In this study, the authors present an algorithm to detect unknown interference in slow frequency-hopped quadrature phase-shift-keying systems. Both partial-band noise interference and multitone interference are considered. The algorithm is developed based on the correlator outputs over one hop. A suitable threshold level is derived for detection. The authors formulate the analytical expressions for probability of detection for both interference models. Numerical results reveal that the proposed algorithm can detect both interference types even at low interference power.

Multipath arrivals in an ultra-wideband (UWB) channel have long time intervals between clusters and rays where the signal takes on zero or negligible values. It is precisely this signal sparsity of the impulse response of the UWB channel that is suitable for the application of compressed sensing (CS) theory. However, these multipath arrivals mainly depend on the channel models that generate different sparse levels (low-sparse or high-sparse) of channels according to which, the authors have analysed and chosen the best recovery algorithms which are suitable for the sparse level for each type of channel model. Criteria for evaluating the algorithms are based on computational complexity, ability to reduce the sampling rate and processing time. Besides, the results of this work are an open topic for further research aimed at creating an optimal algorithm specially for application of CS-based UWB systems.

A new expression of the generalised Marcum Q-function is obtained in terms of incomplete cylindrical function. Based on the new representation, new lower and upper bounds of the first-order Marcum Q-function are formulated. The bounds are represented in terms of the error and modified Bessel functions. Unlike the existing bounds, the tightness of the new bounds is maintained over the entire range of arguments of the Marcum Q-function, which is numerically and theoretically demonstrated. To show the usefulness of the formulated bound, the upper and lower of a generic integral is formulated in the performance analysis of an antenna diversity system under a Nakagami fading channel. The uniform tightness of the bound of the integral is also observed. Then, the authors consider the average bit error rate (ABER) probability of the equal gain combining diversity system in the fading channel, which show that the proposed bound can estimate very tight bound of the ABER probability.

For a fading full-duplex decode-and-forward relay channel, the authors analytically derive optimum power allocation schemes subject to individual power constraints at the source and the relay. The authors prove that the problem is a convex optimisation problem over the feasible power set, and by proposing a systematic technique to solve min–max problems, optimum power allocations are derived in closed-forms. Finally, for a Rayleigh-fading channel model, optimum power allocations are derived and the respective achievable rate and an upper bound are evaluated. The implications of the derived theoretical results are discussed through some graphs.

In this study, the authors obtain a general and new achievable rate region and some certain capacity theorems for multiple-access relay channel (MARC), using partial decode-and-forward (PDF) strategy at the relay, superposition coding at the transmitters and multiple-access and relay channel (RC) decoding schemes. (a) The authors general rate region (i) generalises the achievability part of Slepian–Wolf multiple-access capacity theorem to the MARC, (ii) extends the Cover–El Gamal best achievable rate for the RC with PDF strategy to the MARC, (iii) gives the Kramer–Wijengaarden anticipated rate region for the MARC and (iv) meets max-flow min-cut outer bound for some important classes of the MARC. (b) They extend the results to the Gaussian case as an important practical aspect of MARC and obtain (v) a general and new achievable rate region for Gaussian Slepian–Wolf MARC. Finally, they evaluate their inner bounds for Gaussian MARC numerically, and illustrate specifically that when the relay is closer to the transmitters, their rates are greater than the previous corresponding rates.

The authors propose a distributed robust joint signal and interference alignment design for multiple-input–multiple-output cognitive radio (CR) networks where single primary link coexists with multiple secondary links. Considering two practical challenges of interference alignment: imperfect channel state information (CSI) and finite signal-to-noise ratio, the proposed scheme aims to minimise both the leakage of interference signals and that of the desired signals, while maintaining interference to the primary user below a permissible level. Under the assumption of the ellipsoidal CSI uncertainties, the joint worst-case optimisation problem is decomposed and reformulated as semi-definite programming form by using S-lemma, orthogonal relaxation and semi-definite relaxation. Simulation results verify the effectiveness of the joint design, and robustness of the worst-case design against channel uncertainties.

Utilising the recently-developed unique factorisation of signals and distributed Alamouti coding, a distributed collaborative space-time block code design is presented for a two-way amplify-and-forward (AF) relaying network, where all nodes are equipped with a single antenna. Two asymptotic pairwise error probability (PEP) formulae are firstly derived for both fixed-gain AF and variable-gain AF over Rayleigh channels with the maximum-likelihood detector. Then, subject to the constraints on a fixed transmission bit rate and unity average transmission energy, the optimal constellation combinations with the optimal coefficients are attained by minimising the dominant term of PEP. It is shown that the PEP and the average block error rate of the newly-designed code are superior to those of the conventional distributed Alamouti code while the prior still has linear-decoding complexity.

In this study, the authors present a cooperative spectrum sensing scheme based on opportunistic amplify-and-forward relaying (denoted by CSS-OAFR), which provides higher detection performance by selecting the best cognitive relay and is interesting in distributed cognitive radio networks. Moreover, the authors focus on the detection performance using the energy detector over independent and non-identically distributed Nakagami-m fading channels. In particular, a tight closed-form lower bound of the average missed-detection probability is derived for the convenience of performance evaluation in practice. Finally, simulations are provided to validate the CSS-OAFR scheme and the derived closed-form lower bound.

