Improved tail-biting convolutional codes for 802.16e frame control header

Abstract

In this paper, the tail-biting convolutional code (TBCC) performance of the 802.16e Orthogonal Frequency-Division Multiple Access (OFDMA) frame control header (FCH) is studied It is known that the performance and the weight spectrum of a TBCC depend on the paylod size. Therefore, the search for optimal generator polynomials should be done accordingly. In 802.16e, a rate-1/2, memory-6 TBCC that has the best minimum distance and the smalest number of minimum-weight codewords for larger-than-32-bit payloads is used for both FCH and data channels. The data channel has paylod sizes of more than 48 bits; however, the FCH ha smuch shorter paylod sizes (12 and 24 bits). As a result, suboptimal TBCC performance can be expected for FCH. In this paper, we study other options of TBCC generator polynomials for FCH. In addition to available results in the literature, we have found new TBCC generator polynomials according to the optimum distance spectrum criterion. The performance gains in the AWGN channel over the 802.16e TBCC by using the proposed rate-1/4 geenrator polynomials for length-24 and length-12 are about 1dB and 1.2 dB at FER = 10-4, respectively. Also, the performance gains over the 802.16e TBCC by using the proposed rate-1/4 generator polynomials range from 1dB to 3.7dB at FER = 10-3 in multipath Rayleigh fading channels.