Adaptive joint beamforming and B-MMSE detection under multipath interference

The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency for wireless communications under multipath interference, especially for the applications in a fast fading channel. The authors study the performance of an adaptive beamformer incorporated with a B-MMSE detector, which works on a unique signal frame characterised by training sequence preamble and data blocks segmented by zero-bits. Both the beamformer weight updating and B-MMSE detection are carried out by either LMS or RLS algorithms. The comparison of the two adaptive algorithms applied to both the beamformer and the B-MMSE detector is made in terms of convergence behaviour and estimation mean-square error. The final performance in error probability is also given. Various multipath patterns are considered to test the rapidity of the receiver's response to changing multipath interference. The performance of the adaptive B-MMSE detector is also compared with that of the non-adaptive version, i.e. through matrix inversion. The results obtained suggest that the adaptive beamformer should use an RLS algorithm for its fast and robust convergence property; whereas the B-MMSE filter can choose either LMS or RLS algorithms depending on the antenna array size, multipath severity and complexity.