Adaptive loading strategy for a high speed OFDM-based WLAN

Wireless LANs based on OFDM are limited in their performance by the dips in the frequency spectrum of the indoor multi-path channel. To simulate performance, we first derive a simplified channel model from a ray-tracing analysis of the indoor channel. The performance of OFDM-based WLANs can be augmented by adaptive loading of the subcarriers, which has shown to be very valuable for DMT modems on wired media (for example in ADSL). In this paper, we investigate the application of adaptive loading to a 100 Mbit/s OFDM-based wireless LAN. From the different adaptive loading algorithms, the Fischer and Huber (1996) algorithm is selected because it offers computational advantages for similar performance. This algorithm is then integrated in a complete system by implementing a channel and noise power estimation. Simulations show that the proposed adaptive loading strategy improves the system performance considerably (6 dB gain for a BER=10^-2). Moreover, the simulations confirm that the simplified channel model is a reliable description of the indoor channel