<
back to Services & Technology list 
Telecommunications
>
CCTV
Digital Map Database
GPS Signals
Electronic In-vehicle Tags
Infrared
Detectors
Internet
Internet Service Provider
Microwave Signals
Network
Radar
Signals
Radio
Signals
Telecommunication
Wireless Technologies
Wireline Technologies
Glossary Links
CCTV
Most
video networks used by the ITS community, and other industries,
are analog networks typically based on Frequency Division Multiplexing
(FDM) transmission techniques. Analog video systems are a mature,
proven technology that yields high quality video at relatively low
cost.
Digital Map Database
A digital
map database is used in conjunction with in-vehicle navigation systems
in the following ways : creates a graphical display of a region;
finds a location by using a street address or intersection; devises
a route for a driver; carries out map-matching—comparing information
from other sources against the map database for route corrections
and confirmation; steers the driver along a route; tells the driver
where his vehicle is on the road network or whether it has left
the network; and supplies information about roadside attractions,
events, facilities and landmarks.
GPS Signals
Global Positioning Systems (GPS) are used to track the
location of GPS receivers (often installed in moving vehicles).
A GPS uses 24 earth-orbiting satellites, guaranteeing that at least
four of them are above the Earth’s horizon at any given moment.
These GPS satellites send out radio signals to GPS receivers, which
in turn measure the amount of time it takes for the signal to travel
from the satellite to the receiver; the receiver can then calculate
its longitudinal and latitudinal coordinates.
Electronic In-vehicle Tags
Automatic
vehicle identification tags can be broken down into distinct tag
types based on 1) the degree to which they can be programmed
and 2) the type of power source.
1) Classified by the degree to which they can be programmed:
-
Type I: The information stored in these tags is fixed (read-only),
and the tags do not have any processing capabilities.
-
Type II: These tags contain an updateable (read/write) area on which
the antenna/reader may encode information such as point of entry,
date/time of passage, etc.
-
Type III: Also called Smart Tags, type III tags are used in conjunction
with an in-lane RF antenna/reader to communicate identifying
information about the vehicle, customer, and account balance
information to the toll system. Some portions of the tag information
are fixed (such as vehicle and customer data) while others are
updateable (such as balance information). The Smart Tag contains
a microprocessor, which maintains account balance information
that is updated each time the smart tag is used. Most ETC systems
currently operate with smart cards, or at least have the capability
to communicate with card-based systems.
2) Classified by power source:
-
Active: Power to the transponder is supplied from either an internal
battery or a connection to the vehicle’s power supply. The transponder
is activated by an interrogation signal from the roadside communication
unit, and it responds to the signal from an internal transmitter.
-
Passive: The transponder does not require any internal or external
power supply; the signal from the antenna is modulated and reflected
to the reader.
-
Semi-Active: These transponders are activated only after a signal
is received from the reader, and they use an internal power
to boost the return signal to the reader.
Infrared
Detectors
1) Active Laser infrared Detectors
Laser detectors
operate on the same principles as microwave radar but transmit energy
at higher frequencies (shorter wavelengths). The detector senses
a portion of the reflected energy in its field of view. The distance
of an object from the detector is found by measuring the two-way
travel time of the infrared pulse, from the detector to the target
and back. Lasers provide presence, speed, volume, occupancy, and
classification information in day and night conditions.
2)
Passive Infrared Detectors
Passive
IR detectors do not transmit energy, but rather they measure energy
emitted by objects in their field view. They detect vehicle presence
by measuring the difference in emitted energy (i.e. temperature)
from the road and vehicles. Passive IRs provide volume, occupancy,
and presence information.
Internet
The
worldwide network of computers communicating via an agreed upon
set of Internet protocol.
-
TCP/IP:
Transmission Control Protocol/Internet Protocol - this protocol
is the foundation of the Internet, an agreed upon set of rules
directing computers on how to exchange information with each
other. Other Internet protocols, such as FTP, Gopher and HTTP
sit on top of TCP/IP.
Internet Service Provider
Intermediary companies
that provides connectivity to the internet dial-up, ISDN, T1, or
other connection. An ISP can be either 1. regional (or local) or
2. national
Microwave Signals
Microwaves
are electromagnetic waves that have a wavelength from 10mm to 300mm
(1 GHz to 30GHz). Microwave detectors fall in two categories: Doppler
or radar devices. . Doppler devices, also known as continuous microwave
devices, output a continuous signal to the detection zone and use
the Doppler principle to analyze the change in frequency of the
reflected signal to calculate the speed of the vehicle. Radar devices,
also known as pulse microwave, measure the time it takes for a portion
of the microwave radiation to be reflected from the target area
to a receiver. Microwave radar vehicle detectors transmit electromagnetic
energy at the speed of light in frequency bands between 2.5 to 24.0
GHz. They are able to count vehicles, measure speed and detect vehicle
presence.
