Reliability is an important issue for safety-critical and traffic situation broadcast services in Vehicular Ad-hoc Networks (VANETs). The Packet Reception Rate (PRR) is a key metric to evaluate broadcast reliability. Most researches of broadcasting in VANETs focus on multi-hop routing and connection establishing, taking all one-hop links for granted. A few have focused on the reliability of one-hop in 1-D VANETs. In this paper, we evaluate the PRR for one-hop broadcast in 2-D VANETs at an

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... ection analytically and by simulation. Expressions of the PRR are derived with consideration of the hidden terminal problem and collisions caused by concurrent transmissions. The impact of transmission, carrier sensing and interference ranges; the distances of receivers to the senders and the density of nodes on the roads are investigated and discussed. At last, some important observations to the broadcast at an intersection in VANETs are provided. 87 messages and traffic information. This is used especially to deliver potential safety applications including collision avoidance warning, lane-changing warning, intersection coordination, traffic accident broadcasting, etc. They usually demand a direct one-hop broadcast due to the highly dynamic topology of vehicular networks. Securing the reliable delivery of messages to all surrounding vehicles in a timely manner in the VANETs is very important. Most investigations into broadcasting in VANETs have focusd on multi-hop connectivity, taking all one-hop links for granted. Yet, the apparent reliability of one-hop broadcast is unwarranted because of the many hurdles in VANETs such as the hidden terminal problem, the collisions caused by concurrent transmissions, and the high node mobility. As mentioned in paper [1], reliability is defined as the network's ability to ensure that all intended mobile vehicle nodes receive the broadcast messages within a specified timetable. The authors introduced four reliability metrics in this paper [1] that characterize the behaviors of the one-hop real-time broadcast services in 1-D VANETs. However, calculating reliability in a 2-D scenario in the broadcast ad-hoc networks is still an open problem [1] [2] [3] . None of the research has focused on the reliability of broadcasting in 2-D VANETs at an intersection. In this paper, we try to evaluate one of the reliability metrics-the Packets Reception Rate (PRR) of a one-hop broadcast in 2-D VANETs at an intersection by analysis and by simulation. We extend the 1-D model in [1] to a 2-D model: Two vertical roads with the tagged node broadcasting at the intersection he scenario is shown in Figure 1 . A closed-form expression of PRR is derived. The impact of transmission, carrier sensing, and interference ranges; the distances of receivers to the senders and the density of nodes on the roads are investigated and discussed. The tagged node The receiver Note: Figure 1. A real scenario of a tagged vehicle node broadcasting at an intersection The rest of this paper is organized as follows: Section 2 briefly describes any related work. Section 3 presents an analytical model for developing the closed form PRR expression in the 2-D VANETs at an intersection. Section 4 demonstrates and discusses numerical results obtained from the analytic model and simulation, followed by the conclusion in section 5. Related Work Most broadcast protocols used in VANETs are In order to improve the reliability of broadcasting in VANETs, existing techniques usually rely on handshaking (RTS/CTS), acknowledgement, rebroadcast, etc. The mechanisms, which rely upon existing broadcast techniques, are summarized in [1][4] as follows:  Acknowledgement: the source node collects acknowledgements from the receivers;  Continuous push: the source node repeatedly transmits the data until complete coverage is deduced; and  Continuous pull: receivers keep requesting data from the source node until all of the data is received. In fact, most of the investigations have focused on reducing message flooding, reducing the total number of traveling hops for multi-hop relays based on inter-node distance and node mobility direction, increasing connectivity, etc. for broadcast in VANETs [5] . Paper [6] proposed a vehicle-density-based emergency broadcast (VDEB) scheme to solve the problem of high overhead in VANETs. Paper [7] presented an efficient road-based directional broadcast protocol (ERD) to 102 Yujun Kuang, IEEE and IEICE member, is a full-time Professor at the