Remote Proxy V2V Messaging Using IPv6 and GeoNetworking

Masahiro Kitazawa∗ , Manabu Tsukada∗ , Kai Morino† , Hideya Ochiai∗ and Hiroshi Esaki∗∗ Graduate School of Information Science and Technology

The University of Tokyo
Email: {ktzw, tsukada, jo2lxq}@hongo.wide.ad.jp, hiroshi@wide.ad.jp† Institute of Industrial Science
The University of Tokyo
Email: morino@sat.t.u-tokyo.ac.jp
Abstract—Vehicle-to-vehicle (V2V) messaging plays an importantrole in cooperative intelligent transportation systems (CITS),
which are advanced applications addressing the problems ofroad transport management. In this regard, the Cooperative
Awareness Message (CAM) protocol is standardized in EU for
V2V messaging. However, V2V messages work well only when
all vehicles have transmitters and work well in short range andno obstacle. To solve the former problem, the existance of the
non-ITS road users, in the early deployment phase, we previously
proposed a system called Proxy CAM, wherein roadside sensors
detect target vehicles and transmit V2V messages on behalfof the vehicles. However, the V2V transmission range is still
limited to the wireless range of IEEE802.11p. Therefore, in thisstudy, we propose a system that delivers CAMs over the Internet
using UDP/IPv6 and LTE in addition to the standard specification (i.e., the Basic Transportation Protocol/GeoNetworking
and IEEE802.11p). Moreover, we implement the cellular network
component of the system and evaluate its performance in termsof the packet delivery ratio and packet delay for various distancesand packet frequencies. In our evaluation, we define the average
Proxy CAM update delay and calculate this parameter forboth IEEE802.11p and LTE. We find that using LTE over long
distances is more efficient than using IEEE802.11p.
Keywords–CITS; CAM; LTE; Cellular Network; V2V.

I. I NTRODUCTION
The problem of vehicular traffic, particularly traffic jams
and accidents, has become one of the most important issues in
the world today. In this context, intelligent transport systems(ITSs) have been designed to solve this problem via acquiringand sharing traffic information from vehicle sensors or otherdevices. Examples of ITS include Vehicle Information andCommunication Systems (VICS) [1], which automatically receive information about traffic jams and road construction fromroadside beacons via FM multiplex broadcasting and electronic
toll collection systems (ETCSs) [2] installed at the entrancesand exits of highways by communicating with vehicles via
radio waves. In particular, ITSs that communicate traffic information with other ITSs to improve vehicle safety, durability,
efficiency, and comfort are called cooperative ITSs (CITSs). A
typical CITS consists of an application layer, facilities layer,
network&transport layer, access layer, management layer, andsecurity layer [3].
A CITS communicates by means of Cooperative AwarenessMessages (CAMs) [4] and Decentralized Environmental Notification Message (DENM) [5] protocols. A CAM contains
information on the positions and movements of road users(vehicles, bicycles, pedestrians) along with other dynamic
information. According to [4], all ITS-installed devices areencouraged to create and broadcast messages with the use of
CAM, and the desirable frequency range for CAM broadcasting is 1 to 10 Hz. Further, single-hop broadcasting is also
desirable. Upon receiving CAM information, a CITS processes
the CAM to update the Local Dynamic Map (LDM) [6].
The Cooperative Awareness basic service (CA basic service)in the facilities layer, the Basic Transport Protocol (BTP)[7]/GeoNetworking(GN) [8] in the network&transport layer,
and IEEE802.11p [9] in the access layer are used to send
and receive CAMs. The CA basic service also manages to
encode and decode CAMs and provide CAM information to
the LDM and application layer, while BTP provides end-toend connectionless communication. This protocol is aimed
at transmitting multiple messages from different processes in
the facilities layer at the same time along one packet path.
However, it is to be noted that BTP does not guarantee theorder, integrity, and reliability of packets. Meanwhile, theGN protocol provides the packet path while IEEE802.11p
specifies the wireless communication system developed forcommunication between vehicles. This makes communication
between fast-moving vehicles possible in the frequency band of
5.85∼5.925 GHz. The bandwidth is narrow compared to other
IEEE802.11 series, and therefore, the communication speed isless, but resistance to multipath propagation is strong.
A CITS cannot function without communicating with othervehicles; however, there are certain problems with the current
communication protocols. First, the communication protocols
do not cover non-CITS road users such as vehicles with no
CITS and pedestrians. In this regard, it is noteworthy that there
are no CITS products commercially available today in Japan.
Thus, the commercialization of CITS vehicles requires thesystem functionality to detect neighboring non-CITS vehicles
and pedestrians. While computer vision can be utilized to solve
this problem, there is a possibility that computer vision cannot
detect vehicles in the case that they are in blind spots. There
are always blind spots at intersections, and vehicles may not
be able to avoid accidents with other vehicles or pedestrians
emerging from such blind spots. Second, IEEE802.11p uses thefrequency band, 5.85∼5.925 GHz. This range of frequencies
is so high that these waves hardly undergo diffraction; thus,
they cannot travel around obstacles. Finally, the signal strengthof such wireless radio systems also decreases with increasing
distance.
In the above context, this study proposes the usage ofcellular networks (UDP/IP) and LTE in addition to the original Proxy CAM [10] system’s protocol stack, BTP/GN +IEEE802.11p, to solve the abovementioned problems. In ourstudy, we design a Remote Proxy CAM system that uses computer vision sensors installed along the roadside to generate
Proxy CAMs from the acquired images and broadcasts themusing BTP/GN + IEEE802.11p (as does the original Proxy
CAM system). In addition, the Remote Proxy CAM system
uses a server-client model to send request-based Proxy CAMs
to the client.
In the study, we also implement a prototype of a part ofthis system using a cell phone, and we measure the latency
and delivery ratio of the packets. We find that packets using
UDP/IP + LTE exhibit short delay times and high delivery
ratios and function efficiently over long distances.
The contributions of this work are:••••Analysis of problems of Proxy CAM
Proposal of a communication protocol stack in addition to the original one
Prototype implementation of a part of the proposedsystemExperimental evaluation of the prototype

