26-02-2013, 09:25 AM
VEHICLE TO VEHICLE COMMUNICATION :FAIR TRANSMIT POWER CONTROL FOR SAFETY CRITICAL INFORMATION
VEHICLE TO VEHICLE.docx (Size: 303.07 KB / Downloads: 39)
INTRODUCTION
Direct vehicle-to-vehicle communication based on radio technologies represents a key component for improving safety on the road. Various public and private organizations worldwide are funding national and international initiatives that are devoted to vehicular networks, such as the Internet ITS Consortium [1] in Japan, the Vehicle Infrastructure Integration (VII) Initiative [2] in the U.S., the Car2Car Communication Consortium (C2CCC) [3] in Europe, and the Network on Wheels (NoW) Project [4] in Germany. Currently, the IEEE 802.11p Working Group [5] is developing a standard that is based on carrier-sense multiple access (CSMA) and tailored to vehicular environments. The effort is assisted by initiatives from various parts of the globe. Direct radio-based vehicle-to-vehicle communication can provide a fundamental support to improve active safety, i.e., accident prevention, by making information available beyond the driver’s (or other car sensor’s, e.g., radar) knowledge with almost minimal latency. Active safety is composed of sensing and communication activities. This paper concerned with active-safety-related communications.
PERIODIC AND EVENT-DRIVEN MESSAGES
Safety applications can be enabled by two types of messages:
1) Periodic messages
2) Event driven messages.
Periodic status messages are intended to exchange state information from the sending vehicle, i.e., position, direction, speed, etc., and, possibly, aggregated information of the surroundings. Through this beaconing activity, safety applications acquire an accurate knowledge of the surroundings and can therefore detect potentially dangerous situations for the driver.
The key challenge related to this beaconing activity is to control the channel load to avoid channel congestion. Previous studies envisioned that several messages per second from each vehicle will be needed to provide the required accuracy for safety applications. Furthermore, additional transmission repetitions could be considered to overcome the effects of packet losses due to collisions and fading. Finally, according to recent studies safety-related messages will be relatively large, i.e., between 250 and 800 bytes.
The reception rates of periodic broadcast messages for different configurations of transmission power and packet generation rate indicates that, increasing the generation rate of beacon messages decreases the probability of successful reception of each of them. And also increasing the transmission power extended the communication range to farther distances, it could also lead to a congested wireless medium where reception rates for vehicles close to the sending vehicle decreased due to packet collisions. So the packet generation rate should be fixed at the minimum required by safety applications and to adjust the transmission
DISSEMINATION OF EMERGENCY INFORMATION
The second main goal is the dissemination of event-driven emergency information within a geographical area. To deliver a message that contains information about an existing threat, an effective strategy that offers short delay is required. It is assume that a vehicle that detects a hazard issues an event-driven emergency message to warn the drivers that approach the danger. The originating node, according to the corresponding safety application, specifies the relevant area for dissemination of the alert (dissemination area). The alert must be distributed in the complete area, i.e., up to the border of the dissemination area (Fig. 4.1), possibly via multihop transmissions, with high reliability and short delay.
EMDV Performance
Performance of the EMDV protocol, when operating with D-FPAV Off and in synergy with the D-FPAV protocol is done here. Fig. 5.4 presents the probability that the emergency information is successfully received by vehicles located inside the dissemination area when max messages = 1. With D-FPAV off, it is observed that the reception rate of 90.9% averaged over the dissemination area. The use of the D-FPAV protocol increases the emergency information reception rates up to an average of 99.9%. The result shows the dependency of the success of the dissemination strategy on the channel load conditions.