Connectivity Improvement in Urban Intersections
Obstructed by Buildings using RSUs
Pablo Ortega1 , Sandy Bolufé1 , Sandra Céspedes1 , Cesar A. Azurdia-Meza1 , Samuel Montejo2 ,
and Fermı́n Maciel-Barboza3
1
Dep. of Electrical Engineering, Universidad de Chile, Santiago, Chile,
pabloortega@ug.uchile.cl,(sbolufe,scespedes,cazurdia)@ing.uchile.cl
2
Dep. of Electrical Engineering, Universidad Tecnológica Metropolitana, Santiago , Chile,
smontejo@utem.cl
3
Fac. of Mechanical and Electrical Engineering, Universidad de Colima, Colima, México,
fermin_maciel@ucol.mx
1 Introduction
Modern vehicles are equipped with detection technolo-
Abstract
gies like ultrasonic sensors used for parking assistance
systems, video cameras employed to monitor the lane
or detect pedestrians, and radars used to detect and
Vehicular collision avoidance systems can im- measure the distance from a vehicle to nearby obsta-
prove road safety by means of periodic ex- cles [Cai+14]. However, the proper performance of
change of status information between neigh- these detection technologies can be affected by natural
bouring vehicles. At urban intersections, the factors such as snow, rain, and non-line of sight, which
effect of shadowing caused by buildings has are very common in vehicular environments. Fortu-
a severe impact on the communication links, nately, these problems can be overcome with vehicle-
leading to a connectivity performance degra- to-vehicle (V2V) communication.
dation due to attenuation of the radio sig- V2V communication offers a platform for the de-
nal. A solution to the shadowing problem is ployment of cooperative road safety and traffic effi-
to use vehicles or dedicated Road-Side Units ciency applications. The goal of safety applications
(RSUs) as relay nodes, in urban intersections is to alert drivers about potentially hazardous situa-
obstructed by buildings. In this paper, we tions with sufficient time to take proper actions. Road
analyze how an RSU improves connectivity safety can be increased by means of periodic exchange
in scenarios where vehicles are approaching of status messages, called “beacons” [ETS14], which
over perpendicular roads on an intersection contain data such as the position, speed, acceleration,
with obstructing buildings. We evaluate the and direction of transmitting vehicle, among others.
connectivity provided by the system in terms With the information provided by the beacons, the
of the notification position, number of bea- vehicles create a map of their surroundings, which is
cons received, and link life time. The sim- used by safety applications for a variety of purposes.
ulation results show that using an RSU in
Drivers are vulnerable to traffic in intersections.
this scenario significantly improves connectiv-
Without a clear map of the vehicles located in the
ity, hence, providing better conditions for the
nearby area, they may be not aware of the danger
operation of road safety-oriented applications.
coming from vehicles driving in the perpendicular di-
rection, resulting in a high possibility of car crashes
[GCG17]. In this urban scenarios, the line of sight be-
Copyright c by the paper’s authors. Copying permitted for tween vehicles is often affected by obstacles such as
private and academic purposes.
buildings, and parked or moving vehicles [SED14]. At
In: Proceedings of the IV School on Systems and Networks
(SSN 2018), Valdivia, Chile, October 29-31, 2018. Published
the moment when the vehicles have communication
at http://ceur-ws.org or line of sight between them, it might be very late
because due to the speed of the vehicle, the safety
distance could be surpassed and an accident could
take place. At intersections, the effect of shadowing
caused by buildings affects drastically the communi-
cation range of vehicles. This issue impacts negatively
on the capacity of road safety systems to detect neigh-
bours that approach to the intersection [MKH11]. In
[SED14], the authors examined the use of parked vehi-
cles as relay nodes for improving cooperative awareness
and road traffic safety in urban and suburban environ-
ments. The authors showed the use of parked vehicles
as relay nodes to be effective and to improve the coop-
erative awareness among all nearby nodes if the node
density is high. This, however, requires both a high
traffic density and a high percentage of equipped ve-
hicles (i.e., substantial market penetration of DSRC
Figure 1: Utilization of RSU as relay nodes can in-
devices). A possible solution to the low percentage
crease cooperative awareness in vehicular security ap-
of DSRC-equipped vehicles, as well as the shadowing
plications. Building blocks safety messages and reduce
problem at the intersection, is to use dedicated Road-
the safety range between vehicles.
