Indirect Spatio - Temporal Equalization

Combined spatial and temporal equalization with a multi-antenna decision feedback equalizer is considered for a TDMA mobile radio system. Unless the time frame allocation is synchronized for all surrounding base stations, the co-channel interferers may start to interfere at arbitrary time instances during a base stations reception. A co-channel interferer may thus be present during the data sequence of the time frame while it is not present during the training sequence. In order to handle this situation, adaptation to changing interference environment is introduced. Two versions of the equalizer are considered. The covariance matrix estimates needed for tuning the equalizer parameters are partitioned into a signal part and a noise plus interference part. The signal part is derived from identiied signal channels, while the noise plus interference part is constructed by only considering the spatial correlations of the residuals from the identiication procedure. The rst algorithm is adapted by updating the noise plus interference part of the covariance matrix estimate, combined with a retuning of the equalizer at appropriate intervals. The second algorithm performs the adaptation by tuning a number of separate beamformers. This adaptation requires considerably less computations, at the price of a potential performance degradation. For the investigated scenario, the performance degradation is however minor.