The rest of the paper is organized as follows. Section II
highlights related works, and Section III analyzes the issues ofProxy CAM and summarizes the requirements of the solution.
Section IV presents the design of our system along with its
implementation. Section V demonstrates and evaluates theimplementation, and finally, Section VI concludes our paper
and presents our future studies in this direction.
II. R ELATED W ORKS
In this section, we introduce and discuss two main related
concepts, Proxy CAM and cloud-based pedestrian road-safety.
The Proxy CAM approach is used to generate CAMs by proxy
while cloud-based pedestrian road-safety involves communication between vehicles and pedestrians using a cellular network.
A. Proxy CAM
In general, when CITS cars broadcast their CAM information in the vicinity of obstacles such as buildings, there
is a possibility that the CAMs cannot reach cars the otherside of the buildings, which may lead to accidents. Further,
the presence of non-CITS cars (which cannot broadcast their
CAM information) cannot be detected by CITS cars without
computer vision. To solve this problem, we propose the Proxy
CAM [10] system that works with any vehicle-sensing technology. This system consists of a roadside sensor, sensor fusion
database, Proxy CAM generator, and Proxy CAM transmitter.
In our scheme, first, roadside sensors detect vehicles andacquire their position, speed, acceleration, and other optional
information. Next, the sensors tag each vehicle with an ID
that is sent to the sensor fusion database along with the otherinformation. Any type of road traffic sensor can be utilizedwith the system if it can detect vehicles and acquire therelevant information. The sensor fusion database receives thevehicle data and stores it in the sensor fusion local dynamicmap (SFLDM). This database also has the functionality toidentify a single vehicle from the data from multiple sensors
and integrate the data. Next, the Proxy CAM generator uses
the SFLDM and composes Proxy CAMs. Some of the CAM
fields are labeled as ‘unknown’. The Station ID field of theproxy CAM contains 24 bits set to ‘1’ and 8 random bits.

