IIR Conference June 1999
Maximising your Analogue PMR/PAMR Network to Deliver
Simultaneous Voice and Data Applications. Brian Seedle T.S.M.G
Abstract
First published in 1988, for the U.K markets, MPT1327 rapidly became a defacto global standard for analogue trunked PMR systems. MPT still remains the most widely supported trunking protocol in the world. This paper provides an overview of the development of this now mature technology, and its current position in the world.
Introduction
The trunking concept is not new. It was first developed in the 1970’s to improve spectrum efficiency. When channels are scarce and traffic is high, operators need to maximise the use of the spectrum while maintaining the grade of service. The modern radio trunk technology addresses the spectrum issue and at the same time provides a platform for a wide range of facilities for users. (Spectrum efficiency is of advantage only to the regulator and the network operator who needs spectrum to offer services to the end user). These facilities accommodate an extensive menu of speech and data call types, which can be connected over a wider geographical coverage area than most conventional PMR mobile radio systems.
The MPT1327 specifications actually comprise four documents – MPT1327 defines the message and modulation format: MPT1343 is an access interface document for terminals: MPT1347 is an access interface for base stations: MPT1352 is a test document for terminals.
The MPT specifications were not designed as an international standard. They were developed for the U.K market to make efficient use of a block of spectrum released from the closure of VHF television transmissions. The British Ministry of Posts and Telecommunications (now the U.K Radio Agency) sponsored the drafting of the MPT Standards through the formation of the MPT1327 Drafting Group. This group was represented by manufacturers, and other professional bodies representing particular interests, including transport, fuel and power, and later, Network Operators. Because MPT1327 is an open standard, equipment from different manufacturers can operate seamlessly – both terminals and infrastructure.
The Standard was first published in 1988, although a compliant system was
in place on the British Telecom tower as early as 1986, operating under the
name ‘Baselink’. At this time other systems using a very similar
protocol were installed on British Rail. These early networks imparted confidence
that the MPT protocol would work.
The MPT Standards were revised in 1991 and saw a moderate expansion in 1996
where some features were added. It is a tribute to the original drafting group
however that a radio terminal conforming to the 1988 Standard would remain
compliant today.
Electronic copies of the Standards are available on the Internet from several sources including www.open.gov.uk/radiocom/rahome.
The fact that this was a truly open standard was a catalyst for its rapid growth. A variety of manufacturers’ equipment became available for both network infrastructure and terminals. This competition stimulated quality, functionality and most importantly, price. As early as 1990, MPT systems had been commissioned as far as Australia and Siberia. By 1993, regional and national systems were in place in Europe, including Germany, France, Netherlands, Italy and Spain. In the global arena, regional networks were installed in most continents. Today, over 84 countries are known to have installed MPT systems. At least 16 independent manufacturers offer MPT infrastructure and 18 companies manufacture MPT terminals.
Evolution of new technologies
Quotes from Telecommunications analysis’s papers taken from previous conferences.
(1992) The global market for GSM will reach 15 million by the year 2000
WRONG – There are now 170 million phones sold (June 1999).
(1989) The UK market for MPT will reach 350,000 by 1992
WRONG – The correct number was ~ 35,000
(1989) Data is expected to form 30% of the activity on PMR and PAMR networks
by 1992
STILL waiting
Which Technology Wins!
The last twenty years have seen an incredible explosion in personal communications systems. Often, by the time a new technology has reached the marketplace, the market assumed in the original business plan has dramatically changed. The expansion of cellular industry continues to exceed all predictions and terminal units are truly in mass production, driving down prices. In today’s radio communications markets, other technologies are measured against cellular products. Unless a competing technology can offer a clear technological or price advantage to the user, that technology will struggle to succeed. There are many enterprises involved in the supply chain from the manufacturer, the network operator, the service provider, the dealer and the end user. If any one of these entities cannot make a profit, the whole will not survive. This was the fate of Telepoint despite an investment of more than $120 million. Telepoint attempted to develop its network at a time when cellular prices were falling. By the time the product has reached the marketplace, it could not compete against cellular.
It is not always the better technology who wins. Many other factors define if a particular solution will succeed. One valid criticism of MPT is that it was very badly marketed. A parallel can be drawn with the VHS/Betamax video standards. Betamax was the technically superior system, but marketing and licencing issues sunk Betamax without trace. TETRA has done a much better marketing job, at least as far as our industry and potential large corporate users are concerned.
