In this paper we deal with a single-antenna discrete-time flat-fading
channel. The fading process is assumed to be stationary for the
duration of a single data block. From block to block the fading
process is allowed to be non-stationary. The number of scatterers
bounds the rank of the channels covariance matrix. The signal-to-noise
ratio (SNR), the user velocity, and the data block-length define the
usable rank of the time-variant channel subspace. The usable channel
subspace grows with the SNR. This growth in dimensionality must be
taken into account for asymptotic capacity results in the high-SNR
regime. Using results from the theory of time-concentrated and
band-limited sequences we are able to define an SNR threshold below
which the capacity grows logarithmically. Above this threshold the
capacity grows double-logarithmically.


Non-coherent capacity, non-stationary time-variant channel,
Slepian basis expansion, Fourier basis expansion, prolate spheroidal

-||-   _|_ _|_     /    __|__   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 May 10 13:01:03 2006