Nonlinear Precoding Methods to Remove Intersymbol Interference
Two nonlinear precoding methods that can be used in transmitters to remove intersymbol interference are presented in this chapter. The first method was disclosed independently by Tomlinson  in 1971 and Harashima  in 1972. The second method was discovered by Laroia, Tretter, and Farvardin (LTF) [47, 48] in 1992. Both methods transmit a signal that is the sum of the input constellation point sequence and a dither sequence that depends on the channel impulse response and precoder input. The advantage of the LTF precoder is that the dither signal is much smaller than for the Tomlinson/Harashima precoder so that the shaping gain of the input constellation is essentially preserved. The Tomlinson/Harashima precoder destroys shaping gain. Shortly after the LTF precoder was presented to the ITU-T V.34 study committee, additional refinements were made [43,30] that further reduced the dither signal power by arranging the constellation point selector, precoder, and channel trellis encoder in a feedback loop and the technique was incorporated in Recommendation V.34. This refinement is the subject of Chapter 10.
KeywordsAttenuation Autocorrelation Convolution
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