Optimization of Power Allocation and Outage
Probability of Cooperative Relay Networks
Jiawen Wu
1
, Dan He
1
, Jianrong Bao
1,2
, Xiaorong Xu
1
, and Bin Jiang
1
1
School of Communication Engineering, Hangzhou Dianzi University, Hangzhou 310018, China
2
National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China
E-mail: 444862274@qq.com, zhuanxinwan51@163.com, {baojr, xuxr, jiangbin}@hdu.edu.cn
Abstract—In order to solve the extra power consumption
caused by reducing complexity in cooperative relay networks, an
optimized power allocation algorithm is proposed for the efficient
incremental selection hybrid decode-amplify forward (ISHDAF)
scheme. In the ISHDAF scheme, the transmission efficiency is
improved by optimizing the power allocation, which is
constrained by constant total power. And the outage probability
is used as the objective function to optimize the whole power
allocation. Then, rational allocation of the power of source and
relay nodes can be obtained by the optimization of equal power
allocation algorithm in the power limited wireless communication
system. Simulation results show that the outage probability of a
relay network is effectively reduced by the proposed scheme for
the ISHDAF relay network. For an instance of a total power of
40W, there is a certain optimization of outage probability, when
compared with that of the current HDAF scheme. Therefore, the
proposed power allocation algorithm for the ISHDAF scheme can
be effectively applied to optimize the power consumption in the
relay network systems.
Keywords—cooperative communication; hybrid decode-amplify;
outage probability; power allocation
I. INTRODUCTION
In wireless transmissions, cooperative communication
contributes to the realization of the efficient Multiple-Input
Multiple-Output (MIMO) systems. The messages of a source
node can be processed and forwarded by a single or multiple
relay nodes, while the destination node can combine the
received signals from the source and relay nodes in the
cooperative communications. It can significantly reduce the
energy consumption and achieve the diversity gain. According
to the processing modes at the relay nodes, there are mainly
several relay cooperation schemes, such as the amplify-and-
forward (AF) scheme, the decode-and-forward (DF) scheme,
and so on. Due to the problem of noise amplified by the relay
nodes in the AF protocol, and error propagation caused by
incorrectly decoding at the relay nodes in the DF protocol,
some new protocols are proposed to alleviate these shortages,
such as the incremental selection amplify-and-forward (ISAF)
[1], the incremental selection decode-and-forward (ISDF) [2],
and the hybrid decode-amplify and forward (HDAF) [3], and
so on. Based on the HDAF scheme and ISAF scheme, Zhang
has proposed the incremental selection hybrid decode-amplify
forward (ISHDAF) strategy [4], which obtained higher average
spectral efficiency than that of the HDAF strategy. As well as
the bit-error-rate (BER) and outage probability are dramatically
improved, when compared with that of the ISAF strategy. But
all these results are analyzed under the equal power allocation
algorithm for the purpose of reducing the complexity. So, few
performance gains are obtained. In [5], the outage probability
of the AF and DF single relay system in the Rayleigh channel
and Nakagami-m channel were studied. The outage probability
representation of each protocol was given, but it did not carry
out the relevant analysis of power allocation. Then, a different
evolution algorithm was proposed, performed by power
allocation, where lower symbol error rate was achieved [6].
Moreover, some efficient power allocation schemes were
proposed for the AF, DF and HDAF protocol, respectively, in
[7], which took the minimum transmit power as the objective
function and achieved a tradeoff between communication
quality and energy consumption. Recently, Liu analyzed the
outage performance of HDAF and other relay networks with
the constraint of the total power [8]. But they did not consider
the better strategy, e.g., the ISHDAF strategy.
In this paper, based on the above discussions, the ISHDAF
single relay cooperative network is investigated, and an
optimized power allocation algorithm is proposed and analyzed.
The algorithm gives a reasonable power allocation, which takes
the total power as the constraint and the outage probability as
the objective function. In a relay network, each relay node
chooses the corresponding working mode according to the link
performance. Therefore, the power allocation algorithm can
greatly reduce the system power consumption according to the
link performance change. By the numerical simulation of the
HDAF and ISHDAF scheme, the experimental results show
that the outage probability of the cooperative relay network is
well improved, as well as the incensement of the transmission
efficiency. Meanwhile, the optimal relay location for minimum
outage probability in ISHDAF scheme and HDAF scheme are
analyzed and both of them obtain good performance too.
The remainder of the paper is organized as follows. Section
II introduces the cooperative system model and lays out the
mutual information situation of the ISHDAF protocol. Then,
starting with the calculation of the system outage probability,
Section III gives the process of the proposed optimized power
allocation algorithm with the ISHDAF protocol, which is used
in the HDAF protocol too. In Section IV, numerical
simulations and the analyses are given to verify the excellent
performance of the proposed algorithm, and the best node
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