Energy-efficient Power Allocation Scheme for Multi-
relay Cooperative Communications
Yinlong Xu
1, 2
, Zhiquan Bai
1
, Bing Wang
1
, Peng Gong
3,*
, and Kyungsup Kwak
4
1
School of Information Science and Engineering, Shandong University, China
2
Key Lab. of Higher Education of Sichuan Province for Enterprise Informationlization and Internet of Things, Sichuan University
of Science and Engineering, China
3
National Key Laboratory of Mechatronic Engineering and Control, Beijing Institute of Technology, China
4
Graduate School of Information Technology and Telecommunications, INHA
*
Corresponding author: penggong@bit.edu.cn
Abstract—For the increasing cost of energy and infrastructures of
wireless communication systems, energy-efficient communication
technologies become an important concern for the
standardization authorities and cellular operators. In this paper,
we propose an energy-efficient relay selection and power
allocation strategy subject to a total power constraint. The
proposed scheme first selects the transmission mode according to
the energy efficiency of the different transmission link. Then, we
analyze the energy efficiency of the proposed system and present
the optimal number of the relay nodes and the best power
distribution factors in broadcasting phase and the cooperative
transmission phase. Closed-form expressions of the energy
efficiency of the proposed scheme are derived. Simulation results
show that the proposed scheme achieves good energy efficiency in
both low and high signal-to-noise ratio region.
Keywords—Energy Efficient; Cooperative Communication;
Green Communication; Outage Probability; Power Allocation .
I. INTRODUCTION
With the rapid development of telecommunication industry,
modern communication systems consume more and more
energy. Energy efficiency in cellular networks is an important
concern for the standardization authorities and cellular
operators. Verizon has set its own energy-consumption
standard (TEEER) and established an associated measurement
process for new telecommunication-related equipment. The
requirement of energy efficiency in communication systems
will become increasingly strict.
Cooperative communication technology allows single
antenna users to exploit the other users’ antennas and
generates a virtual multiple-input multiple-output (MIMO)
system without additional investment. The research on energy
efficiency of cooperative communication system can reduce
the energy consumption and satisfy the requirements of user
quality of service (QoS). Recently, various energy efficient
schemes in wireless communications have been proposed.
Hasan presented a brief survey of the methods to improve the
power efficiency of cellular networks [1].
The author
discussed how the cooperative concepts can be made more
energy efficient at the system level. The energy-efficient
precoding scheme has been investigated in [2] considering that
the terminals are equipped with multiple antennas.
Opportunistic decode-and-forward (ODF) switches the
transmission mode between the direct transmission (DT) and
relaying depending on the achievable rate [3]. The results
obtained in the paper proved that the proposed dynamic
cooperation scheme improves the overall performance
compared to the non-cooperative or the fixed type cooperative
strategies. Osama in [4] presented an opportunistic energy-
efficient (OEE) relay selection cooperative scheme which uses
the energy efficiency metric to select the best relay or resort to
the direct transmission.
In this paper, we follow the recent trend towards cooperative
communication systems that support the green vision of the
next-generation wireless networks [5]. The relay selection and
power allocation strategies are investigated under energy
efficiency principle. We first select the transmission mode
between the DT and relaying based on the energy efficiency of
the transmission link. Then, the energy efficiency principle is
applied in the random distributed multi-relay DF cooperative
system. Different relay selection and power allocation
strategies are presented in low and high signal to noise ratio
(SNR) regions. Simulation results show that the proposed
scheme can achieve good system energy efficiency both in low
and high SNR regions.
The rest of this paper is organized as follows. In Section II,
the cooperative protocol considering the energy efficiency and
channel model are introduced. The energy efficiency of the
system and the corresponding power allocation strategy are
derived in Section III. In section IV, simulation results about
the BER performance and energy efficiency of the system are
provided with comparison to the conventional cooperative
system. Finally, the conclusions are drawn in section V.
II. C
OOPERATIVE SYSTEM MODEL
In this paper, we consider a cooperative network with N
relay nodes distributed randomly within a two-dimensional
circle centered with the source node as shown in Figure 1. The
link among the terminals are modeled as independent, quasi
static Rayleigh fading channels, where the channel will be
considered as constant during the transmission of one block,
February 16~19, 2014 ICACT2014