Sphere constrained block DFE with per-survivor intra-block processing for CCK transmission over ISI channels

In the wireless local area network (WLAN) standard IEEE 802.11b, complementary code keying (CCK) modulation has been adopted for the high data rate transmission mode. In this paper, complexity reduction for block decision-feedback equalization (bDFE), tailored for CCK transmission over frequency-selective channels, is considered. Since the CCK signal may be viewed as a linear block code with respect to the chip phases of the codeword, a trellis diagram with a minimum number of states can be designed that represents the properties of the CCK code set. The Viterbi algorithm (VA) with per-survivor processing is applied to the CCK trellis for decoding and accounting for the inter-chip interference, while inter-codeword interference is canceled by decision feedback. The resulting scheme is denoted as bDFE-pS and has a significantly lower complexity than bDFE with brute-force search. By introducing a sphere constraint on the CCK trellis (SC-bDFE-pS), the complexity of bDFE-pS can be further reduced. Omitting trellis states that violate the sphere constraint, edges that emanate from such states can be pruned, and the average number of metric calculations per CCK trellis segment can be reduced. Simulation results show that the performance of bDFE-pS and SC-bDFE-pS, respectively, is essentially equivalent to that of bDFE with brute-force search.