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

In [1], Lindskog and Paulraj (LP) 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 3dB array gain) as can be achieved by using one transmit antenna and two receive antennas. This scheme generalizes Alamouti’s [11] transmit diversity scheme (which works best for flat channels) to dispersive channels. In this paper, we show how the transmit diversity (TXD) scheme of [1] can be deployed in GPRS/EGPRS networks. A low-complexity receiver structure for demodulating 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 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 Typical Urban channel of GSM/EDGE.