Researches On Key Techniques For Software Receivers

This dissertation focus on the key techniques for IF sampling software receivers, emphases are put on digital channel processing, timing recovery, carrier recovery and demodulation algorithms. The spurious performance of DDS (Direct Digital Synthesizer) is also analyzed.The first chapter briefly introduces the concept and development status of Software Radios. It discusses the basic architecture of a software radio and key techniques of a software receiver.The second chapter focus on the digital channel processing techniques for IF sampling software receivers. Firstly, digital mixing and carrier synchronization based on DDS are studied. Multi-rate signal processing techniques including decimation, interpolation and their polyphase decomposition are introduced. The realization of multi-stage decimation is discussed. Finally, the design of matched filter is studied.In chapter 3, emphasis is put on timing recovery. Firstly, a new timing recovery algorithm using baudrate sampling is presented, in which the ratio of hi and h.\ to ho acts as timing function. Simulation results show that estimation performance is greatly improved compared with the algorithms using h] or h.j as timing function. Secondly, the timing recovery algorithm using digital filtering described in [12] is improved. Thirdly, interpolation equation, polynomial interpolation filter and interpolation control for timing adjustment are studied. The performance of interpolation loop is simulated.In chapter 4, algorithms of carrier recovery are studied. Firstly, the algorithms for estimating carrier phase and timing phase jointly based on maximum likelihood criterion and high sampling rate are studied. Secondly, a new carrier recovery algorithm is presented, in which timing phase estimation is derived using the digital filtering algorithm described in [12], then near optimum samples are obtained through interpolation, carrier phase estimation is obtained with the near optimum samples according to maximum likelihood criterion. Finally, the performance of a BPSK demodulation system consisting of digital PLL , timing recovery , decimation and filtering is simulated.In chapter 5 , emphasis is put on demodulation algorithms. Firstly, the demodulation algorithms for AM and FM signal and their anti-noise performance are analyzed. Secondly, a new demodulation algorithm for QPSK signal is presented when there existsfrequency offset. The demodulation algorithm for QPSK signal based on high sampling rate is also studied. Simulation results show that the new algorithm can achieve better performance. Finally, a new demodulation algorithm for n /4DQPSK signal is presented. The demodulation algorithm for n/4DQPSK signal based on high sampling rate is studied.Chapter 6 analyzes the spurious performance of DDS. The phase error signal due to the phase truncation is analyzed, and the regularity of its spectral lines is obtained. The spectrum function of DDS is derived, and the regularity of the spurious lines of DDS output spectrum due to phase truncation is obtained.