Novel Techniques to Reduce Performance Sensitivity to Spatial Correlation and Timing Offset in Space-Time Coded MIMO Turbo Equalization

Spatial correlation among antenna elements both at transmitter and receiver sides in MIMO communications is known to have a crucial impact on system performances. Another factor that can severely degrade receiver performances is the timing offset relative to the channel delay profile. In this paper we derive a novel receiver for turbo MIMO equalization in space-time-trellis-coded (STTrC) system to jointly address the problems described above. The equalizer is based on low complexity MMSE filtering. A joint detection technique of the several transmit antennas is used to reduce the receiver's sensitivity to the spatial correlation at the transmitter and receiver sides. Furthermore, only the significant portion of the channel impulse response (CIR) is taken into account while detecting signals. The remaining portion of CIR is regarded as the unknown interference which is effectively suppressed by estimating its covariance matrix. By doing this the receiver's complexity can be reduced since only a portion of the CIR has to be estimated and used for signal detection. Furthermore, by suppressing the interference from the other paths outside the equalizers coverage the receiver's sensitivity to the timing offset can be reduced. The proposed receiver's performance is evaluated using field measurement data obtained through multidimensional channel sounding. It is verified through computer simulations that the performance sensitivity of the joint detection-based receiver to the spatial correlation is significantly lower than with the receiver that detects only one antenna at a time. Furthermore, the performance sensitivity to the timing offset of the proposed receiver is shown to be significantly lower than that of the receiver that ignores the existence of the remaining multipath CIR components