A concatenated multitone multiple-antenna air-interface for the asynchronous multiple-access channel

In this paper, we present a novel transmission technology approach for application in the asynchronous multiple-access wireless channel (uplink). It is based on the concatenation of an inner filtered multitone (FMT) modulator with transmission over multiple antennas, and an outer space-time cyclically prefixed discrete multitone (ST-CP-DMT) modulator. The inner modulator is used to efficiently realize frequency-division multiplexing of the users by partitioning the FMT subchannels among them. The outer modulator copes with the residual subchannel intersymbol interference and it further implements a form of transmit diversity. Frequency and space diversity is exploited via direct sequence (DS) data spreading across the DMT tones. The design parameters are flexible and are chosen to make the proposed air-interface robust to the time and frequency offsets between uplink users, as well as to the channel time-frequency selectivity. Furthermore, the ST-CP-DMT modulator with DS spreading provides sensible performance gains. In particular, it yields a diversity gain for the users that transmit at low rate and occupy a fraction of the overall spectrum.