Page 93 - ITU Kaleidoscope 2016

RESOURCE ALLOCATION FOR DEVICE-TO-DEVICE COMMUNICATIONS IN
MULTI-CELL LTE-ADVANCED WIRELESS NETWORKS WITH C-RAN ARCHITECTURE

Sajjad Mehri Alamouti and Ahmad R. Sharafat

Faculty of Electrical and Computer Engineering, Tarbiat Modares University, Tehran, Iran

ABSTRACT unlicensed spectrum to communicate via the D2D link with-
out traversing a base station. D2D links underlaying a cel-
Device-to-device (D2D) communications underlaying LTE- lular network may use the same channels also used by cel-
Advanced wireless networks reuse cellular frequency spec- lular users (CUs), which would cause interference [4]. In
trum to establish direct links between users without travers- order to moderate these interferences, different resource al-
ing base stations or the cellular network. In this paradigm, location and interference management schemes have been
there is a need to optimally allocate resources with a view proposed [5–12]. In [5–11], static power allocation to D2D
to maximizing the utility, e.g., the total throughput, and miti- pairs is considered, and in [12], dynamic power control for
gating the interference caused by sharing the same spectrum all D2D pairs sharing a common channel orthogonal to the
between cellular users (CUs) and D2D pairs. This paper cellular channels in a single cell is proposed.
proposes a scheme for optimally allocating transmit power
In general, existing schemes assume a single cell and ignore
levels and channels to maximize the total number of active
inter-cell interference, except for [5, 6]. It is also generally
D2D pairs and reused channels while minimizing the aggre-
assumed that each D2D pair is situated in one cell, and uses
gate transmit power pertaining to CUs and D2D pairs. We
only one channel. In [5], a heuristic near-far interference
consider a multi-cell scenario in which the transmitter and
avoidance scheme is proposed to establish a D2D link be-
the receiver of each D2D pair can be in the same cell or in
tween two users in adjacent cells. In doing so, the interfer-
two different cells, and each user can simultaneously trans-
ence from D2D users on CUs is ignored, and the interference
mit over multiple reused channels. The optimization is done
from CUs on D2D pairs is mitigated by base stations. In [6],
via a centralized baseband processing in the cloud radio ac-
a resource allocation scheme for cross-cell D2D users is pro-
cess network (C-RAN) architecture. Simulations show that
posed, where the interference from D2D users on CUs is ig-
via our proposed scheme, more users (both cellular users and
nored; and a heuristic scheme that utilizes information from
D2D pairs) can simultaneously communicate and the total
base stations is devised to identify a channel to be utilized by
system throughput is also significantly increased.
the D2D pair.
Keywords— D2D, spectrum sharing, LTE-A, C-RAN, multi- A distributed power control scheme is proposed in [9], where
cell. D2D pairs can opportunistically reuse cellular uplink fre-
quency spectrum only when their interference on base sta-
tions is within an acceptable margin. This margin forces CUs
1. INTRODUCTION
to increase their transmit power levels, which may be very
undesirable.
Global mobile data traffic will increase nearly eightfold and
Establishing D2D links can be facilitated via C-RAN, which
grow at a compound annual growth rate (CAGR) of 53 per-
is a novel architecture that can reduce network cost and en-
cent from 2015 to 2020, reaching 30.6 exabytes per month by
ergy consumption, and increase spectral efficiency. In this
2020. Moreover, there will be 11.6 billion mobile-connected
architecture, the radio unit, called the remote radio head
devices (including machine-to-machine modules) by 2020,
(RRH), is separated from the baseband unit (BBU), and
exceeding the world’s projected population at that time (7.8
BBUs are pooled together in a cloud environment. The first
billion) [1]. In order to cope with these tremendous growth,
commercial deployment of C-RAN includes 1000 servers
new technologies have been introduced to use the limited
(BBUs) in one BBU Pool, where each server manages 144
resources (frequency spectrum, network infrastructure, mo-
base stations [13].
bile device battery, etc.) more efficiently. Device to device
We propose a novel resource allocation scheme for D2D
(D2D) communications [2] and cloud radio access network
pairs underlaying a LTE-A network with C-RAN architec-
(C-RAN) architecture [3] are among such technologies.
ture. Specifically, the central unit in the C-RAN architecture
In next generation cellular networks, nearby users may set
determines the channels and the transmit power levels for
up a direct D2D link with the help and control of cellular
each D2D pair with a view to maximizing the number of
infrastructure, and use the licensed cellular spectrum or the
active D2D pairs and reused channels while minimizing the
aggregate system uplink transmit power. This paper is an
This work was supported in part by Tarbiat Modares University, Tehran,
Iran. extension of [7], and our contributions are as follows. We
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