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Trunking communication networks “Analog-to-Digit”
Consideration is given to the issued of migration from analog to digital modes of operation in trunking
radio networks. Information materials on individual technical solutions are presented.
Key words: radio communication, trunking, PMR, MRT-1327, DMR, Simulcast.
Introduction
This article will be of interest for specialists with experience in the construction and operation of
trunking communication systems. The information presented here, to our point of view, can be useful
to users planning upgrading their current trunking radio communication networks or construction of
new networks.
In brief, trunking technology can be described as “offering the users of a limited resource
(communication channels) on demand, with a dynamic distribution of the resource between users”.
The key purpose of using trunking technology в PMR is the frequency resource saving.
Today, all trunking communication systems feature the same set of basic functionalities:
-‐ individual call;
-‐ group call;
-‐ calling fixed communication network subscribers;
-‐ status message service;
-‐ short message service;
-‐ arbitrary volume data service.
Nowadays equipment and technology state features a steady tendency to the all-round
implementation of digital technologies. This tendency did not skirt the PMR industry either.
Practically all Manufacturers offer these or those ways to migrated from analog equipment samples to
those digital.
Present on the market are both digital and analog trunking communication systems. However, such
splitting is not fully correct. If the system supports trunking technology, then there is transmission of
signal (digital) information Thus, all trunking communication systems are all digital with regard to
implementing signaling functions! The “analog-to-digit” splitting refers to voice transmission only.
In the users’ environment there is a stable statement that speech quality in digital systems is
admittedly superior than that in analog systems. For PMR radio networks, this statement does not
correspond to reality.
At the dawn of digitization of communication networks, analog signal coding methods were
standardized. Thus, on PSTN use is made of PCM coding at 64 kbit/s. Voice transmission using PCM
within PMR frequency band technically can not be implemented. Digital stream speed corresponding
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to one voice transmission path is 2.4 to 3.6 kbit/s for modern PMR systems. To code voice signal into
digital form use is made of vocoders. Vocoders code only some parameters (amplitude, tone noise,
tone pitch, etc.) of the voice signal and synthesize speech at the receive end. Such coding ensure
excellent characteristic values for signal-to-noise ratio. However, there are substantial voice distortions
due to the coding mechanism proper. Hence, PMR networks analog-to-digit migration of does not
allow improving voice quality.
Then what are the purposes of the analog-to-digit migration? They are different for trunking
communication system users and equipment manufacturers. We see these purposes as follows:
Analog-to-digit migration targets:
For users - to ensure the following: For equipment manufacturers – to ensure the
following:
Higher radio frequency spectrum efficiency. “Design-production-sales” technological cycle integrity.
Security of conversations Lower production costs. Using digital signal processing technology – it provides repeatability of device characteristics and lowers adjustment operations labor content1.
Lower expenses on using fixed communication networks. PMR analog networks, as a rule, make use of TDM technology Digital PMR networks are oriented on using IP-networks.
Creation of additional possibilities to obtain profit at the expense of designing and implementation of additional applications.
Provide access to the trunking communication network for various automation equipment complexes.
Prepare for phasing out analog trunking communication equipment2
1 For the sake of truth, it is worth noting that if the production process becomes less extravagant, then the process of designing new solutions and equipment samples, vice versa, becomes substantially more expensive 2 Manufacturers will remove current equipment from production and cease its technical support.
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In spite of substantial differences in the suppliers and manufacturer, it should recognized that
migration from analog PMR trunking systems to digital systems is inevitable.
What migration ways do we consider correct? This article suggests to consider one of the migration
ways. Let’s consider MPT-1327 systems as most popular analog trunking communication networks,
whereas DMR systems - as digital networks. DMR standard is the only digital standard permitted for
use in the PMR system traditional frequency bandwidths on the Russia’s territory.
Technical solutions for the “analog-to-digital” migration The information presented below refers to solutions offered by LLC “MPT-Service Project”. These
technical solutions are not “the only possible”. Other equipment Manufacturers, system integrators can
offer their own versions.
The migration activities set depends on the radio communication network structure. The migration
activities in question are applied to upgrading of radio communication network built using Fylde
Micro or “AMGA-1327” infrastructure.
