Precoder design with statistical channel state information over MIMO Rician channels
多入多出萊斯信道中基於統計信道信息的預編碼器設計
Student thesis: Doctoral Thesis
Author(s)
Related Research Unit(s)
Detail(s)
Awarding Institution  

Supervisors/Advisors 

Award date  15 Jul 2014 
Link(s)
Permanent Link  https://scholars.cityu.edu.hk/en/theses/theses(0514123d12144c6facd05fb9c6018f47).html 

Other link(s)  Links 
Abstract
A precoder is a processing block that exploits channel state information (CSI) at the
transmitter (CSIT) by transforming the input signal prior to transmission. By acting
as a combination of the input matching matrix, power allocator, and beamformer,
the precoder matches the input signal to the channel and distributes transmit power
over eigenbeams. When a perfect CSIT is available, the system performance can
be enhanced by dynamically adjusting transmission parameters according to CSIT.
However, the acquisition of a perfect CSIT is costly and sometimes infeasible due
to delayed feedback, channel estimation, and quantization errors. The bandwidth
overhead for CSI feedback is also a vital concern. So the design of an optimal precoder
that is based on imperfect or partial CSIT, i.e., statistical CSIT, becomes important
in practice.
The objective of this thesis is to investigate precoder design methods that are
based on statistical CSIT for multipleinput multipleoutput (MIMO) wireless communication
systems. We consider two MIMO systems: pointtopoint communication
and cooperative relay networks. First, we propose a statistically robust precoding
scheme for a pointtopoint MIMO system with orthogonal spacetime block codes
(OSTBC) to minimize the Chernoff bound of pairwise error probability (PEP). The
conventional Kronecker channel model with general transmit and receive correlation
matrices is adopted. We assume that the receiver obtains instantaneous CSI, whereas
only statistical CSI, i.e., the channel mean and correlation matrices, is available on the
transmitter side. By defining new power control variables and exploiting the eigenmode
structure of the precoder, the optimization problem becomes convex when the
power allocation and beamforming matrix are iteratively solved. An iterative procedure
for constructing the eigenstructure, which includes an efficient algorithm for
determining the number of eigenbeams with positive power, their power allocation,
and a simple scheme using Givens rotations for updating the beamforming matrix, is derived. Based on a low signaltonoise ratio (SNR) asymptotic analysis, a unitary
matrix that reduces the precoder design to a power allocation problem, which contains
significantly lower computational complexity, is derived for the PEP criterion. For a
given Rician Kfactor, the asymptotic analysis reveals that the precoder approaches a
singlebeam mode that is dependent on the channel mean at a low SNR. Conversely,
for high SNR, the power allocation approaches an equal power scheme. These asymptotic
behaviours are affected by the constellation size. However, for a given SNR, as
the value of the Rician Kfactor increases, the optimal precoder tends to use fewer
eigenmodes and finally becomes a singlemode scheme. This contrary effect of a
large SNR and Kfactor on the design is dependent on the specific channel mean and
correlation. The analysis also indicates that the lowrank channel mean matrix yields
better PEP performance than the highrank channel mean matrix in the low SNR region.
The numerical results demonstrate better performance of the proposed method
compared with existing methods with significantly lower computational complexity.
We propose a novel precoding scheme for spacetime coded MIMO relay networks.
We assume that the destination terminal perfectly knows the CSI, whereas only statistical
CSI is available at the source and relay nodes. The majority of the existing
methods use mean square error (MSE) criterion with the Wiener filter as an equalizer
in the design of the precoding system. However, the optimum design derived from
this approach may not provide satisfactory PEP. To directly relate the optimization
to error probability in this thesis, a lower bound of an accurate approximation of the
total average SNR at the destination is adopted as the performance criterion. The
optimal receiver at the destination terminal is demonstrated to be a maximum ratio
combiner (MRC) and the precoding matrix for relay nodes should be block diagonal
with its main diagonal matrices as the precoding matrices at the relay nodes. Two
system configurationsa configuration with the direct channel and a configuration
without the direct channelare examined. These configurations can be established by
controlling the combined weight factors for the two received signals in two different
time slots at the destination terminal: one signal is received directly from the source
and another signal is received from the relays. By appropriately expanding the SNR
expression, the relay precoder can be solved with a generalized Rayleigh quotient.
The maximization of the SNR results in an optimal source precoder of a singlebeam
structure. To reduce the feedback overhead and processing burden on the relays, we
also investigated the scenario in which a single antenna is used in the relay nodes. The numerical results demonstrate that the proposed method outperforms the equal
power allocation scheme and existing methods. The error performance improves with
the number of relays or the total antennas on relays. The bit error rate (BER) performance
of a robust design for statistical CSI is similar to the perfect CSI case, in
which the Rician Kfactors for all channels are sufficiently high. When the Rician Kfactors
of the cascade channel are high and the Rician Kfactor of the direct channel
is low, the cooperative network with a sufficiently large number of relays can provide
adequate system performance without a direct channel as if a direct channel were
deployed, which implies a reduction in feedback overhead.
 Wireless communication systems, MIMO systems, Coding theory