Robust channel estimation in Wireless LANs for mobile environments

摘要

The recently developed wireless LAN systems, HIPERLAN/2 and IEEE 802.11a, operate in the 5GHz frequency range and have originally been designed for stationary terminals in slowly time-varying environments. Hence, pilot symbols for channel estimation are only provided at the beginning of a burst (in the preamble), since the channel behaviour is assumed not to change significantly over the burst duration. In order to support new scenarios with higher terminal mobility, it is essential to track the changes of the channel transfer function over time. In this paper, the focus is directed to techniques for a robust channel estimation, mainly based on enhanced pilots (EP). In more detail three different channel tracking schemes are developed and applied to the HIPERLAN/2 and the IEEE 302.lla system, namely 1) use of scattered pilots, 2) use of midambles, and 3) an additional decision-directed technique, combined with the midamble concept The performance of the different methods is studied and compared quantitatively. As a result, suitable channel tracking techniques for the different terminal speeds and data rates are proposed.