Cross Layer Approach for Efficient Dissemination of ... - IEEE Xplore

Cross Layer Approach for Efficient Dissemination of Emergency Messages in VANETs Mahadev A. Gawas, Palash Hurkat, Varun Goyal, Lucy J. Gudino Department of Computer Science and Information Technology Birla Institute of Technology and Science(BITS) Pilani K.K.Birla Goa Campus Email id: {mahadev, lucy}@goa.bits-pilani.ac.in, { palashhurkat, varungoyalbits }@gmail.com

governs the delivery ratio of the broadcast messages, especially over densely populated networks [5]. The multimedia safety messages need high reliability and high priority to effectively broadcast safety messages. Thus, the end-to-end delay for broadcasting messages should be minimized. Without any control mechanism for broadcasting messages, flooding of broadcast messages can occur between vehicles, because the wireless channel is shared by all vehicles in the transmission range. This can lead to poor network resource utilization, under-utilization of bandwidth, excessive re-transmission of messages. To accomplish multi-hop data delivery and to prevent this message redundancy, VANET needs to select an optimal next hop vehicle as the forwarder to disseminate safety messages through a platoon which typically covers a few kilometers [6]. Various metrics can be used for selecting suitable forwarder. For example, geographical information like the location of a vehicle through the GPS can be used to select a suitable forwarder. Most of the proposed multi-hop broadcast protocols select the farthest vehicle in broadcast range as the forwarder [7][8]. Although the end-to-end broadcast delay and the number of forwarding hops are decreased in that case, high contention delay is introduced in the case of high vehicle density.

Abstract— This paper proposes a cross layer approach for efficient dissemination of emergency messages in VANETs (CLDEM) by minimizing the message redundancy and maintaining low end-to-end communication delays. We propose a scheme to select a one-hop neighbor relay as a potential forwarder for relaying the broadcast messages to improve the transmission reliability in a platoon of vehicles. The relay selection metrics compose of vehicular density, vehicular velocity, and the geographical location. The selected relay controls the broadcast messages with minimum overhead and with minimum bandwidth consumption. To provide the service differentiation to different traffic classes, we adopt 802.11e MAC. The cross layer is further extended to the transport layer to dynamically adapt the data transmission rate based on the physical channel state. The extensive simulation analysis conducted reveals that the proposed cross-layer scheme effectively propagates the critical broadcast messages with minimum latency. Keywords—Cross-layer; dissemination; emergency messages; VANETs;

I. INTRODUCTION Cooperative communication in Vehicular Ad-hoc Networks (VANET) has become the de-facto in enabling technology to improve its efficiency. Recently, the intelligent transportation systems (ITSs) have been used in wireless communication to enhance the road transportation systems. Most of ITS applications utilize VANETs to provide the communications between inter vehicular communication (IVC). VANETs are one of the promising wireless technologies that are largely applied to enhance the driving safety and passenger comfort. VANETs can improve driving safety by dissemination of safety and caution messages in the case of accidents. VANETs can also be used to avoid traffic congestion and provide location services, thus increasing passenger comfort, reducing travel time, etc [2]. In recent years, although the progress in VANETs has evolved rapidly due to their diverse and useful applications, but several technical problems still need an attention. For example, guaranteeing the data delivery due to the high mobility of the moving vehicles, network topology changes regularly, which leads to volatile links in inter-vehicle communication [3][4]. Different types of vehicles are present on the road, each having contrasting processing power, the amount of memory present, the types of the antenna used, which can lead to various different scenarios in a realistic environment. Multi-hop messaging is the fundamental form of communication in VANETs. Most of the existing IVC techniques use a broadcast method to disseminate time critical safety information and selects the farthest vehicle in broadcast range as the forwarder to reduce the number of forwarding hops. In the design of multi-hop broadcast messaging technique, proper relay node selection is crucial, which highly

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In this paper, we propose a cross-layer based distributed cooperative safety messages broadcast algorithm. The proposed scheme uses cross-layer coupling of the network, MAC, and physical layer to broadcast the messages through a cooperative relay in the network. The highlights of proposed CL-DEM are listed as follows: 1.