“AMGA-1327” radio communication network structure designed by LLC “MPT-Service
Project”
“AMGA-1327” radio communication network structure is defined by the controllers equipment type.
Channel, site and region controllers are built using Fylde Micro (Great Britain) completing part. The
structure is based on a radial-zone topology. Provision is made for measures on improving resistance
of the equipment to failures: failure of one element does not result in total loss of communication, but
only lowers the system functionality. Fig. 1 shows the system functional diagram.
Fig.1 “AMGA-1327” trunking communication system functional diagram
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“Analog-digit” migration activities
The migration first step includes replacement of transponders equipment. The current transponders
support only analog mode. Transponder offered for replacement support both analog and digital
(DMR) mode. This replacement does not affect functionality of the current analog network but creates
a technical background for migration.
The migration second step can be carried out using one of the two methods: a “revolutionary” and an
“evolutionary”. When using a “revolutionary” method, after all the radio communication system
transponders are replaced and configured for operation in the DMR mode. It is worth noting that
“AMGA-DMR-BS-160-450” transponders are fully equipped for operation in the DMR mode.
Trunking network operation is effected in full compliance with the DMR Tier II specifications. Radio
communication system functional diagram for the “revolutionary” version is shown in Fig. 2
Fig. 2 “Revolutionary” method functional diagram
When using the "evolutionary" method only some repeaters are switched over to DMR mode. Thus,
there are two subsystems MPT-1327 and DMR Tier III - operating in one and the same network
simultaneously. When using an “evolutionary” method, there is a possibility to split in time the
migration activities and the related costs. Besides, provision is made for terminal equipment fleet
operation. Fig. 3 shows radio communication system functional diagram for the “evolutionary”
version.
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Fig. 3. “Evolutionary” method functional diagram
An important step in the migration is the replacement of subscriber terminals. Currently terminal
equipment market has already presented samples capable of operation in a DMR + MPT-1327 radio
communication network combined structure.
The migration version considered can technically be implemented owing to unique characteristics of
“AMGA-DMR-BS-160-450” transponders (Fig. 4).
Fig. 4. “AMGA-DMR-BS-160-450” equipment appearance
Technical characteristics of equipment “AMGA-DMR-BS-160-450”
“AMGA-DMR-BS-160-450” repeaters are manufactured by LLC “MPT-Service Project” using
completing parts and software manufactured by “Radio Activity” (Italy). The transponders are capable
of operation in the following modes:
-‐ Analog;
-‐ Simulcast analog;
-‐ DMR Tier II;
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-‐ DMR Tier II Simulcast;
-‐ DMR Tier III trunking;
-‐ DMR Tier III trunking Simulcast;
Not all users are familiar with the Simulcast technology specifics. Let’s consider the basic functioning
principles of such radio networks by the example of operation of the Simulcast single-channel radio
communication system.
Transponders are arranged on the terrain and interconnected using land communication links. One of
the transponders is configured as a master station, whereas the rest transponders are configured as
slave ones. All transponder, including those with their coverage interleaving, make use of only one
pair of frequencies. Subscriber terminal signal can be received by several receivers at the same time.
All the network receivers on receiving the signal, direct it to the master station. Master station
controller serves as the received signals voter (selecting the best signal). The selected signal is directed
to all the network transmitters. Special provision is made to synchronize transmitters working
frequencies, synchronize radiation time and provide similarity of the signal transmit channels
characteristics throughout the fixed communication network. Owing to these measures, the terminal
can receive the signal from several transmitted simultaneously, without degrading the signal quality.
The main advantages of Simulcast networks lie in the economy of the frequency resource and
simplicity of the network scaling. Roaming feature in Simulcast networks is integrated by default as
distinguished from other technologies of creating geographically-distributed radio communication
networks. Fig. 5 shows the Simulcast network layout.
Fig. 5. Simulcast network layout
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“AMGA-DMR-BS-160-450” equipment set features the following specifics:
-‐ Space diversity reception is implemented;
-‐ Provision is made for comprehensive facilities providing interaction with external
communication networks;
-‐ DMP Tier II mode allows construction of bridged taps based on DMR radio channels.
