Minimum decoding trellis length and truncation depth of wrap-around Viterbi algorithm for TBCC in mobile WiMAX

Abstract

The performance of the wrap-around Viterbi decoding algorithm with finite truncation depth and fixed decoding trellis length is investigated for tail-biting convolutional codes in the mobile WiMAX standard. Upper bounds on the error probabilities induced by finite truncation depth and the uncertainty of the initial state are derived for the AWGN channel. The truncation depth and the decoding trellis length that yield negligible performance loss are obtained for all transmission rates over the Rayleigh channel using computer simulations. The results show that the circular decoding algorithm with an appropriately chosen truncation depth and a decoding trellis just a fraction longer than the original received code words can achieve almost the same performance as the optimal maximum likelihood decoding algorithm in mobile WiMAX. A rule of thumb for the values of the truncation depth and the trellis tail length is also proposed.

Burst allocation method to enable decision-directed channel estimation for mobile WiMAX downlink transmission

“…Before encoding, the encoder memory is initialized with the last six data bits of the FEC block to be encoded. Thus, the initial state of the code trellis is the same as the end state, and the convolutional code is converted into a short block code called tail-biting convolutional code (TBCC) [16,17]. Each codeword, which is called coded FEC block, is interleaved and constellation-mapped into modulation symbols that in turn are mapped to slots of the data burst.…”