If the sensor or SFLDM identifies the vehicle information asthat of a previously detected vehicle, the Station ID field of
its Proxy CAM is set to the same value as the one createdpreviously. Finally, the Proxy CAM transmitters broadcast thegenerated Proxy CAMs using the ETSI standard protocols,
BTP/GN in the networking&transport layer, and IEEE802.11p
in the access layer. The CAM transmitters should be installed
at locations ensuring a clear line-of-sight to the vehicles.
B. Cloud-Based Pedestrian Road-Safety
Pedestrians can be detected only with the use of computer
vision by CITS cars because pedestrians cannot create andbroadcast CAMs. However, the accuracy of computer vision
depends on the weather and daylight conditions (day or night).
Thus, to accurately detect the presence of pedestrians, we need
another method. In this regard, in a previous study [11], theauthors used the cell phones of pedestrians to communicate
with CITS cars However, CITS cars can only communicate
using IEEE802.11p while cell phones do not use IEEE802.11p.
Thus, the authors of the study installed cell phones in CITS
cars, and the phones were connected to the CITS. However,in cellular networks, broadcasting is not allowed. Thus, theauthors used a cloud server to communicate with pedestrianand the CITS cell phones. In the scheme, both sets of cell
phones (vehicular and pedestrian) always send their positions
to the server. The pedestrian’s cell phone communicates at low
frequencies because the communication consumes electrical
power and the capacity of the cell phone battery is limited.
The server always verifies the positions of both the pedestrianand CITS phones. If the two parties approach each other, theserver sends a request to the pedestrian’s cell phone to switch
the communication frequency to ‘high’. After receiving therequest, the pedestrian’s cell phone switches to the designatedhigh frequency. If the server estimates the possibility of acollision between the pedestrian and car, it sends an alert
message to both of them.
Our approach is also inspired by several other relevant
studies, which we briefly present here. In [12], the authors
used power lines to communicate between ITS users andthe transport management system. In [13], Vehicular Ad-Hoc
Networks (VANETs) were utilized for communication, andthe authors designed two VANET sampling protocols named
SAME and TOME to collect vehicular traffic information anddetect incidents in real-time. Further [14] used parked cars to?hop? CAMs from cars on the opposite sides of a building.
III.

P ROBLEM S TATEMENT

In this section, we discuss the problems of Proxy CAM in
detail. Subsequently, we analyze the design requirements forthe solution.
A. Problem
Figure 1 illustrates the operation of Proxy CAM and the
problems of the system. The Proxy CAM device 1) detects thetarget vehicle and 2) delivers the proxy CAM to the receiver
over IEEE802.11p. However, the system suffers from two
significant problems, as described below.

1) Limited wireless range: As indicated by label a) in
Figure 1, we observe that a message cannot be delivered
beyond the wireless range. According to [15], if a car drives
at 60 km/h, IEEE802.11p’s packet delivery ratio (PDR) is
nearly 100% for a received signal strength indicator (RSSI)
value of -85 (about 800 m). However, the authors performed
their experiments on level land in the absence of buildings
and other electromagnetic interference; on the other hand,urban environments contain buildings and other forms ofelectromagnetic waves, which can lead to packet delivery
failure beyond certain distances. Further, [10] have reported
that the packet reach distance is about 60∼70 m if there arebuildings in the environment. Moreover, a CITS vehicle at 60km/h cannot stop before an intersection. Thus, it is necessary
to widen the coverage of Proxy CAM transmission.
2) Interference and Obstacles: Theoretically, Proxy CAMs
can be received at roads connected to intersections. However,
if a car is in a situation where another obstacle blocks the lineof sight to the CAM transmitter, as indicated by label b) of
Figure 1, it cannot receive Proxy CAMs. Further, if there is avehicle such as a truck between a car and Proxy CAM device,
the car cannot receive Proxy CAMs. Therefore, it is necessary
to ensure that the Proxy CAMs surmount such obstacles.

()*+,-./0%12#31
59-@#A#61%-B#)1$1??-)5&'1

4) Using existing protocol and wireless communication
system: For interoperability among countries, CITSs are developed based on a given architecture, protocols, and technologies. From the perspective of practical application, the systemshould not use new resources; it should consist of existing
protocols and use wireless communication.
IV.

