Radio Modulation techniques For Public Safety
RADIO MODULATION TECHNIQUES FOR PUBLIC SAFETY
General Info
Land Mobile Radio Technology Overview - info from Motorola about trunking, securenet, smartnet, iden, and MPT-1327 - Motorola
Smart Net info - Smart Net
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There are more related websites at the bottom of this file.
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The dates listed below indicate when the radio gear was developed or built.
Note - "APCO Journal" was renamed to "Public Safety Communications Magazine" in ?November 1998.)
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Amplitude Modulation - ?1920s - still used by aircraft and some FDs in the UK - more prone to electrical interference but uses a narrower bandwidth than FM
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Frequency Modulation - ?1940s
FCC licenses for 1999 show 20F3 for UHF channels and 16F3 for VHF 150 Mhz listings (to me this means that the bandwiths are either 16khZ or 20kHz wide for these 2 modulation techniques) - (?95% of all energy is kept within these parameters) - ?also known as direct FM
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Single Side Band - ?1930s
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Carrier Wave - ?1910s ?= Morse Code
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Frequency Shift Keying (FSK) - ?pimarily used for radio teletype - sends two tones out via a carrier wave and shifs between tones to form a digital pattern - ?1930s
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Amplitude Compandered Side Band - ?1970s
never really caught on in the USA
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Spaced Carrier System - UK - ?1960s
This is more a "radio system scheme" than a modulation technique. For countywide coverage with a single radio frequency, public safety forces in the UK placed multiple base stations around the county and vary the Xmit freq by 2.5kHz - base station 1 would be on 100.0025Mhz - base station 2 would be on 100.005Mhz - base station 3 would be on 100.0075Mhz - since the channel spacing was 50kHz or 25KhZ, mobiles would have wide receivers to allow them to receive all three base stations - and since the AM base stations were all on slightly different freqs, there was only minor problems with hetrodynes when a mobile would find itself located halfway between 2 base stations. (The dispatchers would be transmitting on all 3 base stations at the same time)
In 1999, Quasi-Synchronous base stations are used in the UK - anyone know what this is?
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USA cellular - started as AMPS (analog FM) - went to TDMA with a ?4 to 1 improvement per channel - ?now going to CDMA in 1999 in some areas
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GSM = European cellular - 1992 first commercial networks went into operation - as of 1999, has been implemented in many European and Asian countries with cell phones at 800 and 900Mhz - modulation appears to be a mixture of CDMA, TDMA, FDMA, and freq hopping - see www.gsmdata.com
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Time Division Multiple Access - ?1980s (a ?class of various modulation techniques)
TETRA + DIMRS + IDRA
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Code Division Multiple Access - ?1980s
latest incarnation of USA cellular
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Frequency Division Multiple Access - ?1980s (a ?class of various modulation techniques)
APCO25 + TETRAPOL + EDACS
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ASTRO - by Motorola (Astro may be a radio product line more than a specific modulation technique or vocoder technique) - ?1980s - VCELP (voice digitizing) protocol (sounds like soft DES (Digital Encryption Standard) - (can be received on a normal FM receiver) - VCELP stands for Variable Code Excited Linear Prediction - ASTRO is either VCELP or IMBE (APCO25) - VCELP is a proprietary format which is not TDMA nor CDMA
Apparently, VSELP/VCELP/IBME is the voice digitization/compression technique which is combined with the radio wave modulation technique to produce the Astro signal.
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Linear Modulation - ?1996 see articles in ?MRt and ?Radio Resource
Comm Space Corp Advanced Linear Modulation
Nati onal Rural utilities ?Telecomms ?Council 220 Mhz site
June 1999 Mobile Radio Technology Magazine - page
4 - at recent IWCE Conference, Comm Space
demonstrated their new digital carrier, multiple
access (DCMA) radio gear - 8 voice paths can exist
within a 25kHz bandwidth - audio sounded watery per
one person - sounded OK per another person.
Intek
Global had a LM 220Mhz portable transceiver - big and
heavy and expensive
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APCO 25 - per page 32 of March 1999 APCO Journal - FDMA - a family of 2 modulation techniques (C4FM and CQPSK) that utilize a common 6.25kHz bandwidth receiver - C4FM fits within a 12.5kHz channel mask and uses constant envelope modulation (therefore does not require a linear or linearized amplifier) - CQPSK fits within a 6.25kHz channel mask and requires the use of either a linear or linearized amplifier.
