  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.
