Performance of Partial Response CPM in the Presence of Adjacent Channel Interference and Gaussian Noise

Partial response continuous phase modulation (CPM) schemes have found wide acceptance because of their compact spectra and comparable performance with other traditional modulation schemes. Although optimum receivers are complex, simple suboptimum receivers are found to yield very good performance in special cases. Performance of such modulation schemes is of interest in a multiple user environment where adjacent channels are spaced closely to improve the system capacity. This paper presents the performance of partial response CPM in the presence of adjacent channel interference and Gaussian noise. The meansquare crosstalk in CPM systems employing MSK-type receivers is formulated. Based on this formulation, a number of modulation schemes employing different receiver filters are analyzed for their ACI rejection. Comparison of results proves that receiver filters, in addition to the spectral occupancy of the signal, play an important role in deciding the crosstalk. The error performance of various schemes evaluated using simulation technique is compared, and it is found that in the presence of adjacent channel interference, certain schemes perform better than minimum shift keying (MSK). The results of the simulation further prove the inadequacy of Gaussian assumption for the adjacent channel interference. It is seen that judicious choice of modulation scheme and receiver filter can result in better spectrum utilization.