The optimal one hop forwarder is selected based on multiple metrics like distance, position, and velocity rather than selecting a random farthest vehicle as a forwarder.

2.

One hop forwarder vehicle is selected which is moving in the same direction as that of source by computing its moving direction.

3.

To provide service differentiation to emergency messages, 802.11e MAC is modified with an additional access category.

4.

A variable data rate is chosen to disseminate emergency messages rather than a base data rate.

The next section will first review the related work. Section III discusses the proposed protocol for next hop forwarder selection and a scheme for message dissemination. We provide simulation results and conclusion in section IV and in section V, respectively.

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inversely proportional to distance from the transmitter. Also, the vehicle with lowest delay has the highest priority.

II. RELATED WORKS Many research works have been studied in VANETs to find the most effective way of transmitting emergency messages through the network. However, still researchers are working to find a solution which is ideal for all scenarios. All the methods proposed in the literature till today, come with its own drawbacks. Some of them include simple flooding which causes the broadcast storm problem in VANETs. The simultaneous broadcasting leads to frequent packet loss and collision due to contention in dense areas. In wireless networks, achieving highly efficient multi-hop broadcast or coverage is a challenging task [4]. However, the broadcast problem can be solved by adjusting the delay or probability which mitigates the channel contention brought by the flooding broadcast. Recently, some protocols have been proposed for emergency message delivery in IVC.

Another delay-based protocol ReC [15] uses geographical information by selecting the nearest vehicle to the centroid of neighbors that have not received the message as the forwarding vehicle. It reduces the unnecessary transmission by immediately retransmitting message received by selected forwarder. However, its major drawback is to adapt quickly to high mobile environments. III. PROPOSED PROTOCOL The proposed routing protocol disseminates a safety message during the emergency situation from the source to the destination. During the routing process the optimal forwarder is chosen based on the vehicular density, vehicular velocity and geographical position of the vehicle. The proposed scheme uses cross-layer coupling of the transport, network, MAC, and physical layer to broadcast the messages through a cooperative relay in the network.

In [9], Jagruti Sahoo et al., addresses the issue of the emergency message dissemination in VANETs. The proposed protocol repetitively divides the area inside the transmission using binary partition based approach to obtain the farthest possible segment. The protocol adapts well to complex road structure and accomplishes directional broadcast for highway scenario. Another advantage of this protocol is the constant contention delay irrespective of the vehicle density.

The considered network scenario with k types of vehicles is in a multilane highway environment as shown in Fig.1. Since the transmission range 𝑅𝑅, is much larger than the road width, the network scenario can be simplified as a onedimensional VANET with road length of 𝐿𝐿. Each vehicle can detect its location through GPS facility equipped with it. In addition, the vehicle can also detect it’s one-hop neighbors within its transmission range by exchanging a beacon message.

Samara et al., [10] have proposed Particle Swarm Optimization Contention Based Broadcast (PCBB) for fast and effective dissemination of emergency messages within a geographical area to distribute the emergency message and achieve the safety system. It makes more accurate analysis and increases the percentage of the emergency message reception without affecting the channel collision.

A. Handshake Mechanism In the proposed protocol, to efficiently disseminate safety message to optimal neighbor node, we perform a handshake procedure by exchanging REQB and RREB control packets between adjacent one hop vehicles.

In [11], Srinivetha R. et al., proposed a new adaptive approach which uses the information about the urban environment, thus increasing efficiency of warning message dissemination processes. It identifies vehicles in a dangerous position and immediately sends warning messages to them.

Whenever the node has a critical safety message to broadcast to vehicular traffic in the region, it broadcasts the REQB control packet and starts the timer TimerREQB. The REQB packet composed of the source node address (S_info), and its position(Sx and Sy), velocity (t_velocity ) which denotes current broadcast node’s moving velocity, Dmessage is the direction of the safety message, position ( Rx and Ry ) which indicates the current broadcast node’s position, and the sequence number(Sseq).

