Diversity techniques mitigate the adverse effects of fading in wireless communications. One of the several forms of diversity is spatial diversity, which creates multiple fading paths between the transmitter and the receiver. Achieving spatial diversity in a mobile unit requires the use of multiple antennas, which, in turn, increases its hardware complexity and size. To overcome this problem, a recent development envisages a type of spatial diversity called distributed spatial diversity, where mobile units that are distributed in different geographical locations generate multiple communication paths. Practical implementation of distributed spatial diversity requires some sort of cooperation among the mobile units. A new method of cooperation called user cooperation, where mobile units share their antennas with other mobile units, thereby forming a virtual antenna array.
In this project a fundamental cooperative diversity system is considered, where the source transmits the symbol using phase shift keying to the destination as well as to the relay in a flat Rayleigh fading environment. The relay decodes the symbol and forwards to the destination. The symbols available at the destination are combined using maximal ratio combining (MRC), equal gain combining (EGC), selection combining (SC).
Due to synchronization errors in a cooperative system, there is a considerable performance degradation which is shown in analytical and numerical results. Due to synchronization errors timing errors caused by cooperative multiple input single output (MISO) system is high, which in turn nullify the gains achieved due to cooperation. An optimum power allocation algorithm based on symbol error rate (SER) performance analysis in cooperative communication system over channels with path loss and fading for exact timing should be developed. In this project a three node decode and forward cooperative communications which is operating under Rayleigh fading channels under certain power constraints is considered. Timing errors are considered for each communication links which degrade the performance, where as equal power allocations seems to be not the optimal solution when there are timing errors.As shown in the figure, using relay node R, a source node S communicates with a destination D. Cooperative communication consists of two stages. During first phase, S sends the message whilst D and R listen. In the second phase, R processes the signal from S , transfers it to D . Then D combines the signal received from both R and S . Each of the received signal at relay R or at destination D , from the transmission end U. Detailed calculations are provided in the link given below.