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URL:
http://www.tetramou.com
http://www.etsi.org
http://www.project25.org
http://www.apcointl.org
Trunking refers to the automatic and dynamic sharing
of a small number of radio channels among a large number of radio users.
Trunked Mobile Radio promises greater airtime efficiency, ease of use and
higher availability, compared to other technologies. A TMR system efficiently
distributes message traffic among available channels and reduces queuing time.
Large organizations, such as local governments (or utilities) that need to
establish their own dedicated radio network typically select a trunked radio
scheme. TMR systems offer privacy, wide-area dispatch, economical
infrastructure, and more efficient use of radio spectrum. TMR is primarily
talk-group based and enables access to multiple facilities by multiple users.
TMR services take place in a one-to-many or one-to-one application.
The majority of trunked radio systems are
proprietary. However, the TErrestrial Trunked Radio system (TETRA) is an open
digital trunked radio standard defined by the European Telecommunications
Standardization Institute (ETSI). The TETRA Memorandum of Understanding (MoU)
was established in December 1994 to create a forum for discussion, promotion and development of the standard.
The Association of Public Safety Communications
Officials (APCO) Project25 developed the 102 series of technical specifications
for digital, land mobile radio communications systems. The process was led by a
users' Steering Committee, and the standardization work was done by the
Telecommunications Industry Association. The result is a suite of ANSI/EIA/TIA
standards, TIA/EIA Interim Standards, and TIA Telecommunications System
Bulletins. Although Project25 originally was an initiative of public safety,
the resultant documents are usable in any application for digital, land mobile
applications. Projrct25 work includes key attributes: (i) backward
compatibility with existing systems, (ii) scalable trunked and conventional
capabilities from single channel to regional trunking, (iii) spectral efficiently
from 12.5 kHz to 6.25 kHZ, and (iv) interoperability between neighboring
systems.
Main Features of Technology
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Technology
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Radio
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Frequency
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800 MHz
range
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Bandwidth
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25KHz/12.5KHz
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Operation
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Can be
configured as single site, voted or simulcast system. all channels are shared
and automatically switched.
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Capacity
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Better
utilization of frequencies or channels, hence more capacity, by allowing
users to share all available channels for voice and data, i.e. trunking
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Coverage
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Coverage
can be extended through use of repeaters, voting receivers and simulcast
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Data rate
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2.2Kbps
throughput low due to call setup delay and small bandwidth
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No of
Channels
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Multiple
frequencies or channels, typically 10-20 channels per system
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Modulation
method
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FSK, PSK
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Power
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Repeater
station 50-100W, control station 10-40W, mobile 10-30W
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Regulatory
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Frequency
licensing required
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Key Advantages
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Capacity
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Better
utilization of frequencies by users sharing all channels
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Coverage
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Can extend
coverage by using repeaters
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Interference
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Licensed
frequencies protect mobile units against outside interference
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Reliability/Availability
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Reliability
is better because network is more fault-tolerant. Availability is definitely
better than mobile radio because more channels are available and different
configurations can be used to improve system performance.
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Cost
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Relatively
high due to more sophisticated trunking equipment
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Key Disadvantages
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Data rate
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2.2kbps
but low throughput
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Regulatory
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Trunking
frequencies require licensing and the process is time consuming
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Keywords:
wireless, mobile, radio, physical layer
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