Applications of adaptive antenna combining to digital radio communications within buildings

The authors describe a time-division multiple access (TDMA) system in which adaptive antenna arrays function on a training sequence to identify the desired signal and to discriminate against interference and other unwanted signals. Signals received from the antenna array elements are amplitude weighted, phase shifted and summed to produce a combined response. The weight coefficients are adjusted such that the reception of the desired signal is enhanced and the combined effect of all other signals is attenuated. The weight coefficients are updated on a block-by-block basis using a complex least-mean-square algorithm based on the method of steepest descent. Computer simulations are presented for narrowband transmission over slow fading (Rayleigh/Rician) channels with coherent π/4-QPSK modulation