Abstract—As extension of MIMO technology in cellular system
with multiple cell sites, Cooperative Network MIMO is a hot topic
for the research of future wireless communication.
In current study of TD-LTE-Advanced (LTE-Advanced TDD)
system, various coordinated beamforming schemes have shown to
be very promising candidates. In this paper we introduce a few
implementations of coordinated beamforming technology with
different levels of coordination, together with system level
simulations and analysis.
Index Terms—Beamforming, Coordinated Network MIMO,
TD-LTE-Advanced, LTE-Advanced, TDD
I. INTRODUCTION
HE very challenging date rate of 1Gbps is expected for the
future wireless system. As one of the promising
technologies to achieve such goal, Multiple-Input-Multiple
Output (MIMO) has been intensively studied in recent years.
MIMO technology exploits the spatial components of the
wireless channel to provide higher spectrum efficiency. [1]
In cellular networks, spectrum resource is typically reused
over cells/users to optimize the sum-rate performance. In this
case co-frequency interference will be a main factor to impact
the performance, especially in case of MIMO link which
usually requires relatively higher SNR (Signal to Noise Ratio).
This constraint motivates the study of Cooperative Network
MIMO which improves link situation by coordination across
multiple base stations in the network [2].
3GPP LTE-Advanced system is designed for next generation
of wireless communication, i.e. IMT-Advanced. Its TDD (Time
Division Duplexing) mode is also known as
TD-LTE-Advanced. [3] For its very high performance target,
inclusion of Network MIMO technology is being taken into
consideration. During the study cooperative beamforming has
appear to be a promising candidate both from performance and
practicability point of view. In the other hand it inherits and
further improves the beamforming technology which is
currently deployed in 3G TD-SCDMA network.
In this paper, we investigate several implementation schemes
of Network Cooperative beamforming which is currently being
studied in the design of TD-LTE-Advanced system. We
introduce these schemes followed by simulation and analysis of
the performance results.
The paper is organized as follows: Section II describes the
investigated implementation schemes. Section III introduces
simulation model and analysis of the performance results.
Finally, conclusion remark is given in Section V.
II. I
MPLEMENTATION SCHEMES
In this section we introduce several schemes of beamforming
which can be implemented in the network with different levels
of coordination. It includes single cell/single user scheme as
baseline, and then extends to multiuser case to exploit the
spatial dimension. Furthermore, by introducing inter-cell
coordination scheduling of neighboring cells can be
coordinated. The situation of inter-cell interference can then be
optimized to improve performance of the overall system. In
case of good connection among cells (i.e. capacity and latency
aspects), sufficient information can be exchanged among cells
to further support more sophisticated schemes which take the
cooperated scenario which involves several base stations and
user as a whole broadcast channel and optimize its capacity (e.g.
dirty paper algorithm [4]).
For the purpose of description we assume that each cell is
equipped with 4 correlated antennas and each UE is equipped
with 2 antennas in following expressions.
A. Baseline Single User Beamforming
Assume the downlink channel from cell to UE is
24
×
.
Typically we can obtain the beamforming matrix by
Eigenvalue decomposition as
1
2
000
000
0000
0000
TT
d
d
UDV U V
⎤
⎥
⎥
==
⎥
⎥
⎦
(1)
First two columns of V can then be used as beamforming
Lin Hui
Beijing university of Posts and
Telecommunications
linhui@catr.cn
Coordinated Beamforming technology in
TD-LTE-Advanced system
T
Wang Wen Bo
Beijing university of Posts and
Telecommunications
wbwang@bupt.edu.cn
2010 International Conference on Communications and Mobile Computing
978-0-7695-3989-8/10 $26.00 © 2010 IEEE
DOI 10.1109/CMC.2010.23
213