Javed Ma et. al., [12] proposed an efficient time-slotted multi-hot broadcast protocol. This protocol selects a segment leader who is responsible for forwarding the warning message on a particular road segment. It allocates separate time slots for warning messages to avoid interference. It ensures reliable delivery through the signalling mechanism while maintaining high reception rate and low end-to-end delay for single-hop safety messages. This protocol also reduces the number of transmissions and ensures timely delivery of warning messages. In [13], a black-burst based ad hoc multi-hop broadcast (AMB) protocol allows a neighboring node to send a channel jamming signal with the time duration that is proportional to its distance. However, it's major drawback is the long delay of emergency messages caused due to largest jamming duration used by the relay candidate. An efficient 802.11-based protocol called urban multi-hop broadcast (UMB) is proposed in [14]. UMB assigns broadcasting delay to each node based on the distance between the vehicle and transmitter. The broadcasting delay is

Fig.1. Demonstration of considered environment

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The neighbor nodes on receiving the REQB packet undergo the qualifying test to be eligible for the relay node. The neighbor nodes based on QoS metrics such as moving direction, velocity, and vehicular neighbor density, determines if it is suitable to act as a relay to propagate the broadcast message efficiently. The neighbor node estimates its weight Wrelay based on QoS metrics as given in (1). (

)

(

)

( )

(1)

Where, and can be dynamically determined according to the vehicle density and broadcast radius in practical, ds-r is the distance between source and relay node, ds-n is the distance between source and farthest node, ρ is the density of neighbor vehicles on a highway, ρmax is maximum vehicular density, v is relative speed and V is maximum speed. The neighbor node qualifies to be a relay if its Wrelay value is within the window of Wrelaymin and Wrelaymax. In order to avoid the collision of REPB from multiple nodes qualified to be a relay, each qualifying neighbor node waits for an addition λ time after sifs time. The value of λ is assumed equivalent to difs. We divide the λ time slot into multiple τ slot of length σ. The σ and τ are computed as:

Fig.2. Handshake sequence of control packets

B. Packet Prioritization using 802.11E We propose a mechanism to update the priority of AC4 with following modification to the EDCA function. In EDCA, the contention window is used to calculate the number of time slots to backoff before gaining the channel access. The value of the contention window (CW) is doubled every unsuccessful packet transmission due to collision, and the contention window is reset to the minimum value for successful packet transmission. By default, these values are statically set for each ACs. We have proposed a scheme in which increasing CW limits on transmission failure or resetting due to success is done in a gradual and non-uniform manner within the window range {CWmax[i], CWmin[i]}. For any unsuccessful transmission of emergency messages due to collision from AC4, our scheme performs the following measures. It checks its current CW[i] value. If it is less than twice that of its CWmin[i], its CW is increased at a faster rate by multiplying by a factor of 1.5.

(2) ⌊ ⌋

(3)

where, Pdelay is a channel propagation delay, and Tswitch is transceiver switching time. We further divide the time slots τ into ɸ to map Wrelay value, which is given as:

if (CW[i] < 2

(4)

CWmin) CW[i]=min(CW[i]*1.5, 2*CWmin[i])

Whenever there is a successful transmission of emergency packets, we do not reset the CW[i] value to CWmin[i]. For AC4, contention window is linearly decremented if CW[i] is less than twice that of CWmin[i] otherwise it is decreased by a factor of 0.5.

Each source node starts its ɸ counter from zero, and when reaches to its Wrelay value, sends REPB in that time slot. Thus, a node with minimum Wrelay gets the channel access. The REPB is composed of the sequence number, address, density, and speed. The neighbor nodes eligible to be relay node, on hearing the REPB packet from the neighbor node, it sets its stop its own back-off timer and update its NAV as per the value included in the received REPB frame, and defer their transmission accordingly. The source node on receiving REPB within TimerREQB prepares for safety message broadcast. Fig.2 demonstrates the handshake sequence of packets exchanged between the source and a relay.

if (CW[i] < 2 CWmin[i]) CW[i]=max(CW[i]-1,CWmin[i]) Else CW[i]=max(0.5*CW[i],2*CWmin[i]) This assignment resulted in maximizing the probability of transmitting emergency messages for a given time. This approach uses transport layer to regulate the volume of emergency messages on the channel.

