245 research outputs found
A Group-Theoretic Approach to the WSSUS Pulse Design Problem
We consider the pulse design problem in multicarrier transmission where the
pulse shapes are adapted to the second order statistics of the WSSUS channel.
Even though the problem has been addressed by many authors analytical insights
are rather limited. First we show that the problem is equivalent to the pure
state channel fidelity in quantum information theory. Next we present a new
approach where the original optimization functional is related to an eigenvalue
problem for a pseudo differential operator by utilizing unitary representations
of the Weyl--Heisenberg group.A local approximation of the operator for
underspread channels is derived which implicitly covers the concepts of pulse
scaling and optimal phase space displacement. The problem is reformulated as a
differential equation and the optimal pulses occur as eigenstates of the
harmonic oscillator Hamiltonian. Furthermore this operator--algebraic approach
is extended to provide exact solutions for different classes of scattering
environments.Comment: 5 pages, final version for 2005 IEEE International Symposium on
Information Theory; added references for section 2; corrected some typos;
added more detailed discussion on the relations to quantum information
theory; added some more references; added additional calculations as an
appendix; corrected typo in III.
FBMC system: an insight into doubly dispersive channel impact
It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur
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