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A Directional Broadcast Protocol for Emergency Message Exchange in
Inter-Vehicle Communications
Yuanguo Bi1,2, Hai Zhao1and Xuemin (Sherman) Shen2
1. Department of Computer Science and Technology, Northeastern University, Shenyang, 110004, China
2. Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
Email: {ygbi, xshen}@bbcr.uwaterloo.ca, zhhai@neuera.com
Abstract— Broadcast is an effective approach for safety-related
information exchange to achieve cooperative driving in vehicular
ad hoc network (VANET). However, it suffers from several funda-
mental challenges such as message redundancy, link unreliability,
hidden terminal and broadcast storm, etc., which degrade the
efficiency of the network greatly. To address these issues, this
paper proposes a position based multi-hop broadcast protocol
(PMBP) for emergency message dissemination in inter-vehicle
communications. By adopting a cross-layer approach considering
both the MAC and Network layers in the proposed scheme,
the candidate vehicle for forwarding an emergency message
is selected according to its distance from the source vehicle
in the message propagation direction. Analysis and simulation
results show that PMBP can not only quickly deliver emergency
messages, but also reduce broadcast message redundancy signif-
icantly.
I. INTRODUCTION
Inter-vehicle communications (IVC) [1] have recently drawn
much attention from government, academic community and
auto industry due to its support of safety related applica-
tions such as congestion avoidance, accident warning, and
comfort applications, e.g. entertainment, online game, weather
report and traffic data sharing, etc.. For instance, the U.S.
Federal Communications Commission (FCC) has approved
75MHz bandwidth for Dedicated Short-Range Communica-
tions (DSRC) systems in support of Intelligent Transportation
Systems (ITS) applications [2].
In IVC, how to effectively deliver emergency messages
to nearby and remote vehicles with low time latency in the
absence of topology information and roadside infrastructure is
a challenging research topic. Broadcast plays an important role
for information advertisements in traditional ad hoc network.
Nevertheless, it poses a series of problems to IVC. First,
lots of redundant messages may be exchanged, and a node
(the terms “node” and “vehicle” are used interchangeably
throughout the paper) could receive duplicate messages from
different neighboring nodes, which incurs a significant waste
of the limited network bandwidth. Second, since there are no
acknowledgements to broadcast messages, packet lost can’t
be neglected due to packet collisions, and consequently it is
probable that a node close to the accident spot may not be
able to receive the warning message. Similarly, hidden terminal
problem can also induce packet collisions due to the lack
of RTS/CTS handshake [3]. As a result, the unreliability of
broadcast messages would lead to more accidents. Finally,
This work was supported by China Scholarship Council (CSC) and the
Natural Science and Engineering Research Council (NSERC) of Canada.
without any rebroadcast control mechanisms, a node will
straightforward rebroadcast the received broadcast message.
This gives rise to the broadcast storm problem [4], which
would greatly consume bandwidth resource, and the network
collapses eventually.
To address the aforementioned issues, we propose a direc-
tional broadcast protocol, named PMBP, for multi-hop emer-
gency message dissemination. The highlights of the proposed
scheme includes: i) by a cross layer approach, the current
relaying node selects the neighboring node with the farthest
distance from the source node in the message propagation
direction as the next relaying node, which ensures emergency
messages can be delivered to remote nodes with the least
time latency; ii) At each hop, the emergency message is only
broadcast once, therefore, redundant broadcast messages are
greatly reduced; iii) by adopting revised RTS/CTS handshake,
there is no hidden terminal problem in PMBP, and it ensures
every node could correctly receive the emergency message,
which makes the scheme more reliable; and iv) the emergency
message has the highest priority to access the channel, and
it guarantees the emergency message be broadcast as soon as
possible.
The remainder of this paper is organized as follows. We
briefly review the related work in Sec. II. PMBP is proposed
in Sec. III. After introducing several important performance
metrics, we give detailed derivation of them in Sec. IV. The
simulation results are shown in Sec. V, followed by conclusions
in Sec. VI.
