Channel Coding Of Digital Terrestrial Television Using Turbo Codes

The goal of communication work has always been the reliability and validityof information. Because of the inherent noise and the fading characteristic ofcommunications channel, the signal which achieves the end of the receivingcorrespondence by the transmission of the channel can be inevitably disturbed anddistorted.In order to monitor and correct the intelligence transmission mistake,which is produced by the channel distortion, we usually use error control coding,which is a very important method.The channel coding plays a very important part in DTV, because it can greatlydecide the error correction performance of the DTV system and the signal to noiseratio threshold, so it plays the pivotal role of the systematic overall peormancequality of DTV. Usually, the DTV system uses RS codes, convolutional codes orparallel concatenation codes.The decoding performance of turbo codes, which was proposed by FrenchC.Berrou in ICC'93, was almost close to the Shannon theoretical limits due to theuse of the random nature of the coding conditions well. The simulated results showthat Turbo codes appear excellent performance which has difference of theShannon limit only 0.7dB under certain conditions.Turbo codes have the far-reaching effects to the areas of access codes. First,the Turbo codes provide parallel concatenation codes under a low SNR conditions;Second, it changed the thoughts of the researchers who can design code, it meansthe smallest distance from the largest digit to the smallest of the low-digit, alsochanged the criteria to judge code, it near the theory of the Shannon limits;third,Turbo incorporated idea gives the new thought to the interactive channel estimationand signal detection.This article mainly changed Turbo decording algorithm and improved itsperformance.All the work and lessons summarized as follows:(1) Compared all kinds of the Turbo decoding algorithms, and also gave theirsimulation performance curves in the same circumstances.(2) Analyze the factors which affect the nature of the Turbo codes.(3) Changed the MAX-Log-MAP algorithm, carried on the linear fitting to itsabbreviation modification factor. Contrast with the original algorithm through thesimulation experiment, the algorithm which has been changed has the betterperformance.The thesis has the problems at present and the improvement places:The problem is the simulation, that have no enough time to print more exactlysimulation charts.Moreover, the channel used is limitated.I think that it also has some development directions:(1) In the technology of the decoding, we can put scale factor in the frontbranch measure in MAP algorithm, and then combine with the method of thesimilar.(2) At present, the changed algorithm's performance is also lower thanLog-MAP algorithm, in order to reduce their spatial difference as far as possible,weneed work hard .(3) The thesis only change the decoding algorithm, in the future, we maysolve other problems.Such as frequency band movement, frequency losing and soon.(4) Make up with the technical of the channel codes and the technical of themodulation, Such as OFDM .if it used in DTV, may solve the disturbance inchannel better.