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.

Reed–Solomon (RS) codes possess excellent error correction capability. Algebraic soft-decision decoding (ASD) of RS codes can provide better correction performance than the hard-decision decoding (HDD). The low-complexity Chase (LCC) decoding has the lowest complexity cost and similar or even higher coding gain among all of the available ASD algorithms. Instead of employing complicated interpolation technique, the LCC decoding can be implemented based on the HDD. This study proposes a modified serial LCC decoder, which employs a novel syndrome calculation, polynomial selection, Chien search and Forney algorithm block. In addition, an improved two-dimensional optimisation is provided to reduce the hardware complexity of the proposed decoder. Compared with the previous design, the proposed decoder can improve about 1.27 times speed and obtain 1.29 times higher efficiency in terms of throughput-over-slice ratio.

In a sensing-based hybrid spectrum sharing paradigm, cognitive radio first performs spectrum sensing to identify primary users’ states (idle/busy) and then adapts its transmit power according to sensing outcomes and channel conditions. To investigate the capacity of such systems in fading channels, existing works modelled fading channel in transmission phase while additive white Gaussian noise channel in spectrum sensing; however, sensing channels also exhibit fading characteristics in practice. Therefore a more realistic system model with channel fading in both sensing and transmission is considered in this study. Under the new system model, spectrum sensing and power allocation are coupled in the ergodic capacity and an equivalent decoupling processing is proposed via mathematical manipulations. Further, joint sensing and power allocation over Rayleigh fading is studied under average interference and transmit power constraints. The optimal and suboptimal schemes are obtained by alternating optimisation and Lagrangian dual method. Finally, system performance is evaluated via extensive numerical simulations.

This study concerns joint channel and power allocation scheme for multi-user orthogonal frequency division multiple access system. The author's highlight is margin adaptive (MA) resource allocation problem namely minimising the total transmit power of users with rate requirement constraints. MA is generally provable NP-hard; the typical methods are either to relax and round, or to fix the transmission mode of users (e.g. modulation and coding). Differently, they reorganise MA problem with only power variables left and design a novel relaxation scheme to enable the convexity. The polynomial-time algorithm-interior-point method-is employed to solve the relaxation problem and the theoretical complexity is further presented. Simulation results demonstrate that the author's scheme can provide high energy efficiency compared with the existing methods, 100% relative error bounds with respect to the optimum in most cases, and low computational complexity.

A Luby transform (LT) coding scheme providing unequal error protection (UEP) is proposed. As an enhanced method, the proposed UEP-LT coding scheme can be easily applied to the existing UEP rateless codes to achieve further bit error rate (BER) performance improvement. In the proposed UEP-LT encoder, a number of the so-called fixed symbols are added to the original source symbols. The level of importance of them can be assigned as that of any subset of the original source symbols. When the encoded symbols are generated, the proposed encoder only XOR the original source symbols. Therefore the efficiency of the UEP-LT codes remains unchanged. It is found that this can benefit the belief propagation decoding. Using the And–Or tree analysis technique, the asymptotic BER performance of the proposed method is analysed in detail. Compared with some existing UEP rateless codes, the asymptotic BERs of the proposed UEP-LT codes are much lower when the parameters are properly chosen. Besides, the proposed method needs less decoding iterations to converge, which means the source symbols can be recovered earlier. Simulation results show that the BER performances are improved when the proposed scheme is applied to the existing UEP rateless codes.

There is a great interest in considering the energy efficiency (EE) as an important performance evaluation recently for its contribution to both energy saving and environmental conservation. In this study, the authors focus on the optimal energy-efficient design for downlink multi-cell environment with coordinated scheduling and beamforming. The EE is defined as bit-per-joule capacity to indicate how efficiently energy is consumed for transmitting information. They set up the optimum model for maximising the EE of coordinated cells subject to a total power constraint at each base station and study the resource allocation (RA) for it, including user selection, power allocation and beamforming vectors optimisation. They consider an equivalent non-fractional form of the original problem and propose an iterative algorithm to optimise the spectrum RA and beamforming vectors alternatively. In each iteration, the beamforming vectors are updated by the iterative algorithm based on the first-order optimality conditions, while the user scheduling policy is updated by the enhanced greedy algorithm. Performance studies show that the proposed algorithm has a rapid speed of convergence and achieves significant performance gain in EE for cellular networks.

