Asynchronous Cooperative Communication System Using Opportunistic Selection Diversity Technique

Abstract

ABSTRACT The revolutionary concept of space-time coding introduced in the last decade has demonstrated that the deployment of multiple antennas at the transmitter allows for simultaneous increase in throughput and reliability because of the additional degrees of freedom offered by the spatial dimension of the wireless channel. A new form of realizing transmit diversity has been recently introduced under the name of user cooperation or cooperative diversity. The basic idea behind cooperative diversity rests on the observation that in a wireless environment, the signal transmitted by source node is overheard by other nodes, which can be defined as “partners/relays”. The source and its partners can jointly process and transmit their information, creating a “virtual antenna array”, and therefore emulating transmit diversity. This report presents an asynchronous cooperative diversity method using opportunistic selection diversity technique. In this technique the cooperative diversity schemes are considered that do not require symbol-level timing synchronization or orthogonal channelization between the relays employed. Our scheme first selects the best relay from a set of M available relays, and then uses this “best” relay for cooperation between the source and destination. We develop and analyze a distributed method to select the best relay that requires no topology information and it is based on local measurements of the instantaneous channel conditions. The success (or failure) to select the best available path depends on the statistics of wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Most of the ongoing research efforts in cooperative diversity assume coordination among the relays allows for accurate symbol level timing synchronization at the destination and orthogonal channel allocation, which can be quite costly in terms of signalling overhead in ad hoc networks, which are often defined by their lack of a fixed infrastructure and difficulty of centralized control. Therefore, main focus will be on asynchronous cooperative diversity technique in the proposed work to circumvent this problem. The simplicity of the technique allows for immediate implementation in existing radio hardware, and its adoption could provide for improved flexibility, reliability, and efficiency in future 4G wireless systems.