An Asynchronous Multitone Multiuser Air Interface for High-Speed Uplink Communications

We describe a transmission technology approach that is suited for application to high-speed asynchronous multiuser wireless channels, i.e., reverse WLAN/cellular links. The scheme is based on concatenated multitone modulation and multiplexing. The design parameters are flexible and are chosen to cope with the users' time and frequency offsets, as well as with the timefrequency channel selectivity. Frequency hopping, and DS spreading can also be included for improved diversity and interference averaging benefits. The principles of this modulation and multiplexing approach are illustrated for an asynchronous reverse link over a 3.84 MHz channel. The key aspect of the proposed asynchronous multitone (AMT) air-interface is its intrinsic robustness to multiple access interference, and channel time-frequency selectivity. We emphasize that the approach is applicable to other contexts with wider bandwidths as those available in 802.11a, Hiperlan II, and those that will become available in future 4G cellular systems.