The only issues visible to the end-users are reliability,
speech quality, price, battery life, style.
In evaluating the needs of users, the industry must heed that mobile communications is not the primary concern of land mobile users. Rather it is just another tool to help them efficiently and effectively run their business. Equipment must be easy to use at affordable prices. Users do not care about the technology. The only issues visible to users are reliability, speech quality, price and battery life. MPT trunking is now an established and mature technology. Manufacturers in this market recovered their development costs at a time when competition was not so severe. The cost of MPT infrastructure and terminals can now meet the most stringent financial targets. The capital cost for complete MPT base station site (controller, R.F base station, combining, antenna) currently stands at less than $100 per user. Portable terminals are around $400. Small private organisations needing radio communications and only a small chequebook still find MPT attractive. Until the digital technology finds the economy of scale to reduce prices, MPT will continue to find new markets. Of course if any new technology is highly complex, potential manufacturers may not be prepared to fund the enormous development costs. If this restricts the number of global players, competition may be stifled, and prices remain high. This ‘chicken and egg’ situation where low prices require mass markets, but mass markets require low prices must be broken by reaching a critical mass.
One sure way to lower terminal prices and at the same time improve battery
life is by custom silicon. Dedicated chips are now in production for Tetrapol.
TETRA requires this custom silicon to move quickly to second generation products.
Progress of MPT 1327
When the MPT Standards were first published, manufacturers were under pressure to roll out their networks. The first generation MPT networks offered simple half duplex speech calls, single site or wide area: single site group calls: limited PSTN/PABX: and status messaging. Further development followed and by 1992 most networks and terminals offered a wide range of features including –
Call Types
Individual Speech Calls to
Mobile subscribers
Line connected services – PABX/PSTN
Call priorities, normal high, emergency
Group Calls
Single Site
Wide Area Multi-site
Call Diversion
Call Transfer
Include Call
Voice Mail
Full Duplex Calls
Pre-emptive emergency calls
Late Entry Groups
SST’’s and MST’s
Channel Segregation
A number of variants of MPT have been employed in Europe. These differences are small and may be accommodated by configuration of equipment during installation.
Number Schemes and variants to MPT1327/43
MPT1343 (Mandatory in UK BandIII frequency band)
ANN
TRAXYS (Holland)
REGIONET43 (Germany)
PA2424 (France)
CPS, CPSX, CPSXG (China)
In areas of the world where cellular is well-established and good telecom’ links are in place, it is now far more difficult to attract new trunking business. Recently, there has been a move by manufacturers to provide features that will differentiate trunking from cellular. Manufacturers have redirected their marketing, and now tend to target security and emergency services, docks and harbours, transport, and long distance remote routes. The features where trunking can have a strong advantage over cellular are –
Instantaneous call set-up
The fastest call set-up speed for MPT is actually just over 200mS for groups
and just over 400mS for single prefix speech calls.
Prioritising of calls
Priority and Pre-emptive emergency access is essential in security and emergency
environments.
Sharing of channel resource with other systems
A traffic channel can be shared with a conventional channel. (for example such
a channel may already be in use for a community base station). The system can
be programmed to statistically favour either the trunking or conventional use
of the channel. As users migrate, the odds can be adjusted to or from conventional
use.
Site backup power
For Emergency services, 48-hour backup is often essential
Pooled Channels
Pool Channels have identical frequencies on two or more sites where the coverage
pattern overlaps. The network may be configured to either a) only use the channel
at one of the sites at any one time or b) always attempt to use the common
channel frequency for calls between the sites. Messages generated when the
PTT is pressed by the user switches off the remote site transmitter.
Groups and wide area groups
Wide area groups encompass a specified number of sites. Wide area groups allocate
a traffic channel on more than one site. (This not spectrum efficient). The
Network keeps a map in its database of the sites to be allocated.
Open Channel Working
This is barred in the UK BandIII Networks. The feature
is specified in Regionet43 in Germany. In some areas of the world it is essential.
This is s terminal
feature.
Dispatcher operation
Line connected dispatchers were designed into the first generation MPT networks.
By far the most popular today is radio-connected dispatcher.
Virtual User Groups
Virtual user groups are groups of terminals that have exclusive use of a
number of traffic channels. Independent Network Operators may share a single
control
channel.