The advisability of the “analog-to-digit” migration shall be substantiated. Currently, migration is not
advisable or is impossible due to financial issues. MPT-1327 analog systems approved themselves as a
reliable solution for construction of PMR trunking networks. To our opinion, such networks will be
operated and constructed for the nearest decade to come. Functional capabilities of MPT-1327
trunking networks can be substantially expanded by implementing up-to-date application. Data
transmission feature in the MPT-1327 “analog” network are not less developed compared to that in the
DMR networks. Thus, information exchange speed in transmitting arbitrary format data and in using
traffic channel in MPT-1327 networks can be twice as high compared to that in DMR. However, using
the wide range of the MPT-1327 capabilities requires special technical personnel: engineers –
specialists in radio engineering with experience in software programming. No higher educational
institution trains such specialists. On the contrary, DMR designers provide tools comprehensible to
most programmers. It is not coincidental that today we observe real boom conditions in the
development of various applications for DMR Tier II networks.
Information on applications developed by LLC “MPT-Service Project” for MPT-1327 radio
communications networks
LLC “MPT-Service Project” developed the following applications for implementation on AMGA-
1327 equipment radio networks:
− “Track” hardware/software complex.
The complex is designed to perform transport monitoring functions. Used as positioning data source
are GLONASS receivers The onboard monitoring set features an open architecture and makes it
possible to connect external signals via CAN and RS-485 interfaces. Provision is made for connection
of the fuel level monitoring equipment. Data transmission is based on using SDM procedures. Use is
made of the client/server data acquisition and processing system. Reports preparation procedures are
made in the form of separate applications. One of the applications has no countertypes. The application
makes it possible to construct a real radio coverage map based on the data processing statistics.
− Conversations recording system
The system is capable of recording voice call. Each call is identified by time and terminal number that
initiated the call/ Access to data is ensured via WEB-interface.
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− Data transmission controller
The controller is designed and manufactured in compliance with the MAP-27 specifications. Provision
is made for using both SDM and arbitrary format data transmission.
Conclusion
So, the basis for the “analog-to-digit” migration is as follows:
-‐ Frequency resource deficiency, expansion of the current network;
-‐ Necessity in ensuring stealthiness of conversations;
-‐ Impossibility of using fixed TDM communication channels.
It is appropriate to construct new trunking communication networks supporting 2 operation modes -
MPT-1327 and DMR. Thus provision will be made for the network reliable operation inherent in
MPT-1327 systems, and engineering basis will be prepared for migration to the digital technology. I
should not be forgotten that DMR technology is a young one and DMR implementation imply risks.
DMR networks implementation risks are related to the incomplete process of protocols
standardization, possible incompatibility (at the protocols level) of equipment by different
manufacturers, availability of mistakes both in the base and terminal equipment.
In the short term, PMR networks “analog-to-digit” migration is and actual task only for some
radio communication networks. This activity involves substantial expenses and shall be planned
with the account of sufficient grounds.
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Glossary:
PMR Professional mobile radio
MPT-1327 Signaling protocol for trunking radio networks with a dedicated control
channel. Developed by Ministry of Post and Telegraph (Great Britain)
DMR Digital Mobile Radio. PMR standard. Developed by ETSI (European
Telecommunications Standards Institute)
Simulcast PMR technology. Provides for construction of the system based on several
base station operating synchronously using one pair of radio frequencies
PCM Pulse-code modulation
TDM Time Division Multiplexing
BS Base station
IP Internet Protocol - provides routing in data transmission systems, namely in
Internet
DMR Tier II DMR standard specifications set specifying operation of dispatcher
networks, without trunking feature control
DMR Tier III DMR standard specifications set specifying trunking networks operation
GLONASS Global navigation system
CAN Controller Area Network - a standard defining controller network
functioning procedure. Widely used in automobile industry
RS-485 Recommended Standard 485 – a standard for acynchronous interface.
Developed by two associations: EIA — Electronics Industries Association
and TIA — Telecommunications Industry Association
SDM Short Data Message. As a rule, format of these messages is included in the
trunking communication protocol description
MAP-27 Data transmission protocol in MPT-1327 trunking radio networks
communication