Non-cooperative Communication Of Mpsk / Of Mqam Signal Blind Demodulation Technology Research

In non-cooperative digital communication systems, the modulation type of the transmitter is uncertain for the receiver, so the modulation parameters required by completion of information receiving consist of carrier frequency, symbol rate, and roll-off factor of the transmitter are unknown for the receiver. In order to demodulate the receiving signal correctly, the receiver must extract necessary parameters from the received signal and adopt blind demodulation technologies.The investigation of blind demodulation technologies is the foundation of reasonably designing the receiver to obtain the best demodulation performance in non-cooperative digital communication systems. To achieve blind receiving performance improvement with bigger parameter estimation error, this dissertation deeply investigates the mismatched roll-off factor on receiving performance, symbol synchronization acquisition-aiding method, the joint carrier synchronization and blind equalization technology for MPSK/MQAM signals.The main contents of this dissertation are as follows:Chapter 2 investigates the symbol synchronization acquisition-aiding method with larger symbol rate offset. As most of the present research work of symbol synchronization is based on simple cooperative communication model and few considers that how to correct big symbol rate offset in complex environment, this chapter proposes the symbol synchronization acquisition-aiding method by scanning and adjusting loop bandwidth. With the help of this method, the timing recovery loop can capture less than 5% symbol rate offset quickly with good steady performance.Chapter 3 investigates the effects of roll-off factor error and the mismatched filter order on the receiving performance for the receiver with timing recovery or without receiving processing (without timing recovery). It is reasonable to set the roll-off factor of the receiving square-root raised cosine filter to be 0.5-0.7 without knowing the roll-off factor of the transmission square-root raised cosine filter and it has the least influence on receiving performance. Moreover, the higher order (which means greater out-of-band attenuation) of receiving filter can not improve the receiving performance obviously, instead, increases the implementation complexity.Chapter 4 investigates the joint carrier recovery and blind equalization technology. Channel distortion caused by multi-path fading and doppler frequency shift brings a great challenge to the correct demodulation in non-cooperative communication. Blind equalization is one of the key technologies of blind demodulation to compensate the channel distortion. A modified joint receiver structure with carrier recovery and blind decision feedback equalization is proposed for MPSK/MQAM signals to compensate channel distortion and correct large carrier frequency offset and phase offset. The carrier recovery adopts general carrier recovery loop. For MPSK signals blind DFE adopts SG-CMA-DD-LMS algorithm (Stop-and-Go Constant Modulus Algorithm + Decision-Direct Least-Mean-Square) and for MQAM signals blind DFE adopts SG-MCMA-DD-LMS (Stop-and-Go Modified Constant Modulus Algorithm + Decision-Direct Least-Mean-Square) algorithm. Simulation results show that the proposed scheme could achieve distorted channel equalization and large carrier acquisition scope in distorted channelsThe last part is the summary of this dissertation, and future research work is pointed out.