In this study, the authors study the diversity-multiplexing trade-off (DMT) of multi-input–multi-output (MIMO) systems in which linear dispersion (LD) codes are used. They first focus on an LD-coded 2 × 2 MIMO systems at the high signal-to-noise ratio (SNR) regime. By using the joint eigenvalue density, the outage probability is presented in a very compact expression, which establishes the DMT framework at this regime. Simulation results show that the derived expression for the outage probability is sufficiently accurate at high SNR regimes but less accurate in the transition region. Finally, for the special case of multi-input–single-output, they derive both the outage probability and the DMT framework inexact and closed form formulas at all SNRs, including finite SNRs.

In this study, the authors present the measurements performed on a free space optics (FSO) communications link using an indoor atmospheric chamber. In particular, the authors have generated several different optical turbulence conditions, demonstrating how even the weak turbulence regime can strongly affect the FSO link performance. The authors have carried out an in-depth analysis of the data collected during the measurements, and calculated the turbulence strength (i.e. scintillation index and Rytov variance) and the important performance metrics (i.e. the Q-factor and bit error rate) to evaluate the FSO link quality. Moreover, the authors have tested, for the first time, an appositely developed temporally-correlated gamma–gamma channel model to generate the temporal irradiance fluctuations observed at the receiver. This has been accomplished by using a complete analysis tool that enables the authors to fully simulate the experimental FSO link. Finally, the authors compare the generated time-series with the collected experimental data, showing a good agreement and thus proving the effectiveness of the model.

In this study, the authors’ present a scheme, denoted as BMST-MSK, which combines the block Markov superposition transmission (BMST) with the minimum shift keying (MSK) signalling. The BMST-MSK can be implemented in two forms – the BMST with recursive MSK (BMST-RMSK) and the BMST with non-recursive MSK (BMST-NRMSK). The BMST-MSK admits a sliding-window decoding/demodulation algorithm, where two schedules with or without iterative processing between the BMST and MSK (referred to as outer iteration) are discussed. To analyse the asymptotic performance of BMST-MSK, the authors’ first assume a genie-aided decoder and then derive the union bound for the equivalent genie-aided system. Numerical results show that the performances of the BMST-MSK match well with the derived lower bounds in the low error rate regions. From simulations, the authors’ found that the outer iterations can provide performance improvement for the BMST-RMSK, but not for the BMST-NRMSK. Taking a (2,1,2) convolutional code with input length of 10 000 bits as the basic code, the BMST-NRMSK achieves a bit-error-rate of 10⁻⁵ at E _b/N ₀ = 0.45 dB over additive white Gaussian noise channels, which is away from the Shannon limit about 0.25 dB.

For conventional subcarrier pairing scheme in cooperative orthogonal frequency division multiplexing decode-and-forward multi-relay networks, to avoid interference, each subcarrier pair (SP) is assigned to a single relay. Over a specific subcarrier, the destination receives signals transmitted from the relay. In this study, to better exploit the degrees of spatial freedom, the authors propose to assign each SP to multiple relays. Thus, over a specific subcarrier, the destination receives signals transmitted from multiple relays. Under the total network power constraint, to maximise the sum transmission rate, they propose a joint resource allocation scheme, in which they jointly optimised the four types of resources: assisting relays selection, transmission mode selection, subcarrier pairing and power allocation. They further propose a suboptimal algorithm which can significantly reduce the computational complexity of the aforementioned optimal allocation scheme with sacrificing little on the performance. It is shown from simulation results that the author's proposed schemes have significant performance improvement over the resource allocation schemes in the literature.

Increased mobility coupled with a possible reduction of cabling costs and deployment time makes wireless communication an attractive alternative for the industrial process monitoring and control. The major obstacles towards the utilisation of wireless industrial systems are predominantly the timing and reliability requirements. In this study, the authors take jointly the timing and reliability requirements, limited wireless resources and the cyclic data feature into consideration, and study the performance bounds and two-stage time- and channel-optimal convergecast scheduling algorithms for wireless industrial systems with hierarchical star and mesh architecture. Specifically, they consider the convergecast communication for wireless industrial systems operating according to the recent wireless network for industrial automation–process automation standard; and they will provide bounds on the minimum convergecast schedule length and bounds on the minimum number of channels for cluster-line and cluster-tree routing structures. In both cases, they propose time- and channel-optimal two-stage scheduling algorithms. They evaluate the author's two-stage scheduling algorithms by both simulation and real hardwares. Numerical results demonstrate that their algorithms are efficient compared with traditional time division multiple access-based convergecast scheduling algorithms.

