Proc. IEEE Int. on Global Communications Conf., Dec. 1-5, 2003, vol. 4, pp. 2146-2150, San Francisco, CA USA.

Minimum Intersymbol Interference Methods for Time Domain Equalizer Design

Ming Ding (1), Brian L. Evans (1), Rick Martin (2), and C. Richard Johnson, Jr. (2)

(1) Department of Electrical and Computer Engineering, Engineering Science Building, The University of Texas at Austin, Austin, TX 78712-1084 USA -

(2) Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14850 USA -

Paper - Talk

ADSL Research at UT Austin - ADSL Research at Cornell


During initialization, discrete multitone receivers train a time domain equalizer (TEQ) to shorten the channel impulse response to a preset length, v+1. Arslan, Kiaei, and Evans report a Minimum Intersymbol Interference (Min-ISI) method for TEQ design. Min-ISI TEQs give the highest bit rates among single-FIR TEQs amenable to real-time implementation on programmable fixed-point digital signal processors (DSPs). The Min-ISI method, however, has several disadvantages: (1) sensitivity to transmission delay, (2) inability to design TEQs longer than v+1 taps, and (3) sensitivity to the fixed-point computation in the Cholesky decomposition. In this paper, we develop an alternate Min-ISI cost function, from which we derive (1) a fast search method for the optimal transmission delay, (2) extensions to design arbitrary-length Min-ISI TEQs, and (3) an iterative Min-ISI method. The iterative Min-ISI method avoids Cholesky decomposition, designs arbitrary length TEQs, and achieves the bit rate performance of the original Min-ISI method.

Questions and Answers

Question: "I was trying to implement the adaptive min-ISI method from your paper, titled 'Min-ISI methods for TEQ design' for the upstream ADSL channel. Hoever [However], I find using the adapive [adaptive] min-ISI method, I am obtaining complex values for the equalizer taps."

Answer: "You should be able to get real-value results. I think you should carefully check your gradient. The cost function matrix is complex-valued, hence, the gradient is a little bit different formed. Look at equation (12), X is hermitian, [and] X+X' should give you real values."

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Last Updated 01/16/06.