Random FM in Mobile Radio with Diversity

The probability density function and autocorrelation function of random FM in a mobile radio system are derived for the case where postdetection selection diversity is used. Closed-form solutions for the autocorrelation function have been found for no diversity and two-branch diversity and infinite series expansions for higher orders. The use of two-branch selection diversity is shown to reduce the random FM by 13.5 dB in a typical case, with a further 2.5-dB reduction when three branches are used. The effect of other forms of diversity on random FM is briefly assessed, but not pursued in detail.