Abstract

We investigate the influence of feedback on the capacity of
multiple-input multiple-output (MIMO) non-coherent fading channels
with memory. We derive an upper bound on the feedback capacity of
regular fading channels, which is shown to coincide with a
previously known upper bound on the capacity without feedback.
Hence, it is concluded that whereas feedback does in general
increase capacity, this increase is relatively small in the sense
that the same upper bound holds for both scenarios. From this bound
we derive an upper bound on the MIMO fading number in the presence
of feedback and show that in the single-input single-output (SISO)
case this bound is tight, i.e., the SISO fading number is not
changed by feedback.

Next, we derive an upper bound on the feedback capacity of
spatially independent MIMO Gaussian fading channels. From this bound
we derive a new upper bound on the corresponding fading number and
show that in the multiple-input single-output (MISO) case this bound
is tight.

Finally, in the case of a non-regular SISO Gaussian fading process
we show that feedback does not increase the pre-log, i.e.,
the ratio of the capacity to the logarithm of the signal-to-noise
ratio log SNR is not changed in the limit when the SNR tends
to infinity.

-||-   _|_ _|_     /    __|__   Stefan M. Moser
[-]     --__|__   /__\    /__   Senior Scientist, ETH Zurich, Switzerland
_|_     -- --|-    _     /  /   Adjunct Professor, National Yang Ming Chiao Tung University, Taiwan
/ \     []  \|    |_|   / \/    Web: https://moser-isi.ethz.ch/

Last modified: Wed May 10 13:01:03 2006