Study On IEEE 802.16d/e Channel Codecs And Its DSP Implementation

The task of source coding is to represent the source information with the minimum of symbols.When a code is transmitted over a channel in the presence of noise, errors will occur.The task of channel coding is to represent the source information in a manner that minimises the error probability in decoding. Channel coding requires the use of redundancy to increase the reliability of communication.This thesis studies the channel codings (RSCC, BTC and CTC) of Wimax, which is the most promising communication techniques.The RS code has an excellent performance when dealing with burst errors, hence widely used in wireless communication, magnetic and optical storage.The convolutional code, which is fit for correct random errors, is used in GSM and 3GPP mobile communication system. RSCC, which is an excellent concatenated code composed of the RS and convolutional code, is widely used in deep space communication, DVB-T,etc.In this thesis, the RS code is derived from a systematic (255,239) RS code. As it's a shortened and punctured code, the decoding algorithm requires modifications to cope with the puncture of the parity codes. We modifiy the initial conditions of the Euclids algorithm and prove its validity by simulation, and compare the performance difference between RSCC and convolutional code. We also introduce the DSP implementation of RSCC in detail.BTC is a product code, which encode each row and columon of an information block to make all the rows and columons detect and correct errors. The product code is usually used in burst errors channels, e.g. IEEE802.16 protocols. In this thesis, the BTC has two kinds of component codes - extended Hamming code and parity check code.The decoding process of BTC includes BTC block decoding, BTC SISO decoding and extended Hamming code / parity check code decoding. BTC SISO decoding is also called row / columon decoding, it calculates the reliability of the hard decision of extended Hamming code and parity check code. We adopt a sub-optimum algorithm here and have reduced the decoding complexity greatly.CTC is a non-binary Turbo code, which has a strong ability to cope with delines and interferences. IEEE802.16d/e introduce CTC to solve the problem that the system throughput decreases caused by adding tail bits to terminate the Turbo code. But the CTC decoding is more difficult than Turbo: firstly, the non-binary trellis is much more complex than binary trellis; secondly, the decoder of CTC has to cost several iterations to estimatie the initial state of encoder. In this thesis, Log-MAP algorithm is used to decode CTC, which is developed from Turbo decoding algorithm.At the end of this thesis, we also compare and analyse performance curves of the three channel codings of IEEE802.16d/e, get the comparison conclusion under AWGN channel.