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On Relay Placement Schemes for Multi-cell LTE-A
System Under Co-channel Interference
Chunshu Lil,2, Xiaoyan Zhoul, Wen Chenl
1 Department of Electronic Engineering, Shanghai Jiao Tong University, China
2 Department of Physics Electrical Information Engineering, Ningxia University, China.
Email: {lichsh;shine_zhou;wenchen} @sjtu.edu.cn
Abstract-Due to the frequency reuse, LTE-A is interference limited system, the small rates can only been obtained by celledge users. Cooperative communication through using relays is an efficient approach to resolve this problem. In this paper, We proposed a dynamic relay placement scheme to maximize either the total cell capacity or the total cell-edge user capacity in a LTE-A network under co-channel interference. Two strategies, Amplify-and-Forward (A F) and Decode-and-Forward (DF) for cell-edge user are compared. The simulation results show adding relays and optimizing relays position in the cell can significantly increase the capacity for the cell-edge users. The performance of AF strategy is better than the performance of the DF strategy for cell-edge users. The result of simulations prove that this approach can ensure a fair capacity distribution over the cell.
Index Terms-Cooperative communication, relay placement, amplify-and-forward, decode-and-forward, LTE-A .
I. INTRODUCTION
LTE-Advanced (LTE-A), also known as LTE Release 10,
has been a candidate of 4G (The 4th Generation Mobile Com
munication) wireless network standards by ITU (International
Telecommunication Union) [1]. In contrast to LTE, LTE-A of
fers higher peak rates, higher throughput and larger coverage.
In order to increase the spectrum efficiency and overall capac
ity, frequency reuse technique is normally adopted in LTE-A.
LTE-A adopts a reuse-l OFDMA-based access scheme, thus
offering higher overall cell rate, especially for cell-centre users
(CCUs) rate. However, cell-edge users (CEUs) performance
are degraded obviously due to the co-interference. A variety
of approaches have been suggested to overcome the co-channel
interference and improve the performance of the edge users.
Relaying communication obtained a lot of research attention
because it can not only enhance the capacity of cell-edge
users but also improve the performance of the whole cellular
network. It has been accepted as a key technique of LTE-A [1].
Relay stations (RSs) can enhance the link strength between e
Node B (eNB) and edge-user equipment, thus increasing the
link capacity and reliability.
In [2], Cover and El Gamal first proposed the ideas of
the cooperative communication based information theoretic
properties of the relay channel. From then, cooperative com
munication has attracted many attentions of researchers due to
improving the spectral efficiency of each user. In genera\, the
relay stations are placed in the communication network, where
This work is supported by the National 973 Project #2012CB316106, by NSF China #61161130529, and by the National 973 Project #2009CB824904.
they overhear the transmitted data by eNE, then cooperate
with it to forward the message to cell-edge users experiencing
large channel fading with the eNB. Amplify-and-Forward (AF)
and Decode-and-Forward (DF) are the two main forwarding
schemes proposed several different cooperative protocols in
wireless network by 1. Laneman, D. Tse and G. Wornell in
[3]. For AF transmission, the relay receives the data from
eNB, then amplifies and retransmits it to the UE; for DF
transmission, the data are decoded and re-transmitted to the
UE by RS.
In the LTE-A network, the placement problem of the relay
node is a critical issue. Researchers have provided many
schemes in literatures. In [4], the authors studied the optimal
placement problem of a given number of relays in WLAN,
and proposed an efficient algorithm based on Lagrangian re
laxation with sub-gradient iteration to maximizing the network
throughput.In [5], two types of RSs, fixed RSs (FRSs) and
nomadic RSs (NRSs), have been studied for relaying data
transmission between the BS and SSs, the RS placement and
bandwidth allocation are jointly considered for the capacity
maximization. In [6], a mathematical model of the users traffic
demand and cover the request service area is introduced,
where the objective function is to minimize the number of
relays under a WiMAX network. In [7], the authors studied
a general cooperative cellular network, where the subscribers
cooperate and relay information to each other to maximize
the sum of network capacity. An efficient algorithm was
proposed to determine which node should act as a relay,
which relay strategy should be used (AF or DF) and which
frequency should be used for relaying. In [8], the optimal
RS placement about coverage extension in an LTE-A network
has been studied. In [9], the authors studied the problem of
relay placement and proposed an optimization framework to
maximize total cell capacity or total cell-edge capacity in a
LTE-A.
In this paper, we consider an LTE-Advanced relay enhanced
cooperative cellular network, where the main objective is the
optimal placement of a given number of RSs in a certain cell in
order to maximize either the total cell capacity or the cell-edge
capacity to ensure a fair capacity distribution over the cell. The
effect of inter-cell interference as well as intra-cell interference
are considered between the relay stations and the eNE. The
rest of the paper is organized as follows. Section II describes
our system model. Section III present the problem formulation
and the description of the simulation setups. Section IV offers
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2 3 sum of centra-user equipment
Fig. 8: Sum rates of cell-center users of no relays, fixed relays,
optimal relays with DF and AF schemes
2 3 sum of edge-user equipment
Fig. 9: Sum rates of cell-edge users of no relays, fixed relays,
optimal relays with DF and AF schemes
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