Space-time block-coded multiple access through frequency-selective fading channels

Mitigation of multipath fading effects and suppression of multiuser interfe rence (MUI) constitute major challenges in the design of wide-band third-ge neration wireless mobile systems. Space-time (ST) coding offers an effectiv e transmit-antenna diversity technique to combat fading, but most existing ST coding schemes assume flat fading channels that may not be valid for wid e-band communications. Single-user ST coded orthogonal frequency-division m ultiplexing transmissions over frequency-selective channels suffer from fin ite-impulse response channel nulls (fades), Especially multiuser ST block-c oded transmissions through (perhaps unknown) multipath present unique chall enges in suppressing not only MUI but also intersymbol/chip interference. I n this paper, we design ST multiuser transceivers suitable for coping with frequency-selective multipath channels (downlink or uplink), Relying on sym bol blocking and a single-receive antenna, ST block codes are derived and M UI is eliminated without destroying the orthogonality of ST block codes, Th e system is shown capable of providing transmit diversity while guaranteein g symbol recovery in multiuser environments, regardless of unknown multipat h. Unlike existing approaches, the mobile does not need to know the channel of other users, In addition to decoding simplicity, analytic evaluation an d corroborating simulations reveal its flexibility and performance merits.