Physical-layer issues for deploying transmit diversity in GPRS/EGPRS networks

Lindskog and Paulraj (see ICC-2000, June, 2000) proposed a transmit diversity scheme for dispersive channels which by utilizing two transmit antennas and only one receive antenna achieves the same diversity benefit (except for the 3 dB array gain) as can be achieved by using one transmit antenna and two receive antennas. This scheme generalizes Alamouti's (see IEEE JSAC, vol.16, no.8, p.1451-58, 1998) transmit diversity scheme (which works best for flat channels) to dispersive channels. We show how the transmit diversity (TXD) scheme of Lindskog et al. can be deployed in GPRS/FGPRS networks. A low-complexity receiver structure for demodulating Lindskog and Paulraj (LP) encoded signals is presented based on a combination of a novel pre-filter and a delayed decision feedback sequence estimation (DFSE) equalizer. This pre-filter is designed to simultaneously achieve three desired effects: (1) the effective baseband channel seen by the equalizer has half the number of taps of the original baseband channel; (2) the effective response of the baseband channel becomes minimum-phase; and (3) the effective baseband noise is whitened. An information-theoretic analysis is also presented to demonstrate the advantage of the LP scheme over other TXD schemes (e.g. over delay diversity). A burst format for transmitting LP encoded signals which is compatible with the existing GPRS/EGPRS burst format is also presented. Finally, simulations results are presented to verify the benefit of using the LP scheme in the typical urban channel of GSM/EDGE.