Pole-zero decision feedback equalization with a rapidly converging adaptive IIR algorithm

Abstract

A decision feedback equalizer (DFE) containing a feedback filter with both poles and zeroes i s proposed for highspeed digital communications over the subscriber loop. The feedback filter is composed of two sections: a relatively short finite impulse response (FIR) filter that cancels the initial part of the channel impulse response, which may contain rapid variations due to bridge taps; and a pole-zero, or IIR, filter that cancels the smoothly decaying tail of the impulse response. Modifications of an existing adaptive IIR algorithm, based on the Steiglitz-McBride identification scheme, are proposed to adapt the feedback filter. These new algorithms have comparable complexity to gradient-based adaptive IIR algorithms when the number of poles is small, but converge significantly faster. A measured subscriber loop impulse response is used to compare the performance of the adaptive pole-zero DFE, assuming a two-pole feedback filter, with a conventional DFE having the same number of coefficients. Results show that the pole-zero DFE offers a significant improvement in mean squared error (i.e., 4 dB at a signal-to-noise ratio of 25 dB) relative to the conventional DFE. Furthermore, the speed of convergence of the adaptive pole-zero DFE is comparable with that of the conventional DFE using the standard LMS adaptive algorithm.

Lattice implementation of adaptive channel shortening in multicarrier transmission over IIR channels

“…In fact, when the channel is characterized by its long tail, it can be approximated by a reduced-parameter model. Actually, the problem of approximating a long FIR filter by a pole-zero filter with a small total number of coefficients had been investigated by many researchers [17,18], some of them had especially developed a stable pole-zero model of the DSL loop as a way to reduce the implementation complexity of the DSL channel equalization [9]. Thus, the transfer function of long FIR channel can be as follows:…”

Equalizing filter design for crosstalk cancellation

“…Equalizing filters have been used effectively for cross-talk cancellation in acoustic applications such as telephone line subscriber system [1][6] [7]. Recently, they have been used to compensate for the frequency-dependent attenuation of transmission lines [2].…”

“…Using least squares minimization, the equalizing filter design problem is equivalent to the problem of designing equalizing filters to determine the values for the filter coefficients that minimize the This method is used in optimal pre-emphasis equalizing filter design in [2][19] to build serial links that operate at over 1 Gigabits per second. Also it is widely used to design equalizers for telephone subscriber systems [1][6] [7]. …”

On-chip data communication : analysis, optimization and circuit design

“…Another alternative that was already proposed quite some time ago in [151] (and recently applied in [139]) is to use a combination of a FIR and IIR filter. This enables both cancellation of high-frequency artifacts with the FIR and cancellation of dominant poles with the IIR.…”

“…However, in [150] and [151], discrete-time IIR filters are still used, while it is also possible to use an analog continuous-time filter. In this project (and later also in [139]), a continuous-time filter was used as feedback filters, as these types of filters can have simple implementations with good power-efficiency.…”