Analysis And Application Of Turbo Codes

A novel channel coding scheme called Turbo codes, is one of the most exciting channel coding schemes introduced in the last two decades. The coding system is a novel combination of iterative decoding with Soft-Input/Soft-Output (SISO) algorithms and Recursive Systematic Convolutional (RSC) codes in parallel connected by an interweaver. With these components, Turbo codes can approach to Shannon limit and perform very well in AWGN channels. Their performance in correlated fading wireless channels remain a question. The wireless channel is particularly dynamic due to multipath fading and Doppler spread. These effects have strong negative impact on the transmission of Turbo codes. In such condition, it is important to study Turbo codes in wireless channel.Firstly , this paper reviews the history of channel code and presents the status of Turbo codes, recommends the code-decode structure and basic principle of Turbo Code. Some decoding algorithm of Turbo codes in common use are compared in their capability and complexity.Secondly, this paper discusses some design issue of Turbo Codes. By programming emulator, transmission of Turbo Codes is simulated with different parameters, such as code restrict length, iterative decoding times, interweave length, rate etc, which can help us to analyze and choose the right parameters to improve its capability. To reduce the decoding delay and the average iterative times, some stop-iterative-criteria in common use are compared and an improved CRC-SCR stop-criteria is brought forward, the new criteria can adopt different criteria based on different channel conditions. It can be seen that the improvedmethod decreases the average iterative times evidently with few capability loss.Lastly, the paper studies the application of Turbo Codes in wireless channel, compares the Turbo Codes capability in AWGN and Rayleigh channels, and points out the infection of the channel interweave and BTs to Turbo Codes. The emulating results show that the Turbo codes capability in AWGN performs 1.5-2.5dB better than that in Rayleigh channel. They also show that the channel interweave and the increasing of BTs can advance the capability of Turbo codes.