=Paper=
{{Paper
|id=Vol-1727/ssn16-final8
|storemode=property
|title=Enhancing Vehicular Applications by Exploiting Network Diversity
|pdfUrl=https://ceur-ws.org/Vol-1727/ssn16-final8.pdf
|volume=Vol-1727
|authors=Felipe Valle,Sandra Céspedes
|dblpUrl=https://dblp.org/rec/conf/ssn/ValleC16
}}
==Enhancing Vehicular Applications by Exploiting Network Diversity==
https://ceur-ws.org/Vol-1727/ssn16-final8.pdf
Enhancing Vehicular Applications by Exploiting Network Diversity
Felipe Valle Sandra Céspedes
Department of Electrical Engineering Department of Electrical Engineering
Universidad de Chile NIC Chile Research Labs
Universidad de Chile
In this work we propose a dissemination scheme that
exploits the network diversity in a heterogeneous ve-
Abstract hicular network by integrating a set of decision rules.
The novelty of this approach is that it allows the
In this work we introduce a new model for application data to flow through the individual net-
exploiting network diversity in vehicular en- work with the most favorable conditions in terms of
vironments, which integrates ad-hoc commu- throughput and delay for each data packet, without
nications with the existing cellular infras- the need of a preselected scheme like the ones employed
tructure aiming to meet the diverse commu- in [emZLTT14, ASF14, LYC+ 12]. In this poster we re-
nication requirements of vehicular applica- port the work-in-progress toward the construction and
tions. Although there are a plethora of re- validation of the proposed scheme.
ported studies on either 802.11p Digital Short
Range Communications (DSRC) or cellular 2 System Framework and Develop-
networks, joint research of these two areas ment
mostly focuses on the offloading aspect when
the two networks are available. This work The scheme utilizes all different network capabilities
presents current advances in the design of a at the same time by integrating a set of decision
novel framework aimed at enhancing the per- rules that allow data packets to flow through the net-
formance of applications deployed over a het- work with the most favorable conditions in terms of
erogeneous vehicular environment. We intro- throughput and delay. The proposal is illustrated in
duce and evaluate a decision system that ex- Fig.1. It is observed that the application data gener-
ploits, simultaneously, the advantages of each ated by a single user can travel through any of the in-
individual network. dividual networks (802.11p, LTE and 802.11p ad-hoc
mode). More specifically, depending on the applica-
tion requirements, the control and signaling flows may
1 Introduction for example travel through DSRC while the data flow
Among the open research fields in communication pro- may go through the cellular infrastructure. In this
tocols and technologies for vehicular communications, way, we can exploit the different advantages of each
the heterogeneous vehicular network is the topic of in- network such as transmission speed and local dissemi-
terest in this work. In the vehicular networking con- nation for DSRC, or high capacity for LTE infrastruc-
text, a large part of existent research has been focusing ture.
on developing and studying the performance of net- This framework is expected to improve the perfor-
work protocols for a specific radio access technology. mance of the network both in terms of total through-
In particular, the 802.11p DSRC technology has drawn put and end-to-end delay by allowing a single appli-
most of the attention from researchers. However, it cation to take full advantage of all the individual net-
has been widely accepted that the supporting infras- works working in parallel. Currently, we have charac-
tructure and communications technologies for vehicu- terized the group of applications, and are developing
lar networks will be heterogeneous in nature, hence the performance model for each individual networks.
providing network diversity. Large coverage access To this end, we have decided to focus on measuring the
networks, such as 4G/LTE, will be combined with throughput and packet delay at the MAC layer for each
technologies specifically designed for vehicular envi- network, this means that we need to select a model for
ronments, such as the 802.11p DSRC. EDCA (802.11p), DCF (802.11 ad-hoc) and LTE.
Copyright c by the paper’s authors. Copying permitted for
3 Preliminary Results
private and academic purposes. 3.1 Decision Tree and Experimental Models
This work is partially funded by Project FONDECYT No.
11140045. Proceedings of the Spring School of Networks, San- Fig.2 illustrates the decision tree for user-to-user com-
tiago, Chile, November 2016, published at http://ceur-ws.org munication scenario. It is important to notice that
Figure 1: System Framework
each data flow has its own set of rules, which depends scenarios requiring only 2 Hz.
on the network type and conditions, application re- In Fig. 3 we illustrate the total MAC layer de-
quirements, and link direction (uplink or downlink) lay that an application experiences when transmit-
because a user typically has less information available ting a beacon to all its neighbors using a single access
than the network itself at the moment of the decision. network. We consider infrastructure-based 802.11p,
This hierarchical tree characterizes the decision pro- 802.11p ad hoc mode, and LTE as the available net-
cess of a single application when sending data to other works for transmission. It can be observed that the
vehicles in the network. The idea is that for each data total delay for the 802.11p networks (infrastructure-
flow, the sender attempts to minimize the end-to-end based and ad hoc mode) increases proportionally with
delay and boost the throughput of the system with- the number of neighbors in range, which is expected
out compromising the reliability requirements of the because the access mechanism is contention-based.