In this study, the authors propose a fine granularity resource allocation algorithm for enhancing overall quality of users’ received video in the orthogonal frequency division multiple access system. Subcarrier's contribution for video transmission is used as the guideline of resource allocation in this algorithm. The subcarrier with the largest contribution is given priority to be allocated on the basis of two-level paths search in the whole resource allocation tree. Moreover, the authors design the full search implementation scheme and the simplified implementation scheme for the resource allocation algorithm, respectively. The full search implementation scheme can obtain superior performance gain with high complexity. For reducing the complexity, the authors further propose a simplified implementation scheme subject to some minor quality degradation. At last, the authors compare the fine granularity resource allocation algorithm with other existing resource allocation algorithms for video transmission. In the simulation results, it is shown that the proposed algorithm acquires much more superior performance in overall quality of users’ received video.

An adaptive multiuser detection (MUD) technique using the complex radial basis function (CRBF) network is proposed for space division multiple access–orthogonal frequency division multiplexing (SDMA–OFDM) system. Among various MUDs, the linear minimum mean-square error (MMSE) MUD suffers from poor performance and the maximum likelihood (ML) detector is restricted by high computational complexity. Hence, the cost function minimisation-based detector like minimum symbol error rate (MSER) is preferred because of significant performance gain over MMSE MUD and complexity gain over ML detector. Moreover, the MSER detector also has a potential of surviving in overload scenario, where the number of users are more than that of the number of receiving antennas. However, in all these techniques, the requirement of channel estimation adds an extra complexity whereas, the proposed CRBF detector approximates the channel parameters in training phase and detects signals in testing phase. It also has low complexity, better performance compared with MSER MUD and also supports overload scenario. Each neuron in the proposed CRBF network is assembled with ‘sech’ activation function, as this function can do better complex non-linear mapping than Gaussian activation. The simulation study and performance evaluation of CRBF MUD is investigated, considering both data and image transmission.

Maximum likelihood (ML) carrier-frequency offset estimation for orthogonal frequency-division multiple access uplink is a complex multi-parameter estimation problem. The ML approach is a global optima search problem, which is prohibitive for practical applications because of the requirement of multidimensional exhaustive search for a large number of users. There are a few attempts to reduce the complexity of ML search by applying evolutionary optimisation algorithms. In this study, the authors propose a novel canonical particle swarm optimisation (CPSO)-based scheme, to reduce the computational complexity without compromising the performance and premature convergence. The proposed technique is a two-step process, where, in the first step, low resolution alternating projection frequency estimation (APFE) is used to generate a single better positioned particle for CPSO, followed by an actual CPSO procedure in second step. The mean square error performance of the proposed scheme is compared with existing low complexity algorithms namely APFE and linear particle swarm optimisation with mutation. Simulation results presented in this study show that the new scheme completely avoids premature convergence for a large number of users as high as 32.

An undetermined measurement matrix can capture sparse signals losslessly if the matrix satisfies the restricted isometry property (RIP) in compressed sensing (CS) framework. However, existing measurement matrices suffer from high computational burden because of their completely unstructured nature. In this study, the authors propose to construct a novel measurement matrix with a specific structure, called sparse block circulant matrix (SBCM), to reduce the computational burden. The RIP of the proposed SBCM is also guaranteed with overwhelming probability. The simulation results validate that SBCM reduces the computational burden significantly whereas keeps similar signal recovery accuracy as Gaussian random matrices.

Optical packet switching (OPS) is being considered as one of the switching technologies for a future optical internet. For contention resolution in an optical packet switching (OPS) system, the wavelength dimension is generally used in combination with a fibre delay line (FDL) buffer. In this study, the authors propose to reduce the number of tunable wavelength converters (TWCs) by sharing TWCs for cost-effective design of an asynchronous OPS system with a shared or an output FDL buffer. Asynchronous and variable-length packets are considered in the OPS system design. To investigate the number of TWCs needed for the OPS system, an algorithm is proposed, which searches for an available TWC and an unused internal wavelength, as well as an outgoing channel. This algorithm is applied to an OPS system with a shared or an output FDL buffer. Also, the number of internal wavelengths (i.e. the conversion range of the TWC) needed for an asynchronous OPS system is presented for cost reduction of the OPS system.

Ultra wideband-impulse radio (UWB-IR) transmission, which can provide high data rate for real-time transmission and low-power consumption in transceivers, is one of promising transmission technologies in implant body area networks (BANs). Some studies on UWB-IR propagation characteristics in implant BANs have reported that UWB-IR signals suffer from large attenuation in human body channels. It is therefore necessary to clarify the actual performance of UWB-IR modulation and demodulation methods in implant BANs. In this study, the authors focus on experimental evaluation of the correlation detection and energy detection for UWB-IR transmission with multi-pulse position modulation (MPPM). For this purpose, the authors develop a UWB-IR communication system with MPPM scheme, and experimentally evaluate the transmission performance of the developed systems with the two detection methods. In addition to the experimental evaluation, the authors also theoretically analyse the bit-error rate (BER) performance of the correlation detection and energy detection methods by using Gaussian approximation. From the experimental results, the developed system has achieved a BER of 10^{− 2} at the propagation loss of 75 dB with a data rate of 2 Mbps in the correlation detection. This result shows the feasibility of reliable UWB-IR communication in actual implant BANs.

Equations (17), (18) and (19) are incorrectly given in the above study. In this study, we give the correct versions of those equations.