JID:VEHCOM AID:34 /FLA [m5G; v1.159; Prn:11/09/2015; 12:14] P.1(1-15) Vehicular Communications ••• (••••) •••–••• Contents lists available at ScienceDirect Vehicular Communications www.elsevier.com/locate/vehcom 1 67 2 68 3 69 4 70 5 71 6 72 7 73 8 74 9 75 10 76 11 77 12 78 13 79 14 80 15 81 16 82 17 83 18 84 19 85 20 86 21 87 22 88 23 89 24 90 25 91 26 92 27 93 28 94 29 95 30 96 31 97 32 98 33 99 34 100 35 101 36 102 37 103 38 104 39 105 40 106 41 107 42 108 43 109 44 110 45 111 46 112 47 113 48 114 49 115 50 116 51 117 52 118 53 119 54 120 55 121 56 122 57 123 58 124 59 125 60 126 61 127 62 128 63 129 64 130 65 131 66 132 Dynamic spatial partition density-based emergency message dissemination in VANETs Mehdi Sharifi Rayeni ∗ , Abdelhakim Hafid 1 , Pratap Kumar Sahu 1 University of Montreal, Montreal, Canada a r t i c l e i n f o a b s t r a c t Article history: Received 15 November 2014 Received in revised form 6 June 2015 Accepted 21 July 2015 Available online xxxx Keywords: Broadcasting Exponential distribution Intelligent transportation systems Partitioning algorithms Vehicle safety Location and density based emergency message broadcasting has attracted researchers attention in vehicular ad-hoc networks. However, most of current approaches do not provide good performance, in terms of delay in both light and dense traffic scenarios. Reliability in message delivery is another significant performance metric, especially in dense traffic scenarios. In this paper, we have analyzed and implemented a reliable time-efficient and multi-hop broadcasting scheme, called Dynamic Partitioning Scheme (DPS), which works well in both dense and light traffic scenarios. Our solid analytical evaluation and simulation results indicate that our proposed scheme outperforms five efficient broadcasting protocols in VANETs in terms of delay and reliability in emergency message broadcasting. © 2015 Elsevier Inc. All rights reserved. 1. Introduction Transportation safety is an important goal of Intelligent Trans- portation Systems (ITS). In future ITS environments, vehicles will be able to send and receive information about traffic conditions, collisions and road safety situations; this will let them be aware of emergency situations and have a wider knowledge of traffic condi- tions. Vehicular Ad-hoc Networks (VANETs) allow vehicle-to-vehicle and vehicle-to-roadside communications and are a special class of Mobile Ad-hoc Networks (MANETs). The main features of VANETs include high speed of vehicles, dynamic autonomous topology patterns and restricted node moving directions. DSRC (Dedi- cated Short Range Communication) technology, which operates on 5.9 GHz, enables vehicle ad hoc communications and has led to IEEE 802.11p and IEEE 1609.x [1,29,30]. Data exchanged in VANETs may be categorized into (i) safety- related data: it includes routine beacon messages and emergency warning messages (e.g., accident warning); and (ii) non-safety data: it involves a vast area of multimedia and infotainment communi- cations, such as hotel advertisements on the road and parking lot information. Beacon messages include information about location, velocity, acceleration and direction that each vehicle broadcasts pe- * Corresponding author. Tel.: +1 514 476 7259; fax: +1 514 343 5834. E-mail addresses: sharifim@iro.umontreal.ca (M.S. Rayeni), ahafid@iro.umontreal.ca (A. Hafid), sahupk@iro.umontreal.ca (P.K. Sahu). 1 A. Hafid and P.K. Sahu are with the Department of Computer Science and Oper- ation Research. riodically to update other vehicles about its state. Emergency mes- sages are broadcasted by a source vehicle when an emergency situ- ation occurs (e.g., hard brake and vehicle crash) to alert other vehi- cles about the event. The task of broadcasting emergency messages in VANETs is a high priority and time-critical procedure which needs to be addressed in future deployments of DSRC [2,31]. There are two key requirements for broadcasting emergency messages in VANETs (i) short delay dissemination of emergency messages; and (ii) high reliability in terms of high delivery ratio of emergency messages [3]. Packet collisions reduce reliability; hidden terminal problem is the main cause of packet collisions in VANETs. Two nodes are called hidden when each is out of range of the other and a third node is in range of both; thus, if the two nodes communi- cate simultaneously with the third node, packet collisions happen. In case of unicast communications, RTS/CTS messages may be used to avoid hidden nodes from colliding; however, this strategy is not suitable in broadcasting [4]. Instead, some researchers [13,14] have used RTB/CTB to provide reliability in broadcasting. In this paper, we assume that every vehicle is equipped with an OBU wireless transceiver/receiver and has a GPS receiver that updates vehicle’s location on the road. Since vehicle transmission range is limited, single-hop communication cannot satisfy emer- gency requirements; therefore, we focus on multi-hop dissemi- nation of safety warning messages considering local density of vehicles which follow the broadcasting vehicle. Messages are dis- seminated over a region, called Region of Interest (RoI), that covers a certain distance (e.g., 5 km) starting from the source. Generally, RoI depends on the road topology and the application; for instance, http://dx.doi.org/10.1016/j.vehcom.2015.07.002 2214-2096/© 2015 Elsevier Inc. All rights reserved.