Communications and Network, 2013, 5, 136-139
http://dx.doi.org/10.4236/cn.2013.53B2026 Published Online September 2013 (http://www.scirp.org/journal/cn)
A Joint User Selection and Resources Optimization
Scheduling Algorithm for CoMP
Xincheng Zhong, Weihai Li, Yuqin Lv
School of Electronic Engineer, Beijing University of Posts and Telecommunications, Beijing, China
Received April, 2013
Coordinated Multi-point (CoMP) transmission technology is one of the key techniques in LTE-Advanced, Which can
share the channel and data information in multiple cells, and optimize the whole system performance. In order to opti-
mize the average sector throughput and improve the fairness of resource scheduling, a scheduling algorithm based on
the resource is mainly investigated. In this algorith m, users in the netwo rk are classified fi rstly and then we combine the
fixed resources division and flexible scheduling. System level simulation platform is set up to validate the algorithm
and the results turn out that the average throughput is better compared with the traditional scheme.
Keywords: CoMP; User Selection; Resource Scheduling; System Level Simulation
As one of the key techniques in LTE-Advanced, CoMP
is discussed in detail in the 3GPP. With its effect in re-
ducing interference between neighboring cells, optimi-
zating the whole system performance of multiple cells
and expanding the coverage of high data rate, people pay
more and more attention to it. Its basic principle is
through the coordination of different base transceiver
stations (BTS), the interference can be converted to use-
ful signal. According to the information can be shared
among multiple transport nodes or not, CoMP technol-
ogy can be divided into the joint processing (JP) and
Resource scheduling algorithm for JP is a research
hotspot in CoMP to further improve the system per-
formance[3,4], as the CoMP system requires the alloca-
tion of resources in multi-point coordinated cells, and
single-cell resource scheduling can’t meet the require-
ment of the system scheduling, we need to design sched-
uling algorithm which can consider interference between
adjacent BTSs. The author in  has investigated a us-
er-centric scheduling scheme in downlink channel to
provide coordination for majority of users, so as to im-
prove the average throughput, but the increasing of the
system complexity was not consid ered. In , centralized
control in CoMP system was researched and the author
proposed to use the MAC layer to transport the informa-
tion of channel status, so as to reduce the system com-
plexity. In order to avoid the waste of resources and re-
duce the scheduling complexity, collision avoidance re-
sources scheduling scheme for CoMP was proposed in
In this paper, the scheduling scheme based on re-
sources for single-user multi-input multi-output (CoMP-
SU-MIMO) is researched, which improves the traditional
scheme of dividing the users into cell-edge users and
cell-center users by the SINR values, and 2 or 3 sec-
tors coordination is added to reduce the waste of re-
sources, at the same time, on the basis of the scheme to
divide the frequency into fixed two parts, resources op-
timization is considered in one part to ensure profit both
edge and center users. We also set up a system level si-
mulation platform and the simulation results also verify
the effectiveness of the proposed algorithm.
The rest of paper is organized as follows: In section II,
the system model of JP in CoMP is described. Section III
introduces the specific scheduling algorithm and the si-
mulation results are showed in section IV. Then conclu-
sions are drawn in section V.
2. CoMP JP System Model
The downlink of a cellular network with M hexagonal
cells is considered and each cell is partitioned into 3 sec-
tors with K active users served within the coverage of
each sector. The total number of BTSs in the system is M.
Each BTS which corresponds to one sector is equipped
with Nt transmit antennas, while each user has Nr receive
antennas. We assume each three adjacent sectors as a
cluster, show as in Figure 1.
1) Considering the serving BTS m, and user k in clus-
ter c severed in the CoMP mode, the received signal is
opyright © 2013 SciRes. CN
X. C. ZHONG ET AL. 137
Figure 1. The system model of CoMP JP.
()() ()() ()
kmk kknk kk
where the first item in the right-hand-sid e(RHS) of equa-
tion(1) presents the transmission signal of BTS m, Hm,k(t)
denotes the NrNt channel matrix from BTS m to user k,
sk(t) denotes the signal from BTS m to user k, wk pre-
sents the precoding matrix of sk(t). The second item pre-
sents the coordinated signal from the BTSs of cluster c,
Hn,k(t) denotes the channel matrix form other BTSs in
cluster c to user k. The third item presents the interfer-
ence signal from the BTSs out of the cluster c to user k.
Assuming that each BTS has perfect channel state in-
formation(CSI) of all the users in the sector coverage,
and BTS within the same cluster can fully share CSI and
user data, the SINR of user k is given as:
where pk presents the transmit power from BTS m to user
k, pn is the transmit power from other BTSs in cluster c to
user k, and pj presents the interference power from BTSs
out of cluster c to user k.
2) Considering user k in cluster c severed in the No-
CoMP mod e, and th e ser vin g BTS is m, then the received
signal is given as:
()() ()() ()
where the second item is not the coordinated signal but
the interference signal from BTSs of the cluster c to user
k, then the SINR of user k is given as:
where presents the transmit power from BTS m to user k,
is the interference power from other BTSs in cluster c to
user k, and i presents the interference power from
BTSs out of cluster c to user k.
