In recent studies (Verde et al.), capitalising on randomised space–time block coding (STBC), a decentralised coding method has been developed for amplify-and-forward (A&F) relays, which can closely achieve the performance of a centralised A&F linear dispersion coding (LDC) scheme and notebly outperform the decentralised A&F LDC counterpart, by requiring a reduced amount of signalling and processing overhead. However, A&F relaying process introduces correlation among the noise samples at the destination which, along with the non-Gaussian nature of the relaying channel and the fact that the relays are located in different positions, significantly complicates the performance analysis of the system. In this study, a theoretical performance analysis of the randomised STBC A&F rule is carried out in terms of average pairwise error probability to evaluate its attainable diversity order. Numerical results are provided to corroborate the analytical findings.

A key issue in the full-rate alternate-relaying cooperative communication systems is the interference which is caused by the simultaneous transmission of the source and one of the relays. In this study, the authors propose maximum-likelihood (ML) detectors to mitigate the interference in such systems. Unlike previous work in which interference cancellation is required at the destination, the authors exploit the interference signal as a beneficial resource to develop an optimal detector. It is shown that the optimal detector can be implemented by parallel Viterbi algorithms. The major drawback of the proposed optimal detector is the delay because the destination has to receive and store the entire frame before performing data detection. Owing to the inevitable delay restriction, a sub-optimal detector is developed. In contrast with the optimal detector, the sub-optimal detector exploits two consecutive received packets to decode one packet. It turns out that the sub-optimal detector significantly reduces the required delay, memory size and bandwidth loss, with a slight increase of the bit-error-rate and the computational complexity. Extensive simulation results have been presented to demonstrate the effectiveness of the proposed detectors.

The authors propose an adaptive transmission scheme for cooperative communication networks. The cooperative network with the proposed scheme chooses the transmission rate and decides to involve the relay in transmission, adapting to the channel state estimated from limited feedback information (e.g. positive/negative acknowledgement (ACK/NACK) feedback). Considering that the limited feedback information provides only partial knowledge about the actual channel states, the authors design a decision-making algorithm on cooperative transmission by using a partially observable Markov decision process framework. The simulation results show that, when the feedback overhead is taken into account, the proposed scheme outperforms even the scheme with which the states of all relevant channels are estimated and fed back.

In this correspondence, the authors study the performance of multi-user transmitter preprocessing (MUTP)-assisted cooperative downlink (DL) transmission for multi-carrier code division multiple access (MC-CDMA) system, where multi-user interference (MUI) and inter-relay interference (IRI) are the principal channel impairments. Relaying is facilitated with the aid of fixed infrastructure-based relays that perform additional signal processing like formulating the preprocessing matrix for mitigating MUI in addition to forwarding the information they receive from the base station (BS). Specifically, in this study, the authors analyse the performance of cooperative communication-aided DL MC-CDMA system by employing three cooperation strategies: (i) all users supported by a single relay with dominant MUI at the relay and mobile stations (MSs); (ii) each user supported by a single relay where, MUI and IRI are dominant at the relays and MSs, respectively, as well as weak IRI at the MSs; and (iii) all users supported by L relays where MUI is dominant at the relays, and MUI and IRI are dominant at the MSs. Our simulation study shows that MUTP-aided cooperative DL transmission results in better achievable bit error rate than the multi-user detection-aided system as the MUI at the relays and MUI and IRI at the MSs are perfectly eliminated.

In network multiple-input–multiple-output (MIMO) systems, cooperative base stations (BSs) and mobile terminals (MTs) are in general at different geographic locations. Correspondingly, the channel gains with respect to different BSs and/or MTs may obey different distributions, which resulted from, different pathlosses, different strength of line-of-sight (LOS) components and so on. Furthermore, future wireless communication systems are expected to be equipped with multiple antennas for transmission/receiving. In these multiantenna systems, signals received by the antennas of one BS from one MT may be correlated. Against the above-mentioned scenarios, in this contribution, the authors study the capacity of the generalised uplink network MIMO systems with multicell cooperation (MCoP), when propagation pathlosses, fast Rician fading with various LOS components and spatial correlation are simultaneously considered. Specifically, the theory of operator-valued free probability is introduced to derive the approximate eigenvalue distribution (AED) of the correlation matrix of the equivalent channels. Based on the AED, the approximate capacity of uplink network MIMO systems is then studied. Furthermore, a range of special cases are analysed by specialise the authors model and modifying their results. Finally, both numerical and simulation results are provided for characterising the capacity of network MIMO systems with MCoP.

This study addresses the issue of intercell interference coordination in a multicell orthogonal frequency division multiple access network with universal frequency reuse, which aims at improving the network spectral efficiency, especially for the cell edge areas. According to different degrees of information sharing within the engaged network, both a joint and a distributed solution are proposed respectively trying to determine the most appropriate power control strategy along with the user scheduling policy. The joint power control and user scheduling scheme with full access to the network information is capable of gaining considerable enhancement on the network capacity and also a performance improvement for users suffering from strong intercell interferences. The distributed scheme with the same purpose manages to adapt the power control and user scheduling strategy on the basis of dynamic programming with respect to both current and future utility of the network with only local information available. Numerical results have shown the advantages of the proposed schemes in achieving better spectral efficiency under both joint and distributed circumstances.