Local PSTN
A PSTN interface at a site (or group of sites) is a very important feature
in countries where fixed telecommunications is sparse or unreliable. The
Network uses some criteria such as number of dialled digits to determine
if the call
will be routed to the local connection or the central call router.
Selectable Individual Groups
The user can enter a group identity into the terminal to define a new group
to which that terminal will belong.
Dynamic Regrouping
The Network has the ability to transmit a new group definition to a radio
terminal
Remote Stun/Unstun
The Network has the ability to disable a radio terminal remotely.
Adapting MPT to foreign practices
In areas of the world where there is an established trunked industry, MPT may be alien to normal working practices. Such is the case of LTR trunking in America. LTR uses predominantly groups. The implementation of MPT wide area groups and ‘late entry’ enable the MPT to mimic the LTR operationally.
In areas of the world where the fixed telecommunications structure is very limited or non-existent, MPT1327 systems have been a great success. Examples include oil pipelines, rail routes and road transport routes. Many of the roadside telephones in remote areas in the Far East are in fact modified MPT terminals.
Linear Modulation
The MPT 1327 standard defines the modulation as F.M in 12.5KHz channel spacing. There are also a number of F.M 25KHz networks around the world. Although F.M is simple to modulate/demodulate it does suffer disadvantages.
(i) F.M is not spectrally efficient.
(ii) Data performance is poor; the constant envelope modulation has a maximum
capacity of ~ 5kb/s in 12.5kHz bandwidth maximum
Linear modulation (L.M) is a technique that allows the transmission of information over a radio path using narrow band channels. Most commercial systems in use today employ 5KHz or 6.25KHz channel spacing. L.M has been around for some time. It is only recently however that commercial equipment has been possible since the technique requires DSP (Digital Signal Processor) chips. A system using L.M in a 5LHz channel has –
(i) Speech quality equivalent to 25KHz F.M
(ii) Data capability in a moving vehicle at a rate of 16.8Kb/sec (14.4K after
trellis coding)
The L.M terminal is completely soft – that is the modulation is produced by the DSP applying a particular mathematical algorithm to a linear modulation block (I,Q modulator). By changing the algorithm, it is possible to change the modulation to A.M, F.M, QPSK, QAM etc. It is therefore possible to manufacture a multi-standard terminal that will function on F.M MPT networks and Narrow-Band Networks.
O.K. So where are these Narrow Band L.M Systems?
Most L.M MPT1327 networks are installed in America. The F.C.C allocated spectrum specifically for narrow-band technology and invited licence applications. Currently there are about 300 sites of equipment in commercial use in America. E.T.S.I has recently produced EN301 166 to cover Narrow-Band in Europe.
Data developments in MPT1327
There is a wide difference in the take-up of data around the world. In some countries such as South Africa, the data transactions account for 60% of the control channel loading. This is a mix of dispatcher forwarding of jobs and GPS data for vehicle tracking
Taken as a whole, the type of data user that was expected has not materialised. What is most popular is the forwarding of small data items from units that collect information remotely. The most widely used application is GPS vehicle location. It is possible to procure the MPT radio, GPS receiver and antenna for $500.
What has not significantly materialised is long data. Maybe this situation will change through new recent interest in EMAIL and the Internet.
The MPT1327 standard only prescribes how the data messages are formatted at the air interface. There was not corresponding access interface protocol. In 1994 however an access interface document was produced called MAP27. This enabled data applications to interface with compliant radio terminals independent of radio manufacturer.
Migrating Users to MPT1327
There are still hundreds of thousands of users in Europe who use conventional PMR dispatcher radio systems and Community Base Stations. There is a benefit if existing channel resources can be shared during the transition from conventional to trunking. At least one MPT manufacturer has a facility whereby a traffic channel can be shared with a conventional channel. The system can be programmed to statistically favour either the trunking or conventional use of the channel. As users migrate the odds can be adjusted away from conventional use.
Providing Bridges to MPT1327
It is very desirable if an MPT network can bridge to other systems. Bridges and interfaces are known for the following –
Smartnet Trunking
DID Exchanges
Internet EMAIL server
X25
Migrating users from Analogue to Digital Trunking
Tactic #1
Persuade the analogue users that the new features, speech quality, coverage,
battery life are irresistible - EVERYONE WANTS ONE
In order to attract users to change quickly, the advantages must be overwhelming. As an analogy consider the migration from vinyl records to CD’s. There was a clear advantage in CD’s of superior music quality and smaller size, but players were initially expensive and required mass production to achieve economy of scale. (The music program makers also took the opportunity of raising the price, an issue that has never been redressed). This migration took over 15 years.
