On Equalization and Beamforming for Mobile
Licentiate Thesis, Report UPTEC 95069R,
82pp, April 1995.
Paper copies of the thesis can be obtained from
Signals and Systems Group, Uppsala University,
Box 528, SE-75120 Uppsala, Sweden.
Papers included in the Thesis:
When digital data are transmitted over dispersive radio channels,
a Decision Feedback Equalizer (DFE) can be utilized to estimate transmitted symbols.
This detector subtracts an estimate of the intersymbol interference
caused by previous symbols, before making symbol-by symbol
The present thesis focuses on two questions related to the
use of DFE's:
- Robust design, to reduce the effect of model uncertainties and
- The use of DFE's in receivers with multiple elements.
Many coefficients may then have to be adjusted based on
short training sequences.
The use of Decision Feedback Equalization for mobile radio
applications is considered.
Algorithms for indirect model-based MMSE design, which are
robust against imperfect channel and
noise modelling as well as error propagation, are presented.
These algorithms can also be designed to be robust against
a slow time-varying dynamics of the transmission channel.
An example for a GSM-type mobile radio channel is included.
Algorithms utilizing a circular antenna array are also considered.
The challenge here is that detectors with a rather large number of
filter parameters are to be adjusted based on short training sequences.
Several algorithms based on combined spatial and temporal
are suggested. Both direct and indirect schemes of low complexity are
investigated. Separate tuning of the beamformer coefficients
and subsequent equalization yields better performance
for short training data records than a simultaneous adjustment
of all coefficients. All the investigated
algorithms perform well in spite of co-channel interference.
To avoid ill-conditioned matrices in the solution for very short
data records, regularization is introduced in some algorithms.
An adaptive inteference cancellation scheme for an indirect
spatio-temporal equalizer is also addressed.
Finally, beamforming with a modified version of the sample inversion
method is considered. It is applied to a GSM signal with
- Summary. (In Postscript :
compressed(gz) 37K ,
(In Pdf 290K.)
- Robust Decision Feedback Equalizers
- Designing Decision Feedback Equalizers to be Robust with Respect to Channel Time Variations
- Combined Spatial and Temporal Equalization
Using an Adaptive Antenna Array
and a Decision Feedback Equalization Scheme
- Spatio-Temporal Equalization
for Multipath Environments in Mobile Radio Applications
Spatio-Temporal Equalization and Adaptive Interference
Cancellation for Multipath Environments in Mobile Radio Applications
with the Sample Matrix Inversion Method for a GSM
Signal with Sampling Offset.
- An Appendix with a derivation of the robust
DFE is also included.
- Related publications:
PhD Thesis by Erik Lindskog.
- Later Conference paper
on the implementation of Viterbi algorithms in antenna arrays.
Later Conference paper
on direction-of-arrival parametrization.
Later Conference paper (Asilomar'95),
on utilizing adjacent TDMA frames.
utilized as multi-user detectors, in IEEE PIMRC'95.
Robust filter design
and uncertainty modelling, as described in Automatica 1993.
based on exactly known IIR model (IEEE Trans. IT 1990).