Bit-error-probability for non-coherent orthogonal signals in fading with optimum combining for correlated branch diversity

The paper presents an analysis of the bit-error probability for optimal receivers in which the diversity branches are correlated. Non-coherent orthogonal digital modulation (NCODM) with Rician and Rayleigh slow, non-selective fading models are assumed. The maximum likelihood diversity combining laws are derived and simple implementation structure is deduced. The authors find that Rayleigh fading can be better than Rician fading in correlated diversity environments: a situation quite different from the independent diversity case. Also, for the Rayleigh fading model with correlated branch diversity, an equal-weight, square-law combiner usually has the same error performance as the more complex optimum combiner. However, the authors find that this is not the case for a Rician fading model with the same correlation environment. Compensation schemes for the lossy effect of the correlation are designed and found effective when the dominant noise and interference have almost the same correlation distribution as the fading signals. The diagonalization of quadratic forms is used both for error probability analysis and for optimal diversity receiver simplification