Adaptive equalizer

An adaptive equalizer is an equalizer that automatically adapts to time-varying properties of the communication channel.^[1] 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 .^[2]
• RLS

A well-known example is the decision feedback equalizer,^[3][4] a filter that uses feedback of detected symbols in addition to conventional equalization of future symbols.^[5] Some systems use predefined training sequences to provide reference points for the adaptation process.

See also

• Equalizer
• Intersymbol interference

References

1. ^ S. Haykin. (1996). Adaptive Filter Theory. (3rd edition). Prentice Hall.
2. ^ Tutorial on the LMS algorithm
3. ^ Decision Feedback Equalizer
4. ^ Warwick, Colin (March 28, 2012). "For Decision Feedback Equalizers, Beauty is in the Eye". Agilent Technologies. http://signal-integrity.tm.agilent.com/2012/decision-feedback-equalizer-beauty-is-in-the-eye/. 
5. ^ Stevens, Ransom. "Equalization: The Correction and Analysis of Degraded Signals". http://cp.literature.agilent.com/litweb/pdf/5989-3777EN.pdf.