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Designing Decision Feedback Equalizers to be Robust with
Respect to Channel Time Variations
Erik Lindskog,
Mikael Sternad
and
Anders Ahlén
Proceedings of NRS, Nordic Radio Symposium
on Interference Resistant Radio and Radar,
Uppsala, Sweden, June 1993.
In Pdf
- Outline:
-
When digital data are transmitted over dispersive radio channels,
a Decision Feedback Equalizer (DFE) can be utilized to
estimate transmitted symbols.
The paper presents a model-bases methodology for
robust design, aimed at reducing the effect of model uncertainties and
of slow time variations of the channel.
- Abstract:
-
Design equations are presented for a robust realizable decision
feedback equalizer, for FIR channels with uncertain channel
coefficients and white noise. The mean MSE averaged over the class
of channels is minimized, assuming correct past decisions.
An example using a robust DFE for a fading
GSM-channel at 1800MHz is presented.
The channel identified during the training sequence
is used for the nominal model. This model is complemented
by a stochastic uncertainty model, consisting of two additive parts.
One part is the variance error in the channel estimate obtained
by least squares during the training sequence. If the noise is white,
this error can be quantified exactly for short training
sequences.
The second part describes the
average uncertainty caused by the channel variability during
the data part of the burst. Such an estimate can be computed
if the speed of the mobile is known or estimated.
Based on the nominal model and error model, the robust DFE
can be design. A robust design results in a significant
performance improvement
at low SNR's and high speeds of the mobile, as compared to
a nominal design.
- Related publications:
-
PhD Thesis by Erik Lindskog.
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Licentiate Thesis
by E Lindskog 1995, which includes the paper.
Conference paper in IEEE ICASSP,
for IIR channels, coloured noise and decision errors.
PhD Thesis
by Kenth Öhrn May 1996, on the robust design of
filters.
1
Paper in IEEE Trans. IT 1990,
on the nominal model-based design of DFE's.
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