Prompt Rate Adaptation in WiMedia Considering Time Variant UWB Channels

In this paper the performance of the rate adaptation scheme specified by the WiMedia Alliance is investigated and a new, fast link feedback mechanism is proposed, which can be implemented without major modifications of the existing WiMedia UWB standard. After introducing the considered link adaptation mechanisms, a time variant UWB channel model is derived. Basic properties of UWB channels are summarized and the widely used IEEE 802.15.3a channel models are enhanced with respect to correlated variations in time domain. The delay caused by the link feedback scheme and the channel fluctuations are of paramount importance for the overall performance. Both link feedback mechanisms are modeled using the specified PHY layer and they are compared against each other in short-range scenarios based on real measurements. It was found that rate adaptation in general provides large gains in WiMedia UWB and that the fast link feedback scheme outperforms the standardized mechanism in case of swift channel variations. Consequently, the new scheme is seen as a general enhancement for mobile UWB devices.