Research And Implementation Of Baseband Processing Algorithms In Digital Communication System

With the continuous development of modern communication technology, its applications are also expanding. People have higher requirements of the speed and performance of signal transmission. The application environment of communication devices is very complex in real life. The signals will be affected by the attenuation and interference when it transmits in a non-ideal channel, so the received signals may be errors. The efficiency and speed of transmission also will be affected. The task of baseband processing is to make the communication system efficient and stable transmission signals. But in order to guarantee the high throughput and low latency of baseband processing, we need to use a high performance digital signal processor. The solution based on FPGA can be used to meet the above requirements.This paper first introduced the basic framework and basic principle of a digital communication system and baseband processing system, and then analyzed and studied the key technology of baseband processing in detail. The key technologies of digital communication systems were studied in this paper include channel coding, digital modulation and spread spectrum. Channel coding is mainly used to resist the impact of channel impairments for signal transmission; Digital modulation is used to convert the data into to the signal which matches the characteristics of channel; the signal after spread spectrum can confront or suppress interferences, reduce the sending power to hide signals and encrypt information.Finally, this paper designed a baseband processing system for communication between fixed base stations. Channel coding was used convolutional codes, Channel decoding was used Viterbi decoding; Modulation was used DQPSK modulation; Spread spectrum was used direct sequence spread spectrum and its spreading factor is 32. It used Verilog HDL to realize the baseband processing system. It completed functional simulation by Modelsim and verified the baseband processing system on FPGA hardware board. As well as it tested the performance of this system in the environment with different signal-to-noise ratio and frequency offset, and then provided the corresponding performance curve.