To provide safety messages with higher priority than other packets, we use the priority-based IEEE 802.11e MAC for service differentiation. In our proposed scheme CL-DEM, we modified the 802.11e (EDCA) to incorporate the fifth access category apart from existing four differential access categories as shown in fig.3. The newly introduced fifth access category (AC4) is reserved for emergency messages.

The source node estimated the transmission rate DRi based on the bit error rate (BER), estimated from the received signal of REPB. The source node waits for SIFS time and broadcast the message to the selected relay at a rate DRi. The relay replies with the ACK on successful reception of the message. Similarly, the selection of the next broadcast relay node is executed. The neighbor nodes keep the record of overheard safety messages to avoid redundancy and deal with traffic congestion.

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Table I : Priority to Access category

Fig.3. Modified 802.11e EDCA to accommodate emergency messages

Algorithm: Parameters: {

User Priority (UP)

Access category (AC)

Designation

1

0

Background

2

0

Background

0

1

Best effort

3

1

Best effort

4

2

Video

5

2

Video

6

3

Video

7

4

Emergency Message

C. Proposed Cross Layer Architecture The traditional hierarchical TCP/IP layer architecture used in networking is inflexible. The existing layered design is incapable of coping up with the dynamics of MANETs supporting real time multimedia applications. In the proposed CL-DEM protocol, we propose a cross layer architecture framework, where information is passed across the layers to improve the network efficiency. The CL-DEM utilizes the geographical location and vehicle velocity information available at the physical layer for next hop forwarder selection at the network layer. Based on the signal strength of received REPB packet from relay node, the transport layer decides the data rate for transmitting emergency messages. The MAC layer is implemented with 802.11e EDCA functionality and modified to include a additional access category AC4, to accommodate emergency messages. Thus, giving higher priority to emergency messages. The fig.4 explains the cross layer approach proposed in CL-DEM algorithm.

: Distance between source and relay node : Distance between source and farthest node ρ : density of neighbour vehicles : Maximum vehicular density υ : Relative velocity V : Maximum velocity

} Initialization: { = 0.4 = 0.4 = 0.2 } One-hop neighbor on receiving REQB message: { from (1) Calculate If ( < < ): { //node qualifies to be a relay Calculate σ from (2) Calculate τ from (3) Wait(sifs) Wait for time slot Send REPB } } Source node on receiving REPB: { Wait(sifs) Estimate the transmission rate 𝑅𝑅 Prepare for safety message broadcast Insert the message in AC4 queue } One-hop neighbor on receiving the emergency message { Send ACK Repeat the process for selection of next hop forwarder }

IV. SIMULATION ENVIRONMENT The simulation platform used is NS-2.35 network simulator [17]. Physical and MAC layer are simulated using IEEE 802.11e inbuilt ns2 modules. The primary alterations include 5.9 GHz as the carrier frequency and 10 MHz as the width of the control channel band. Initially, there is a uniform distribution of vehicles on a highway segment of approximately 4 km length, having 4 lanes, the width of the each lane is 3.7 meters.

Fig.4. Proposed cross layer architecture in CL-DEM

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density is less, we receive slightly poor performance in terms of the packet delivery ratio with the proposed method, as compared to FD and 802.11p. However, with an increase in the number of vehicles, CL-DEM outperforms the other popular protocols such as 802.11p and FD. The analysis also shows that when the number of vehicles exceeds 100, 802.11p provides the worst performance in the simulation scenario.

