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. This work was presented in parts at the 2006 IEEE Wireless Communications and Networking Conference (WCNC), Las Vegas, Nevada, USA. This work was generously supported by the Natural Science and Engineering Research Council of Canada (NSERC) and Le Fonds “Nature et Technologies” du Quebec (NATEQ). Martin Cudnoch is with SR Telecom Inc., Montreal, Quebec, Canada. Alexander M. Wyglinski is with the Information and Telecommunication Technology Center, The University of Kansas, Lawrence, Kansas, USA. Fabrice Labeau is with the Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Room ENGMC-754, Montreal, Quebec, Canada, H3A 2A7, Tel.: +1 514 398-7140, Fax: +1 514 398-4470, E-mail: [email protected]. October 1, 2006 DRAFT WILEY WIRELESS COMMUNICATIONS AND MOBILE COMPUTING 2