Study On Technique Of AGC And DMF In Spread Spectrum Receiver

Nowadays, wireless communication is widely applied in commerce, meteorology, military affairs and civilian fields. Wireless communication technology is in an interim from analog system to digital system. Conventional analog receiver depends on hardware much more, and it has many unconquerable obstacles, such as signal distortion. With the fast development of Digital Signal Processing and hardware, digital receiver which has higher sensitivity, higher selectivity, higher signal to noise ratio has became research hot point.In wireless communication, with increasing receiving signal dynamic range receiver'dynamic range is required higher and higher. This thesis studies the algorithm for Automatic Gain Control (AGC) circuit and it compares different algorithms. Based on the simulation and analysis of AGC algorithms, hardware description language is used to simulate and program to AGC. In order to reduce the complexity of hardware realization and according to different estimations modulus, this thesis brings forward a simplified AGC circuit diagram. Result of simulation and indicates that the simplified algorithm can reduce hardware resources on the premise of insuring process accuracy.Spread spectrum communication system requires adopting spread spectrum code of good Auto-correlation and Cross-correlation feature. Common pseudo noise code m sequence cannot provide enough sequence codes in which user code does not change when multi-user communicate. The priority of m sequence to forming Gold code sequence solves the problem that spread spectrum codes are no enough. Based on theory of pseudo noise and design, this thesis makes simulation to the Auto-correlation and Cross-correlation feature of common pseudo noise code m sequence and Gold code sequence, and complete design plan.Digital Matching Filter, which is widely applied in digital communication, has the advantage of fast and accurate acquire signal. Using Digital Matching Filter to acquire spread spectrum of DSSS communication system can be realized within one period. This thesis simulates the acquirer performance of matching filter to PN code at different signal-to-noise, and completes digital design of digital matching filter. It designs a complete digital spread spectrum receiver based on this digital matching filter, it gives analysis and simulation to every part of whole system. Test result presents the design is normal.System simulation, FPGA design, and hardware realization indicate that application of this digital matching filter and digital AGC circuit, which is used in spread spectrum communication system, is feasible.