In this study, the authors propose a novel power allocation scheme in time division multiple access (TDMA)-based distributed multiple-input multiple-output (MIMO) channels. By modelling the problem with a TDMA MIMO interference channel, the authors have derived closed-form expressions for power and time slot assigned to each MIMO transmission. Although our scheme is sub-optimal, with the aid of Jensen's inequality, it is shown to be superior to solutions based on channel inversion. In addition, the proposed scheme is compared with the optimal solution, and also with the scheme proposed by Dohler. By applying our proposed power allocation to the hierarchical cooperation strategy, the authors have shown that this scheme significantly improves the overall network throughput compared with the channel inversion solution. However, the improvement gain (which is at high-signal-to-noise ratio values) reduces when the method is compared with Dohler's solution.

In conventional multicast scheme (CMS), the total throughput of multicast group is constrained by the user with the worst channel quality. In order to overcome this problem of limited throughput, the authors introduce a resource allocation algorithm by exploiting layered coding combined with erasure correction coding for multicast services in the downlink of orthogonal frequency-division multiple access-based multi-antenna system. To reduce the feedback overhead of uplink, the authors design a novel transmission scheme with limited feedback. Then, the joint subcarrier and power allocation problem for the data of base layer and enhancement layers are formulated, which is shown to be non-deterministic polynomial- hard. Hence, in order to reduce the computational complexity, they propose a three-phase suboptimal algorithm. The algorithm is designed to maximise the system throughput, whereas at the same time guarantee the quality of services (QoS) requirements of all multicast groups. It is composed of precoding scheme, proportional fairness subcarrier allocation algorithm and modified water-filling power allocation algorithm with QoS guarantees (MWF-Q). To further decrease the complexity of MWF-Q, a power allocation algorithm with increased fixed power allocation algorithm with QoS guarantees is introduced. Simulation results show that the proposed algorithms based on limited feedback scheme significantly outperform CMS and any other existing algorithm with full feedback. Moreover, the proposed scheme can efficiently reduce 50% of the full feedback overhead.

The authors perform an outage probability analysis of a cooperative communication system which transmits over multi-path channels with best single, or best two relay pair selection and amplify-and-forward two-hop relaying. The probability density function of the multi-path links is modelled in the time domain with an Erlang distribution function. The analytical expressions for the probability density function and cumulative density function of the end-to-end signal-to-noise ratio are obtained for an arbitrary number of relay nodes and multi-path channel lengths of 2 and 3 with best single and best two relay pair selection from N available relays; from which outage probabilities are calculated. The spatial and temporal cooperative diversity of the network is then analysed. Finally, the theoretical results are compared with simulations to confirm the validity of the analysis, and the advantage of two relay selection is verified through bit error rate evaluation.

In this study, the authors explore a joint cross-layer optimised routing and dynamic power allocation for intermittently connected deep space backbone layer in deep space information networks via predictable contacts. First, the authors build up the payoff function and state dynamics based on differential game theory via two defined cost function paradigms. Then they establish a general differential game model for dynamic power allocation by the associated payoff function and state dynamics, and further propose the theoretical results of dynamic power allocation in a cooperative or non-cooperative manner. To describe the routing metric, they introduce the concept of hybrid link homeostasis which illustrates the connection between the predictable contact and the transmitted power along the corresponding backbone link. In addition, they propose a polynomial time algorithm of cross-layer optimised routing, which realises joint routing selection, transmitted power allocation and predictable contact schedule simultaneously. The numerical results demonstrate the effectiveness and feasibility of the authors proposed joint cross-layer optimised routing and dynamic power allocation.

This study investigates collaboration among neighbouring base stations for the downlink of multi-carrier cellular networks, in the absence of a centralised control unit, which is a defining characteristic of future wireless networks. The authors propose a novel scheme for collaboration in resource allocation among a cluster of three neighbouring base stations. In this scheme, the results of an initial calculation are shared among neighbouring cells, then the scheduling decision is made locally and independently by each cell. This scheme does not require complex and iterative calculation. The information is exchanged only once during each scheduling epoch, which results in reduced overhead on the backhaul links. The scheme is implemented in a distributed manner. Simulation-based performance analysis demonstrates effectiveness of the proposed collaborative resource allocation scheme among the neighbouring base stations for multi-carrier systems, particularly for the users located near the cell edges.

In this study, the authors propose a cross-layer resource allocation scheme for orthogonal frequency multiple access (OFDM) systems based on the subcarrier channel distribution information (CDI). Here, in contrast to most of the previous works, the authors consider practical discrete rate adaptation in which rate is adapted using a predefined set of modulation levels corresponding to fading regions. The OFDM system supports ‘streaming traffic’ that requires a minimum guaranteed average delay, as well as ‘elastic traffic’ with flexible rate requirements. The main objective is to maximise the total average transmission rate of elastic users, whereas the average delay is also guaranteed for streaming traffic, all subject to the maximum average transmission power constraint. The authors then propose an algorithm which finds suboptimal fading regions, as well as suboptimal subcarrier allocation based on dual decomposition method. In the proposed method, the solution of optimisation problem remains valid, until the channel distributions and/or the packet arrival and packet length distribution of the users are changed. This significantly reduces the computational complexity since there is no need to solve the optimisation problem for each channel side information (CSI) feedback. The proposed scheme also reduces the signalling overhead since corresponding to each user the CSI is required only for the assigned subcarriers. Particularly, the proposed method is suitable for cases in which wireless channel distributions is not changed, or can be simply estimated, for example, cases where a parametric distribution is fixed and only statistics such as average and variance is changed. Using simulations, the authors study the impact of number of fading regions and packet arrival rate on the achievable rate of elastic traffic.