II. RELATED WORK
In [5], broadcast protocols in mobile ad hoc network
(MANET) are classified into four categories: i) simple flood-
ing [6,7], in which a node will directly rebroadcast the message
that is received at the first time, and finally all the connected
nodes receive this message; ii) probability based methods,
in which protocols are divided into two classes: a) a node
will rebroadcast the received broadcast message according to
a predefined probability, and this scheme falls into simple
flooding if the probability is set 1.0; b) a node decides whether
to rebroadcast a message based on the number of the same
messages received from neighboring nodes in a constant time
interval; iii) area based method, in which a node that can cover
more additional area is selected to rebroadcast the received
broadcast message; and iv) neighbor knowledge method, in
which a node makes a decision on forwarding the received
message according to the knowledge of its one-hop or two-
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hop neighbors. However, the protocols mentioned in [5] are
aimed to reduce redundant messages on the network layer, and
they don’t take hidden terminal problem, packet collisions, etc.
into consideration on the MAC layer. Therefore, they can’t
be directly applied to IVC, in which reliable broadcast for
emergency messages must be guaranteed.
Recently, some broadcast protocols have been proposed for
VANET. In [8], a node selects the farthest neighboring node
as the next hop relaying node. Nevertheless, each node must
maintain a neighboring node list which needs to be updated
frequently due to the fast movement of vehicles. In [9], a black
burst broadcast protocol is proposed for multi-hop emergency
messages exchange. On receiving a revised RTS packet, a node
sends channel jamming signal (black-burst) with the duration
proportional to the distance from the current relaying node,
and thus the farthest neighboring node wins the opportunity
to access channel. Another black-burst based scheme is also
proposed to provide deterministically prioritized access for
voice traffic in [10]. Nevertheless, the jamming signal greatly
consumes the channel resource, and the throughput of the
network drops eventually.
III. PROPOSED PMBP
In this paper, we adapt the priority based IEEE802.11e
protocol to support reliable emergency message broadcast in
IVC. By obtaining the position information (we assume that
each vehicle in the system is equipped with a GPS device)
from the revised RTS packet, PMBP selects the neighboring
node with the farthest distance from the source node in the
propagation direction as the next relaying node at each hop.
This process repeats until all nodes in the system get the
emergency message.
A. BRTS/BCTS handshake
In the proposed scheme, an emergency message is protected
by BRTS/BCTS handshake. As shown in Fig. 1, we add fields
position x,position y,em info into the traditional RTS
packet, and (position x,position y) is the position of the
current relaying node that prepares to broadcast the emergency
message. The field em info takes the information of the
source node which initially transmits the emergency message,
and it is constituted by: i) the source node address init addr,
the emergency message sequence number em seq, and the
source node position (init x,init y). Other fields in the BRTS
packet are the same as those in the RTS packet. Let Rrepresent
the transmission range of a node, and it is divided into a series
of distance block denoted by dis slot (actually its value should
be the average length of vehicles). Therefore, the value of the
duration fieldinBRTSis:
tbrts d=tsif s +(R
dis slot )·tslot +tbcts +tsif s
+tdata +tsifs +tbrts
=3tsif s +tbcts +(R
dis slot )·tslot +tdata +tbrts ,
(1)
where tbrts,tbcts and tdata are the time for transmitting a
BRTS packet, a BCTS packet and an emergency message,
respectively, and tsif s,tslot denote SIFS interval and time slot.
A node with an emergency message broadcasts a BRTS packet
frame_control duration em_infoposition_yposition_x fcs
source_addrdestination_addr
init_addr init_yinit_xem_seq
Figure 1. Format of the BRTS packet.
first, and then starts the BRTS retransmission timer, the value
of which could be calculated by:
tbrts r=tbrts +tsif s +(R
dis slot )·tslot +tbcts.(2)
If there is no BCTS packet response within tbrts r, the node
will rebroadcast the BRTS packet until the rebroadcast time
reaches rmax. A neighboring node receives a BRTS packet,
and decides whether to reply a BCTS packet according to
the position information in the BRTS packet. If its position
is between the source node and the current relaying node, it
won’t reply a BCTS message and drop this BRTS message.
