Tracking of Time-varying Mobile Radio Channels,
Part II: A Case Study.
, Ericsson Infotech
, Uppsala University
, Uppsala University and
, Ericsson Infotech.
IEEE Transactions on Communication,
Vol. 50, January 2002, pp. 156-167.
A brief version of the paper,
"Tracking of Time-varying Mobile Radio Channels
with WLMS Algorithms:
A Case Study on D-AMPS 1900 Channels"
M. Sternad, L. Lindbom and A. Ahlén,
is published at
IEEE Vehicular Technology Conference - VTC200-Spring
Tokyo, Japan, May 15-18, 2000, pp 2507-2511.
The IS-136 digital mobile
TDMA systems are widely used on the American
continents and a similar standard exists in Japan.
Their relatively low symbol rate and long data slots
(6.67 ms) cause severe fading. In such 1900 MHz systems,
one or two fading dips can be expected
within each data slot.
Large variations in fading rates and
frequency selectivity are encountered.
Well designed channel estimators are
therefore crucial for
obtaining adequate performance.
Estimates obtained from training sequences
cannot be used within the whole slot and
interpolation of channel estimates
between training sequences provides
The same is true for the
decision-directed LMS and RLS adaptation algorithms.
We will here investigate
the application of WLMS algorithms
to the estimation of the fading channels.
Low-complexity WLMS adaptation algorithms, of use
for channel estimation, have been
derived in a companion paper.
Their use and design is here evaluated
on the fast fading radio channels
encountered in IS-136 TDMA systems,
with the aim of clarifying several issues:
How much can channel estimation performance be
improved with these tools, as compared
to LMS adaptation?
When can an improved tracking MSE be expected
to result in a
meaningful reduction of the bit error rate?
prediction of future channel estimates
significantly improve the
equalization in fast fading environments?
Can one single tracker with fixed gain be used for
all encountered Doppler frequencies and SNRs, or
must a more elaborate scheme be adopted?
These questions are here investigated
and by simulation. An exact analytical expression
for the tracking MSE on two-tap FIR channels
is presented and utilized.
With this tool, the MSE performance and robustness
of WLMS algorithms based on different
can be investigated.
A simulation study then compares the
uncoded bit error rate
of detectors, where channel trackers are used
in decision directed mode in conjunction with
A Viterbi detector combined with
WLMS, based on second order autoregressive fading
models possibly combined with integration, provides
and robustness at a reasonable complexity.
Part I: The Wiener LMS
of the general constant-gain adaptation algorithms.
of stability and performance, for slow and fast variations.
PhD Thesis by Lars Lindbom.
Licenciate Thesis by Lars Lindbom,
on averaged Kalman designs (KLMS)
and on deterministic sinusoid modelling of fading channels.
Master Thesis by Magnus
Falkenström, on the grid approach to robust
design of channel estimators.
Conference paper (IFAC Como 2001)
on averaged robust design for uncertain fading models.
Conference version, VTC2000S Tokyo: :
Postscript, 238K ;
Conference poster , VTC2000S Tokyo:
Postscript, 200K ;
Paper version (IEEE-COM):
Postscript, 391K ;
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