APCO 25 - per page 20 of the May 1999 APCO Bulletin/Public Safety Communications Magazine - APCO25 is a form of Quadrature Phase Shift Keying (QPSK) where each successive symbol is shifted in phase from its predecessor by 45 degrees. (C4FM) - in Phase II of APCO25, where the move to 6.25kHz channels take place, both the phase and amplitude will be modulated - this is denoted as Compatible Quadrature Phase Shift Keying. - ?Dade Co FL is moving to Phase II in ?5/99?
As of ?1/99, there is no APCO25 compliant trunked radio gear available. (per 3/99 APCO Journal page 30)
APCO 25 - old style - ????same as Phase 1
www.apcointl.org has info on APCO25 modulation - they have the great article from the March 1999 Public Safety Comms Magazine - look under ?APCO 25 - there is also a APCO 25 mailing list (at www.onelist.com) with a 64K bit bylaws document
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PSK31 QPSK - BPSK data modulation - download at http://aintel.bi.ehu.es/psk31.html - can carry 31 bits per second in a 31 HERTZ wide signal - see article in May 1999 QST Magazine - sounds phenomonal to me! (combined with a powerful voice digitizing scheme, it looks like PSK31 could be a very potent wireless modulation technique)
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NEXTEL - proprietary ?FDMA - in USA
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TETRA - TDMA - European consortium - primary mode uses B/4DQPSK modulation that requires a linear or linearized amplifier and fits four slots within a 25kHz channel mask. Another method is proposed for radio to radio (?direct) comms in the abscence of a master timing signal.
Max recommended power levels for TETRA radios are way lower than APCO25 radios (bases 25W versus 500W / mobiles 10 watts versus 110 watts / portables 1 watt versus 5 watts). Simulcast operation with significant site seperation may not be possible with TETRA/TDMA (this seems to make no sense - if there is significant site seperation then sites will not interfere with each other - right?)
four slot 25kHz channelization - TDMA - per channel bit rate of of 9,000 bits per second - linear/linearized amplifiers are required and there is a fairly high peak/average power ratio.
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DIMRS - Canadian - 6 slot TDMA system using 16QAM modulation that fits within a 25khz channel mask. Motorola is the primary manufacturer under the name IDEN. Please click here for a basic explaination of iden
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IDRA - Japan - 6 slot TDMA system using 16QAM (16 level Quadrature Amplitude Modulation) that fits within a 25kHz mask - the major difference from DIMRS is the use of a different vocoder - ?Motorola is the principal manufacturer
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FHMA - Israel - Frequency Hopping Multiple Access -
apparently different from FDMA and TDMA - frequency
hopping and sectorized base station antennas are used
- Geotek Inc of the USA is the principal manufacturer
(?now bankrupt? - 5/99)
radios are not complex - in operation in a number
of major USA cities
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TETRAPOL - proposed mainly for private systems -
constant envelope FDMA modulation technique that fits
within a 10kHz mask - multi systems in use -
principal manufacturer is Matra of France (March 1999
APCO Journal page 32)
Overall bit rate of 8 kbits/s and can be
channelized to 10kHz channel spacing - see the
TETRAPOL NEWS at www.tetrapol.com - they claim to
have a greater range than TDMA systems
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EDACS Aegis by Ericcson - FDMA - Swedish - constant
envelope modulation technique and has 4 different
selectable levels of deviation and filtering that can
result in a signal fitting within 25kHz and 12.5kHz
channel masks.
overall bit rate of 9.6 kilobits / second
(9,600 bits per second) - can be channelized within
either 25kHz or 12.5 kHz channels
see ???www.ericcson.com
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DAMA mode - digital - used on military satellites
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DCMA - see linear modulation above
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Sites to See
Modulation <
/a>
Speech
Coding Tutorial - 1995 - first section broken as of
6/99
Modulation Info -
look under Signals + Measurements
Modulation Info Shown Via
Graphs
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by Peter Szerlag - May 25, 1999 - June 2, 1999 -
6/17/99 - 9/4/99
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