DSP implementation of a bit loading algorithm for adaptive wireless multicarrier transceivers

In this paper, we present a proof-of-concept, fixed-point, DSP hardware implementation of an adaptive bit loading algorithm that is designed for wireless multicarrier transceivers. Adaptive bit loading is used to enhance the performance of multicarrier transceivers by tailoring the subcarrier signal constellations to the channel conditions, which can vary across the subcarriers. Since most bit loading algorithms possess a high computational cost and are unable to cope with rapid variations of wireless channels, they are seldom used in present wireless standards. To prove that adaptive bit loading is feasible for wireless transceivers, our work focuses on the implementation of a known bit loading algorithm that can quickly search for the final bit allocation in an iterative manner. The goal of this algorithm is to yield the largest-possible throughput while satisfying a mean BER constraint. The performance of the hardware implementation operating in time-varying channel conditions is studied in terms of the overall throughput. Furthermore, the robustness of the hardware implementation is evaluated, relative to sudden changes in the channel that interrupts the run of the algorithm. Real-time operations and fixed-point representation issues are included in the discussion. Additionally, we propose a modified algorithm implementation that is more robust to channel variations. Copyright (c) 2007 John Wiley & Sons, Ltd.