400 research outputs found
Optimal Precoders for Tracking the AoD and AoA of a mm-Wave Path
In millimeter-wave channels, most of the received energy is carried by a few
paths. Traditional precoders sweep the angle-of-departure (AoD) and
angle-of-arrival (AoA) space with directional precoders to identify directions
with largest power. Such precoders are heuristic and lead to sub-optimal
AoD/AoA estimation. We derive optimal precoders, minimizing the Cram\'{e}r-Rao
bound (CRB) of the AoD/AoA, assuming a fully digital architecture at the
transmitter and spatial filtering of a single path. The precoders are found by
solving a suitable convex optimization problem. We demonstrate that the
accuracy can be improved by at least a factor of two over traditional
precoders, and show that there is an optimal number of distinct precoders
beyond which the CRB does not improve.Comment: Resubmission to IEEE Trans. on Signal Processing. 12 pages and 9
figure
On Optimum End-to-End Distortion in MIMO Systems
This paper presents the joint impact of the numbers of antennas,
source-to-channel bandwidth ratio and spatial correlation on the optimum
expected end-to-end distortion in an outage-free MIMO system. In particular,
based on an analytical expression valid for any SNR, a closed-form expression
of the optimum asymptotic expected end-to-end distortion valid for high SNR is
derived. It is comprised of the optimum distortion exponent and the
multiplicative optimum distortion factor. Demonstrated by the simulation
results, the analysis on the joint impact of the optimum distortion exponent
and the optimum distortion factor explains the behavior of the optimum expected
end-to-end distortion varying with the numbers of antennas, source-to-channel
bandwidth ratio and spatial correlation. It is also proved that as the
correlation tends to zero, the optimum asymptotic expected end-to-end
distortion in the setting of correlated channel approaches that in the setting
of uncorrelated channel. The results in this paper could be performance
objectives for analog-source transmission systems. To some extend, they are
instructive for system design.Comment: 35 pages, 10 figures, submitted to EURASIP Journal on Wireless
Communications and Networkin
The Use of Short-Count Methods on Field Collected Diatom Communities to Determine Water Quality of Small Streams
This study was undertaken to determine if short-count methods for calculation of diatom species diversity could be used to determine the water quality of small streams. Two small streams, located in North Central Iowa, were selected for study; one was chosen because it appeared to be in a relatively healthy condition and the other because it appeared to be highly polluted. Diatom samples were collected by direct field collection of the predominant diatom growths in each stream. Short-counts of 50, 100, 200, 500, and 1000 diatom valves were made and species diversity computed by 2 methods, the Shannon Index of General Diversity and the Sequential Comparison Index. A one-way analysis of variance using mean species diversity values was run on all diatom counts both within and between the samples of each stream. The results showed that short-counts could be used to determine differences in water quality of the 2 small streams studied and further suggest that such analyses might be suitable for other small streams
Large System Analysis of Linear Precoding in Correlated MISO Broadcast Channels under Limited Feedback
In this paper, we study the sum rate performance of zero-forcing (ZF) and
regularized ZF (RZF) precoding in large MISO broadcast systems under the
assumptions of imperfect channel state information at the transmitter and
per-user channel transmit correlation. Our analysis assumes that the number of
transmit antennas and the number of single-antenna users are large
while their ratio remains bounded. We derive deterministic approximations of
the empirical signal-to-interference plus noise ratio (SINR) at the receivers,
which are tight as . In the course of this derivation, the
per-user channel correlation model requires the development of a novel
deterministic equivalent of the empirical Stieltjes transform of large
dimensional random matrices with generalized variance profile. The
deterministic SINR approximations enable us to solve various practical
optimization problems. Under sum rate maximization, we derive (i) for RZF the
optimal regularization parameter, (ii) for ZF the optimal number of users,
(iii) for ZF and RZF the optimal power allocation scheme and (iv) the optimal
amount of feedback in large FDD/TDD multi-user systems. Numerical simulations
suggest that the deterministic approximations are accurate even for small
.Comment: submitted to IEEE Transactions on Information Theor
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