application. Also, using the ad-hoc mode is faster because the com-
In order to obtain some preliminary results we use munication between vehicles is direct while in infras-
simplified models for the delay for each of the single tructure mode the messages have to go through an
networks, for a given access mechanism the total end- 802.11p RSU. While both modes of 802.11p are com-
to-end delay can be expressed as TDelay = TAccess + pletely capable of delivering the 2 Hz frequency bea-
TT ransmission + TP ropagation + TP rocessing . cons in less than 100ms for up to 40 neighboring ve-
To model performance for the 802.11 ad-hoc mode hicles, in a more realistic case of 10 Hz beacon fre-
we employ the Distributed Coordination Function quency, the 802.11p network gets saturated at a value
(DCF) system model. Based on [AS11], we obtain of approximately 20 neighbors. At this point, the net-
the saturation throughput for a single hop as well as work becomes incapable of reaching all the neighbors
for a path that may consists of multiple hops from a in less than the critical time, either via ad hoc mode
given source to destination. In the case of 802.11p or via infrastructure. According to the results, the
using infrastructure mode, the Enhanced Distributed DSRC network is more than capable of achieving high
Channel Access (EDCA) mechanism includes the use throughput and low latency in low density scenarios;
of the Arbitration Inter Frame Space (AIFS) differen- however, as the vehicle density increases, the LTE net-
tiation and virtual collision mechanism specified in the work shows to be able of maintaining a more stable
802.11e standard. Therefore we can use the equation latency because of its high capacity nature.
developed in [TM05] for the access time in basic mode In Fig. 4 we illustrate the case in which the decision
(without RTS/CTS). tree is used to exploit the heterogeneous network. As
Meanwhile, in LTE the main difference between we mentioned before, the infrastructure-based and ad
particular delay models arises from the underlying hoc modes are only able to reach less than 20 neigh-
scheduling mechanism used. In [ALG+ 13] the au- bors under the critical time of 100ms for a beacon fre-
thors develop an analytical model for using the Physi- quency of 10Hz; nonetheless, the decision tree allows
cal Uplink Shared Channel (PUSCH). Among the ad- us to set a threshold for the number of neighbors, so
vantages of scheduling via PUCCH are high reliability that the transmitter can employ the LTE network to
and nearly deterministic data delay values. Using such improve the performance both in terms of packet de-
a model, we obtain an average channel access delay lay and total throughput under the critical time. Since
E = 5.9[ms] which is under the critical time, therefore more neighbors are reached under 100ms the system
we can use this mechanism to access the LTE base sta- throughput is boosted by the latency reduction. More-
tion and use it to reach a fraction of the neighbors so over, by using the decision tree, a boost in performance
that it improves the performance of the whole system. is observed even for the low beacon frequency case: al-
3.2 Analytical Results though a single access network is enough to cover the
required number of neighbors, the combined use with
Consider a typical safety application in which every LTE helps improve the general performance.
vehicle continuously sends CAM messages to all its In both frequency cases, once the 20 neighbors are
neighbors. The most important thing to consider is reached and the combined use starts, a latency reduc-
that the end-to-end delay for a transmission must not tion of approximately 70% is achieved using the de-
exceed 100ms, otherwise the receiver does not have cision tree with infrastructure-based 802.11p + LTE,
time to react, especially in the case of emergency ap- whereas a 64% improvement can be achieved with the
plications. For most scenarios, a sending rate of 10 Hz combined use of 802.11p ad hoc + LTE. This ulti-
is required by the ETSI standard, but there are also mately results in a 25% increase in total throughput
Figure 2: Decision Tree (User-to-User Communication)
the access networks, developed the rule set for a typi-
cal safety application family and used analytical sim-
ulations to obtain some preliminary results. The pre-
liminary results validate the decision system approach
showing a boost in application performance when di-
versity is exploited both in terms of latency reduc-
tion and an increased throughput under a fixed critical
time.
Future work will focus on running more advanced
simulation scenarios that allows us to test the entire
decision tree and modify it if its required. Since the
Figure 3: Total Dissemination Delay per Number of Neigh- framework developed aims to exploit network diversity
bors for any particular application it is likely that differ-
ent variations of the tree will be required for different
application families so the decision system must be
adapted to improve robustness and flexibility.
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