Network
Any connection of two or more computers that enables them to communicate.
Networks may include transmission devices, servers, cables, routers
and satellites.
Radar
Signals
Radar detectors use
radio waves to detect and monitor various objects (i.e.
moving vehicles). Radar detectors can indicate the distance between
itself and another object by emitting a concentrated radio wave;
if there is an object in the path of the radio waves then it will
reflect some of the electromagnetic energy back to the radar device.
Radar devices can in turn calculate how far away an object is based
on the amount of time it takes the radio signal to return. Vehicle counts can be determined by accumulating each vehicle
detected. Radar can also be used to measure the speed of
an object by 1. emitting radio waves in the direction of the moving
object 2. measuring the frequency changes in the radio waves that
are returned back to the radar device.
Radio Signals
A radio wave is an electromagnetic wave propagated by
an antenna. Radio waves have different frequencies, and different
signals can be received by tuning a radio receiver to a specific
frequency. A radio system requires a transmitter and a receiver.
The transmitter encodes a type of message (i.e. a voice) onto a
sine wave and then uses an antenna to transmit it via radio wave
to the receiver. The receiver captures the radio wave using its
antenna and decodes the message from the sine wave.
Telecommunication
1) Any transmission, emission, or reception of signs, signals,
writing, images and sounds or intelligence of any nature by wire,
radio, optical or other electromagnetic systems.
2) Any transmission, emission, or reception
of signs, signals, writings, images, sounds, or information of any
nature by wire, radio, visual, or other electromagnetic systems.
Wireless Technologies
1) Cellular Networks
A cellular network is
created when a city is divided into cells which form a network similar
to that of a hexagonal grid. Each cell in the grid contains a based
station that consists of a tower and a small edifice that contains
the radio equipment. Each cell phone carrier per city has its own
Mobile Telephone Switching Office (MTSO) which controls the base
stations in that region. As a cell-phone user moves to the edge
of his/her cell, that cell’s base station notes the attenuation
of the cell-phone’s signal strength. Meanwhile, the base station
in the cell that the cell-phone user is moving towards detects the
increase in the cell phone’s signal. The two base stations coordinate
with one another through the MTSO, and the cell phone receives a
signal to change frequencies, and thus the cell phone is switched
to the new cell.
2) Wireless Communications
Wireless communications
is a type of network or terminal that uses electromagnetic waves
(including radio frequency, infrared, laser, visible light–and acoustic
energy) rather than wireline conductors for telecommunications.
There are three common technologies used by cell-phone networks
for transmitting information:
-
Time division multiple access (TDMA) uses
a narrow band that is 30 kHz wide and 6.7 milliseconds long
that is split time-wise into three time slots. TDMA is also
used as the access technology for Global System for Mobile communications
(GSM). GSM operates in the 900-MHz and 1800-MHz bands in Europe
and Asia, and in the 1900-MHz (sometimes referred to as 1.9-GHz)
band in the United States.
-
Code division multiple access (CDMA) digitizes
then spreads out data over the entire available bandwidth. Multiple
calls are overlaid on each other on the channel, with each assigned
a unique sequence code. CDMA is a form of spread spectrum, which
means that data is sent in small pieces over a number of the
discrete frequencies available for use at any time in the specified
range.
Wireline Technologies
Wireline implies a network
or terminal that uses metallic wire conductors (and/or optical fibers)
for telecommunications.
1) Fiber Optics: Fiber-optic lines are strands
of thin, optically pure glass that transmit digital input signals
(i.e. voice, data, and video information) over modulated light beams
that pass through the fibers. Basic fiber optic systems consist
of 1. a transmitting device, which generates the light signal 2.
the optical fiber cable, which carries the light and 3. a receiver,
which accepts the light signal transmitted. The fibers’ high bandwidth
and long-distance capabilities allow hub electronics to be centrally
located
2) T1: A T1
1 line is a type of fiber optic cable that can carry 24 digitized
voice channels, or it can carry data at a rate of 1.544 megabits
per second. When the T1 line is being used for telephone conversations,
it is connected to the phone system; if it is being used to carry
data then it is connected to the network's router. The other end
of the T1 line is connected to an Internet Service Provider (ISP).
Glossary
Links:
FCC
Telecommunications Glossary
American
National Standard for Telecommunications: Glossary
Internet
Glossary
Author: Lauren Smith
Last
Update: 01/09/02
|
