In-service monitoring of multipath delay-spread and C/I for QPSK signal

A simple method of multipath delay-spread monitoring in a digital mobile radio channel using π/4-shift QPSK or conventional QPSK as the modulation scheme is described. By simply measuring a difference of absolute values of I-channel and Q-channel detector outputs, multipath delay spread is shown to be estimated. The method is, then, shown to be applicable to the monitoring of carrier to cochannel interference ratio, an important parameter for a cellular system. Although it is difficult to monitor them accurately when both multipath delay spread and cochannel interference exist, it is shown that the measured output is a good measure of bit-error-rate performance, and thus might be useful as a criterion for decision making in intracell handoff, for instance