3. The Proposed Scheduling Algorithm
3.1. User Selection
Proposed in , the network is divided into a number of
disjoint clusters, where each cluster contains 3 adjacent
sectors, and all of the users are divided into cell-center
users and cell-edge users according to the SINR, which
work in the No-CoMP and CoMP mode respectively.
When in CoMP mode, all the three sectors in the cluster
send signals to one user at the same time. But fixed three-
sectors coordination can’t guarantee the best scheduling
of resources, as shown in Figure 2, when the channel
situation is not good enough between the user and the
BTS, the sector of the BTS is not suitable to coordinate
with the adjacent sectors. Considering this situation, two-
sectors CoMP mode is added.
1) three-sectors CoMP user: According to the equa-
tions (2) and (4), we can describe the SINR of user k
working in No-CoMP and CoMP mode as SINRno-CoMP
and SINRthree-CoMP, then user k works in three-sectors
CoMP mode if
three CoMPNo CoMP
2) two-sectors CoMP user: According to the equation
(2), considering user k works in CoMP mode with two
sectors which contain better channel gain in the cluster,
we can describe the SINR of user k as SINRtwo-CoMP, then
user k works in two-sectors CoMP if
no CoMPtwo CoMPno CoMP
3) cell-center user: Other users are cell-center users
which wor k in No -C oMP mode.
3.2. Resources Optimization Scheduling
In traditional scheduling scheme, the frequency band is
divided into two parts, one for CoMP mode and the other
for No-CoMP mode. PF scheduling algorithm is imple-
mented separately in each frequency zone for different
Figure 2. An example of clusterd network.
Copyright © 2013 SciRes. CN
X. C. ZHONG ET AL.
work mode. However, this scheme can hardly guarantee
the fairness within the system while improving the sys-
tem throughput at the same time. In addition, the tradi-
tional schemes arrange the CoMP frequency zone at the
beginning of the whole frequency band, which may not
be the best RBs to cell-edge UEs for CoMP-SU-MIMO
transmission. A kind of resources optimization schedul-
ing scheme is proposed in this paper, The basic idea is
the combining of the fixed partition and flexible sched-
uling of resources. One part of the resources are used to
ensure the demand of the cell-center users and in the
other part, starting from each resource block(RB), the
most appropriate way of scheduling is selected. In this
way, cell-center users which are the larger part can get
sufficient resources and at the same time, the cell-edge
users can also get the most appropriate scheduling re-
sources. System performance and fairness is balanced
and the main steps are as follows:
1) For all the RBs in the network, we take a specific
proportion to be used for the cell-center users, as shown
in equation (7),
is the ratio of factors which can set
different values according to the state of channel, so that
the fixed RBs used for the cell-center users in different
clusters can be adjusted according to the different load.
NoCoMP threeCoMP twoCoMP
2) Assume the set of all the cell-edge users in the co-
ordination cluster is c, the set of cell-center users in
sector 1 is 1, the set of cell-center users in sector 2 is
, and the set of cell-center users in sector 2 is
3) The set of fixed RBs which are allocated to the
cell-center users is 1
, and the other flexible RBs are in
the set of 2
4) RBs in 1
are selected for cell-center users, ac-
cording to the PF scheduling algorithm, for the RBs in
, calculate the highest priorities c、1、2
the users in c、1
respectively, and the
selected users are k, j1, j2, j3.
5) We compare them as follows
If the left-hand-side of (8) is no less than the
right-hand-side, the system will perform the CoMP mode
in the RB and user k is scheduled for transmission
through BTSs coordination with two or three sectors;
otherwise, the three BTSs of cluster c will operate single
sector No-CoMP transmissions for users j1, j2, j3 inde-
6) The schedule of RBs is completed, and if all the
RBs are allocated, the schedule is over, otherwise, a=a+1,
the RB continues to be scheduled. The flow chart of the
proposed scheme is as Figure 3.
4. Simulation Results
In this section, the performance of the proposed algo-
rithm is evaluated through our syste m level si mulation. A
cellular system with 19 hexagonal cells is assumed, and
the distance between base stations is 500 m. The channel
bandwidth is 10 Mhz with 50 RBs and each one is 180
khz with 12 subcarriers. We choose the number of an-
tennas to be Nt=Nr=2. Each BTS has perfect CSI of all
the users in the sector, and BTSs within the same cluster
an fully share CSI and user data.
Figure 4 compares the normalized user throughput
CDF of Round Robin No-CoMP and r esources optimiza-
tion CoMP, and th e result illustrates the use of CoMP can
greatly improve user throughput in hexagonal cells with
the coordination of the different base stations.
Figure 5 compares the normalized user throughput
CDF of three differ ent CoMP scenarios which are Round
Robin CoMP, the traditional fixed frequency CoMP and
the resources optimization CoMP. The result illustrates,
due to the resources optimization algorithm, the majority
cell-center users can get fixed resources and at the same
time, each other RB is able to choose the optimal sched-
uling according to channel state, the throughput of the
users is effectively improved and resource utilization is
Figure 3. The flow chart of the proposed scheme.
Copyright © 2013 SciRes. CN
X. C. ZHONG ET AL.
Copyright © 2013 SciRes. CN
This paper is supported by Beijing Municipal Science &
Technology Commissio n (Grant No . Z11110006651 1007)
and Fundamental Research Fund for the Central Univer-
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