The Research Of Digital Intermediate Frequency Receiving System Based On Software Defined Radio

Software defined radio(SDR) is praised as another revolution in the field of wireless communication, since analog communication has developed into digital communication. In the recent decades, SDR has got quite quickly evolution, and becomes the base of 3rd and 4th generation mobile communication system.In this thesis, the design approach of the layer-based architecture and bus-based architecture have been analyzed firstly, and a modified layer-based reconfigurable model has been derived, which gives a excellent extensibility, standardization and flexibility to the SDR systems. This model divides the SDR architecture into 8 layers of RF/IF, data interface, switching, data processing, management control/configuration, application, network interaction and data processing service, each of which has an explicit definition and function. A system based on this model has been designed with both software and hardware scheme.Synchronization algorithm is most significant part of SDR system. Aiming at burst communication mode, time synchronization, carrier synchronization and frame synchronization algorithms are discussed in detail. For the time synchronization algorithm based on squares filtering timing recovery, the statistical characteristics of its unbiased estimation is discussed, and the original algorithm using Kalman filter is improved to obtain a better anti-noise capability of synchronization estimation algorithm. Carrier synchronization algorithm employs an algorithm based on the theory of minimum mean square error linear prediction and the convergence characteristic of carrier synchronization algorithm have been verified by simulation. The simulation result shows that in the case of a synchronization symbol number less than 20, the algorithm achieves carrier synchronization quite well. For the frame synchronization algorithm, the design standard of synchronization sequence is given, and a synchronization sequence required by actual systems is also designed.For the SDR hardware, the design approach of AD converter, digital down converter and reconfigurable unit are mainly discussed in the IF SDR receiver system. According to the band-pass sampling theory, the required center frequency and sampling frequency is derived; and the main parameters of down converter in the QPSK demodulator are also given. According to the policy of reconfiguration, the method of system reconfiguration has been discussed and the reconfiguration circuit for DSP, FPGA has been designed.