| The total number of radio station which can be accommodated within the ultrashort wave band is large and the anti-interference ability of ultrashort wave communication is strong, hence high economic benefit can be reached. This thesis focuses on some of the key technics in the design of ultrashort wave communication systems based on efficient modulations, which can be seen as a new candidate for ultrashort wave communication.Firstly, anti inter symbol interference (ISI) EBPSK modulation is introduced. Due to ultra-narrow bandwidth, the design of RF band-pass filter in EBPSK communication system is difficult. So, the RF band-pass filter is transformed into a baseband low-pass filter, and is implemented digitally. Generally, the baseband low-pass filter increases the ISI. Follow design instructions introduced in this paper can reduce the ISI significantly.Secondly, a method of frame-bit co-synchronization used in EBPSK communication system is proposed. Synchronizer is important in wireless communications, and the performance of synchronizer can influence the performance of the system. Frame-bit co-synchronization can implement frame synchronization and bit synchronization simultaneously, hence improves the efficiency and the accuracy. Other advantages of this method include the reduced cost.Then, synchronization information corrected sum-product decoding of LDPC is introduced. Sum-product decoding algorithm is one of the LDPC soft decoding algorithms. Using frame-bit synchronization information to correct the sum-product decoding of LDPC, the performance is improved. The result of simulation shows that the new algorithm can accelerate the convergence of the decoding process while the error rate is not enlarged under high SNR, and can reduce error rate under low SNR.Finally, the implementation of communication system based on efficient modulation is introduced.The key technics proposed in this paper are applicable to other bands, since they are established on intermediate frequency. |
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