Otherwise it will start a defer timer and prepare to reply a
BCTS message. If a neighboring node at (x,y) prepares to reply
a BCTS packet, the time of the defer timer tdis set according
to both the distance to the source node at (init x,init y)
and the distance to the current relaying node at (position x,
position y), and denoted by:
d1=(x−init x)2+(y−init y)2,(3)
d2=(position x−init x)2+(position y−init y)2,
(4)
td=tsifs +((R−(d1−d2))
dis slot )·tslot,d
2<d
1.(5)
Therefore, the farthest neighboring node from the source node
defers the least time, and has the highest priority to reply a
BCTS packet. If other neighboring nodes that have already
started their defer timer hear a BCTS packet replying the
same BRTS packet, they will perform the following procedure:
i) stop the defer timer; ii) drop their BCTS packets; and
iii) update their network allocation vectors (NAVs) according
to the time duration included in the received BCTS packet.
After replying a BCTS packet, a node starts its retransmission
timer which would arouse a retransmission process (refer to
Sec.II.E). The duration field in a BCTS packet is used for up-
dating NAVs of the neighboring nodes to avoid hidden terminal
problem, and its value tbcts d=tsifs +tdata +tsif s +tbrts.
The time intervals tsifs ,tbrts are used to reserve channel for
the next hop BRTS broadcast as illustrated in Sec. II.C.
B. Emergency message broadcast
If the current relaying node successfully receives a BCTS
packet, it will broadcast the emergency message after a SIFS
interval. The farthest neighboring node that has just replied a
BCTS packet becomes the next relaying node after receiving
the emergency message, and it will broadcast a BRTS packet to
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acknowledge this message after a SIFS interval. Every node
in the system has a list that is used to record all received
emergency messages, and each element of the list keeps the
address of the source node, and the sequence number of the
emergency message. Each node that receives an emergency
message will check the list to decide whether to drop this
message or receive it.
C. Multi-hop emergency messages relaying
To achieve delivering the emergency message as quickly as
possible, the proposed scheme adopts a cross layer method,
and the relaying node is selected by BRTS/BCTS handshake.
On receiving an emergency message, the farthest neighboring
node broadcasts a BRTS packet after a SIFS interval, which has
twofold objectives: i) it acknowledges the received emergency
message, and the relaying node considers that the emergency
message has been successfully received after receiving the
BRTS packet from its farthest neighboring node; and ii) it
selects next hop relaying node. Since the farthest neighboring
node has already reserved the channel by its previous BCTS
packet, it directly broadcasts its BRTS packet after a SIFS
interval on receiving the emergency message. A neighboring
node that hears this BRTS packet decides whether to reply a
BCTS packet according to the principle illustrated in Sec. II.A.
TAB LE I
PARAMETERS FOR DIFFERENT SERVICES
Service AC CWmin CWmax AIFSN
Best effort 0CW MIN CW MAX 2
Video probe 1CW MIN CW MAX 1
Vid eo 2(CW MIN+1)/2-1 CW MIN 1
Voice 3(CW MIN+1)/4-1 (CW MIN+1)/2-1 1
Safety 4(CW MIN+1)/8-1 (CW MIN+1)/4-1 1
D. Priority
In PMBP, we adapt the IEEE802.11e to support safety
related applications in IVC. Services in the system are divided
into five classes, and different classes of services have different
priorities to access the channel based on the access categories
(AC), as shown in Table I. The values of CW MIN and
CW MAX are defined the same as those in IEEE802.11b.
Complying with IEEE802.11e, after sensing the channel idle
for arbitration inter-frame space (AIFS) interval, a node will
start its backoff timer, and the computation of AIFS and
contention window (CW) are the same as IEEE802.11e. They
are:
AI F S[AC]=tsif s +AIF S N ·tslot,(6)
CW[AC ] = min (CW[AC ]+1)·PF,CWmax[AC].(7)
The value of persistence factor (PF) is set to 2.0 for all
services, and emergency messages have the highest priority to
access the channel by adjusting AIFS, CWmin and CWmax.
