Method and apparatus for varying the length of an adaptive equalizer based on doppler frequency

摘要

Systems and methods according to the present invention are described for adjusting the number of taps in an adaptive equalizer over time as the rate of change of a communications channel varies. The number of taps or "equalizer length" is adjusted based on an estimate of the Doppler frequency between the devices communicating over a channel. The Doppler frequency is reflective of the rate of change of the communications channel. Greater Doppler frequencies indicate a more quickly varying channel, and vice versa. It is therefore desirable to change the equalizer length (by adding or dropping taps) based on a measurement of the Doppler frequency. Equalizer length is increased as the Doppler frequency decreases. Conversely, equalizer length is decreased as the Doppler frequency increases. This enables the equalizer to achieve a better compromise between the competing goals of adaptation speed (less taps) and ISI reduction (more taps).