CoMP for the Uplink of LTE-advanced System
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Uplink of LTE-advanced System
Coordinated Multiple Point Reception Scheme for the
Jing Jin, Qixing Wang*, Li Zeng, Hongwen Yang and Yafeng Wang
Wireless Theories and Technologies Lab (WT&T), Beijing University of Posts and Telecommunications
Research Institution of China Mobile*
Beijing, P.R.China
Email: jinjing@bupt.cn
Abstract—LTE-Advanced system based on orthogonal frequency
division multiplexing (OFDM) can eliminate intra-cell
interference since data are carried on the orthogonal subcarries;
however, it can not mitigate inter-cell interference (ICI) which
affects the performance severely. Therefore, coordinated multiple
point (CoMP) reception scheme was proposed to reduce ICI and
improve the cell capacity for the uplink of LTE-Advanced system.
The basic idea of CoMP is to extend the conventional system to a
multi-cell MIMO structure by sharing necessary information and
received signals across multiple evolved Node Bs (eNB). This
paper focus on evaluation of the CoMP scheme in which joint
detection with minimum-mean-square-error (MMSE) algorithm
is configured at the eNB side to cancel the ICI from other users.
To guarantee fairness of the cell-edge users, proportional fair (PF)
scheduling method is adopted. Simulation results for uplink show
that the CoMP scheme can significantly improve the average cell
throughput and reduce ICI for the cell-edge users.
Keywords-LTE-Advanced; CoMP; multi-cell MIMO; OFDM;
ICI
I.
0B
I
NTRODUCTION
Future advancement of long term evolution
(LTE-Advanced) has started since March, 2008. This evolution
concerns significantly increased instantaneous peak data rates,
decreased latency, higher spectrum efficiency and improved
coverage [1]. In order to reach these requirements, several new
techniques, such as the coordinated multiple point (CoMP)
transmission and reception [2] have been proposed and
included into the technical report of 36 series of 3GPP in
August, 2008.
LTE-Advanced system based on orthogonal frequency
division multiplexing (OFDM) technology [3] has immunity to
intra-cell interference, for OFDM splits a high rate data stream
into a number of lower rate streams and transmit them by a set
of orthogonal subcarriers. However, inter-cell interference (ICI)
can not be eliminated by OFDM technology in the cellular
system.
Multiple-input multiple-output (MIMO) is a promising
technology to increase the spectral efficiency by using the same
frequency bandwidth through all transmit antennas. Recent
researches have shown that dramatic capacity gains can be
achieved by the use of multiple antennas for point-to-point
communication [4]-[6]. However, in uplink direction, the
realization of multiple transmit antennas is limited due to the
cost and size of user equipment (UE). Therefore, virtual MIMO
was introduced in [7], which allows two or more users each
with single transmit antenna to transmit on the same
frequency-time resource independently. However, in the
multi-cell system, the transmission of one cell is the
interference to others, and it has showed that the system
capacity improved by MIMO decreased severely in the
multi-cell system [8]. Therefore, CoMP, a particular technique
of base station coordination, is designed for the multi-cell
system structure to reduce ICI and extend virtual MIMO to the
multi-point to multi-point communication. By sharing
necessary information and configuring joint processing at the
receiver, ICI can be minimized or even cancelled for the uplink
of the cellular system.
Some ICI coordination measurements, such as fractional
frequency reuse (FFR) [9] and soft frequency reuse (SFR) [10]
are employed to improve the cell-edge performance. FFR,
which firstly proposed for GSM networks and afterward for
LTE and WiMAX systems, is based on the idea of applying a
frequency reuse factor of one in cell center and a higher reuse
factor in cell edge. SFR adds power planning to the FFR
scheme and was firstly proposed for LTE. However, users at
the cell edge are able to exploit only a fraction of the total
bandwidth under both of the two schemes. This may affect the
cell-edge spectrum efficiency since the frequency reuse factor
at cell-edge is larger than 1.
CoMP is a cooperative technology which coordinates
multiple geographically separated cells. The cooperative
evolved Node Bs (eNB) across multiple cells share necessary
information, such as data, scheduling information and channel
state information (CSI) to mitigate the ICI. The conventional
wireless communication system is extended to the new
multi-cell MIMO structure with joint processing at the receiver.
Joint detection using MMSE algorithm is applied for uplink.
To guarantee fairness of the cell-edge users, proportional fair
(PF) scheduling method is applied. Simulation results show
that the CoMP scheme benefits the average users, especially for
the cell-edge users over the conventional MIMO scheme.
The rest part of this paper is organized as follows. Section
II presents the system structure for the CoMP scheme in detail.
The joint reception algorithms and scheduling methods are
described in section III and IV. Section V gives the simulation
results and comparison of the conventional system and CoMP
architecture. Finally, conclusions are made in section VI.
II.
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S
YSTEM
S
TRUCTURE
In the conventional cellular system, transmission of one cell
acts as interference to neighboring cells. This ICI will cause
severe degradation of system performance. However, in the
This work is supported by Research Institution of China Mobile
P
roceedings of the 15th Asia-Pacific Conference on Communications (APCC 2009)-053
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