Cooperative Communications in Wireless Networks

Next-generation wireless networks will go beyond the point-to-point or point-to-multipoint paradigms of classical cellular networks. They will be based on complex interactions, where the involved nodes cooperate with one another in order to improve the performance of their own communication and that of the global network. Cooperative communications based on relaying nodes have emerged as a promising approach to increase spectral and power efficiency, network coverage, and to reduce outage probability. Similarly to multiantenna transceivers, relays provide diversity by creating multiple replicas of the signal of interest. By properly coordinating different spatially distributed nodes in a wireless system, one can effectively synthesize a virtual antenna array that emulates the operation of a multiantenna transceiver. The demand for new-generation wireless networks has spurred a vibrant flurry of research on cooperative communications during the last few years. Nevertheless, many aspects of cooperative communications are open problems. Furthermore, most of the cooperative systems proposed so far are based on ideal assumptions, such as unfeasible synchronization constraints between the relay nodes or the availability of perfect channel state information at the resource allocation unit. There is a need for research on practical ways of realizing cooperative schemes based on realistic assumptions. The objective of this special issue is to contribute to this twofold objective: to advance in the understanding of cooperative transmission and to explore practical limitations of realistic cooperative systems. The first four articles of this special issue focus on the first objective, mainly. They analyze and, eventually, optimize the performance of cooperative protocols. Cooperative diversity is expected to provide significant improvement in terms of outage probability in systems affected by slow fading and shadowing. Nevertheless, the analysis of relay-assisted systems affected by lognormal fading has not received much attention. In the first article of this special issue, D. Skraparlis, V. Sakarellos, A. Panagopoulos, and J. Kanellopoulos analyze the effects of correlated lognormal fading in regenerative relay-assisted networks assuming maximum ratio combining (MRC) or selection combining (SC) at the destination. An exact analytical expression of the outage probability has been provided for both orthogonal relay schemes based on time or frequency division multiple-access protocols and nonorthogonal schemes supported by full-duplex relays and directive antennas at the sources. The analysis points out the significant impact that the fading correlation has on the system performance. Additionally, the quality of the source-relay link is shown to be a critical factor in the performance of all the …