R EMOTE P ROXY CAM

To satisfy the abovementioned requirements, we designed
the Remote Proxy CAM.
A. System Design
In our system, we use LTE and the cellular network tosatisfy the communication requirements. Since broadcasting
is not allowed in cellular networks, we use unicast communication to access the dynamic vehicular information. We
use IPv6 for the Remote Proxy CAM because it fulfills
the CITS requirements through its extended address space,embedded security, enhanced mobility support, and ease ofconfiguration. It also uses UDP because the delivered message
comprises real-time data. By using UDP/IPv6, the packet canbe transmitted over the LTE and a cellular network. Figure 2
shows the protocol stack of the proposed method. The vehicle
with our proposed system receives Proxy CAMs via BTP/GN+ IEEE802.11p as well as UDP/IPv6 + LTE.

7131#21):9-;16136#*&!"#$%$&$'(

4++2',"&$5'.3*",'1'((.6',5$#'45)'1689-()*+,-./0!9-<&61)=1)1&31-5&%->!?653$1)'&*+,-./
0,"1(2+,&.

!"#$%#&'!"#$%#&'
7131#21)

708

:;8

9)

<85=

<>>>?@ABCC2

D0>

43E.6&"1F",F

GH,.2,+2+("%7131#21)

Figure 1. OVERVIEW AND PROBLEMS OF PROXY COOPERATIVE
AWARENESS MESSAGE (CAM)

B. Requirements
To solve the abovementioned problems, we designed asystem that uses a new protocol stack in addition to the original
protocol stack, BTP/GN + IEEE802.11p. The following section
lists the requirements of the new system.
1) Message Transmission Coverage: In urban environments, CAMs should be able to cover a range of distances.
Our system can send CAMs to everyone in the coverage area
regardless of the presence of buildings or large vehicles.
2) Availability: A CAM contains information regarding
neighboring cars. Thus, the unavailability of a CAM for even5 s can lead to an accident. Consequently, a system should
allow CAMs to be sent any given time. Importantly, thecommunication should be stable (i.e., the PDR should benearly 100%).
3) Real-Time Information: The position of a vehicle is dynamic, and therefore, CITS cars should always obtain updated
information reflecting the real-time situation. That is, the time
between the creation of a CAM and its reception should be
as short as possible. Moreover, delays in sensing and message
transmission must be minimized.

3##'((.

Figure 2. PROTOCOL STACK OF REMOTE PROXY COOPERATIVE
AWARENESS MESSAGE (CAM).

Figure 3 shows the overview of the proposed method. First,
a roadside computer vision sensor detects vehicles around theintersection and creates the corresponding CAMs. Next, thesensor broadcasts the CAMs. At the same time, the vehicle
sends a Remote Proxy CAM request to the Proxy CAM
device along the vehicle route as per the demand of the ITS
application. When the Proxy CAM device receives a request
message from a vehicle via the cellular network, it sends a
Proxy CAM reply to the vehicle via the cellular network. If
the vehicle receives Proxy CAMs via both IEEE802.11p andLTE, it updates the LDM entry with the newest information.
Here, we remark that the IP address discovery of theProxy CAM device is out of the scope of the paper. Possible
solutions for the IP address discovery include embedding theIP address in the digital map, downloading the static list of IP
addresses, or resolving the IPv6 address from the geographicalinformation by means of a DNS-like system.

1) Vehicle: A vehicle sends a request message for CAMs tothe nearest Proxy CAM device along the vehicle route via thecellular network using UDP/IPv6 and LTE. If the vehicle does
not receive a CAM response from the Proxy CAM devices
after a given interval, it sends a request again. The vehicle
always checks for CAMs using IEEE802.11p or LTE, and if
it receives CAMs, it updates its LDM with the newest ones.
2) Proxy CAM device: The created CAMs are broadcasted
using standard protocols based on ISO and ETSI. Our broadcast uses IEEE802.11p in the access layer and BTP and GN in
network&transport layer. At the same time, the created CAMs
are transmitted to vehicles that have sent requests for CAMs
in the unicast via the cellular network. This communication
uses LTE in the access layer and UDP and IPv6 in the
network&transport layer. Further, this transmission continues
for a specified interval, after which it is terminated. The
transmission is resumed if the Proxy CAM device again
receives a request.
8+?#2+&!"#$%&'()&"+BC+<2>72+"7+2!"#$%&'()&*+,-.+