Side Units (RSUs) as relay nodes. Placing an RSU at a
strategic position can strengthen the connectivity be- only Node 1 regularly broadcast beacons. The idea
tween vehicles traveling on perpendicular roads of an is to evaluate the capacity of Node 1 to notify its
obstructed intersection (see Figure 1). In this work, presence to Node 0 without and with an RSU. Both
we analyze how an RSU can improve connectivity at vehicles and RSU employ the IEEE 802.11p EDCA
urban intersections blocked by a building. We use a model [ES12] of the Veins framework to represent the
realistic simulation framework to evaluate the connec- MAC/PHY layer. This is an open source implemen-
tivity provided by the system in terms of the following tation, which fully captures the distinctive properties
performance metrics: notification position, number of of IEEE 802.11p radio access technology. Node 1
beacons received, and link life time. We focus on the broadcast beacons to the communication channel us-
worst case scenario, which considers that a building ing a rate of 10 beacon/s. The radio signal propaga-
totally obstructs the communication link between ve- tion is simulated using the Simple-Obstacle Shadowing
hicles. Further, we study the impact of using different model [Som+11]. With the Simple-Obstacle Shadow-
values of the path loss exponent for direct line of con- ing model, the building obstructs the communication
nectivity. We aim at demonstrating that, by improv- link between vehicles until they arrive at intersection.
ing connectivity, we also improve the operation condi-
tions of road-safety applications, hence, providing an Table 1: Simulation Parameters
increase in road safety for the participant vehicles. Parameter Value
CCH center frequency 5.890 GHz
Channel bandwidth 10 MHz
2 Experimentation Transmission power 20 dBm
Beacon rate 10 beacon/s
We conducted the experiments using the Veins frame- Beacon size 250 bytes
work [SGD11], which bidirectionally couples the OM- CW (3, 7)
NeT++ network simulator and the SUMO road traffic AIFSN 2
simulator. We have employed as test scenario an urban Path Loss Exponent (2.8, 3.0, 3.5)
intersection located on the following streets: Beauchef Receiver sensitivity - 90 dBm
Thermal noise - 110 dBm
with Blanco Encalada, in Santiago, Chile.
Data rate 6 Mbps
This intersection is obstructed by a building, which Antenna type Omnidirectional
can be noted inspecting Fig. 2. The scenario seen
from Google Earth and SUMO traffic simulator is il- The path loss exponent values α = {2.8, 3.0, 3.5}
lustrated in Fig. 2a and Fig. 2b, respectively. At were selected according to [Fer+14]. The communica-
this intersection, we have designed two experiments. tions are established on control channel (CCH) with-
In the first one, two vehicles are moving on perpen- out considering the effect caused by multi-channel op-
dicular roads blocked by a building, as shown in Fig. eration. The beacons’ size is 250 bytes and are trans-
2c. In the second one, we placed an RSU on the mitted with a priority corresponding to voice access
intersection to retransmit the beacons received from category (AC VO). Each vehicle is 5 m long, 2 m wide,
Node 1, as shown in Fig. 2d. In these experiments and has maximum acceleration of 0.8 m/s2 , maximum
may not be sufficient to react to potentially dangerous
situations. Note that the path loss exponent does not
have an impact in this case. However, the notification
position increases significantly with the presence of an
RSU. Fig. 3a shows that Node 0 receives the first bea-
con from Node 1 when it is located at 155.43 m from
the crossing point for α = 2.8. Moreover, with a poor
(a) (b) reception (i.e., α=3.5) the notification position is still
twice in comparison to the situation without the RSU,
as shown in Fig. 3c.
Figure 4 shows the BRT computed by Node 0, which
implicitly includes the LLT of the vehicles while ap-
proaching the obstructed intersection. The RSU sig-
nificantly increases LLT and reduces the distance be-
tween the point the first beacon was received respect
to the intersection, especially for lower path loss expo-
(c) (d) nents. Fig. 4a shows an increase in LLT of 17 s when
the RSU is used as a relay node for α = 2.8. With
Figure 2: Evaluation scenario seen from: a) Google the most aggressive path loss exponent α = 3.5, the
Earth, b) SUMO, c) OMNeT++ without RSU, d) RSU still provides a gain of 5 s in LLT, and the first
OMNeT++ with RSU. notification is realized 3 s in advance. This time of
deceleration of 4.5 m/s2 , and maximum speed of 50 anticipation is vital for the performance of vehicle col-
km/h. The antenna height of vehicles is 1.5 m, whereas lision avoidance systems, which need to alert drivers
the height of the dedicate RSU is 2.2 m. Table 1 in- with sufficient time and distance to take proper ac-
cludes the additional simulation parameters. tions. Table 2 shows a summary of the metrics studied
for the different path loss exponents.
