Linear Equalization

  • Jan W. M. Bergmans


Baseband data transmission is often hampered by linear intersymbol interference (ISI) and noise (see Chapters 2 and 3). In the present chapter we deal with the oldest technique to counter these two disturbances, namely linear equalization. The linear equalizer (LE) is just a linear filter that suppresses ISI at the periodic instants at which decisions are taken. The name of the technique originates from the fact that the filter must essentially equalize the transfer characteristics of the channel across a band that ranges from DC up to about the Nyquist frequency. A roll-off beyond this band serves to suppress out-of-band noise. The LE can be analog, digital or a mixture of the two. The digital portion of the LE is called T-spaced when the sampling rate coincides with the symbol rate 1/T, and fractionally-spaced when it is oversampled with respect to symbol rate. If the channel characteristics are a priori known then the LE can be a fixed filter. More often than not, however, channel characteristics are uncertain and the LE is adaptive. In the present chapter we are mainly concerned with the desired transfer characteristics of the LE, and to a lesser extent with the problem of achieving or approximating these desired characteristics with a practical equalizer implementation. That problem is inherent in adaptive equalization as discussed in Chapter 8.


Impulse Response Matched Filter Linear Equalization Linear Equal Noise Enhancement 
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Copyright information

© Springer Science+Business Media Dordrecht 1996

Authors and Affiliations

  • Jan W. M. Bergmans
    • 1
  1. 1.Philips ResearchEindhovenThe Netherlands

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