Field trial of space-time equalizer using multiple single-constrained array processors and MLSE equalizer

The field trial of a space-time (ST) equalizer, for a high data-rate TDMA mobile communication system, is presented. A cascaded connection of a pair of single-constrained array processors and branch-metric-combining maximum-likelihood sequence-estimation (BMC-MLSE) equalizer is implemented for the ST equalizer. The pair of array processors maximizes the signal-to-interference-and-noise ratio (SINR) on both the direct and one-symbol-delayed path components and the BMC-MLSE equalizer then derives a path diversity gain from the SINR-improved path components. The radio frequency was 3.35 GHz, modulation was QPSK and the transmission rate was 4.096 Mb/s. The bit error rate (BER) performances of the ST equalizer and array processor alone were simultaneously measured in real time, along with delay profiles. The results show that the ST equalizer provide better than 10 dB of E_b/N₀ improvement at BER=10^-3 as compared with the array processor alone in a field where the instantaneous delay spread spans less than 1 μsec. A delayed diversity transmission (DDT) using two transmitting antennas at a mobile was also tried for the ST equalizer. 0.5-symbol DDT provided more than 1 dB E_b/N₀ improvement at BER=10^-3 in a field where average delay spread is 0.2 μsec.