An adaptive equalizer is an equalizer that automatically adapts to time-varying properties of the communication channel. It is frequently used with coherent modulations such as phase shift keying, mitigating the effects of multipath propagation and Doppler spreading.
Many adaptation strategies exist. They include:
- LMS Note that the receiver does not have access to the transmitted signal when it is not in training mode. If the probability that the equalizer makes a mistake is sufficiently small, the symbol decisions made by the equalizer may be substituted for .
- RLS
A well-known example is the decision feedback equalizer, a filter that uses feedback of detected symbols in addition to conventional equalization of future symbols. Some systems use predefined training sequences to provide reference points for the adaptation process.
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