Negatively Correlated Diversity Branches Using Various Modulation Methods and Maximal Ratio Combining

A diversity system using maximal ratio combining, and in which the diversity branches are negatively correlated, is considered. The performance of some digital systems, namely PSK, DPSK, CFSK, and NFSK, are compared. The error probability as a function of frequency differences between the branches is given. Also, error probability averaged over time delay difference τ is given as a function of direct as well as indirect signal-to-noise ratio. The sensitivity of the error probability to the form of the density function of τ is investigated. M th order of diversity is considered, but second- and third-order diversity are specifically analyzed.