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Tail-biting convolutional codes (TBCC) are simple and powerful forward error correction (FEC) codes. They have been adopted as the FEC scheme for data and/or overhead channels in many wireless communications systems, including IS-54, EDGE, WiMAX and LTE. A convolutional code is called tail-biting (or circular) if the beginning state of its encoding trellis is always equal to the ending state after encoding. However, the circular state information is not available to the receiver. One important task in decoding TBCC is to estimate the circular state based on the received soft bit values. Many efficient algorithms have been proposed for decoding TBCC. Among them the wrap-around Viterbi algorithm (WAVA) provides near-ML (maximum likelihood) performances with the lowest complexity. In this paper, we propose several algorithms to further reduce the average number of decoding iterations and the memory usage in WAVA. Simulation results show that the complexity reduction from our proposed algorithms comes with no or almost negligible performance degradation.

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.

One of the main design goals of cdma2000 1xEV-DV is the efficient support of packet data services without detriment to existent voice services. This paper investigates the performance of the 1xEV-DV RL in the presence of voice users. In particular, several algorithms are investigated to support the three MAC mechanism defined in the 1xEV-DV standard. The results show that for the common rate control mechanism, the algorithm introduces no cost to mixing voice and data at low voice loads. However with the common rate control mechanism operating with higher voice load or the dedicated rate control and grant based scheduling mechanisms, the mixing of data and voice results in modest loss in performance. The amount of loss varies and is a result of the interplay of incrementally increasing resources for voice service and the ability of the system to target higher system loads as voice load increases. Nevertheless, these results show that 1xEV-DV can efficiently support both voice and packet data traffic.

In this paper, we investigate the code allocation problem of forward link channelization, i.e., allocation of Walsh codes and quasi-orthogonal functions (QOF's) in cdma2000 systems. Given multipath power profiles, geometry factors, and allocated codes of mobile stations (MSs), we propose a simple solution for the total sector transmit power. It is shown that the sector transmit power can be expressed in terms of a single variable, namely, the lumped geometry factor (LGF), which accounts for MS geometry factors, code channel activities, and cross-correlations among all the allocated codes. The formula is used to devise a code allocation algorithm that is proven optimum in the sense of maximizing capacity, under the condition of single-path channels.