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Research and Implementation of convolutional code codec FPGA OFDM baseband system

Author: ZhongDongBo
Tutor: WuJun
School: Jiangxi University of Technology
Course: Communication and Information System
Keywords: soft-decision ACS unit path metric normalization 1_norm Trace-back
CLC: TN919.3
Type: Master's thesis
Year: 2011
Downloads: 39
Quote: 0
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Abstract


Now OFDM has became the physical layer connect technology of several communication standards. It is also expected as the key technology of fourth generation mobile communication,which has an extensive application prospect.IEEE 802.11a is a Wireless LAN Standard which adopts OFDM as the physical layer connect technology. It uses (2.1.7)convolution code whose generating function is G(133.171)8 as channel coding scheme. As very important sections of base- band processing system in the protocol, their move speed and power dissipation have the crucial affect of the whole system performance. This paper analysis OFDM technology, provides the basic model of OFDM baseband system,discusses error coding control of IEEE802.11a. On these bases, we use FPGA implement Multi-rate convolutional encoder and Viterbi decoder .Multi-rate convolutional encoder can meet different code rate of1/2、2/3 and 3/4, also has a very high coding speed. Newly designed Viterbi decoder highlights features as follows:(1).It adopts 1_norm to replace Euclidean distance as soft decision distance to save hardware cost、.(2).It emploies a modified method of path metric normalization efficiently to solve the overflow of PMU、(3).It applies an blocked cyclic memory trace-back scheme to reduce the delay of decoding .This article presents hardware architecture of Multi-rate convolutional encoder and modified Viterbi decoder and ascertain of the hardware parameter. It also provide Verilog source code、compilation report and analysis of the simulation result of several modules. Experiments show that the modified decoder use the fewer hardware cost to achieve a faster speed of decoding, completely meet the of technical requirements IEEE802.11a , can be used as a sub-module of receiver of OFDM baseband system and have higher practical value.

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