In this study, we propose a four-dimensional modulation, referred to as modulation network coding (MNC), to address the problem of decoding a signal from multiple source node transmissions in mobile fast fading channels. The MNC scheme judiciously mixes a two-dimensional (2D) pilot symbol with a 2D information symbol, and makes use of a π/4 rotated M-pulse-amplitude modulation (PAM) constellation to guaranty an effective decoding of all the interfering symbols even in the case of a smaller channel Doppler spread compared with the period of the MNC symbol. In addition, because the MNC scheme makes use of an additional dimension introduced through orthogonal pulse waveform, the use of the pilot symbols does not reduce the effective information rate. The analytical and simulation results show that it is possible to achieve a low symbol error probability with a good signal-to-noise ratio when controlling a few parameters impacting the performance of the system such as the synchronisation in time and in frequency of the source nodes.

With the advent of small-cell networks (SCNs) to support growing wireless data volumes and thus reduced cell sizes, cooperative communications are significantly facilitated. Applicable to Third Generation Partnership Project long-term evolution-A, the authors propose a novel channel/queue-aware user pairing and scheduling scheme in a cooperative virtual multiple-input–multiple-output (VMIMO) system. The queueing performance of the VMIMO system with the scheduling scheme is analysed based on the finite-state Markov model (FSMM), and compared with that of non-cooperative systems. Bounds on the average queuing delay of users are derived by using a semi-definite programming (SDP) approach. The presented analyses are validated through comparing the analytical and simulation results. It is found that the introduced VMIMO pairing process is able to significantly reduce service delays, bringing on a positive impact of cooperative techniques on next generation wireless systems.

Owing to limited resources, it is hard to guarantee minimum service levels to all users in conventional cellular systems. Although global cooperation of access points (APs) is considered promising, practical means of enhancing efficiency of cellular systems is by considering distributed or clustered jointly processed APs. The authors present a novel ‘quality of service (QoS) balancing scheme’ to maximise sum rate as well as achieve cell-based fairness for clustered jointly processed cellular multiple access channel (referred to as CC-CMAC). Closed-form cell level QoS balancing function is derived. Maximisation of this function is proved as an NP hard problem. Hence, using power-frequency granularity, a modified genetic algorithm (GA) is proposed. For inter site distance (ISD) < 500 m, results show that with no fairness considered, the upper bound of the capacity region is achievable. Applying hard fairness restraints on users transmitting in moderately dense AP system, 20% reduction in sum rate contribution increases fairness by upto 10%. The flexible QoS can be applied on a GA-based centralised dynamic frequency planner architecture.

Frequency domain blind channel estimation methods for orthogonal frequency division multiplexing (OFDM) systems with multiple antennas are proposed, in which the cross relation between the channel gains and a single snapshot of the received signal on each subcarrier is utilised. Necessary and sufficient conditions for the identifiability of a single-input multiple-output OFDM channel estimator are derived and, furthermore, using a first-order perturbation analysis, the approximation of mean-squared-error (MSE) is analytically obtained, which shows that the proposed estimator is approximately unbiased at high signal-to-noise ratio. The proposed estimator exhibits lower MSEs than those of both the existing subspace-based and deterministic blind channel estimators and is less sensitive to the estimation error of the number of multipaths. Finally, the extension of the proposed channel estimation to multiple-input–multiple-output OFDM is presented.

In this study, the authors propose a novel equalisation digital on-channel repeater (EDOCR) with a feedback interference canceller (FIC) for a single frequency network of the advanced television systems committee terrestrial digital television system. The proposed EDOCR with an FIC not only has high output power by the cancellation of feedback signals caused by insufficient antenna isolation through the FIC, but also shows better quality of output signals than conventional digital on-channel repeaters (DOCRs) by removing multipath signals existing between the main transmitter and DOCR, as well as residual feedback signals through an equaliser. Computer simulation results are provided to demonstrate the superior performance of the proposed EDOCR with an FIC.

The authors consider a relay communication system, where all nodes are equipped with multi-input multi-output antennas, and there is a direct path/channel between the source and the destination. Assuming a linear non-regenerative relaying, the relay matrix is designed by maximising the signal-to-noise ratio of the system. The authors derive the optimum relaying matrix for different power constraints in the relay, including the fixed relay power constraint and constraint on the maximum transmitting power from the relay. Under the constraint of fixed total transmit power, they derive the optimum power budgets of the relay and source that only depend on four positive quantities. They prove that there always exists a rank-one relaying matrix, which transmits signal in one-dimensional subspace and leaves the other subspaces clean. In addition, when the quality of the source–destination (SD) channel is poor, this matrix is the best rank-one relaying transform that maximises mutual information between the source and the destination. Finally, they conclude that the relaying is beneficial only if the link quality for the source–relay is twice better than that of the SD, where the link quality is proportional to the ratio of the channel power gain to the received noise variance.

