MOTOTRBO: The MPT1327 option board (Part 1)

To ensure a smooth migration to digital, MOTOTRBO radios are available with a MPT1327 option board. This allows you (or your customer) to use MOTOTRBO radios on their existing analogue trunked radio system while they migrate to digital.
The option board is pre-installed inside the MOTOTRBO radio and allows the radio to process the FFSK signaling and handle the channel allocations required to set up calls. In effect, the option board takes over control of the radio.
MOTOTRBO radios can be ordered with the option board pre-installed or you can install them yourself, if you have the correct tools and skills.

The option board is programmed with the MPT OB CPS, available on Motorola Online. There is also some configuration required in the host radio, this is done via the MOTOTRBO CPS, also available from Motorola Online.

In order to set up the option board, some information about the MPT system is required. There are three important parameters that will make the radio work (or not work, if you get it wrong) on a MPT system:
  • The system ID
  • The radio ID (or ident.)
  • The frequencies (channel numbers)

There are other parameters which are important, but the above three will make the radio register on the system and the user will be able to make and receive calls by dialing a number.

Sometimes the System Identity is not known or is presented in an uusual format. The best way to determine this would be to read any existing radio and copy this to the MOTOTRBO radio. Fortunately, the MOTOTRBO MPT OB CPS has the ability to open .PER (Personality) .NET (Network) and .RAD (Radio) files which were created by older versions of Motorola MPT CPS or DPS.

If your existing radios are from another manufacturer, the only way would be to print the configuration settings and create the MPTOTRBO MPT codeplug from scratch.

System Identity

The system Identity is a 15bit number continuously transmitted on the control channel (part of the CCSC). A radio will search for the control channel(s) and will look at the System Identity. If the information, in the radios codeplug, matches that which is in the decoded System Identity, and the signal strength is sufficient, the radio will attempt to register.

There are two possible bit arrangements for the System Identity:

  1. In a regional network, the first bit in the System Identity is 0. This also means that bits 2 and 8 are used for the Operator Identity (OPID) and bits 9 to 12 for Network Dependant Data (NDD).
  2. For a national network, the first bit is 1; bits 2 to 3 are used for the Operator Identity and bits 4 to 12  are for NDD.

In both cases bits 13-15 are used for the Label (LAB) sub field.

System ID bit structures for national and regional

The LAB field allows the system operator (infrastructure owner) to selectively disallow certain groups of radios access to certain sites - on a per site and even on a per control channel basis. In almost all cases, LAB is set to the "allow all" value 001 (otherwise known as control category A).

The NDD bits are also made up of some additional data: Area; Zone and Free. These three (in most cases only Area and Zone) allow a network operator (infrastructure owner) to control the roaming characteristics of radio units on a wider area basis.
NDD Example
The above table illustrates one possibility for using NDD to restrict or control site access. Each block above represents one site or multiple sites in a MPT1327 system. The number in red is just a site number for ease of reference. The Four bit (digit) number below that in black is the NDD value for that/those site(s).

In the radio, not only do we have to specificy the Area and Zone data but also the length of these. The Length of Area indicates the number of bits used to determine the area NDD value and is counted from the most significant bit to the least siginificant bit (i.e. from left to right).

It also means that in a regional network, the Length of Area (LA) and Length of Zone (LZ) values cannot be higher than 4. In a national network, LA and LZ can be as high as 12.

In the above NDD example, if we wanted to restrict a group of radio to zones 1-8, we would set LZ to 2 (meaning the first 2 bits are counted) and would add two values to the NDD Table (in the radio), namely 0 and 1. So a LZ of 2 tells the radio to look at the first two bits of the NDD (i.e. bits 9 and 10) and if these match  decimal 0 (binary 00) or decimal 1 (binary 01), the radio should continue with the registration process or, at least, add this control channel to the hunted list.

So by manipulating Area; Zone; LZ and LA, one can control who is allowed to go where in the network. If we wanted all radios to go anywhere, we would simply have the same information in all radios.

Radio Identity

In a MPT1327 network, each group and radio is allocated a unique number. This number is made up of two parts: the Fleet (NP) and the Individual (FIN).
MPT1327 allows for some customization of these numbers: here I will only discuss MPT1343.

MPT1343 allows us to split the MPT1327 number into a Prefix; Fleet and Individual number for radio units and a Prefix; Fleet and Group for talkgroups. This makes it easier for us to remember and allows users to dial understandable numbers to reach members of their team. Although different, the number used for a talkgroup and for a radio unit tie back to unique numbers in MPT1327 format.

In MPT1343 format, there are two possible lengths for the Talkgroup and Individual number. For smailler radio fleets, the Individual number can be 20-89. For larger fleets this would be 200-889. Similarly for smaller fleets, the Talkgroup number would be 90-99 or 900-998 for larger fleets.

Note that you cannot have a mixture of two and three digit Individual numbers!

  • The MPT1343 Prefix is based on the MPT1327 Prefix plus 200.
  • The MPT1343 Fleet is based on the MPT1327 Individual divided by two, then rounded to the next integer and added to 2000.
  • The MPT1343 Individual is based on the MPT1327 Individual plus 20 or 200 depending on the fleet size.

This means that a radio with a MPT1327 (base) number of 000 0001 will have a MPT1343 number of 200 2001 200. Users who want to dial this radio, and who are within the same Fleet, simply need to dial 200. Users in another fleet would need to dial 2001 200 and users with another prefix would have to dial the full number 200 2001 200.

  • For the Talkgroup number, 900 is added to the MPT1327 Prefix. 
  • 9000 is added to the MPT1327 Individual which is divided by two and rounded to the next interger. 
  • Then for the Talkgroup either 89 or 899 is added to the MPT1327 Individual.

More information about Radio Number can be found in the MPT1327 and MPT1343 standards.

The Frequencies

MPT1327 allows for two possible channel allocation methods:
  1. Standard Channel Plan
  2. Flexible Channel Plan
The standard channel plan would be used where all the RF channels in a system can be represented as a multiple in relation to a lowest common denominator frequency known as the LBBF (Lowest Baseband Frequency). The frequencies would also have to have the same TX-RX separation.
If the above does not apply, then the flexible channel plan should be used.

With the standard channel plan, the LBBF is regarded as the mathematical channel zero in the radios and system/site controller - all channel numbers are hence based on this value.

The flexible channel plan allows the system operator to define custom channel numbers and frequencies. The only require
ment is that the channel number in the infrastructure (system/site controller) matches that which the radio has.

Relationship between LBBF and Channel Numbers - Standard Channel Plan
Part 2 to follow soon....
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