E. BCTS packet collisions
It is possible that two nodes in the same distance block
reply the same relaying node, therefore, BCTS packet colli-
sions occur. In the proposed scheme, a node starts a BCTS
retransmission timer after delivering a BCTS packet. If it has
not received an emergency message until the timer overflows,
it will start the backoff timer and retransmit the BCTS packet.
However, since the value of distance block is set to the average
length of vehicles, different vehicles can’t locate in the same
distance slot, and the probability of BCTS packet collisions
could be disregarded.
IV. PERFORMANCE ANALYSIS
In this section, to make the proposed scheme tractable, we
make the following assumptions:
1) All vehicles enter into a one-dimension highway from
the same entrance, and move in the same direction.
2) All vehicles run at the velocity v.
3) The number of vehicles that run into the entrance is
Poisson distributed, and λdenotes its mean value per
time unit.
4) The physical channel is reliable and error-free.
A. Number of informed nodes per hop
Let xdenote the random variable of vehicles that enter into
the highway between time [0, t], therefore the probability mass
function (PMF) of xcan be represented:
Pr
x(k)=(λ·t)k·e−(λ·t)
k!,(8)
E(x)=λ·t. (9)
Since the number of vehicles that get into the entrance is Pois-
son distributed, the time interval between two adjacent vehicles
denoted by random variable yis exponential distribution with
parameter λ, and we have Pr
y(m)=λ.e−λ·m. Let random
variable zrepresent the space between two adjacent vehicles,
and it is equal to v.y. We assume two adjacent vehicles are
within each other’s transmission range, so zR, and we have:
Pr(zn|zR)= 1−e−(λ·n
v)
1−e−(λ·R
v),(10)
E(z)= v
λ−R
e(λ·R
v)−1.(11)
Finally, the average number of neighboring vehicles within
the transmission range of the current relaying node in the
emergency message propagation direction is:
E(w)=R
E(z)=R.λ ·(e(λ·R
v)−1)
v·(e(λ·R
v)−1) −λ·R.(12)
B. End to end delay
The end to end delay defines the time taken from the source
vehicle to the last one. When a node detects an accident, it
will immediately initiate an emergency message and contend
for channel access, and consequently the first hop emergency
message exchange is contention based. However, from the
second hop, the emergency message exchange is contention
free since the current relaying node has reserved channel
resource for its BRTS packet by replying a BCTS packet to its
former relaying node. As a result, the time taken by delivering
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an emergency message at the first hop is longer than that at
the following hops, and the end to end emergency message
delay Teis:
s=E(x)−1
E(w),(13)
Te=Tf+(s−1) ·T+Tl,s1,(14)
where Tfis the time taken at the first hop, and Tdenotes
one-hop delay at intermediate hops, and Tlrepresents the
time spent at the last hop. For the emergency message at the
first hop, Tf=AI F S(4) +B(4) +T(4)
d, where AI F S(4)
is arbitration inter-frame space, T(4)
dis the time taken for
exchanging an emergency message, while B(4) is the sum
of time taken in the backoff process, neighboring nodes’
collisions and neighboring nodes’ successful transmissions. We
can easily get the value of AIF S (4) from Eq. (6) and TABLE
I. As to T(4)
d, it includes the time of BRTS/BCTS handshake
and the time for broadcasting an emergency message. So, it
can be calculated as:
Td(4) =tbrts +tsif s +(R−E(z)·E(w)
dis slot )·tslot
+tbcts +tsifs +tdata
=(R−E(z)·E(w)
dis slot )·tslot
+2tsifs +tbrts +tbcts +tdata,(15)
B(4) is the time taken by the source node to access the
channel, and it has already been studied in many previous
work. Followed the analysis of the access delay in [11], B(4)
could be represented as:
B(4) =
rmax
−1
j=0
((1 −c4).c4j·E(Bj(4))
1−c4rmax ),(16)
where c4is the collision probability of BRTS packets,
E(Bj(4))is the total time taken in the backoff process, defer-
ment due to neighboring nodes’ successful transmissions, and
delay caused by neighboring nodes’ collisions on backoff stage
j. Detailed derivation of c4and E(Bj(4))can be found in [11].
