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 payload 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 smallest number of minimumweight codewords for larger-than-32-bit payloads is used for both FCH and data channels. The data channel has payload sizes of more than 48 bits; however, the FCH has much shorter payload 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 generator polynomials for length-24 and length-12 are about 1dB and 1.2dB 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.