One problem in the application of fibre optics to military systems is that nuclear (and space) radiation is known to produce colour centres in optical materials, causing a reduction of light transmission over a spectrum of wavelengths. These radiation effects could cause permanent or temporary disruption of a fibre optics transmission system. Thus, the study has investigated the harmful effects of gamma irradiation on fibre communication system links under thermal environment effects over a wide range of operating parameters. Both the ambient temperature and the irradiation dose have severe effects on the system transmission link characteristics and consequently the performance characteristics of optical communication systems. It is also to be noted that the model has deeply developed the modelling basics of transmission communication systems, which may be used to analyse total pulse dispersion, transmitted signal bandwidth, transmission bit rates, radiation induced loss and optical received power by using the soliton transmission technique after different gamma irradiation doses and irradiation times.

This article studies adaptive modulation for QR decomposition and successive interference cancellation receivers in multiple-input multiple-output systems over slow- and fast-fading channels. In slowly fading channels, adaptive modulation schemes with finite-rate feedback under the constraints of a constant total transmit power, discrete-rate and a target bit-error-rate (BER) are proposed. Specifically, the authors first develop adaptive modulation with modulation order feedback only. For power allocation and modulation order feedback, the authors establish an optimisation scheme that can be solved easily and analyse the effect of power-level quantisation on the achievable data rates. For the fast fading channel case, the authors analyse the probability distribution of the ‘ R ’ matrix and derive a scheme that only requires feedback of the statistical information of the channel for adaptive modulation with optimal bit loading to guarantee that the BER target is met.

Future 4G systems require transmission of richer multimedia services which inevitably implies an increase in data rate. Orthogonal frequency and code division multiplexing (OFCDM) technique has shown promising results in achieving a high data rate while simultaneously combating multipath fading. OFCDM is an amalgamation of orthogonal frequency division multiplexing and two-dimensional (2D) spreading. 2D spreading helps to achieve diversity gains in both time and frequency domains. The present OFCDM systems employ 1D orthogonal variable spreading factor (OVSF) codes to achieve the required 2D spreading in code multiplexed channels. However, 2D OVSF codes have better correlation properties in comparison to 1D OVSF codes. Motivated by this principle, the authors propose a spreading scheme for OFCDM systems using 2D OVSF codes. The spreading scheme is designed to increase the system throughput and reduce multi-code interference. Here, the authors study the OFCDM system performance using the proposed spreading scheme in a multipath fast fading channel with varying spreading factors in both time and frequency domains. The results are compared with the existing OFCDM systems using 1D OVSF codes.

In this study, the authors propose a transceiver system for large-scale multiple-input–multiple-output (MIMO) (LSM) wireless communications. The authors present the main challenges facing such LSM system, also, they find solutions for those problems. The transmitters in this proposed downlink system uses a simple fair user scheduling based on limited-feedback algorithm with basic random precodeing algorithm. On the other side, receivers employ constrained partial group decoder to detect their desired signals. Simulation is used to evaluate sum-rate performance of this LSM downlink system against the total number of users and signal-to-noise ratio, using different number of scheduled users and with various group sizes of jointly decoded users. Numerical results interestingly show an encouraging performance for the proposed transceiver system in this study to be considered as a candidate scheme for LSM communication systems.

In this study, the average throughput maximisation of a secondary user (SU) by optimising its spectrum sensing time is formulated, assuming that a priori knowledge of the presence and absence probabilities of the primary users (PUs) is available. The energy consumed to find a transmission opportunity is evaluated, and a discussion on the impacts of the number of PUs on SU throughput and consumed energy are presented. To avoid the challenges associated with the analytical method, as a second solution, a systematic adaptive neural network-based sensing time optimisation approach is also proposed. The proposed scheme is able to find the optimum value of the channel sensing time without any prior knowledge or assumption about the wireless environment. The structure, performance and cooperation of the artificial neural networks used in the proposed method are explained in detail, and a set of illustrative simulation results is presented to validate the analytical results as well as the performance of the proposed learning-based optimisation scheme.

The delay characteristics of network coding nodes and Butterfly network are investigated. First, the probability mass function (PMF) of delay and the average delay of general network coding nodes having multiple input links and one output link are analysed. It can be shown that the PMF and average delay can be readily evaluated from the recursive equations derived. Then, the delay performance of the Butterfly network is investigated. Specifically, the authors consider four different scenarios in the context of the packets transmitted over the Butterfly network. The PMFs of delay as well as the average delays of these four scenarios are analysed and, correspondingly, a range of formulae are obtained. Finally, the delay performance of network coding nodes and Butterfly network is investigated based on the numerical results evaluated from the formulae derived. The authors studies demonstrate that network coding nodes embedded in a network generate a big impact on the network's delay performance. Usually, in a network including some network coding nodes, the longest path with some network coding nodes may be chosen for approximately estimating the network's average delay.