Peak-to-Average Power Ratio Reduction In OFDM-CPM Systems

As wireless communication quality is increasing day by day, the pursuit of modulation technology with high system performance and spectrum efficiency has become an important research topic. OFDM-CPM joint modulation technology has immeasurable potential for development and prospects, which is a combination of OFDM and CPM technology with superior performance.First of all, this thesis introduces the basic principles of CPM and OFDM modulation technology, mainly including CPM signal model, continuous phase, demodulation principle based on viterbi decoding, as well as the OFDM system frame, the guard interval, the cyclic prefix and the PAPR problem etc. And then we studied the influence of modulation parameters on CPM signal power spectral density and bit error rate to lay a foundation for further study through the simulation.After that, this thesis attempts to use CPM as pre-modulation technology, rather than BPSK、QPSK etc, to realize the perfect combination of CPM technology and OFDM system. Then the principle of the new joint system and three kinds of commonly used subclasses signal were introduced. Finally, we studied the effect of modulation index on the joint system performance through simulation. OFDM-CPM system inherited not only advantages, but also the disadvantages. So it still has the PAPR problem. Next, based on the research of the traditional algorithms for PAPR reduction in OFDM-CPM system improvement, this thesis summarizes the advantages and disadvantages of these three traditional algorithms.Eventually, we attempt to use the combination technology to reduce the PAPR of OFDM-CPM signal. And then two combination optimization algorithms are put forward. First, this thesis tries to reduce PAPR by combining PTS with CPM constellation information. Second, phase modulation technology is applied to OFDM-CPM system to solve the problem of high peak-to-average ratio in OFDMCPM system completely.We can find that the OFDM-CPM is a new modulation technology with excellent performance through the research and simulation in this thesis. It has not only the smaller power spectrum band radiation through a SSPA, but also the lower error code rate by choosing the appropriate modulation index. CPM multi-amplitude algorithm can reduce the PAPR effectively, and at the same time the side information doesn’t need to be transmitted because of the memory characteristics of CPM signal. And PAPR problem can be solved by combining the PM technology and OFDM-CPM system to realize constant envelope completely. The research of these two algorithms for OFDM-CPM technology has great significance in the future development in communication system.