This work builds an intelligent environmental monitoring system for industrial production and safety concerns. There are a number of smart monitoring systems developed for smart grids, bridges or machine system management, temperature/humidity monitoring and so on. As information technology advances at a continuous rapid pace, humans have become connected online and this connection has extended into the interactions between things and humans. Employing the FLAG-PSoC-1605A development board as the platform, all sensor data are transmitted via a ZigBee wireless module, a TCP/IP network module and a long range wireless communication GPRS/SMS module to a remote end PC for analysis. This constitutes a smart network for connections between humans and objects.

This study exploits coordinated proportional fair (PF) user scheduling for in-building distributed antenna systems (DAS) to address the co-channel interference problem. The PF algorithm for multiple remote units in the DAS has been analysed and two sub-optimal solutions have been proposed, which manage to maximise the subcarrier-wise summation of PF ratio either in a brute-force search manner or in a greedy manner with lower complexity. System-level evaluation shows that the throughput of the cell edge users can indeed be significantly improved, whereas the average throughput of radio units in the proposed schemes also outperforms that in the conventional PF scheme.

The authors propose two soft forwarding schemes for unitary space-time modulation, namely estimate-and-forward (EF) and mutual information-based forwarding (MIF), which are ideally suited for rapid piecewise-constant fading scenarios with no channel state information both at transmitters and receivers. In the EF scheme, the relay regenerates signal via the conditional expectation of the source unitary space-time (UST) signal given the received matrix at the relay node instead of hard decisions. The MIF scheme employs the instantaneous mutual information between the source UST signal and received matrix at the relay node as a measurement for maximum-likelihood detection. The authors provide the relay forwarding functions, the normalisation factors, and the detection methods at the destination firstly. Above all, the generalised signal-to-noise ratio (SNR) at the destination for our unitary space-time modulated relaying system is analysed and simulated firstly. Simulation results reveal that the proposed EF and MIF schemes can outperform the existing amplify-and-forward (AF) and detect-and-forward (DF) schemes in terms of bit-error-rate performances in most scenarios. For a parallel relay network with two relays, the proposed EF scheme achieves 2 and 3 dB SNR gain over AF and DF schemes, respectively. Moreover, the MIF scheme can further give about 1.5 dB SNR gain.

In deep space communications, the received signals are always highly dynamic and very weak, which makes it quite challenging to achieve reliable data reception. To tackle these problems, a robust algorithm which joins tracking and code-aided synchronisation is proposed in this study. The frequency lock loop-assisted phase lock loop is used as the tracking loop, which integrates the characteristics of both outstanding dynamic performance and precise measurement. The code-aided synchronisation is adopted as the demodulation and decoding loop, which utilises the relationship among the coded symbols to assist signal demodulation under the low signal-to-noise ratio condition. It is worth pointing out that the power tradeoff between the main carrier and subcarrier signals which operate in the two loops mentioned above is also optimised to minimise the total transmitting power. Simulation results showed that the proposed scheme with code rate 1/5 low-density parity-check codes could almost eliminate the effect of these factors, with the excellent performance, which closely approximates the ideal decoder in additive white Gaussian noise channel.

In this study, the authors consider distributed orthogonal space–time block coding for relay-based channel state information-assisted amplify-and-forward networks. Specifically, they show that opportunistic relaying (OR) is an optimal solution in terms of instantaneous signal-to-noise ratio (SNR), that is, it provides the maximum instantaneous SNR under the constraint of fixed transmit power for the relays. In particular, instead of allocating the given transmit power to all relays, letting the best relay transmit with this power is an optimal solution for maximising the received SNR. To exhibit this benefit, Monte Carlo simulations are presented showing superior performance of the OR scheme compared to equal power allocation policy for the considered relay networks. For the considered optimal scenario, the authors further derive analytical expressions for the outage probability and symbol error rate (SER) over quasi-static independent, not necessarily identically distributed Nakagami-m fading channels. They further present asymptotically tight approximations for the outage probability and SER in the high SNR regime, rendering insights into the cooperative diversity behaviour. Finally, numerical results are provided to examine the effect of network parameters on the system performance of the considered network.

