Differential detection of multilevel continuous phase modulation for radio applications

In combination with differential detection, continuous phase modulation is a very robust and bandwidth efficient modulation scheme, at the cost, however, of a large degradation compared to the optimal coherent demodulator. We present a new differential detection scheme for continuous phase modulation which shows a performance degradation in the range of only 1 dB compared to a coherent receiver. This is accomplished by using a modified whitened matched filter adapted to the nonlinear nature of the modulation scheme. Further improvements are achieved by exploiting correlations in the noise process and by using reduced-state sequence estimation to cancel intersymbol interference. Due to the state reduction technique the complexity of the baseband processor is dramatically reduced and thus made suitable for integration into an ASIC. The performance of this new detection scheme is evaluated by analysis of the symbol error probability and compared to computer simulations and hardware measurements.