An Analysis of Cascaded Binary Communication Links

The performance of cascaded binary communication links in the presence of additive white Gaussian noise is investigated for the cases of constant and Rayleigh-distributed signal levels. An exact expression is derived for over-all error probability for any number of links with constant signal levels. The reliability of five modulation techniques is examined when independent or dependent Rayleigh fading is present on the cascaded system. It is shown that for any modulation technique the reliability is higher when the fading is dependent than when it is independent. It is also seen that the presence of Rayleigh fading affects reliability more than the degree of correlation of the fading, provided the number of links is small. The results of these analyses afford the designer a basis for a suitable trade-off between the number of relays and individual link reliabilities for a specified over-all system reliability.