Tactic #2
Switch of the analogue network – NO CHOICE
This is more difficult if the owner of the digital network is not the owner of the analogue network. It was used in the past when the old U.K 405 line transmitters were switched off. The cellular operators will have this problem at some time in the future when they attempt to de-commission the TACS Networks.
Tactic #3
Swap out the terminal from analogue to digital at a subsidised price or free.
(The cellular networks have already had a few attempts, offering free upgrades
with limited success. Also note that the tactic to accelerate the take-up
of digital terrestrial television decoders is to give the decoders away)
Migrating users from traditional PMR to digital trunking
Although conventional PMR has not seen the extraordinary growth of GSM, it has maintained its users. The failure of public trunked networks and cellular to remove traditional PMR from the scene indicates that its combination of low costs, good local control and operational simplicity is still in demand. It will be a challenge for the digital trunked networks to convince traditional PMR users to migrate.
Conclusion
In evaluating the future for MPT1327, the public and private networks must be considered separately. The operation of any public Network is fundamentally different to a private system. In a public network, priority or emergency access is difficult or impossible since relevant users will demand performance that statistically cannot be guaranteed. In addition there is always an impact on other users who may be the victim of pre-emption. One of the first generation U.K networks failed to restrict emergency access and soon paid the price. Users soon learned that if a call was queued during busy periods, an emergency call got though. It was not long before the initial step of a normal call was bypassed, so the whole pre-emptive mechanism was doomed. The operation of analogue trunked networks have certainly provided know-how that will have a direct bearing on the topology and management of the new digital networks.
Manufacturers have often been criticised that the styling of traditional and trunked PMR terminals have always been different (and substandard) to that of cellular. This has however differentiated the products. If the manufacturers adopt ‘cellular’ like styling on public networks, there is a danger that the users will expect the terminal to behave like cellular both in terms of operation and coverage.
In recent years, markets for regional systems have been maintained, and, although MPT1327 was never designed for the emergency services, some very successful networks have been built.
MPT1327 equipment has developed wide and varied applications through its rich menu of facilities. It is unlikely that any new large public networks will be installed in Western Europe, but private systems with a coverage area of a small number of sites are still in the manufacturer’s order books, replacing old conventional PMR systems.
Outside Western Europe the market continues to be stable. Cellular still cannot meet constraints where fast call set-up and prioritising of calls is mandatory.
In countries where spectrum is very scarce and high-speed data is an important feature, the LM implementation of MPT1327 will match the performance of digital systems occupying the same bandwidth.
In many areas of the world, the local environment restricts choice. This is –
Lowest cost per user
Restricted or non-existent fixed links to connect the sites
Limited engineering staff/expertise
Varied use including emergency and ‘cellular like’ services
Wide choice of manufacturers equipment
Technology step is modest from conventional systems
Today, only MPT1327 can meet these criteria. Unless digital trunking reaches the critical mass where the cost of the equipment will substantially fall, MPT1327 will continue to be an important and useful technology for many years.
APPENDIX
TSMG Trunking Standards Maintenance Group
When all traffic channels are in use, a priority call is queued ahead of normal calls, and a pre-emptive emergency call clears a normal call to free a channel.
If a radio is switched on when a group is already active on a traffic channel, the control channel will send messages so that the radio joins the group.
SST’s Single Segment Transaction. Allows the transfer of up to 184 bit of information using the control channel only.
MST’s Multiple Segment Transactions. Concatenates SST’s together to transfer up to 184 bytes of information using the control channel. Must be used with care since MST’s have a great impact on control channel loading.
Channel segregation makes a different number of traffic channels available depending on the identity of the calling or called party. This is another way of controlling the priority calls in the system.
Manufacturer of MPT1327 Infrastructure
ADI Alcatel Forward Fylde
GEC/Marconi Key Midland/Intek Motorola
Nokia R & S Rohill Simoco
Storno OTE Tait Vigor
Zetron
Manufacturer of MPT1327 Terminals
ADI Alcatel Bosch Electronica-Dizain
Icom Kaviciom Kenwood Key
Kyodo Maxon Midland Motorola
Nokia OTE Rohill Simoco
Tait Talco
Speaker - Brian Seedle
EMAIL - bseedle@aol.com
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