Vehicular Sensor Networks: General Aspects and Implementation Issues - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 207

consequently, loss of signal in the communication between fast vehicles.
Furthermore, the WMN topology comprises shorter distances among network par-
ticipants allowing for higher quality of the received signal. This makes the links
more reliable without increasing transmitter power in individual nodes. Therefore,
the mesh networking leads to increased network range, network redundancy, and
improvement of the general network reliability, especially under increasing traffic
density situations. Additional advantages of the WMN topology are in its self-
configuration and self-healing capabilities. A WMN network does not need a sys-
tem administrator or a manual configuration, so adding new nodes is simple. The
network discovers the new node and automatically incorporates it into the existing
system. Also, the control of the wireless system is distributed throughout the net-
work, which allows properly equipped vehicles to communicate directly with other
points of the network without being routed through a central control point.
The unique combination of multi-hop communication, WMN topology, and
distributed control is the key for a whole new dimension of sensor communication.
It is being completely exploited in VSNs.

10.3.2 Mobility in VSNs

VSNs are characterized by high mobility of nodes making the mobility issues an
important aspect that should be carefully scrutinized when evaluating any VSN
protocol. The VSNs' mobility models should involve road maps with all the con-
straints related to the vehicular environment in order to get accurate and realistic
results. This section reviews the models that were proposed in the general MANET
context, but are usable in VANETs and VSNs as well. More comprehensive study
of the topic can be found in [ 16 ].
Different mobility models for VSNs differ in many parameters. Some of them
use traffic control mechanisms at intersections, whereas others assume continuous
movements at these points. Some protocols assume roads to be single lanes, while
others support multilane roads. Additionally, some protocols define security dis-
tance , i.e., the minimal distance between vehicles that guarantees safety. This
subsection briefly describes the characteristics of some of the most relevant mobil-
ity models applicable for VSNs.
Freeway is a map-based model where the simulation area represented by a gen-
erated map includes many freeways and many lanes in each freeway (there are no
urban roads and intersections) [ 17 ]. The nodes, which are randomly placed on the
lanes, move using history-based speeds following random acceleration. The dis-
tance that should be maintained between two subsequent vehicles in a lane is also
defined. The model is unrealistic since the vehicles are not allowed to change the
lanes and are forced to move on lanes until reaching the simulation area limit.
Manhattan is also generated-map-based model (containing vertical and
horizontal roads with two lanes for moving in each direction) to simulate an
urban environment. The vehicles are randomly deployed in the area and are