Published in IET Communications
Received on 9th April 2014
Revised on 17th August 2014
Accepted on 23rd September 2014
doi: 10.1049/iet-com.2014.0346
ISSN 1751-8628
Joint resource allocation with subcarrier pairing in
cooperative OFDM DF multi-relay networks
Xueyi Li
1
, Qi Zhang
2
, Guangchi Zhang
1
, Miao Cui
1,3
, Liang Yang
1
, Jiayin Qin
2
1
School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People’s Republic of China
2
Department of Electronics and Communications Engineering, Sun Yat-Sen University, Guangzhou 510006,
People’s Republic of China
3
China Electronics Technology Group Corportation No. 7 Research Institution, Guangzhou 510310,
People’s Republic of China
E-mail: leexueyi@gdut.edu.cn
Abstract: For conventional subcarrier pairing scheme in cooperative orthogonal frequency division multiplexing decode-and-
forward multi-relay networks, to avoid interference, each subcarrier pair (SP) is assigned to a single relay. Over a specific
subcarrier, the destination receives signals transmitted from the relay. In this study, to better exploit the degrees of spatial
freedom, the authors propose to assign each SP to multiple relays. Thus, over a specific subcarrier, the destination receives
signals transmitted from multiple relays. Under the total network power constraint, to maximise the sum transmission rate,
they propose a joint resource allocation scheme, in which they jointly optimised the four types of resources: assisting relays
selection, transmission mode selection, subcarrier pairing and power allocation. They further propose a suboptimal algorithm
which can significantly reduce the computational complexity of the aforementioned optimal allocation scheme with sacrificing
little on the performance. It is shown from simulation results that the author’s proposed schemes have significant performance
improvement over the resource allocation s chemes in the literature.
1 Introduction
Cooperative communication can improve the reliability of
wireless transmission and extend its coverage [1]. For
cooperative orthogonal frequency division multiplexing
(OFDM) decode-and-forward (DF) single relay networks,
the power allocation optimisation problem was considered
to maximise the transmission rate in [2–4]. In [2], the
individual power constraints for the source and the relay
were considered. In [3, 4], the total network power
constraint and individual power constraint were considered.
However, in [2–4], the subcarrier pairing scheme was not
employed. The joint subcarrier pairing and power allocation
optimisation problems with the individual power constraints
for the source and the relay or with the total network power
constraint were investigated in [5–10]. Furthermore, the
proposed schemes in [9, 10] consider the transmission
mode selection, that is, the selection between the relay
mode and direct-link mode.
The researches in [2–10] focus on the cooperative single
relay networks. For coop erative OFDM DF multi-relay
networks, the optimal power allocation scheme subject to
the constraints of individual source power and each relay
power was proposed in [11]. The optimal power allocation
scheme subject to the total network power constraint was
proposed in [12]. When there are multiple relays available,
in order to exploit the degrees of spatial freedom in the
system for performance improvement, the two schemes
allow not just one relay but multiple relays to assist relaying
at every subcarrie rs [11, 12]. However, the subcarrier
pairing was not investigated in [11, 12].
For cooperative OFDM amplify-and-forward (AF)
multi-relay networks, the joint optimisation of subcarrier
pairing, relay assignment and power allocation was studied
in [13], the resource allocation scheme in [13] restrict that
each subcarrier pair (SP) can only be assigned to one relay
to avoid interference among all the relays. In fact, when
there are multiple relays available for each SP, allowing not
just one but all the relays to assist transmission, can achieve
the more space diversity gain. Therefore, in our previous
works [14, 15], we propose that each SP is assigned to all
the relays and all relays have same SPs, investigate the joint
power allocation and subcarrier pairing scheme which
maximises the transmission rate subject to the total network
power constraint, and the performance improvement is
demonstrated by simulation results.
For cooperative OFDM DF multi-relay networks, in
[16–18], the joint subcarrier pairing, relay assignment and
power allocation schemes were obtained to maximise the
sum transmission rate. The schemes proposed in [16–18]
assign each SP to only one relay to avoid interference. Over
a specific subcarrier, the destination receives signals
transmitted from only one relay. This is because of
multi-relay networks, if multiple relays participate relaying
simultaneously and different relays may have different SPs,
interference may be introduced at destination. In this paper,
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IET Commun., 2015, Vol. 9, Iss. 1, pp. 78–87
doi: 10.1049/iet-com.2014.0346