Power control by Kalman filter with error margin for wireless IP networks

A power-control method based on the tracking of interference power by use of a Kalman filter, proposed earlier for packet-switched TDMA wireless networks, does not yield a performance gain in case of short message lengths and/or moderate control delays. The major reason is that the interference prediction by the filter may not be accurate enough due to little interference temporal correlation. In this paper, we enhance the power-control method by introducing an error margin in determining the transmission power. The error margin is obtained based on tracking of the interference prediction error, which automatically captures the impacts due to short message lengths and control delays. Our performance results reveal that the enhanced power-control method is capable of providing a significant performance improvement even for short messages and moderate control delays. Specifically, for the worst case where the message length L=1 (i.e., one packet per message), the 90 and 95 percentile signal-to-interference-plus-noise ratios (SINR) for the enhanced method are 2.69 and 2.96 dB above those for no power control in a system of 4-sector cells with a frequency reuse factor of 2/8. In contrast, the original Kalman-filter method with no error margin yields no SINR gain for L=1. For L=10, we also observe a similar improvement by the enhanced method for control delays up to 3 time slots.