All vehicles move with different velocity in the range of 80-100 km/h, which is randomly assigned from the abovementioned range. Ten data flows are set up at the rate of 15 packets per second. The transmission range of the vehicles is set to 300 meters along with a GPS device and a data processing unit. Also, there is a wireless transceiver which follows the IEEE802.11p standards. Packets of size 512 bytes are emitted by CBR at an interval of 0.05 s. A platoon consists of nodes varying in the range of 100 to 200, which increases by 25 nodes per simulation scenario. A. Performance evaluation The proposed CL-DEM scheme is analyzed and compared against two existing schemes 802.11p standard and FD[18][19]. Fig.5. Shows the relay selection delays for the compared protocols as a function of vehicle density variation. Relay selection delay is defined as the time interval from which the broadcast node attempts to deliver a REQB frame, to the time it successfully receives a REPB frame. Service differentiation is applied in the CL-DEM in which the emergency messages are served with the highest priority. Alternatively, the FD ad 802.11p adopts a basic CSMA/CA mechanism, which doesn’t consider the requirements of delay-sensitive traffic, and priorities of all the packets are same which access the channel. Therefore, the access delay of FD and 802.11p is longer than that of the CL-DEM. Additionally, the node sending the longest channel jamming signal becomes the relaying node in the FD, while a node waiting the shortest time to reply a REQB frame becomes the relaying node in the CL-DEM.

Fig.5. Relay selection delay v/s vehicle density

The results of the broadcast count required to cover all the vehicles are shown in Fig.6 The measurement of message dissemination progress can be done by the broadcast count, which considers both the success and failure broadcast. As a result, two cases can be considered. For larger hop distances, channel conflict probability will be high leading to a higher number of failure broadcasts. However, for smaller hop distances, coverage range is small leading to more relay hops. 802.11p randomly selects the forwarder vehicle and thus has the highest broadcast count, but also requires more relay hops to transmit the message to last vehicles. If the objective is only maximum coverage, then the broadcast count of FD performes better than that of CL_DEM and 802.11p. The performance of CL-DEM is nearly same as that of FD although CL-DEM does not always choose the farthest vehicle as the forwarder.

Fig.6. Broadcast count v/s vehicle density

Fig.7 shows the emergency access delay against the vehicle density. Initially with lower vehicle density, all three protocols incur minimum delay. As the density increases, the result shows that CL-DEM outperforms FD and 802.11p. This is because, firstly CL_DEM uses additional access category by adjusting contention window parameters for transmitting emergency messages with highest priority. Secondly, the CL-DEM uses a higher data rate based on channel quality to disseminate emergency messages. As a result, the speed of dissemination of the message is reduced in CL-DEM. Fig.8 shows the packet delivery ratio for the compared protocols. The figure analysis shows that, when the vehicle

Fig.7. Emergency message access delay v/s vehicle density

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[9]

[10] [11] [12] [13] [14] Fig.8. PDR comparison v/s vehicle density

V. CONCLUSION This paper proposed an effective multi-hop message broadcasting scheme using a cross-layer approach in VANET called CL-DEM. The cross-layer approach blurs the gap between the layers to exploit the exchange of fine grain information to enhance the communication in VANET. The optimal selection of Relay with multi-QoS metric has a direct impact on improving the packet delivery ratio over densely populated VANETs. The safety messages are given highest priority compared to other control packets by adopting 802.11e MAC. Also, messages are broadcast at the highest possible rate based on channel state, minimizing the packet latency. As a future continuation of this research, we would suggest investigating the performance of the CL-DEM scheme over a variant of street topographies along with various obstacle models.