2) Router: In our study, we used the PR-400NE manufactured by NTT as the router. The router and receiver
were connected by means of a 35-m-long Ethernet cable. The
firewall did not filter any kinds of IPv6 packets.
3) Reciever: We used the Tier PC Note GTX970M as
the packet receiver. The processors in the device include theIntel Core i7-4720HQ CPU @ 2.60 GHz×8, with a memory
capacity of 31.3 GB and the OS being Ubuntu 15.04. We
tethered the receiver and cellular device through a USB cable.
We used two programs: one to receive the packets via pathway(a), and the other to receive the packets via pathway (b). To
realize the Pub/Sub model, we ensured that the receiver senta request packet first.

8+?#2+&!"#$%&'()&"+@A%

9/:&;0<+=202-#7

54&6+2+.2-#7
34&!"#$%&'()

8+.+-,+"/0"1+2

Figure 3. OVERVIEW OF REMOTE PROXY COOPERATIVE
AWARENESS MESSAGE (CAM).
Figure 4. NETWORK CONFIGURATION.

B. System Implementation
We implemented the cellular network part of our designed
system as shown in Figure 4. We used the cellular device, REI(FTJ161B-REI) manufactured by FREETEL, in our study. We
tethered the cellular device and the receiver through a USB
cable. Our program was written in C language.
1) Transmitter: We used the LGN-20-00 transmitter manufactured by Commsignia Ltd. as the packet transmitter. The
transmitter communicated with the router via a 50-m-long
Ethernet cable in the access layer (Figure 4(a)). The routerand receiver were connected via a 30-m-long Ethernet cable,
and the transmitter was configured to send packets throughthe cable in order to measure the reference value of thedelay (Figure 4(b)). These two sets of communications used
UDP/IPv6 in the network&transport layer. We used multicast
for pathway (a) and unicast for pathway (b) in Figure 4. The
transmitter used a single program to send the same packet
along the two paths. In order to realize the Pub/Sub model
based on which the Proxy CAM device sends CAMs via
the cellular network after receiving a request, the transmitter
begins to function after receiving a request packet via pathway(a). The IP address of the destination in pathway (a) is thesender IP address in the request packet. As regards pathway(b), we set the global IP address of the receiver interface inadvance.

V. E VALUATION
We evaluated the implementation of our proposed method
in terms of the PDR and delay. We performed our experiments
in a residential area. In the experiment, first, the transmitteris set to create sockets for pathways (a) and (b) in Figure 4
and to wait for the CAM request via pathway (a). When thetransmitter receives the request, it sends out a given number ofpackets at a predetermined frequency. The size of each packet
is 300 bytes, and there is a number in a certain packet that
identifies it as the first packet. Next, the receiver creates sockets
for pathways (a) and (b) and files to record the result. Whenthe receiver receives a packet, it obtains the reception timeusing the gettimeofday function from sys/time.h andrecords the time to the file. After our experiment, we compared
the reception time of the same number packets of the two files
and measured the delay obtained using pathway (a).
We performed our experiments at frequencies of 1, 5, 10,50, 100, 500, 1000 Hz and distances of 10, 30, and 50 m. To
ensure that the PDR was more than three significant figures andthe experiment time more than 60 s, we set the total numberof packets as 100 for 1 Hz, 300 for 5 Hz, 600 for 10 Hz, 3000
for 50 Hz, 6000 for 100 Hz, 30000 for 500 Hz, and 60000 for
1000 Hz.

0.050

0.040

0.040

0.040

0.030

0.030

0.030

0.020

0.010

Latency (s)0.050

Latency (s)Latency (s)

0.050

0.020

0.010

0.000

0.010

0.000
1

5

10
50
100
Frequency (Hz)

500

0.000
1

Figure 5. PACKET DELAY (10 m).

5

10
50
100
Frequency (Hz)TABLE I. NUMBER OF RECEIVED PACKETS FOR VARIOUS
DISTANCE WITH USE OF UDP/IPv6 + LTE.

