Cooperative Diversity Based Multi-Carrier CDMA System with Decode and Forward Relays in Rayleigh Fading channels

Cooperative communication is one of the major diversity techniques which exploit spatial diversity through a virtual antenna array. In addition to cooperation, transmitting the same symbols through different sub carriers (Multi-Carriers) introduces frequency diversity as well. The objective of this paper is to investigate cooperative diversity performance in Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with orthogonal and non-orthogonal spreading codes. We evaluate the Symbol Error Rate (SER) of cooperative transmission in frequency-selective Rayleigh faded uplink channel. We focus on the use of despreading-combining (DC) receiver and coherent detection with Maximal Ratio Combining for the above selected criteria respectively. It is shown that the orthogonal spreading code cancels Multiple-Access Interference (MAI) and the performance is completely independent of the length of the spreading code. The approximate SER derived here for the the transmission scheme is well matched with the increasing number of users in the system. Hence the Gaussian approximation is acceptable for systems which are operating with their maximum user capacities at lower SNR values.