Performance of single-user and multi-user constant-energy bit loading in Hiperlan channels

Several WLAN standards, such as Hiperlan-2, have chosen OFDM as a transmission technique due to its multipath performance. However, in these standards spectrum is not optimized. This paper analyzes the performance of single-user and multi-user constant-energy bit loading in Hiperlan channels. We show that bit rates may be increased up to 12 times in the single-user case and a gain of more than 100% may be achieved relative to Hiperlan-2 in multi-user scenarios.

1. Introduction

Multicarrier modulation techniques have been standardized for Wireless Local Area Networks (WLAN) due to their good performance in multipath environments. In recent standards, such as Hiperlan type 2 and IEEE 802.11a, the number of bits modulating each sub-carrier can be chosen among several possibilities to adapt the transmission to the channel quality. However, the same number of bits is used for every sub-carrier, that is, the signal spectrum is not optimized.