From the second hop of the emergency message exchange, the
relaying node only waits a SIFS interval to broadcast its BRTS
packet because it has reserved the channel by its previous
BCTS packet. So, T=tsifs +Td(4) . Since the number of
vehicles at the last hop may be less than E(w), consequently
Tlis probably larger than T, and it can be denoted:
Tl=tsifs +tbrts +tsif s +tbcts +tsif s +tdata
+(E(z)·(E(x)−1) −E(z)·E(w)·s)
dis slot )·tslot
=3tsif s +tbrts +tbcts +tdata
+(E(z)·(E(x)−1−E(w)·s)
dis slot )·tslot.(17)
When s=0, all vehicles are within the transmission range of
the source node, and the end to end delay can be obtained
from Tf.
C. Ratio of informed nodes to broadcasting nodes
In IVC, emergency messages should be broadcast as quickly
and reliable as possible with the least bandwidth consumption.
In other words, there should be less relaying nodes to rebroad-
cast the emergency message for covering all the nodes in the
system. Therefore, the ratio of informed nodes to broadcasting
nodes is an important metric to evaluate the performance of
IVC. In PMBP, there is only one relaying node to forward the
emergency message at each hop, and consequently the ratio is
1/E(w).
TAB L E I I
PARAMETERS IN SIMULATION
Parameter Value Parameter Value Parameter Value
tsifs 16 µsRTS 20byte dis slot 5m
tslot 16 µsCTS 14byte rmax 3
basic rate 2M BRTS 29byte v20m/s
data rate 11M BCTS 16byte CW MIN 31
R250m Emergency 100 byte CW MAX 1023
V. SIMULATION RESULTS
In this section, we consider the scenario where all vehicles
enter the highway from the entrance with the same velocity,
and after some time interval, the first vehicle initiates an emer-
gency message and delivers it to all other vehicles. To evaluate
the performance of the proposed protocol, we introduce several
important metrics as follows: i) end to end delay, which
defines the time taken by an emergency message from the first
vehicle to the last vehicle; ii) channel occupancy time, which
is the total time that channel is occupied for broadcasting an
emergency message to vehicles in the system; iii) informed
vehicles to broadcasting vehicles. We implemented PMBP in
NS2, and thoroughly evaluate the performance of PMBP. We
also implemented simple flooding for comparison, and the
parameters adopted in simulations are listed in TABLE II.
Fig.2 shows the comparison of end to end delay among
analysis of PMBP, simulation of PMBP and simulation of
simple flooding, and we have several observations. Firstly, at
the beginning, the delay in PMBP is slightly higher than that
in simple flooding, but with the increasing number of vehicles,
the delay in simple flooding is much greater than that in PMBP.
In PMBP, a vehicle detecting an accident must contend for
channel access at the first hop, and it also has overhead such
as BRTS, BCTS packets. Consequently its end to end delay is
higher than that in simple flooding. However, from the second
hop, a relaying node only waits a SIFS interval to deliver
its BRTS packet after receiving an emergency message, since
it has already reserved the channel by the previous BCTS
packet to the former relaying node. Nevertheless, in simple
flooding a relaying node must queue the received emergency
message, and then contend for channel access. Thus, its delay
is much higher than that in PMBP for multi-hop emergency
message propagation. Secondly, because from the second hop
the time spent at each hop is much less than that at the
first hop, the delay in PMBP doesn’t rise sharply with the
number of vehicles increasing. Finally, sometimes the delay
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decreases with the number of vehicles increasing in PMBP.
This is because that a neighboring node closer to the relaying
node takes longer time to reply the broadcasting BRTS packet
than a farther neighboring node, and consequently the delay
sometimes decreases with the number of vehicles increasing.
The channel occupancy time represents how long the chan-
nel would be occupied by the emergency message to be
received by remote vehicles. As shown in Fig. 3, the channel
occupancy time in simple flooding is much higher than that
in PMBP especially in large number of vehicles scenario. In
simple flooding, a node rebroadcasts the emergency message
which is received at the first time, and the channel resource is
wasted by lots of redundant packets. However, there is only
one relaying node to broadcast the emergency message at each
hop in PMBP. As a result, its channel occupancy time is much
less than that in simple flooding.
