Full Rate Collaborative Diversity Scheme for Multiple Access Fading   Channels
  User cooperation is a well-known approach to achieve diversity without multiple antennas, however at the cost of inevitable loss of rate mostly due to the need of additional channels for relaying. A new collaborative diversity scheme is proposed here for multiple access fading channels to attain full rate with near maximum diversity. This is achieved by allowing two users and their corresponding relays to transmit/forward data on the same channel by exploiting unique spatial-signatures of their fading channels. The base-station jointly detects the co-channel users' data using maximum-likelihood search algorithm over small set of possible data combinations. Full data rate with significant diversity gain near to two-antenna Alamouti scheme is shown. 
Indu Shakya, Falah H. Ali, Elias Stipidis
cs.IT math.IT