High Performance Turbo Coding Techniques

Channel coding is one of indispensable techniques which guarantee the reliable information transmission in digital communications. Turbo coding has received tremendous attention due to its excellent error correcting performance close to Shannon theory limit. Turbo coding has been accepted by 3G/B3G systems as one of channel coding schemes. But, the high complexity of turbo decoding is an obstacle to practical applications. The research on low complexity Turbo en/decoding schemes at the guarantee of decoding performance has become a hot point. The thesis mainly discusses several high performance decoding techniques including stop criterion used to reduce the average number of iterations, sliding-window decoding used to reduce decoding storage and low delay parallel decoding.Firstly, the thesis discusses the use of stop criterion to reduce the average number of iterations as much as possible at the guarantee of decoding performance. An improved half-iteration hard-decision-aided(H-HDA) based on HDA and IHDA is proposed. The H-HDA looks iterative decoding as several continuous half-iteration SISO decoders, then compares the hard decisions of the information bits at the output of two continuous SISO decoders and terminates the iterative process if they agree with each other for the entire block. The H-HDA reduces decoding delay about 0.2 iterations.Secondly, two sliding-window schemes are introduced. One is using guard window. The other is passing window boundary beta observations. An improved scheme is proposed based on these two schemes. The proposed scheme passes boundary beta observations of guard window to enhance reliability of beta initialization. So, it reduces invalid beta computation, and enhances decoding efficiency.Thirdly, the sub-block segmentation scheme is introduced. Combining the inherent code property, it is shown that the sub-block segmentation scheme has so-called "sub-block segmentation phenomenon", that is different segmentations have different decoding performance. By employing the dummy bits coding idea, two improved segment-based parallel Turbo decoding schemes are given to achieve reliability improvement without need for the overlapping bits between neighboring sub-blocks. An improved sub-block segmentation scheme is also introduced. The improved scheme replaces overlapping bits with passing sub-block boundary alpha and beta observations. It is shown that the improved scheme enhances computational efficiency and overcomes uncertainty of overlapping bits.Finally, several Turbo coding schemes used to 3G/B3G systems are introduced. Combining schemes of the sub-block segmentation and the sliding-window decoding, a high speed decoding scheme suitable for 3G/B3G systems is given. The scheme adopts the sub-block segmentation scheme passing sub-block boundary alpha and beta observations. For each sub-block, the sliding-window decoding with guard window is adopted. Enhanced Radix-4 Max Log Map algorithm and H-HDA are also adopted. It is shown that the scheme enhances efficiently decoding speed and reduces efficiently decoding storage without changing Turbo encoder. The given scheme has practical application value.