In this study, the authors analyse the impact of channel estimation error (CEE), feedback delay (FD), and co-channel interference (CCI) on the performance of multiple-input multiple-output (MIMO) systems deploying maximum ratio transmission (MRT). In particular, the authors derive closed-form expressions for the ergodic capacity and the symbol error rate (SER) as well as the outage probability (OP). In addition, to reveal the effect of CEE, FD and CCI on the MIMO-MRT system, the authors adopt more simplified and tractable formulas in terms of asymptotic expressions for the ergodic capacity, SER and OP. The analysis shows that the system performance is degraded considerably under imperfect transmission conditions such as CEE, FD and CCI. However, the authors can compensate part of this degradation by deploying MRT transmission with a large number of antennas at the transmitter and receiver. Finally, the selected examples exhibit consistency between analytical results and Monte Carlo simulations.

Although the techniques of cooperative transmission have been developed for terrestrial sensor networks in recent years to improve the bit-error-rate (BER) performance, the unique characteristics of the underwater acoustic communication channel, such as large and variable propagation delay and the three-dimensional network topology, make it necessary to reconsider the implementation and analysis of cooperative transmission in underwater acoustic networks. In this study, two asynchronous forwarding schemes, namely underwater amplify-and-forward (UAF) and underwater decode-and-forward (UDF), are proposed. Although the fading model for underwater channel is complex and there is still no consensus in the research community on a model which is applicable for all underwater channels, the authors simulation results show that both UDF and UAF have better performance than direct transmission under different underwater channel configurations, and there is a breathing effect for BER performance improvement caused by underwater multi-path fading. Finally, some insights on choosing the proper parameters to improve performance of underwater cooperative transmission are provided.

The objective of this study is to design sub-optimal signature matrices for binary inputs for an overloaded code division multiple access (CDMA) system as developed by this author group. In this study, the authors propose to use the sum capacity, the bit error rate and distance criteria as objective functions for signature matrix optimisation. Three optimisation techniques, the genetic algorithm, the particle swarm optimisation and the conjugate gradient (CG) are exploited in this work. Since the optimisation computational complexity increases by matrix dimensions, it is practically impossible to directly optimise the large signature matrices. In order to address this problem, a method is proposed to enlarge small-scale signature matrices. It is also proved that the sum channel capacity of the enlarged matrix is scaled by its enlargement factor. The results indicate that this proposed signature matrices provide higher sum capacity than the commonly used signature matrices. The authors also address that this matrices are applicable for highly overloaded CDMA systems.

The study suggests a new non-line of sight (NLOS) error mitigation algorithm based on Kalman filter and neural network. According to the construction features of the former and the statistic characteristics of the latter, the study theoretically deduces the condition to obtain the unbiased estimation of the true value of TOA, and then the study fixes on the state transition matrix of Kalman filter with neural network in different environment. The simulation results based on wideband code division multiple access (WCDMA) experimental data show that the location performance is improved with better estimation accuracy and robustness.

Distributed antenna systems (DAS) have been paid much attention for low outage probability in future wireless communications, since it can reduce the radio transmission distance between the transmitter and the receiver. In this study, the authors present a study on DAS for two different transmission strategies: blanket transmission scheme  and single selection transmission scheme (SSTS). The outage probabilities of the two schemes are re-analysed over Rayleigh fading adopted non-central limit theorem (NCLT) and compared with central limit theorem (CLT) method. Moreover, the authors derive analytical expressions of the outage probability for both no shadowing and shadowing scenarios, respectively. Then, an energy efficient power allocation strategy is proposed. Finally, extensive simulation results validate the theoretical analysis and demonstrate the proposed NCLT method can describe the system performances more accurately.

This study investigates channel estimation for amplify-and-forward (AF) relaying systems. For a two-hop relaying system, channel estimation of a relay path (source–relay–destination) with AF relaying is unique because both individual source-to-relay (S–R) and relay-to-destination (R–D) links are necessary at the destination to perform the optimum combination of signals received from the direct path (source-to-destination) and relay path if employing a cooperative diversity transmission. Until now, most literature about channel estimation on relaying systems has focused on the composite channel of the relay path, and not its individual links. Current methods to separate the estimation of both individual links require the relay to either deliver a quantised version of the S–R link estimate through an independent feed-forward channel, or to perform discrete Fourier transform/inverse discrete Fourier transform operations before amplifying the received signals. In this study, the respective channel estimations are done at the destination. First, the destination utilises a relay amble (R-amble) to obtain channel estimation of the R–D link. Next, exploiting the R–D link estimate, a maximum-likelihood estimator is proposed for the S–R link in a decision-directed (DD) way. Simulation results show that the proposed scheme out performs the current relay-assisted methods in most circumstances. In addition, numerical results reveal that the mean-square error can be significantly reduced in a DD way for symbol error rates of interest.

This study re-examines the spectrum of quantisation noise and studies the quantisation noise within signal band for sinusoid signals and for uniform quantiser. Both the process of sampling and folding which have not been fully taken into account in previous analysis are considered theoretically. The authors’ results show that the quantisation noise within signal band for sinusoid input decreases in broken line as the sampling rate increases, which suggests that a higher signal to in-band quantisation noise ratio will be obtained if the sinusoid signal is sampled at odd multiple of its fundamental frequency. Moreover, the effects of quantisation step size and the amplitude of sinusoid signal to in-band quantisation noise are presented by computer simulations.