3 Simulation Results
Table 2: Vehicles’ Connectivity Metrics
In order to evaluate the connectivity provided by the Obstructed Urban Intersection
system without and with RSU, we computed in Node Metrics
Without RSU
α = 2.8 3.0 3.5 α = 2.8
With RSU
3.0 3.5
0 the following metrics: NBR 210 210 200 590 540 450
LLT [s] 20.9 20.9 19.9 37.9 32.9 24.9
- Number of Beacons Received (NBR): The NBR Notification Position [m] -15.61 -15.61 -15.61 -155.43 -100.64 -43.91
is directly related with the knowledge collected by
the vehicle when approaching to the intersection.
- Beacon reception time (BRT): The BRT register
the times at which beacons are received for the 4 Future Work
duration of the link.
As future work, we will aim to present a specific re-
- Link Life Time (LLT): The LLT related with
lay strategy scheme. Intelligent algorithms need to be
BRT; it and corresponds to the time duration for
applied in these solutions to control the moment that
a link between two vehicles.
the RSU should participate as a relay node or stay
Negative values of the notification position mean silent for safety applications at intersection. Define an
that the vehicle has not arrived at the intersection, efficient procolo to enable the relays in the obstruc-
whereas zero means that the node is at the intersec- tion zones, is not only permitted improvement the use
tion, and positive values mean that the vehicle passed and channel load but to the the benefits of improv-
the intersection. ing communication distance and link life time for the
Figure 3 shows the potential benefits of using an security applications and so these parameters of the
RSU on obstructed intersection in terms of NBR by offered reaction extends to the drivers or the vehicles
Node 0. Without an RSU, the building blocks di- directly.
rect transmissions between vehicles, reducing drasti- We plan to evaluate the performance of the radio
cally their communication range. In this situation, the signal propagation in obstructed intersections with a
connectivity is only possible when the vehicles are very high density of vehicles. Experimental validation in
close from intersection. In fact, the Node 0 is aware real conditions will be carried out by installing OBUs
of the presence of Node 1 when it is located at 15.61 in vehicles. The experimental results will be compared
m from the crossing point. This notification position with data obtained by simulations.
Path Loss exponent α = 2.8 Path Loss exponent α = 3.0 Path Loss exponent α = 3.5
Number of Beacons Received (NBR)
Number of Beacons Received (NBR)
Number of Beacons Received (NBR)
600 600 600
With RSU with RSU with RSU
500 Without RSU 500 without RSU 500
without RSU
400 400 400
300 300 300
200 200 200
100 100 100
0 0 0
-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60
Position [m] Position [m] Position [m]
(a) (b) (c)
Figure 3: Number of beacons received (NBR) by Node 0 as a function of position from the intersection for
different path loss exponents: a) α = 2.8, b) α = 3.0, c) α = 3.5.
Path Loss exponent α = 2.8 Path Loss exponent α = 3.0 Path Loss exponent α = 3.5
Beacon Reception Time (BRT) [s]
Beacon Reception Time (BRT) [s]
Beacon Reception Time (BRT) [s]
55 55 55
50 With RSU 50 With RSU 50 With RSU
Without RSU Without RSU Without RSU
45 45 45
40 40 40
35 35 35
30 30 30
25 25 25
20 20 20
15 15 15
-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60
Position [m] Position [m] Position [m]
(a) (b) (c)
Figure 4: Beacon reception time (BRT) computed by Node 0 as a function of position from intersection for
different path loss exponents: a) α = 2.8, b) α = 3.0, c) α = 3.5.
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This work has been partially funded by ERANET-
communication-based vehicle safety appli-
LAC ELAC2015/T10-0761.
cations”. In: IEEE SCVT 2014 (2014).
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