The demand of new wireless communication systems with much higher
data rates that allow, e.g., mobile wireless broadband Internet
connections inspires a quick advance in wireless transmission
technology. So far most systems rely on an approach where the channel
state is measured with the help of regularly transmitted training
sequences. The detection of the transmitted data is then done under
the assumption of perfect knowledge of the channel state. This
approach will not be sufficient anymore for very high data rate
systems since the loss of bandwidth due to the training sequences is
too large. Therefore, the research interest on joint estimation and
detection schemes has been increased considerably.

In this project wireless communication channels are investigated under
the assumption that neither receiver nor transmitter has any a
knowledge of the channel state, i.e., the estimation schemes
is incorporated into the system and its analysis. The goal is to find
new insight into the fundamental limits of such communication systems,
in particular, new results about its channel capacity. Since no
assumptions are made about the estimation part of the system, the
channel capacity often is known as non-coherent channel capacity.

Recent results show that non-coherent fading channels become very
power-inefficient at high signal-to-noise ratios (SNR) in the sense
that increasing the transmission rate by an additional bit requires
squaring the necessary SNR. Based on this observation the main goal
of this project is the study of the threshold between the
power-efficient low- to medium-SNR and the highly power-inefficient
high-SNR regime. To that goal the fading number is derived defined
as the second term in the high-SNR expansion of channel capacity. In
particular new expressions are shown for the fading number of
independent and identically distributed (IID) multiple-input
multiple-output (MIMO) Gaussian fading channels with a scalar
line-of-sight component and for the fading number of general MIMO
fading channels with memory.

As a side-product closed-form expressions for so-far unknown
expectations of a non-central chi-square distributed random variable
are derived.


Fading number, flat fading, high signal-to-noise ratio (high SNR),
joint estimation and detection, memory, multiple-input multiple-output
(MIMO), non-central chi-square, non-coherent channel capacity.

-||-   _|_ _|_     /    __|__   Stefan M. Moser
[-]     --__|__   /__\    /__   Senior Researcher & Lecturer, ETH Zurich, Switzerland
_|_     -- --|-    _     /  /   Adj. Professor, National Chiao Tung University (NCTU), Taiwan
/ \     []  \|    |_|   / \/    Web: http://moser-isi.ethz.ch/

Last modified: Wed Dec 5 15:52:38 UTC+8 2007