JOURNAL OF L
A
T
E
X CLASS FILES, VOL. 11, NO. 4, DECEMBER 2012 1
On Efficient Resource Allocation for Cognitive and
Cooperative Communications
Peng Li, Member, IEEE, Song Guo, Senior Member, IEEE
Weihua Zhuang, Fellow, IEEE and Baoliu Ye, Member, IEEE
Abstract—Cooperative communication (CC) can offer high
channel capacity and reliability in an efficient and low-cost way
by forming a virtual antenna array among single-antenna nodes
that cooperatively share their antennas. It has been well recog-
nized that the selection of relay nodes plays a critical role in the
performance of multiple source-destination pairs. Unfortunately,
all prior work has made an unrealistic assumption that spectrum
resources are unlimited and each source-destination pair can
communicate over a dedicated channel with no mutual inter-
ference. In this paper, we study the problem of maximizing the
minimum transmission rate among multiple source-destination
pairs using CC in a cognitive radio network (CRN). We jointly
consider the relay assignment and channel allocation under a
finite set of available channels, where the interference must be
considered. In order to improve the spectrum efficiency, we
exploit the network coding opportunities existing in CC that can
further increase the capacity. Such max-min rate problems for
cognitive and cooperative communications are proved to be NP-
hard and the corresponding MINLP (Mixed-Integer Nonlinear
Programming) formulations are developed. Moreover, we apply
the reformulation and linearization techniques to the original
optimization problems with nonlinear and nonconvex objective
functions such that our proposed algorithms can produce high
competitive solutions in a timely manner. Extensive simulations
are conducted to show that the proposed algorithms can achieve
high spectrum efficiency in terms of providing a much improved
max-min transmission rate under various network settings.
Index Terms—cooperative communication, cognitive, resource
allocation, spectrum efficiency.
I. INTRODUCTION
By employing several single-antenna nodes to form a
virtual antenna array, cooperative communication (CC) has
been shown great advantages in offering high capacity and
reliability in wireless networks [1], [2]. Typically, there are
two cooperative communication modes, namely, amplify-and-
forward (AF) and decode-and-forward (DF). For both AF and
DF, it has been well recognized that the selection of relay
nodes plays a critical role in the performance of CC. For a
single source-destination pair, the full diversity order can be
achieved by choosing the “best” relay node [3], [4]. Based on
this approach, an optimal relay assignment (ORA) algorithm
[5] is proposed to maximize the minimum data rate among
This work was presented in part at IEEE International Conference on
Communications (ICC), June 2012.
P. Li and S. Guo are with the School of Computer Science and Engineering,
The University of Aizu, Japan (e-mail: {d8112105, sguo}@u-aizu.ac.jp).
W. Zhuang is with the Department of Electrical and Computer Engineering,
University of Waterloo (e-mail: wzhuang@uwaterloo.ca).
B. Ye is with National Key Laboratory for Novel Software Technology,
Department of Computer Science and Technology, Nanjing University, China
(e-mail: yebl@nju.edu.cn).
Fig. 1. Cooperative communication in a cognitive radio network
multiple source-destination pairs. Later, a more general model
[6] that allows a relay node to be shared by multiple source
nodes has been studied.
Although the optimal relay assignment problem has been
solved under the models in [5], [6], the spectrum efficiency has
never been addressed, under an assumption that each source-
destination pair communicates over a dedicate channel without
mutual interference. It is unrealistic in modern wireless net-
works with booming growth of various wireless applications,
where the spectrum has become a scarce resource that should
be efficiently utilized. Cognitive radio networks (CRNs) have
been recently investigated extensively due to their potential to
increase the spectrum utilization by allowing unlicensed (i.e.,
secondary) users to opportunistically use the licensed channels
as long as their transmissions do not interfere with licensed
(i.e., primary) users. At any time in a CRN, a set of channels
that are unused by primary users can be provided for secondary
users. As shown in Fig. 1, there are four source-destination
pairs and two relay nodes in a CRN with three channels
b
1
, b
2
and b
3
, which are assigned to primary users P
1
, P
2
and P
3
, respectively. The transmission range of each primary
user is also illustrated in the figure. Each secondary user is
constrained to access a set of channels due to the activities
of primary users. For example, nodes s
1
and s
2
cannot use
channel b
2
since they are in the transmission range of P
2
on
this channel. Obviously, existing relay assignment algorithms
fail to be applied in this scenario with channel constraints. For
instance, although r
1
is the best relay for s
2
, it cannot assist
the transmissions since they are not allowed to work on the
same channel.
In this paper, we study the problem of joint relay assign-
ment and channel allocation (RC) for cooperative commu-
nications in CRNs. Specifically, we aim at maximizing the
minimum achievable transmission rate among multiple source-