Error Rate Considerations for Coherent Phase-Shift Keyed Systems with Co-Channel Interference

The performance of coherent phase-shift keyed (CPSK) systems has been investigated by many authors; 1 - 5 in the transmission of information the CPSK system has been shown to be one of the most efficient techniques for trading bandwidth for signal-to-noise ratio. However, the type of noise considered by these authors is almost always limited to be random gaussian noise although most authors admit that interference other than normal noise must be considered in the design of any modulation scheme for digital transmission. 743 744 TI-IE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1969 Consider the following situation. In the frequency bands above 10 GHz where the signal attenuation resulting from rain storms could be very severe, close spacings of the repeaters are almost always mandatory for reliable communication from point to point and for all periods of time. 6 In such cases the problem of interference may be much more important than the problem of noise in the optimum detection of the desired signal; hence it is very desirable to evaluate the performance of a CPSK system with co-channel and adj acent channel interference so that, for the selection of an optimum transmission scheme, comparative advantages of CPSK over other broadband modulation techniques (like F M ) in combating interference can be determined. We consider in this paper the performance of a CPSK system when the received signal is corrupted by both interference and random gaussian noise.* We first discuss binary (2-phase) and quaternary (4-phase) CPSK systems and show t h a t exact expressions can be obtained for their probability of error Pm.