In the cooperative relay system, different frames from different relays are not aligned in the time domain, and have different carrier frequency offsets (CFOs). Estimation of these timing offsets and CFOs is a crucial and challenging task. In this study, a new training structure is proposed, and a novel time and frequency synchronisation scheme is presented for orthogonal frequency division multiplexing-based (OFDM-based) cooperative systems. The coarse time synchronisation is accomplished by using the symmetric conjugate of the training symbol and the fine time synchronisation is accomplished by segment-moving correlation. The fractional frequency offset is estimated by using the phase difference of the received signal and the integral frequency offset is estimated by utilising the good autocorrelation of the training symbol in frequency domain. The analysis and the simulation results show that, compared with the traditional scheme, the proposed scheme has better timing and frequency offset estimation performance and lower complexity for OFDM-based cooperative systems.

The prediction-error filter is a well-known tool for blind communication channel equalisation. For multipath channels, it has two disadvantages considered here. First, in transversal form, it must be substantially longer than the impulse response of the channel, with a consequent high computation cost; second, it cannot fully equalise mixed-phase channels. Here, the authors examine a recursive version of the linear predictor, used with additional prediction delay for blind channel-shortening of multipath channels with multi-carrier modulation signals using a cyclic prefix. The recursive mode of operation allows the filter length to be significantly shorter than in the transversal, non-recursive form. In tests using modelled channels, they observe two significant results. First, for channels that include maximum-phase terms, the additional prediction delay ameliorates the filter response to maximum-phase terms. Thus, channel-shortening may be achieved, at least partially, unless the maximum-phase terms are severe. Second, the recursive prediction-error filter impulse response adapts to a stable minimum-phase form. This low-cost technique, then, may be used to augment the use of a cyclic prefix in reducing inter-symbol interference in multipath channels.

Rate-adaptive modulation and transmit antenna selection require channel knowledge at the transmitter, typically achieved using a feedback communications path from receiver to transmitter. Feedback delay in such systems causes outdated channel knowledge at the receiver and thus suboptimal switching decisions. This study evaluates the effect of degraded switching and proposes a channel prediction scheme to mitigate against delay-induced performance degradation, specifically when deployed in Rayleigh fading channels using maximum ratio combining at the receiver. Shannon capacity expressions are found and then closed form bit-error-rate and average spectral efficiency expressions derived – all derivations supporting arbitrary number of antennas at both receiver and transmitter. These expressions are developed to allow optimal switching boundaries to be determined for M-quadrature amplitude modulation rate adaptation under different degrees of channel prediction error, system arrangement and number of antennas.

Wavelength-division multiplexing (WDM) technology has been recognised as one of the most promising solutions in optical access network. A general ring-based multi-wavelength optical access network based on WDM technology, which can realise triple-play service including point-to-point service and multicast service is introduced in this study. To effectively utilise the network bandwidth resources, the authors propose a joint bandwidth allocation scheme on dedicated and shared wavelengths. The proposed scheme focuses on quality of services (QoSs) support. It is carried out according to the priority queue discipline to support QoS in terms of average packet delay, packet delay variance and throughput. Moreover, with the fair-awareness in the scheduling scheme, the lower priority services can be prevented from starvation and the over-allocation problem can be avoided. The simulation results show that the proposed scheme can reduce average packet delay and packet delay variance for high-priority services to ensure QoS.

This study presents an effective lazy schedule (LS) for the layered belief propagation (LS-LBP) algorithm; it significantly reduces the number of iterations and the error floors of decoding. This novel LS forces a check node into a sleep status when the reliabilities of its neighbour variable nodes exceed the threshold, and the check node will turn to awake as all the nodes are in sleep status. This LS reduces latency by ignoring useless check-node processes, and it also achieves a low error rate by overcoming some trapping sets. The simulation experiment shows that when compared to the classical layered belief propagation for world interoperability for microwave access (WiMAX), random codes constructed using the progressive edge-growth (PEG codes) algorithm, and digital video broadcasting-satellite-second generation (DVB-S2) codes, this LS increases the decoding convergence speed by up to 36% to achieve the bit error rate 1 × 10^–6 and reduces the error floors to 20–45% for the PEG and DVB-S2 codes. Compared with other schedules for the layered belief propagation, the LS-LBP algorithm is more suitable for the codes with a long block length and has lower complexity.