10 m
100 pkts
300 pkts
600 pkts
3000 pkts
6000 pkts
29987 pkts

500

1

Figure 6. PACKET DELAY (30 m).

A. Packet Delivery Ratio (PDR)
The following table lists the PDR results of our experiments. From the table, we note that the PDR hardly depends
on the frequency and distance. The maximum packet loss rate
is 0.08%. In theory, it can also be said that the distance between
the transmitter and the receiver does not matter because communication occurs between a cellular device and a base station.
This experiment demonstrates that communication between thetransmitter and receiver using the cellular network, UDP/IPv6+ LTE, is possible nearly 100% of the time regardless of thefrequency and distance.

1 Hz (100 pkts)
5 Hz (300 pkts)
10 Hz (600 pkts)
50 Hz (3000 pkts)
100 Hz (6000 pkts)
500 Hz (30000 pkts)

0.020

30 m
100 pkts
300 pkts
600 pkts
3000 pkts
6000 pkts
29980 pkts

50 m
100 pkts
300 pkts
600 pkts
3000 pkts
6000 pkts
29976 pkts

B. Packet Delay
Figures 5,6, and 7 depict the packet delay for different
frequencies and distances. When we performed the experimentat 1000 Hz, the transmitter could not generate packets every
0.001 s. Therefore, we have excluded the result for 1000 Hz.
The overall results indicate that the delay does not depend on
the distance; it is constant at about 30 ms. As mentioned in the
PDR section, the distance between the transmitter and receiver
does not matter in theory.
Next, we attempt to further understand the implicationsof our results. First, to evaluate our results, we defined themisregistration delay as the time from the transmission of a
CAM from a Proxy CAM device to the reception of the next
CAM at the vehicle. This parameter indicates the differencein the position of the vehicle in terms of the CAM and theposition of the vehicle in reality. We defined this parameter as
the sum of the CAM reception interval and the packet delay.

5

10
50
100
Frequency (Hz)500

Figure 7. PACKET DELAY (50 m).

The reception interval can be calculated as the product of the
CAM transmission interval and the reciprocal of the PDR. We
defined the PDR as pP CAM , frequency of CAM transmission
as fP CAM , and packet delay as tP CAM −trans . Consequently,
the misregistration was calculated using Equation (1).
1
pP CAM×1
fP CAM+ tP CAM −trans(1)

We calculated the misregistration delay from our results.
We assumed the frequency of the CAM transmission as 10 Hz
for the maximum desirable CAM broadcast frequency of 10
Hz according to [4]. We set the PDR to 1 because the results
indicate that the PDR did not depend on the frequency anddistance; further, the PDR was nearly 1. We also set the packet
delay to 0.03 seconds. With these values, the misregistration
delay was estimated as 0.13 seconds. We did not perform
experiments using BTP/GN + IEEE802.11p, since it is notlegal for application outside Japan. Therefore, we applied theresult of the IEEE802.11b/g protocol as per the field test of[10]. In this case, the PDR was 90%, 80%, and 75% fordistances of 10 m, 30 m, and 50 m, respectively. For the
packet delay, the distance between the transmitter and receiver
was a maximum of 50 m, and the electromagnetic signals
were considered to travel instantaneously, i.e., the time ofsignal travel was 0 s. For these abovementioned values, themisregistration delay was estimated as 0.11 s, 0.126 s, and
0.133 s for distances of 10 m, 30 m, and 50 m, respectively.
Upon comparing the misregistration delay of UDP/IPv6 +LTE with that of BTP/GN + IEEE802.11b/g, we concluded
that UDP/IPv6 + LTE and BTP/GN + IEEE802.11b/g perform
equivalently in terms of the performance speed.
C. Analysis on intersection scenario
Here, we discuss how our proposed method improves
pedestrian and vehicular safety at intersections with respect tovehicle distance and approach speed towards an intersection.
Let us consider the situation that a vehicle is approachingan intersection with an obstacle close by. To avoid collision
with the obstacle, the vehicle must stop before it enters theintersection. In this study, we analyzed the distance required

for the vehicle to stop before entering the intersection for the
initial speed of the vehicle. We denoted the distance between
the initial position of the vehicle and the intersection as d,
its deceleration as m, which is assumed constant during the
scenario, initial vehicle speed as υ0 , and time interval fromthe instant of consideration as t. The ?safe? distance to avoid
collision can be calculated using Equation (2) as follows:∫ υ0 /md=

