Algorithms for coherent diversity combining of M-ary orthogonal signals

This paper discusses the use of coherent demodulation for antenna array rec eivers employing direct sequence spread spectrum techniques and M-ary ortho gonal modulation, Three different approaches are discussed. The first is a conventional receiver using training sequences and decision feedback for ch annel estimation, The other two techniques employ decisions from a simple n oncoherent combining (())receiver to circumvent the need for training seque nces. The bit error ratio (BER) performance of coherent M-ary orthogonal mo dulation is derived. Some qualitative analysis is also presented for the al gorithms, and simulation results are used to compare their performance in d ifferent scenarios.