[15]

[16] [17] [18]

[19]

REFERENCES [1] M. A. Gawas, L. J. Gudino and K. R. Anupama, "Cross layered adaptive cooperative routing mode in mobile ad hoc networks," 2016 22nd AsiaPacific Conference on Communications (APCC), Yogyakarta, 2016, pp. 462-469. [2] F. Li, Y. Wang, Routing in vehicular ad hoc networks: a survey, IEEE Veh. Technol. Mag. 2 (2) (2007) 12–22. [3] W. Chen, K. Guha, J. Kwon, J. Lee, Y. Hsu, A survey and challenges in routing and data dissemination in vehicular ad-hoc networks, in: Proceedings of the IEEE International Conference on Vehicular Electronics and Safety, Columbus, pp. 328–333, USA, 2008. [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 Netw., vol. 8, no. 2/3, pp. 153–167, Mar. 2002. [5] E. Hossain, G. Chow, V.C.M. Leung, R.D. McLeod, J. Misic, V.W.S. Wong, O. Yang, Vehicular telematics over heterogeneous wireless networks: a survey, Comput. Commun. 33 (2010) 775–793. [6] B.T. Sharef , R.A. Alsaqour , M. Ismail , Vehicular communication ad hoc routing protocols: a survey, J. Netw. Comput. Appl. 40 (2014) 363– 396 0. [7] J. Huang , Y. Huang , J. Wang , Vehicle density based forwarding protocol for safety message broadcast in VANET, Sci. World J. 2014 (2014) 9. [8] C. E. Palazzi, M. Roccetti, and S. Ferretti, “An intervehicular communication architecture for safety and entertainment,” IEEE

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Transactions on Intelligent Transportation Systems, vol. 11, no. 1, pp. 90– 99, 2010. J. Sahoo, E. Wu, P. K Sahu, and M. Gerla, “Binary-Partition Assisted MAC-Layer Broadcast for Emergency Message Dissemination in VANETs”, IEEE Transactions on Intelligent Transportation Systems, Vol. 12, No. 3, September 2011. S. Tareq Alhmiedat, “Intelligent Emergency Message Broadcasting in VANET” using PSO of Computer Science and Information Technology Journal (WCSIT) Vol. 4, No. 7, , 2014. R. Srinivetha., R. Gopi, “Inter Alert Message Dissemination Protocol for VANET to Improve Road Safety” International Journal of Emerging Technology and Advanced Engineering Volume 4, Issue 1, January 2014. M. A. Javed, N. DT, K. JY., “A multi-hop broadcast protocol design for emergency warning notification in highway vanets”. Eurasip journal on wireless communications and networking. 2014, Article 179. G. Korkmaz, E. Ekici, and F. Ozguner, “Black-burst-based multihop broadcast protocols for vehicular networks,” IEEE Trans. Veh. Technol., vol. 56, no. 5, pp. 3159–3167, Sep. 2007. G. Korkmaz, F. ¨ Ozg¨uner, E. Ekici, and ¨ U. ¨ Ozg¨uner, “Urban multihop broadcast protocol for inter-vehicle communication systems,” in Proceedings of the 1st ACM International Workshop on Vehicular AdHoc Networks (VANET ’04), pp. 76–85,October 2004. J. Liu, Z. Yang, and I. Stojmenovic, “Receiver consensus: on-time warning delivery for vehicular ad-hoc networks,” in Proceedings of the 32nd IEEE International Conference on Distributed Computing Systems (ICDCS ’12), pp. 386–395,Macau, China, June 2012. A. Amoroso , G. Marfia , M. Roccetti , Going realistic and optimal: a distributed multi-hop broadcast algorithm for vehicular safety, Comput. Netw. 55 (10) (2011) 2504–2519 . Wireless and Mobility Extensions to the 13s-2 Network Simulator - CMU Monarch Project. http://monarch.cs.cmu.edu/cmu-ns.htm1. C. E. Palazzi, M. Roccetti, and S. Ferretti, “An Intervehicular Communication Architecture for Safety and Entertainment,” Intelligent Transportation Systems, IEEE Transactions on, vol. 11, no. 1, pp. 90-99, 2010. W. Ben Jaballah, M. Conti, M. Mosbah, and C. E. Palazzi, “Fast and Secure Multihop Broadcast Solutions for Intervehicular Communication,” Intelligent Transportation Systems, IEEE Transactions on, vol. 15, no. 1, pp. 433-450, 2014