Energy detection is the most frequently used spectrum sensing technique, however, in uncertain low signal-to-noise ratio (SNR) conditions, it generally suffers from the ‘SNR wall’, that is, a minimum SNR below which it is impossible to reliably detect a signal. To address this issue, an improved energy detection (IED) algorithm based on non-linear parameter-induced stochastic resonator (PSR) is proposed in this study. By adopting the method which combines classic adiabatic approximation stochastic resonance (SR) theory and non-classic parameter-induced SR theory, an analytical expression of SR system parameters is derived. On this basis, a PSR is proposed which is mathematically testified to have the ability to improve the SNR of the received signal. Further, an IED algorithm is proposed by introducing the PSR as the preprocessor of energy detection. Theoretical analyses and simulation results prove that a significantly detection performance and SNR wall improvement can be achieved using the proposed IED algorithm.

In fast fading channel, for reducing detection complexity, a nearly banded channel is adopted in many literatures. For the sake of designing a nearly banded channel perfectly, the authors deduce the relationship between the bandwidth of the nearly banded channel matrix and normalised Doppler frequency shift under certain power of negligible intercarrier interference (ICI) coefficients. Then, in order to take account of all the ICI coefficients when the nearly banded channel matrix is divided into N blocks, a new structure of nearly banded channel matrix is proposed. On the basis of the new proposed structure, sequential detection with successive cancellation and sequential detection with optimal ordering are applied to detect the orthogonal frequency division multiplexing signals in each block. Simulation results show that although a little more computational complexity is costly, the detection methods using the proposed structure can achieve better performance than the detection methods using the original blocks.

In this study, the authors investigate the impact of the frequency-hopping (FH) sequence on the packet transmission performance of the asynchronous frequency-hopping multiple-access (FHMA) network. According to the model of the asynchronous FHMA network given in this study, the authors analyse the impact of the two important FH sequence factors – uniformity and frequency slot number – on the correct transmission probability and the packet transmission frequency efficiency. According to the non-collision probability analysed in this study, the uniformity of the FH sequence is an important issue to determine the correct packet transmission probability. Moreover, based on the definition of the packet transmission frequency efficiency given in this study, the optimal frequency slot number employed to obtain the maximum frequency efficiency is obtained. By employing three typical FH sequences, the simulation results are also included, which validates the theoretical analysis about the packet transmission performance of the asynchronous FHMA network.

This paper presents a comprehensive study on the Full-Rate and Linear-Receiver (FRLR) STBC proposed as a newly coding scheme with the low decoding complexity for a 2×2 MIMO system. It is shown that the FRLR code suffers from the lack of the non-vanishing determinant (NVD) property that is a key parameter in designing a full-rate STBC with a good performance in higher data rates, across QAM constellation. To overcome this drawback, we show that the existence of the NVD feature for the FRLR code depends on the type of the modulation. In particular, it is analytically proved that the FRLR code fulfills the NVD property across the PAM constellation but not for the QAM scheme. Simulation results show that, at a BER equal to 10⁻⁴, utilising the PAM modulation for the FRLR-STBC, provides about 2 dB gain over a use of the QAM when the bandwidth efficiency is 6b/s/Hz. In addition, for the PAM constellation, the FRLR code significantly outperforms some existing full-rate STBCs. Finally, we utilise the moment generating function approach to derive an exact closed-form expression for the average error probability of the FRLR code with the BPSK modulation.

This study presents a solution to the interference management scheme and resource allocation strategy for the two-tier femtocell networks, where the femtocell users (FUEs) share the same frequency band with the existing macrocell users. It is assumed that the FUEs compete for the available spectrum to fulfil their own communication. And the macrocell base station protects itself by pricing the interference from the FUEs, which formulates the Stackelberg game. In this study, two effective pricing schemes, uniform pricing scheme and non-uniform pricing scheme, combining with admission control are proposed to maximise the revenues and protect the quality of service requirements. The Stackelberg equilibriums for the proposed games are investigated. Besides, a novel distributed interference pricing algorithm is provided for the uniform pricing case. Numerical results show that, in two-tier femtocell networks with shared spectrum, the proposed pricing schemes are effective in resource allocation and performance protection.