Vehicular Sensor Networks: General Aspects and Implementation Issues - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 215

generation rate and size are crucial for device performance. Other characteristics of
the suggested fan less box computer include Large Central processing memory (up to
4 Gb), connectivity (10/100BaseT LAN, RS232/485, USB), Peripherals (Keyboard/
mouse, video VGA/LCD, parallel interface, IDE interface, audio/video interface),
incorporated radio transceiver board, GPS possibility, fast multi channel A/D inter-
face, FLASH type of internal and external memory, etc.
The radio transceivers contain all necessary circuitry to send and receive data
over the wireless media: modulator and demodulator modules, digital to analog and
analog to digital converters, low noise and power amplifiers, filters, mixers and
antenna are among the most important components. Radio transceivers usually
work half-duplex as simultaneous transmission and reception of data over the wire-
less media are impractical. Transceivers can operate in different modes (usually
transmit, receive, idle, and sleep operational modes). The sleep mode is a very
important energy-saving feature in WSNs. Some transceivers offer additional capa-
bilities, including several sleep modes that turn different parts of the hardware on
and off. Commercially available transceivers for WSNs have different characteris-
tics and capabilities. Normally, they work on three different frequency ranges: 400
MHz, 800-900 MHz, and 2.4 GHz.
Vehicle sensor devices are usually powered by vehicle starter battery externally
attached to the node. Therefore, power saving is important but is not crucial when
sensors are deployed in the vehicles. If sensors are deployed as roadside sensors,
network lifetime depends on how wisely batteries are used. Using the microcon-
troller and transceiver sleeping modes is crucial for long operation of the WSN
working outdoor.
Finally, vehicle sensors devices are equipped with sensor boards, which contain
application-specific sensors. The variety of sensors and sensor boards that can be
directly interfaced with the wireless sensor device is very large. Temperature, air
quality, pressure, magnetometers, light, acoustic, and accelerometers are just a
small sample of the types of commercially available sensors. This interfacing flex-
ibility is the cause of the wide popularity of WSNs as they serve as a general plat-
form to solve practical problems in VSNs and in many other application domains.
Having discussed the general VSN node architecture, the following subsection
will classify and elaborate on the actual sensor equipment being used in VSNs.

10.5.2 Sensor Equipment

Sensors have a key role in the VSN system structure. They should be accurate, reli-
able, and provide fast response. Depending on the location where they are deployed,
VSN used sensors can be broadly divided into roadside sensors and intra-vehicle
ones. Roadside sensors comprise different types, such as magnetic sensors,
microwave radars, infrared, weather sensors, smog detectors, video detection, and
others. They are used to provide information about the speed, direction, quantity of
vehicles per unit time etc. As for the intra-vehicle sensors, there are distance sensors,