1148 IEEE COMMUNICATIONS LETTERS, VOL. 17, NO. 6, JUNE 2013
Resource Sharing of Underlaying Device-to-Device and
Uplink Cellular Communications
Jiaheng Wang, Daohua Zhu, Chunming Zhao, James C. F. Li, and Ming Lei
Abstract—The benefit of device-to-device (D2D) communica-
tion hinges on intelligent resource sharing between cellular and
D2D users. This letter aims to optimize resource sharing for
D2D communication to better utilize uplink resources in a multi-
user cellular system with guaranteed quality of normal cellular
communications. Despite the nonconvex difficulty, we provide an
analytical characterization of the globally optimal resource shar-
ing strategy, and furthermore propose two suboptimal strategies
with less complexity. The superiority of the proposed resource
sharing strategies is demonstrated through numerical examples.
Index Terms—Cellular system, device-to-device (D2D), non-
convexity, uplink resource sharing.
I. INTRODUCTION
D
EVICE-TO-DEVICE (D2D) communication has been
regarded as an effective technique to provide better
wireless services in local areas. By allowing two physically
close users to communicate directly, instead of being relayed
by a base station (BS), D2D communication may achieve
higher data rates, lower power consumption, and more efficient
resource (e.g., spectrum) utilization [1]. Such a concept has
recently been incorporated into existing and future cellular
systems as an important supplement for local wireless services
[2].
D2D communication as an underlay of cellular systems may
share resources with cellular users in an either orthogonal o r
nonorthogonal m anner [1]. In the orthogonal case, dedicated
resources are allocated to D2D users, which, though easy to
implement, cannot exploit the full potential of D2D communi-
cation to improve spectral efficiency. Therefore, nonorthogonal
resource sharing has also received much attention [ 1]–[7]. In
the nonorthogonal case, intra-cell interference is in general
not negligible, which, therefore, calls for appropriate resource
sharing designs with effective interference management.
Conceptually, D2D communication can exploit either up-
link or downlink resources of a cellular system. In practice,
however, uplink resources are more likely to b e shared than
downlink resources as a result of asymmetric uplink and down-
link service loads. Additionally, D2D commun ication using
uplink resources only causes interference at base stations,
which generally have stronger processing abilities than user
equipments. Therefore, uplink resource sharing has been a
subject of a number of D2D system designs [1]–[6].
Optimizing resource sharing of D2D communication under-
laying cellular systems is an intensively scrutinized subject.
Manuscript recei ved January 30, 2013. The associate editor coordinating
the re view of this letter and approving it for publication was I. Guvenc.
J. Wang, D. Zhu, and C. Zhao are with the National Mobile Communi-
cations Research Laboratory, Southeast University, Nanjing, China (e-mail:
{jhwang, zhudaohua, cmzhao}@seu.edu.cn).
J. Li and M. Lei are with the NEC Laboratory, Beijing, China (e-mail:
{li_chaofeng, lei_ming}@nec.cn).
Digital Object Identifier 10.1109/LCOMM.2013.042313.130239
Cellular
user 1
Cellular
user 2
Cellular
user N
D2D Rx
D2D Tx
BS
Fig. 1. One D2D link as an uderlay shares uplink resources of multiple
cellular users.
In particular, [4] studied resource block allocation among
cellular and D2D users in a single-cell system, while a power
minimization problem for D2D communication underlying a
multiple-cell system was considered in [5]. To suppress the
interference between D2D and cellular users, multi-antenna
techniques were also introduced into underlying D2D commu-
nication [6], [7]. However, due to lack of convexity, only [3]
provided optimal resource sharing between one cellular user
and one D2D link, whereas globally optimal shar ing strategies
are generally unknown in other cases.
In this letter, we consider D2D com munication as an
underlay sharing uplink resources of a multi-user cellular
system. Our goal is to design proper nonorthogonal resource
sharing strategies, applicable to common cellular systems,
such that the D2D link can maximally utilize all possible
cellular reso urces and meanwhile the quality of nor mal cellular
communications is guaranteed. In contrast to most existing
works (e.g., [1], [2], [4]–[6]) based on heuristic or suboptimal
methods, we characterize the globally optimal resource sharing
strategy by a closed-form solution with some insights. Further-
more, we also propose two suboptimal resource sharing strate-
gies with less complexity and signaling overheads. Finally,
the effect of the proposed D2D resource sharing strategies is
verified by proper numerical examples.
II. P
ROBLEM STATEMENT
We consider underlying D2D communication sharing uplink
resources in a cellular system that consists of one BS and N
orthogonal users as shown in Fig. 1, where each cellular user
occupies a frequency band indexed by i =1,...,N (it could
also be a TDMA or synchronous CDMA mode). Without loss
of generality, we assume that the D2D link may reuse all
cellular users’ frequency bands for direct transmission.
Denote the channel from the cellular user i to the BS by h
c
i
,
and the channel from the cellular user i to the D2D receiver
by h
d
i
. Denote the channel from the D2D transmitter to its
receiver on frequency band i by g
d
i
, and the channel from the
1089-7798/13$31.00
c
2013 IEEE