Title page for ETD etd-12122005-094358

Type of Document

Dissertation

Author

Yu, Xinying ,

Author's Email Address

xyu2@ncsu.edu

URN

etd-12122005-094358

Title

Space-Time Coding for Large Antenna Arrays

Degree

PhD

Graduate Program

Electrical Engineering

Advisory Committee

Advisor Name	Title
Dr. Brian L. Hughes	Committee Chair
Dr. Alexandra Duel-Hallen	Committee Member
Dr. Carl Meyer	Committee Member
Dr. Hamid Krim	Committee Member

Keywords

large antenna arrays
MIMO
diversity
space-time coding

Date of Defense

2005-12-09

Availability

unrestricted

Abstract

Multiple-input multiple-output (MIMO) systems can greatly improve
the capacity and performance of wireless communications. In
particular, space-time coding techniques have received much
attention in recent years as an efficient approach to achieving the
performance gains offered by MIMO channels. Thus far, most work on
space-time coding has focused on systems with small antenna arrays
or high signal-to-noise ratios (SNRs), for which it has been shown
that codes should be designed according to the rank and determinant
criteria. For such scenarios, coherent space-time coding and
differential space-time modulation (DSTM) schemes have been
designed, for systems with or without channel knowledge at the
receiver, respectively. In recent years, there has been some work on
coherent space-time coding for large arrays, which indicates that
the code design metric should be chosen diffently from that for
small arrays. In this dissertation, we study the design of
space-time coding for large arrays. We focus on three aspects:
performance analysis, code construction and decoding algorithms.

We first analyze the asymptotic performance of differential
space-time modulation. A new upper bound on the pairwise-error
probability is derived for large arrays. This bound suggests that
Euclidean distance is an appropriate design criterion for DSTM with
large numbers of antennas, which is similar to the design of
coherent space-time coding for the large-array regime. For two
transmit antennas and four or more receive antennas, we use the new
design criterion to obtain several new unitary codes with large
minimum Euclidean distance. The proposed codes outperform some
existing codes, for example, the well-known Alamouti code, for large
receive arrays.

Although the codes designed according to the new design criterion
achieve good performance, most of them require maximum-likelihood
(ML) decoding, which is undesirable for high-rate codes. On the
other hand, the Alamouti code, which is designed for high-SNR
regime, enables simple linear ML decoding. It is of interest to
design codes that perform well for large arrays, but which also
allow simple decoding at the receiver. We first consider the design
of unitary codes, for use with and without channel knowledge at the
receiver. For two transmit antennas, we consider a structure which
is a modification of the Alamouti code. We optimize the new code
with respect to the Euclidean distance criterion. We then show that
the new code allows us to use two suboptimal decoders that have
complexity comparable to the Alamouti decoder. The analytical
bit-error performance and the constellation-constrained capacity are
derived for the suboptimal decoders. For coherent detection, the
coding structure is extended to non-unitary constellations. We also
extend the new code to more than two transmit antennas.

Conventional DSTM assumes that the channel remains constant for two
adjacent transmission blocks, which is questionable for some
time-varying channels. In this dissertation, we investigate the
performance of the new code when fast-fading is encountered. We show
that multiple-symbol decision-feedback differential detection (DFDD)
can be used to reduce the performance degradation of the new code in
fast-fading channels. We also consider the use of suboptimal
decoders in DFDD to further reduce the decoding complexity.

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