Efficient Cooperative Diversity Techniques For Wireless Communication Networks

Wireless communications have seen remarkable progress with an aim not only to satisfy the requirements for current and future wireless systems but also to advance the state of the art of the communication field generating challenging tasks in presence of a fading changing over time environment. 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. Multi-Input Multi-Output (MIMO) technology has recently attracted great attention as a revolutionary technique for wireless communications, which is capable of yielding significant network reliability, low power consumption, high data rate applications. However, MIMO is costly and unsuitable for small devices such as a handheld mobile phone due to size and hardware limitations since MIMO requires implementing a set of antennas at the source and destination nodes.Cooperative diversity based on relaying nodes has alternatively emerged as a promising approach to increase spectral and power efficiency, to improve network coverage and resiliency, and reduce outage probability. Similar to multi-antenna systems, the relays provide diversity by creating multiple replicas of the signal of interest. By properly coordinating different spatially distributed nodes in a wireless system, a virtual antenna array can be obtained to emulate the operation of a multi-antenna transceiver as in MIMO.Amplify-and-Forward (AF) in which a relay keeps on amplifying its received signal from the transmitter node and forwards it to the destination and Decode-and-Forward (DF) where a relay re-encodes and forwards its received signal after correctly decoding it are mainly designed as relaying cooperation protocols. However, AF is limited by noise amplification problem (a relay may strongly amplify the noise in the forwarding process), which may significantly degrade the quality of the end-to-end received signal. While DF suffers from error propagation (a non-zero probability having a relay correctly decodes its received signal is not always obvious to assume) due to the quality of source-relay fading channels. In this research, we explore the fundamental limits of cooperative diversity under AF and DF modes by investigating new class of adaptive relaying strategies to derive new outage performance analysis for cooperative diversity networks. In the adaptive schemes, according to its received SNR, a relay can adaptively shift between AF and DF without getting any feedback information from the destination. More specifically, we present analytical models to evaluate the performance of efficient cooperative diversity schemes through adaptive relaying protocol by deriving closed-form outage probability expressions, investigating optimal power allocation techniques with an aim not only to mitigate the negative effects of AF and DF but also to advance the state of the art of wireless cooperative communication networks. Interestingly, we show that with adaptive relaying protocols,3dB improvements can be obtained using few numbers of relays.