υ(t)dt =
0

1 υ02
· ,
2 m

(2)

where υ(t) denotes the speed of the vehicle at time t andυ0 = υ(0) the initial speed of the vehicle. Figure 8 depicts
this safe distance d as the black solid curve obtained with m
set to 1.0 m/s2 .
600

Initial Position (m)

500

400

300

200

100

0
0

20

40
60
80
Initial Speed (km/h)

100

120

Figure 8. SAFE STOPPING DISTANCES FOR VARIOUS INITIALDISTANCES TO INTERSECTION AND INITIAL VEHICLE SPEEDS.

In this figure, the region under the black curve (coloredin red) indicates the unsafe distance-and-speed range, i.e., thevehicle is moving too fast, and it cannot stop before entering
the intersection. The other four regions lying above the curve
correspond to speeds and distances over which the vehicle
can stop before entering the intersection if it receives a CAM
or the driver sights the object/obstacle beforehand. There are
four possible collision-prevention solutions corresponding toreceiving a CAM or sighting the obstacle. Here, we summarize
the effective distance for each solution. The first solution
corresponds to sighting of the obstacle by the human eyeor computer vision, which works well if the obstacle canbe noticed. In the situation that the obstacle is in a blind
spot, effective preventive action can only be taken when thevehicle is very close to the obstacle. Therefore, we set the
maximum effective (communication) distance for this caseas 10 m. The second solution corresponds to the use of theoriginal CAM system. According to Figure 5(b) of [10], themaximum communication distance for such a system is 30 m.
The third solution considers our Proxy CAM system, wherein
the maximum distance depends on the situation. In the absenceof buildings and other obstacles, CAMs can travel over 800m([15]). However, the effective braking distance is constrainedby the presence of buildings and other large vehicles such astrucks or buses. Thus, we set the maximum distance to 50

m for the Proxy CAM case. The final solution considers theefficacy of our proposed method. This method uses both acellular network and LTE. Thus, in theory, the system can work
anywhere on the road (except in long tunnels). Therefore, its
maximum communication distance can be considered as ∞m.
Each of the abovementioned effective distances determines
the safety margins of the intersection with obstacles nearby.
Thus, the safety regions can be classified into the four regions
shown in Figure 8. Human eyes and computer vision are thepoorest solutions; their use can prevent an accident if the vehicle’s position and speed lie in the orange region. The original
CAM system can prevent an accident if the vehicle’s positionand speed lie in the orange and yellow regions. Meanwhile,
the Proxy CAM system can prevent collision if the vehicle’s
position and speed lie in the orange, yellow, and blue regions.
The green region is still unsafe for all three solutions. However,the proposed method can still prevent accidents corresponding
to the green region because our system can communicate
regardless of the distance. Therefore, our proposed method ishighly effective over existing technologies.
VI. C ONCLUSION AND FUTURE W ORK
We proposed a system called the Remote Proxy CAM thatuses a cellular network with UDP/IPv6 + LTE in addition tothe original Proxy CAM system protocol stack, BTP/GN +IEEE802.11p, in order to widen the coverage of the CAM
transmission and improve failure tolerance. To evaluate thissystem, we implemented the cellular-network component of
the system and performed various experiments. In the experiments, the transmitter sent packets to the receiver with various
frequencies over different transmitter?-receiver distances. Our
results indicated that using the cellular network with UDP/IPv6+ LTE afforded a high PDR (nearly 100%) and low average
delay of about 30 ms, which indicate that the proposed method
is stable and operates in real-time. This method allows CITS
vehicles to stably and consistently receive CAMs of faraway
vehicles in real-time.
We are planning to focus on three aspects of the system inour future works. Currently, we have assumed that the vehicle
knows the position and IP address of the Proxy CAM device;
however, our system needs to have a discovery mechanism
for discovering the proxy CAM device. Further, we need to
examine possible solutions for device discovery, such as IPaddress-embedded digital map, download-based solution, ora DNS-like system, as mentioned in section IV-A. Second,
we require a system that compares the created time of CAMs
across both IEEE802.11p and LTE and then updates LDM
with the newest times. Finally, we performed our experimentswith one receiver while actual situations would require more
receivers. Thus, the proposed method should be tested withmultiple receivers and the signal delay must be investigated.
ACKNOWLEDGEMENT
The authors would like to thank Ye TAO and Xin LI for
their help with the field tests and various comments on thepaper. This work was supported by JSPS KAKENHI Grant
Numbers JP17H04678 and JP26730045.
[1]

