Wideband Equalization Using Multiple Antennas

We explore the concept of combining of multiple antenna signals with complex weights so as to realize an overall transfer function that is as flat as possible over a given bandwidth. This differs from conventional equalization in that no time delay taps are used in the process, and has the advantage of diversity-like noise immunity to deep fades. A frequency-selective fading model is postulated for the propagation paths and the equalization performance is calculated using the optimal complex weights. It is shown that the bandwidth over which a given deviation from flatness can be achieved is proportional to the number of antennas, provided that they are spaced far enough apart so that the fading is independent. Performance of a conventional beamformer with weights consisting of a linear phase progression is also assessed, but is found to be far less effective than optimal weighting provides. Applications are envisaged as an alternative to OFDM for wideband communication over channels with large delay spread, and for channel shortening in OFDM as well as other possible applications.