Research On Key Techniques For CPM Receiver Based On DVB-RCS2

Continuous Phase Modulation(CPM) is widely used in satellite communication systems because of its attractive bandwidth and power efficiency. The DVB-RCS2 standard announced in 2011 incorporates CPM with more flexible and diverse modulation parameters into the return link transmission modes. It brings greater challenges to the techniques for the reception of CPM signals. Based on the DVB-RCS2 standard, this thesis studies and achieves the estimation of symbol rate, the timing synchronization, and the demodulation algorithm of the CPM signals. The work involved in this thesis is part of a project undertaken by the laboratory the author works in.The main work and innovative algorithms proposed are summarized as follows:1. The CPM transmission mode in the return link of the DVB-RCS2 standard is analysed. Based on the analysis of the signaling and the burst waveform generation, the characteristics of the modulation parameters and the key techniques for CPM receiver of DVB-RCS2 are obtained.2. A symbol rate estimation algorithm for CPM signals based on wavelet ridge is proposed. We study the characteristics of the wavelet ridge of CPM signals. Then the discrete spectrum lines are reached after the wavelet ridge of baseband CPM signals is filtered and the FFT operation is carried out. Finally, the symbol rate estimation of CPM signals is reached on the basis of the relationship between the discrete lines and the symbol rate. Simulation results show that, for the CPM signals stipulated in DVB-RCS2, the algorithm is more suitable for the short burst and low signal-to-noise ratio in the return link than the existing algorithms, which can also conquer the effect of carrier frequency offset, phase offset and modulation index.3. A joint timing synchronization and sequence detection algorithm for CPM signals with low-complexity is proposed. Firstly, based on the maximum-likehood structure of decision feedback, the Laurent decomposition is used to reduce the number of matched filters and the complexity of the branch metrics calculation in Viterbi algorithm. Secondly, the structure of decision feedback is improved by reducing the state transition trellis based on the reduced state sequence detection. Finally, the optimization of joint timing synchronization and sequence detection is reached. Simulation results show that, for the CPM signals stipulated in DVB-RCS2, the proposed algorithm is more suitable for the partial response CPM signals than the exsiting algorithms, which has high rate of convergence and estimating accuracy.4. A demodulation and decoding algorithm for serially concatenated continuous phase modulation with low-complexity is proposed. Based on the traditional soft input soft output iterative decoding algorithm, the nonsymmetric nonorthogonal exponential expansion is used to express the reference signals approximately. Then the branch metrics calculation of CPM inner code in the serially concatenated structure is modified, which can still support adequate statistical information with the reducing of calculation complexity. Simulation results show that, for the CPM signals stipulated in DVB-RCS2, the proposed algorithm suffers less performance loss with lower complexity than the existing algorithms.5. The system function modules of parameter estimation and demodulation for CPM signals are realized. Based on the hardware platform, the algorithms is realized in software. Performance test is taken using experimental signals, and the results show that the proposed algorithms can achieve the desired effect. This is fundamental to realize the DVB-RCS2 receiver system.