association scheme with quality of service support for load balancing in heterogeneous cellular networks (HCNs), which jointly considers user's achievable rate and load level of each BS instead of only utilising the former. To reveal how HCNs should self-organise, the authors formulate it as a network-wide weighted utility maximisation problem. Note that the formulated problem is a non-linear mixed-integer one, and its optimal solutions may be very difficult to be found when it is large-scale. To solve the proposed problem, the authors design a low-complexity distributed algorithm via dual decomposition. Numerical results show that, compared with the range expansion association (REA) and best power association (BPA), the strategy has a higher load balancing level (LBL) and a lower call blocking probability (CBP). Meanwhile, the proposed algorithm occupies a very fast convergence rate when its parameters are set properly.

Spread spectrum high performance techniques for a long haul high frequency link

Abstract: Skywave ionospheric communication systems offer a good choice to satellite communications when transmitting from the poles. For the last 10 years the authors have been sounding and testing modulations through a 12 700 km high frequency link from the Spanish Antarctic Station to Spain. Previous tests comparing direct sequence spread spectrum (DS-SS) and orthogonal frequency division multiplexing (OFDM) showed that spread spectrum bit rate error (BER) results outperformed OFDM at the expense of lower bit rates. In this study the authors present three spread spectrum techniques for this long haul link that increase the bit rate and the spectral efficiency of the direct sequence while keeping the good BER performance obtained. Tests have been performed with several symbol periods as well as different bandwidth for each technique, hence the authors can conclude which combination best suits this channel.

Precoded generalised frequency division multiplexing system to combat inter-carrier interference: performance analysis

Abstract: The expected operating scenarios of fifth-generation (5G) pose a great challenge to orthogonal frequency division multiplexing which has poor out of band spectral properties, stringent synchronisation requirements and large symbol duration Generalised frequency division multiplexing (GFDM) which is the focus of this work has been suggested in the literature as one of the possible solutions to meet 5G requirements In this study, the analytical performance evaluation of minimum mean square error (MMSE) receiver for GFDM is presented The authors also proposed precoding techniques to enhance the performance of GFDM A simplified expression of signal-to-interference and noise ratio (SINR) for MMSE receiver of GFDM is derived using special properties related to the modulation matrix of GFDM, which are described in this study This SINR is used to evaluate the bit error rate performance Precoding schemes are proposed to reduce complexity of GFDM–MMSE receiver without compromising on the performance Block inverse discrete Fourier transform (BIDFT) and discrete Fourier transform (DFT)-based precoding schemes are found to outperform GFDM–MMSE receiver due to frequency diversity gain while having complexity similar to zero-forcing receiver of GFDM It is shown that both BIDFT- and DFT-based precoding schemes reduce peak-to-average power ratio significantly Computational complexities of different transmitters and receivers of precoded and uncoded GFDM are also presented

Design and analysis of a spread-spectrum communication system with chaos-based variation of both phase-coded carrier and spreading factor

Abstract: This study designs and analyses a new phase-coded spread-spectrum communication system where both phase-coded carrier and spreading factor are varied based on a chaotic behaviour in the communication process. This design aims to reduce the probability of interception of the considered system. Discrete values generated by a chaotic map are exploited to create a non-return-to-zero (NRZ)-chaos sequence and simultaneously make bit duration variable. The NRZ-chaos sequence is then modulated by binary phase-shift keying technique to produce the phased-coded carrier. Owing to chip duration being constant, the variation of bit duration also leads to the variation of spreading factor. Spectrum spreading in the transmitter is performed by multiplying directly the variable-duration bits with the phase-coded carrier. A coherent receiver relying on a direct correlator is used for recovering the data. Design of the transmitter and receiver as well as analysis of bit error probability for the proposed system in cases of single-user and multi-user under additive white Gaussian noise channel is presented. Simulation results are shown to confirm the operation of the designed structures and the obtained analytical performance.

Phase rotation-based precoding for spatial modulation systems

Abstract: In this study, the authors investigate the benefits of phase-rotation-assisted precoding (PRP) technique in spatial modulation (SM) systems, which are based on maximum free distance d min. First, a closed-form solution of the maximum-d min PRP matrix is derived for the scenario of having two transmit antennas (N t = 2). Moreover, two numerical methods are proposed for dealing with the case of N t > 2. The complexity of the proposed algorithms is presented. The authors simulation results show that the proposed PRP algorithms provide beneficial bit error ratio performance improvements compared with both the conventional SM and with the existing adaptive SM.

User-specific link adaptation scheme for device-to-device network coding multicast

Abstract: User-specific network controlled device-to-device (D2D) communication is a promising method to improve the system performance of the future cellular networks. It is a challenging task to realise the optimal link adaptation for D2D reliable multicast because of the nature of wireless radio channels. In this study, network coding is employed to enhance D2D multicast by introducing the characteristic that different information network-coded into a single multicast packet is destined to different receivers. A user-specific bit mapping algorithm is then proposed to make different information having a different equivalent coding rate before network-coded. A corresponding user-specific link adaptation scheme is proposed to adaptively choose an optimal modulation and coding scheme (MCS) for D2D multicast. Furthermore, the receiver detection procedure is then derived to recover the expected information for different users. As a result, different users obtain their respective information from a single network-coded multicast packet with different equivalent MCS according to the respective channel quality from the transmitter to them. Numerical results show that the user-specific link adaptation scheme can improve the capacity performance of network controlled D2D multicast. The throughput gain varies from 13 to 45% in different channel quality scenarios.

Spectrum combinatorial double auction for cognitive radio network with ubiquitous network resource providers

Abstract: Spectrum auction is an emerging economic scheme to stimulate both primary spectrum operators (POs) and secondary users (SUs) to be involved in spectrum sharing. Previous spectrum auction works mostly assume each PO can only have one type spectrum or each SU can only buy homogeneous spectrum bands from the same PO. However, in a ubiquitous network scenario, each PO possesses heterogeneous spectrum resources such as WiFi, 3G and each SU may request different types of spectrum bands from the same PO. Existing auction schemes cannot be used to effectively solve the problem. Therefore, the authors come out with a lightweight combinatorial double auction to tackle this challenge. Since spectrum combinatorial double auction problem is NP-hard, the authors develop a general greedy algorithm G-Greedy to solve the problem. Inspired by the recent group-buying discounts, they also invent an enhanced scheme E-Greedy to further optimise total utility. They theoretically prove the economy properties of the proposed schemes such as individual rationality, budget balance and truthfulness. Simulation results show that both of the two algorithms can yield higher utilities and are effective.

Low-complexity transmit antenna selection schemes for spatial modulation

Abstract: Link adaptation in the form of Euclidean distance-based antenna selection (EDAS) at the transmitter, has demonstrated a significant improvement in the error performance of spatial modulation (SM). However, when a large transmit antenna array is required, the computational complexity imposed by the EDAS scheme is inherently high. Thus, there is great motivation for the development of low-complexity transmit antenna selection (LCTAS) schemes for SM. In this study, the authors propose several LCTAS schemes for SM. Assuming full knowledge of the channel at the receiver, the proposed schemes select a subset of the candidate transmit antenna elements based on channel amplitude, antenna correlation, Euclidean distance between transmit vectors or a combination of these; demonstrating a significant improvement in error performance compared with conventional SM, while imposing significantly lower computational complexity than EDAS-SM. Moreover, the proposed schemes employ a novel complexity reducing technique, which allows parallel processing of algorithms and can easily be applied to existing schemes.