Soft Timing Synchronization Algorithm for CPM Signals

Continuous phase modulations (CPM) form a class of constant envelop signalling formats that are efficient both in power and bandwidth, which are suitable for satellite communications, deep space communications, mobile communications and so on. In spite of the great advantage, current CPM applications are still limited because of implementation complexity and synchronization problems. Considering the difficulty of timing synchronization for CPM signals, a general soft timing synchronization algorithm for different CPM is proposed. Using the Rimoldi decomposition of CPM signals, the soft timing synchronization algorithm is derived based on maximum likelihood criterion and the Expectation-Maximisation algorithm. The synchronizer and demodulator are iterated jointly, and the soft demodulation information provided by the CPM soft demodulator is used to aid timing estimation. Simulation results indicate that the Root Mean Square Estimation Error (RMSEE) of the soft timing synchronization is very close to the modified Cramer-Rao bound (MCRB) for general CPM signals, and the bit error rate could achieve approximate ideal performance.