R EFERENCES
VehicleInformation
andCommunication
System,URL:
http://www.vics.or.jp/know/about/pdf/vics pamphlet j.pdf, Retrieved:Jun, 2017.

[2]
[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

Outline of ETC2.0, URL: http://www.go-etc.jp/etc2/etc2/index.html,
Retrieved: Jun, 2017.
Draft ETSI EN 302 636-3 v1.1.2(2014-03),Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking; Part 3: Network Architecture, 2014.
ETSI EN 302 637-2 v1.3.2(2014-11), Intelligent Transport Systems(ITS); Vehicular Communications; Basic Set of Applications; Part
2: Specification of Cooperative Awareness Basic Service, 2014.
ETSI EN 302 637-3 v1.2.2(2014-11), Intelligent Transport Systems(ITS); Vehicular Communications; Basic Set of Applications; Part
3: Specifications of Decentralized Environmental Notification Basic
Service, 2014.
ETSI EN 302 895 v1.1.1(2014-09), Intelligent Transport Systems(ITS);
Vehicular Communications; Basic Set of Applications; Local Dynamic
Map(LDM), 2014.
Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking; Part 5: Transport Protocols; Sub-part 1: Basic Transport Protocol, 2011.
Intelligent Transport Systems (ITS); Vehicular communications;
GeoNetworking; Part 4: Geographical addressing and forwarding forpoint-to-point and point-to-multipoint communications; Sub-part 1:
Media-Independent Functionality, 2011.
IEEE Standard for Information technology-Telecommunications andinformation exchange between sy tems-Local and metropolitan area
networks-Specific requirements Part 11: Wireless LAN Medium AccessControl(MAC) and Physical Layer(PHY) Specifications Amendment 6:
Wireless Access in Vehicular Environments, 2010.
T. Kitazato, M. Tsukada, H. Ochiai, and H. Esaki, “Proxy cooperativeawareness message: an infrastructure-assisted v2v messaging,” in 2016
Ninth International Conference on Mobile Computing and Ubiquitous
Networking (ICMU), Oct 2016, pp. 1–6.
M. Bagheri, M. Siekkinen, and J. K. Nurminen, Cloud-Based PedestrianRoad-Safety with Situation-Adaptive Energy-Efficient Communication,
2016, URL: http://ieeexplore.ieee.org/document/7518724/, Retrieved:Jun, 2017.
C. A. Sakurai, C. L. Marte, L. R. Yoshioka, and C. F. Fontana,“Integrating intelligent transportation systems devices using powerline communication,” in Recent Researches in Telecommunications,
Informatics, Electronics and Signal Processing, 2014, pp. 36–42.
A. Baiocchi, F. Cuomo, M. D. Felice, and G. Fusco, “Vehicular ad-hoc
networks sampling protocols for traffic monitoring and incident detection in intelligent transportation systems,” in Transportation ResearchPart C: Emerging Technologies Volume:56, Mar 2015, pp. 36–42.
D. Eckhoff, C. Sommer, R. German, and F. Dressler, “Cooperativeawareness at low vehicle densities: How parked cars can help see
through buildings,” in 2011 IEEE Global Telecommunications Conference - GLOBECOM 2011. IEEE, Dec 2011, pp. 1–6.
O. Shagdar, M. Tsukada, M. Kakiuchi, T. Toukabri, and T. Ernst,“Experimentation towards ipv6 over ieee 802.11p with its station architecture,” in International Workshop on IPv6-based Vehicular Networks,Jun 2012, pp. 1–6, URL: https://hal.inria.fr/hal-00702923, Retrieved:Jun, 2017.