Opportunistic relay selection (RS) is an efficient method to obtain diversity gain in analogue network coding (ANC) protocol with multiple relays. However, in networks with mobile relays, the channel state information (CSI) used in the RS procedure becomes outdated because of the time-varying nature of fading channels, which severely deteriorates the system performance. In this study, the authors study the RS strategy which aims to optimise the outage performance of the ANC protocol with multiple mobile relays. RS schemes for two different cases are designed, that is, (i) the scheme with only the outdated CSI during the RS procedure, and (ii) the scheme with both the outdated CSI and the statistical knowledge of channels during the RS procedure. The closed-form expressions of the outage probabilities as well as the asymptotic expressions are analytically derived for the proposed schemes, and moreover, the achievable diversities are analysed based on the asymptotic expressions. Simulation results are presented to evaluate the performances while validate the theoretical analyses for the proposed schemes.

The essential broadcasting feature of radio propagation channels provides an opportunity for multiple nodes to exchange information and work cooperatively, where each node, for example, mobile sensor or robot, plays both the role of transmitter and receiver. Especially in such machine-to-machine communication scenarios, the network performance and redundancy of information from different providers highly affect the work efficiency of each individual node and the whole system. To address these problems, a relay assisted centralised network model with physical layer network coding implemented in the relay is proposed in this study. This structure has the advantage of flexible data exchange and the capability to reduce redundancy in information. Its theoretical performance is analysed by the diversity multiplexing tradeoff, which proves the proposed model is versatile in reliable and high spectral-efficiency information exchange. Experiments of multiple nodes in a machine-to-machine scenario – unmanned aerial vehicles, further reveal its potential in improving efficiency of communication and cooperation.

Cooperative sensing has been shown to improve the performance of spectrum sensing in cognitive radio (CR) networks where multiple secondary users are sending local sensing information to a CR fusion centre (FC) which makes the final determination on the occupancy of a given frequency band by licensed primary users. In this study, the authors observe the use of a hidden Markov model for evaluating the performance of cooperative sensing at the FC and propose a method that uses the history of FC sensing decisions to estimate the cooperative probabilities of detection and false alarm. The proposed method enables the FC to become aware when the performance of cooperative spectrum sensing degrades without requiring knowledge of the local sensing statistics. Numerical results obtained from simulations confirm the effectiveness of the proposed method for both soft and hard combining schemes in practical scenarios with noise and/or multipath fading.

The authors evaluate the outage probability of a cognitive amplify-and-forward relay network with cooperation between certain secondary users, chosen by single and multi-relay (two and four) selection, based on the underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection is performed either on the basis of a max-min strategy or one based on maximising exactly the end-to-end signal-to-noise ratio. To realise the relay selection schemes within the secondary networks, a predetermined threshold for the power of the received signal in the primary receiver is assumed. To assess the performance advantage of adding additional secondary relays, we obtain analytical expressions for the probability density function and cumulative density function of the received SNR and thereby provide closed form and near closed form expressions for outage probability over Rayleigh frequency flat fading channels. In particular, the authors present lower and upper bound expressions for outage probability and then provide a new exact expression for outage probability. These analytical results are verified by numerical simulation.

The active cooperation between a primary user (PU) and a cognitive user (CU) has the potential of leading to a transmission power reduction and transmission rate increase for both the PU and the CU. Alternatively, the required bandwidth may be reduced and the freed bandwidth may be leased to a group of CUs for their secondary communications. More explicitly, our cooperative protocol allows a CU to serve as a relay node (RN) for relaying the signal of the first PU, which is a source node (SN), to the second PU, which is a destination node (DN). Furthermore, we conceived adaptive turbo trellis coded modulation (ATTCM) for appropriately adjusting both the code rate and the modulation mode according I to the near-instantaneous channel conditions. More specifically, we propose an ATTCM aided two-way relaying cooperative CR scheme that maximises the CU's own data rate and improves the exploitation of the bandwidth released by the PUs. Our numerical and simulation results show that the bandwidth reduction attained by the proposed two-way relay based CR scheme is more than 80% of the PU's bandwidth.

In this study, the authors investigate a maximum incentive that a primary user (PU) can charge a secondary user (SU) on SU's power consumption devoted to delivering its own signal. As a constraint, the PU also should achieve its data rate at a predefined level. Working as a half-duplex relay, SU hears PU's signal in the first phase and sends its own signal superimposed on PU's signal in the second phase. SU optimises power allocation between the two signals in the second phase, accounting for the expense-benefit trade-off in sending its own signal. Depending on SU's receiver mode or the number of SU's receiving nodes, SU's decision on power allocation is differently optimised. The authors also provide optimal incentive for PU by optimal pricing for different occasions. The optimality is proved in this study. Since the optimality is purchased in practice when PU has perfect knowledge of the SU's response on the PU-issuing price, the authors also propose an efficient interactive price-searching protocol between distributed PU and SU. Numerical investigations are given to verify and illustrate the optimality of the proposed price as well as the protocol.