MPT-1327

[http://www.ofcom.org.uk/static/archive/ra/publication/mpt/mpt_pdf/mpt1327.pdf MPT 1327] is an industry standard for trunked radio communications networks. First published in January 1988 by the British Radiocommunications Agency (a DTI Executive Agency) now part of Ofcom (The Office of Communications), and is primarily used in the United Kingdom, Europe, South Africa, New Zealand, Australia and even China. Many countries had their own version of numbering/user interface, the most notable being MPT1343 (UK), Germany – Chekker (Regionet 43),France – 3RP (CNET2424),Belgium & The Netherlands – Entropia Networks (MPT1343),Australia – Multiax, China -Gong An. MPT systems are still being built in many areas of the world, due to their cost-effectiveness. The equipment is cheap and performs very well.

The TETRA trunked radio standard was developed by the European Telecommunications Standards Institute, (ETSI), as a digital alternative to analogue trunked systems. However, TETRA, with its enhanced encryption capability, has developed into a higher tier (Public Safety) product, currently mainly used by Governments, some larger Airports and Government-owned utilities. TETRA equipment is getting cheaper all the time and may eventually compete with MPT 1327 at the same price-point, but this has not yet happened.

The advantage of MPT1327 over TETRA is the cost of equipment, the ease of installation, the familiarity with the equipment, and many believe that MPT1327 is superior to TETRA, due to its uncompressed FM audio, and greater receiver sensitivity. MPT1327 typically has greater range than TETRA, since the TETRA protocol uses a complex modulation scheme that requires a far higher Signal to Noise ratio to function than 1200bit/s FFSK signalling.

Systems based on MPT 1327 only require one, but usually use two or more radio channels per site. Channels can be 6.25 (Entropia Networks in BeNeLux) 12.5 or 25kHz bandwidth. At least one of these channels is defined as the control channel (CC) and all other channels are traffic channels (TCs) used for speech calls.

Typically for an "average" installation, there is around 6-10 channels. A 7 channel trunk, correctly engineered, is capable of handling in excess of 3000 mobile units. The capacity of the system increases exponentially with the number of traffic channels. For example, 1 traffic channel with queuing can not handle many customers, perhaps 2 minicabs with 20 mobiles. In effect this would be a CBS with queuing. However, a 7 channel trunked system can handle 40 minicabs with 20 mobiles with ease. The Erlang formulas are typically used for calculating system capacity.

In some scenarios the Control Channel is classified as "Non-Dedicated". This means it will be used as a traffic channel when all the other traffic channels are busy. The advantage of this is an extra traffic channel, but the disadvantage is loss of queuing, and data cannot be sent on the control channel whilst it is in traffic mode. Also in multi-site systems, the roaming systems within the mobile can be upset, causing mobiles to roam onto non-preferred neighboring sites.

The control channel can also be set to cycle, so each channel in turn becomes a control channel, say every 10 minutes it will change. The advantage of this is that the base does not have to be rated at 100% duty cycle and does not get so hot. However, this can cause problems with queuing.

Speech is sent as narrowband FM. Data messages between mobiles and the network are exchanged on the control channel at 1200 bits per second using FFSK signalling, or a specific "modem call" can be established, whereby 1200 baud data can be exchanged on a traffic channel, without tying up the control channel. With the use of special modems, the speed can be 19.200 bit/s.

Each subscriber in an MPT-1327 trunked radio network has a unique call number. This call number (address) is a compound number consisting of a prefix (3 digits), the fleet number and the subscriber’s call number within the fleet. Different numbering schemes work differently, for example Zetron uses the first 2 digits of the Ident as the fleet number, and the last 2 digits as the Unit number. Idents in the 6000-6999 range are typically used to establish Group Calls. After it has been entered the call number will be converted in the mobile to a 20-bit address. The numbering rules are clarified and expanded by supplementary standards such as MPT-1343.

MPT1327 can also be used for AVL (Automatic Vehicle Location) and online RFID reading by the use of custom software packages.

For the duration of his call a subscriber is exclusively allocated a traffic channel from the available trunk. If all channels are occupied, the call will be queued. If the control channel has become a traffic channel, like in the case of a non-dedicated control channel, the call will be queued in the radio, although radio queuing loses the first come, first served effect, so if there are 7 units queuing, the last unit to queue may get a traffic channel first.

The different types of communications on an MPT-1327 network and their definitions:

Traffic types:

* Mobile-mobile in a cell
* Mobile-mobile in different cells
* Mobile-line access unit via landline or radio
* Mobile-dispatcher station via landline or radio
* Mobile-PABX, Mobile-PSTN

Data Communication:

* Status messages on the CC (5-bit data length)
* Short data messages on the CC (186-bit data length)
* Transparent data transmission on the TC (data communication).

Calls:

* Point to point connections
* Group calls with talk entitlement
* Group calls without talk entitlement (Broadcast Calls)

Broadcast calls can be used to make announcements to the entire customer base on a trunked system. For example, if work is to be carried out on the the trunked system, the owner of the system can initiate a Broadcast Call which calls every mobile on the system. However, the mobiles may not have talk entitlement, so the PTT may not work. By this means the owner can announce to all customers of a short period of inoperation due to maintenance.

Notes