Resource Allocation for LTE-Based Heterogeneous
Vehicular Network in Unlicensed Bands
Ning Wang and Shaoyi Xu
School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing China
Email: {15120142, shyxu}@bjtu.edu.cn
Abstract—The cellular data traffic has been dramatically
increased, a typical approach is considering the operation of the
Long-Term Evolution (LTE) system in the unlicensed spectrum.
Although there are a large number of theoretical researches on
operating LTE in unlicensed bands (LTE-U), researches about
specific devices such as vehicle-to-vehicle (V2V) communication
which can be allowed to unlicensed bands are still lacking. In
this paper, we build a new scene where LTE base station can
divide the V2V devices into two parts, one part will be allowed
to utilize the unlicensed band to serve themselves by Listen-
Before-Talk (LBT) mechanism, and remaining devices will be
regarded as normal users of LTE systems. A Lagrange Dual
Method based algorithm is proposed to solve the problem of
resource allocation, which is efficient and has low complexity.
Numerical results show that the concomitant system has more
excellent performance than a single Wi-Fi system. Furthermore,
the proposed algorithm outperforms the traditional Greedy
algorithm in terms of throughput maximization while satisfying
Quality of Service (QoS) requirements.
Index Terms—LTE-U, Listen-Before-Talk (LBT), Lagrange
Dual, Cooperation, vehicle-to-vehicle (V2V) communications.
I. INTRODUCTION
V2V communications has been recognized as a promising
technology for future communication systems due to the
potential of improving traffic safety, reducing energy consump-
tion, and enabling new services related to agile transportation
systems. In V2V communications, vehicles in close proximity
should share information with each other, which is applica-
ble in services such as collision avoidance. In addition, the
common problems for V2V applications are requirements on
real-time and reliability. A survey conducted by Mobile and
Wireless Communications Enablers for the Twenty-Twenty
(2020) Information Society (METIS) reveals that a maximum
latency of 5ms with transmission reliability of 99% of 1600-
byte packets is necessary for guaranteeing the traffic safety
and efficiency applications. On the other hand, the request
on mobile data will increase by 10-fold by 2019, which will
trigger an issue that there is little resource left for V2V
communication to pledge strict requirements of legacy and
reliability.
Driven by the demand for more spectrum resources, many
researchers pay attention to the interworking of different
technologies, specifically, there is an increasing interest in
LTE-U. Applying LTE-U technology to V2V communication
which could effectively settle the issue about lack of radio
spectrums will be an amazing and worthy discussion.
Generally, Ad-Hoc network based on 802.11p standard is
regarded as a traditional solution for Vehicle-to-Everything
(V2X) communication in [1]. However, a Wi-Fi network that
only supports low speed mobility and lacks of strict QoS
protection. On the other hand, the performance for vehic-
ular communication is not always satisfactory, particularly
in terms of legacy and reliability. Literature [2] provides a
radio resource management solution for Device-to-Device-
based (D2D-based) V2V communication, which transforms
the latency and reliability requirement of V2V communica-
tion into optimization constrains. A heuristic resource block
sharing algorithm to accommodate more vehicular users (V-
UEs) is proposed in [3], which does not limit the number
of V-UEs on one resource block (RB). The authors in [4]
formulate the stringent latency and reliability requirements
for V2V communication mathematically and propose a two-
stage heuristic algorithm which aims to maximize the sum
rate of cellular users (C-UEs) under the condition of fulfilling
vehicular users’ requirements.
With regard to LTE-U technology, the main discussion for
this appealing technology is how to fairly and harmoniously
coexist with legacy Wi-Fi networks. Specifically, listen-before-
talk (LBT) method and duty-cycle method are proposed to
manage the above issue [5]. Literature [6] introduces a net-
work architecture where small cells use the same unlicensed
spectrum that Wi-Fi systems operate in without affecting the
performance of Wi-Fi systems and [7] presents an overview
of the challenges and requirements of the cutting-edge tech-
nology in the 5G LTE-U ultra dense cloud small cell network.
In addition, [8] concentrates on the performance evaluation
of the distributed coordination function (DCF) scheme, in the
assumption of ideal channel conditions and a finite number
of terminals. In [9], the coexistence between LTE and Wi-Fi
has been studied and an adaptive channel access scheme to
address the fair coexistence and joint spectrum management
has been proposed simultaneously. Analogously, [10] develops
an interesting algorithm named fair LBT (F-LBT) for coex-
istence of LTE-U and Wi-Fi in unlicensed bands, where F-
LBT determines an idle period in the frame-based LBT by
jointly considering the fairness between LTE-U and Wi-Fi,
and the total system throughput. A heuristic idea has been
proposed to allow D2D to transmit data on unlicensed bands
in [11]. However, there is seldom outstanding literatures to
describe the problem of coexistence between V2V and Wi-Fi
using LTE-U technology. Motivated by above problems, in this
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