Information Technology Reference
In-Depth Information
vehicular ad-hoc network (VANET), has been quickly developed to deliver
vehicular traffic information. VANET is a form of a mobile ad hoc network.
It supports two types of communication modes: vehicle-to-roadside (V2R)
communication and vehicle-to-vehicle (V2V) communication [4]. A variety of
wireless technologies are expected to implement VANET. Over the fast few
years, a new VANET technology, Dedicated Short Range Communications
(DSRC), has been rapidly developed in Europe, the United States, and Japan
[15]. Currently, the DSRC is developed based on IEEE 802.11a and 802.11p pro-
tocols [3,4]. The transmission range of DSRC is about 1000 meters (a little lon-
ger than a half mile), and the data rate of DSRC ranges from 6 to 27 Mbps.
14.1.1 Basic Concept of real-Time Vehicle Navigation
Real-time vehicle navigation systems are designed to find the quickest path
for guided vehicles, instead of the shortest path. This can be explained with
reference to Figure 14.1. Figure 14.1 is a snapshot of a road graph, where edges
represent roads and nodes represent road junctions. The pair of numbers on
each edge represents the travel time and distance of the corresponding road,
respectively. For example, it takes eight units of time for a vehicle to traverse
from J4 to J6, and the distance from J4 to J6 is three units of length. Due to the
changing traffic conditions on all roads, the shortest path is usually not the
quickest path. For example, in Figure 14.1, the shortest path from the source
node to the destination node is source → J4 → destination. The length of the
shortest path is 7 + 4 = 11 units of length, and the travel time is 14 + 4 = 18
units of time. Another path that is quick: source → J3 → J5 → J6 → destina-
tion. Although the length of the quickest path is 3 + 2 + 5 + 5 = 15 units of
length, and the travel time is 2 + 1 + 3 + 9 = 15 units of time. By taking the
quickest path, the driving time can be reduced from 18 to 15 units of time,
and the traffic congestion can be alleviated.
J1
(3,3)
J2
Destination
(4,4)
Source
(14,7)
J4
J3
J6
J5
Figure 14.1
The quickest path versus shortest path.