A new scheduler with the capability for distributed quality of service (QoS) provision is presented. Based on the game-theoretic concepts of coalition formation and bargaining, this scheduler follows a hybrid approach to allocate subcarriers and to satisfy the minimum rate requirement of the wireless users. In the first part of the allocation process, a greedy approach is used to provide users minimum data rate requirements. Then, in the game-theoretic part of the process, the remaining resources are split in a fair manner between the users by forming dynamically sized coalitions and by allowing users to bargain with each other, using the Nash bargaining solution. The novelty of this approach lies in the fact that it allows the distributed, partly-cooperative provision of QoS in a multiuser wireless channel. This new scheduler is compared against the proportional fair and greedy schedulers and the simulation results indicate that the proposed scheduler offers better QoS outage performance than others. It also offers fairness and sum rate that are comparable to the PF scheduler, while the comparison with the Greedy scheduler indicates significantly better fairness, but lower sum rate.

To overcome the performance loss caused by the Nth single best relay selection schemes, in this study, the authors present the N–Rth dual best relays selection schemes. In the proposed schemes, there are two relays selected out of the available relays to forward the received signals to the destination by using the decode-and-forward protocol. The statistical descriptions of instantaneous end-to-end received signal-to-noise ratios (SNR) are investigated over independent and non-identically distributed Nakagami-m fading channels. By using the appropriate mathematical proof, the authors firstly obtain the closed-form expressions to the probability density function and cumulative distribution function of instantaneous end-to-end SNR. Then, based on the derived results, the outage probability and average symbol error rate (SER) of the proposed N–Rth dual best relays selection schemes are investigated. The comparison analyses between the Nth schemes and the N–Rth schemes show that the proposed N–Rth dual best relays selection schemes can improve greatly the performance of opportunistic relaying systems such as outage probability and average SER. Especially, the proposed dual best relays selection scheme can obtain more outstanding improvement on SER.

Alamouti code is an excellent option for a two-transmitter and one-receiver network owing to its optimal performance and low detection complexity. Unfortunately, with the requirement of odd number of time slots in the frame structure for data transmission of long-term evolution (LTE)-advanced systems, this scheme is not applicable to such systems. In this correspondence, three new space–time block codes (STBCs) are proposed for LTE-advanced systems with two transmit antennas and a receive antenna with three-time-slots. The proposed designs achieve rate of one symbol per channel use and full transmission diversity. The main objective of designing the first and second codewords is to improve the coding gain of STBCs with three time slots. These STBCs are constructed using real rotation of quadrature amplitude modulation (QAM) information symbols in three dimensions. As will be seen later, the idea of real rotation of transmitted symbols using orthogonal matrices allows a decrease in the number of unknown parameters to be determined in order to maximise the coding gain. Using real rotation to encode the transmitted symbols, a new scheme is obtained which has the same minimum determinant (MD) as Alamouti code for 4, 16 and 64-QAM signal constellations. In designing the last codeword, the authors attempt to reduce the maximum-likelihood decoding complexity by decoupling detection of one encoded symbol from others. The simulation results confirm an improved performance of new schemes as compared to recently proposed codes.

In this study, the authors propose a new class of rateless codes applicable to noisy channels, that is, the so-called accumulate rateless (AR) codes, which concatenate the low density generator matrix (LDGM) rateless code with a simple post-code, that is, a post-position accumulator. The new coding structure is not only effective in reducing the ‘error floor’ as observed in traditional LDGM rateless codes such as Luby transform (LT) codes, but also quite simple for realisation as compared with the rateless codes using a pre-coding structure such as Raptor codes. The extrinsic information transfer charts and the corresponding projection of intersectant curves for both the systematic and non-systematic AR codes are analysed. Based on these, their convergence performance and optimal degree distributions are investigated. Simulation results show that, the performance of AR codes over additive white Gaussian noise channel is comparable to that of Raptor codes.

Transform domain communication system (TDCS), as an overlay cognitive radio communication system, has been proposed to obtain a low probability of interception by using spectrum bin nulling to synthesise an adaptive waveform corresponding to the spectrum sensing output. However, its low spectral efficiency limits potential practical applications. In this study, an efficient modulation scheme, namely quadrature cyclic code shift keying (Q-CCSK), is proposed for TDCSs by generating another fundamental modulation waveform as the data-bearing quadrature branch. Although using Q-CCSK doubles the spectral efficiency for TDCSs, the instinct inter-branch interference arises from the added quadrature branch. Through the orthogonality analysis, it is proven that the two branches (in-phase and quadrature- branches) are still satisfied the property of quasi-orthogonality. Moreover, the performances of TDCSs employing Q-CCSK in additive white Gaussian noise (AWGN) and multipath fading channels are discussed, respectively. Analytical and simulation results demonstrate that, compared with conventional schemes, the TDCS employing Q-CCSK can double the spectral efficiency with comparable systematic performance.