Vector Demodulation Design And Implementation For High Rate MQAM

Multi-level Quadrature Amplitude Modulation(MQAM) is a highly efficient digtal modulation regime, which is widely applied in VDSL, mobile communication, digital TV network, deep space communication and other rapid data transmission. But MQAM demodulation technology is facing a series of problems brought about by high rate.In this thesis, the research studies the high rate digital demodulation of MQAM and verification on DSP device. Digital vector demodulation system with the most bit rate of 320 Mbps and 56 MHz bandwidth was designed. The design of high rate MQAM demodulator needs a consideration of both the stable algorithm and real-time process.Firstly, the thesis discusses the principle of each part in demodulation module, and analysis demodulation performance and difficulties. Overall digital demodulation process of MQAM signals is designed.Next, demodulation process consists four critical modules: Matching Filter, Timing Synchronization, Adaptive Equalization, and Carrier Recovery. Among these, the timing synchronization error is extracted by analyzing the amplitude square. For the adaptive equalization algorithm, CMA is analyzed firstly, which is compared with MMA. By doing equalization with MMA, the phase offset and rotation of constellation points causes by the CMA algrithm can be avoided. What’s more, three algorithms of Carrier recovery(DD, RC and polarity decision) are compared in detail. According to the characteristics of each synchronization algorithm and MQAM signals, the synchronization structure is built. The MATLAB simulation results of all kinds of QAM signals show that the demodulation method in this thesis has good performance.Finally, all modules are combined into a complete demodulation system, and the DSP implementation process is designed. The actual signal has been demodulated by DSP program which has verify the actual feasibility on the existing test platform. Testing memory and processing time to analysis the performance of system, the results show that transmission bit rate of 320 Mbps meets purpose of real-time.