Research On Low-complexity Demodulation And Synchronization Algorithms Of CPM

Continuous phase modulation (CPM) has rather good power efficiency and constant envelope characteristic for wireless communications where the transmission power and channel bandwidth are both limited severely. However, the complexity of the CPM receiver increasing exponentially with the modulation parameters such as the pulse length and the alphabet size restricts the extensive application in wireless communication systems.Firstly, the basic properties of CPM are described, and the fairly good power and spectrum efficiency of CPM as well as various realization methods of the modulator are explained. Subsequently, the demodulation algorithms of CPM are studied as a key point, and some merits such as the BER performance and the complexity are analyzed synthetically.Secondly, many different low-complexity demodulation algorithms are reviewd and two novel algorithms are presented: a NSE algorithm for CPM based on exponential functions decomposition and an algorithm for reducing MLSE complexity of CPM based on phase distance. The first algorithm reduces the complexity of the demodulator by two stages: the front-end of the receiver is substituted by signal decomposition followed by the vector multiplication operations, and the sequence decoding part of the back-end is truncated by the exponential window. In the second algorithm, a conception called Phase Distance based on the inherent characteristic of CPM signal is defined and based on this conception, the path number of MLSE algorithm is reduced remarkably. With this algorithm, the computation complexity of the optimum receiver can be reduced considerably. Simulation results show that the BER performance is very close to the optimum receiver with a properly selected threshold.In the following parts, all kinds of timing estimation algorithms of CPM are discussed and a feedforward NDA self-synchronization algorithm based on maximum-likelihood functions is presented. In the end, the Coded CPM is studied and simulation systems based on CPM are presented.