The proportion of informed vehicles to broadcasting vehi-
cles reflects the utilization of channel resource, and our goal
is to inform vehicles in the system with the least relaying
nodes. From Fig. 4, we can observe that the number of
broadcasting nodes in simple flooding is much larger than that
in PMBP. In simple flooding, the number of informed nodes
is equal to the number of relaying nodes, and the efficiency
of the network degrades obviously in dense vehicle scenario.
However, the number of relaying nodes in PMBP doesn’t have
any relationship with the number of informed nodes, and only
one node is selected to broadcast the emergency message in
each hop. As a result, PMBP works efficiently especially with
high node density.
Figure 2. End to end emergency message delay.
VI. CONCLUSIONS
In this paper, we proposed a position based multi-hop
broadcast protocol (PMBP) for emergency messages exchange.
Simulation and analysis results demonstrate that PMBP can
quickly deliver the emergency message with the less resource
consumption, and effectively reduce redundant messages. Fur-
thermore, PMBP has successfully resolved hidden terminal
problem and increased the reliability for safety applications.
For future work, we will consider complicate mobility models
which are more realistic, and other performance metrics will
be also evaluated.
Figure 3. Channel occupancy time.
Figure 4. Informed nodes to broadcasting nodes.
REFERENCES
[1] J. Luo and J. P. Hubaux, “A Survey of Inter-Vehicular Communication,”
Technical Report IC/2004/24, School of Computer and Communication
Sciences, PFL, 2004.
[2] Dedicated Short Range Communications Working Group, [Online],
Available: http://grouper.ieee.org/groups/scc32/dsrc/.
[3] L. X. Cai, X. Shen, J. W. Mark, L. Cai and Y. Xiao, Voice Capacity
Analysis of WLAN with Unbalanced Traffic, IEEE Trans. Veh. Technol,
vol.55, no.3, pp. 752-761, 2006.
[4] Y.-C. Tseng, S.-Y. Ni, Y.-S. Chen, and J.-P. Sheu, “The Broadcast Storm
Problem in a Mobile Ad Hoc Network,” Wireless Networks, vol. 8, no.
2/3, pp. 153-167, 2002.
[5] B. Williams and T. Camp, “Comparison of Broadcasting Techniques for
Mobile Ad Hoc Networks,” In Proc. of MobiHoc’02, pp. 194-205, Jun.
2002.
[6] C. Ho, K. Obraczka, G. Tsudik, and K. Viswanath. “Flooding for Reli-
able Multicast in Multi-hop Ad Hoc Networks,” In Proc. of DIALM’99,
pp. 64-71, Aug. 20, 1999.
[7] J. Jetcheva, Y. Hu, D. Maltz, and D. Johnson. A Simple Protocol for
Multicast and Broadcast in Mobile Ad Hoc Networks. Internet Draft:
draft-ietf-manetsimple-mbcast-01.txt, Jul. 20, 2001.
[8] L. Briesemeister and G. Hommel, “Role-based Multicast in Highly
Mobile but Sparsely Connected Ad Hoc Networks,” In Proc. IEEE/ACM
Workshop MobiHOC, pp. 45-50, Aug. 2000.
[9] G. Korkmaz, E. Ekici, F. Ozguner, “Black-Burst-Based Multihop Broad-
cast Protocols for Vehicular Networks”, IEEE Trans. Veh. Technol,vol.
56, no. 5, pp. 3159-3167, Sept. 2007.
[10] P. Wang, H. Jiang, and W. Zhuang, “IEEE 802.11e Enhancements for
Voice Service,” IEEE Wireless Communications, vol. 13, no. 1, pp. 30-
35, Feb. 2006.
[11] D. X. Xu, T. Sakurai, H. L. Vu, “MAC Access Delay in IEEE 802.11e
EDCA,” In Proc of VTC’06 Fall, pp. 1-5, Sept. 2006.
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