Research And Implementation On SC-FDE Technology For CPM

With the features of constant envelope and high spectral efficiency, continuous phase modulation(CPM) has been widely used as an attractive modulation technique in wireless communiction systems. It has broad application prospects, especially to achieve high-rate data transmission in the amplitude fading channels. However, under fading channels, the design of the channel equalizer is very difficult at the receiver, and the complexity of time-domain equalization is very high. Fortunately, single-carrier frequency-domain equalization (SC-FDE) technology is an effective way to eliminate inter-symbol interference (ISI). Therefore, combining CPM with the SC-FDE technology, not only keeps the CPM’s advantages of constant envelope and high spectral efficiency, but also has SC-FDE’s advantages of low complexity. Thus the study and implementation of the SC-FDE system based on CPM are conducted in this paper, taking the advantages of both technologies.The main contents of this paper are as fellows:First of all, the development of wireless communications is reviewed, and at the same time, the current development and future trends of CPM and SC-FDE technology are also summarized.Secondly, this paper studies the basic theories of the CPM and the SC-FDE technique in detail. The modulation and demodulation principles of CPM signals are introduced. And that this paper investigates the maximum likelihood (ML) criterion and maximum likelihood sequence detection (MLSD) algorithm based on Viterbi algorithm (VA), then analyzes the impact of various parameters on bit-error rate (BER) of the CPM signals. Theoretically, both SC-FDE and OFDM systems are analyzed and compared, and the basic algorithms of frequency domain linear equalization in the single-carrier systems are also studied. SC-FDE has a smaller PAPR than OFDM, and is not sensitive to the carrier frequency offset of the system. SC-FDE is an effective method against multi-path interference in a communication system.Next, the key issues of the combination of CPM with SC-FDE technology are investigated deeply. Frame structure designed by method of phase-zeroing algorithm ensures continuity of the signals phase after the cyclic prefix (CP) is inserted. CPM signals can be easily transformed to the frequency domain with Gram-Schmidt orthogonal representation or Laurent decomposition So the channel equalization can be achieved conveniently in the frequency domain. The question that how SC-FDE technique is applied to CPM signals is analyzed. Then the system performance under COST-207 channel model is estimated by computer simulatioa Then, this paper studies a SC-FDE algorithm applicable to precoded CPM system with specific modulation index. This algorithm improves the system performance significantly, without large increase of the complexity.Finally, the FDE algorithms are described with Verilog HDL to conduct the design of FPGA and simulated by Xilinx ISE and Modelsim software. In comparison with the Matlab simulation results, it can be seen that this hardware design is feasible and it has a good performance.