Introduction to Trunking and the TMR

Bill's Nova Scotia Radio Site

A BRIEF INTRODUCTION TO TRUNK RADIO AND THE NOVA SCOTIA TRUNKED MOBILE RADIO SYSTEM

This brief description is intended for those who have only a passing interest in radio and not a whole lot of knowledge.

If you really do not have much knowledge of radio systems, it is probably a good idea to start at the simple end of things and work up towards trunked radio, so that is what I will do. But don't be concerned about where this will lead. It will not at all be very technical even at its most technical!

Simplex Radio

Radio signals can be moved around in various ways. At the simplest they go direct from the transmitting user to the listener or listeners. The transmissions can be entirely one-way, as in the case of broadcasting or paging, or far more commonly they are in some way two-way, so that users can transmit to each other, taking turns.

Even one-way broadcasting is not as simple as you might think. Yes that FM radio station in the city does broadcast out to all its listeners in the surrounding area and it is one-way. But the transmitter is not right beside the announcers in the studio. It is some distance away, maybe on a hill overlooking the town or region. The signal first has to be sent from the studio location, either by a cable or wire (landline) or via a radio link that would most likely be microwave or UHF radio in a narrow beam to the transmitter site.

In this article I am talking about two-way communications, and these at the simplest involve users with radios who are transmitting back and forth directly to each other. In this kind of radio, the users take turns transmitting back and forth to each other on one particular channel or frequency. This is usually called simplex communications.

A --------------------------à B taking turns with A ß--------------------------- B

Purists would say that simplex is entirely one-way, and that a two-way arrangement as shown above, taking turns, should be designated “semi-duplex”, but most users describe either as “simplex”.

Examples of this are ships, airplanes, flag persons and others who are basically in line of site of each other. It also includes long distance users on shortwave bands such as amateur radio operators and military users whose signals can go round the world direct, with no relays in between. My discussion here relates only to the more line of sight type of communications generally used by industry, commerce and public safety organizations. Simplex also includes the use by all kinds of people of the “walkie-talkie” handheld radios commonly available in blister packs at department stores throughout Canada. These combination GMRS/FRS radios are very short range in nature, despite the wildly exaggerated claims printed on the packaging. By the way, it is conceivably true that a pair of such radios might have the advertised range of many kilometres, but only between the tops of two very high mountains, and certainly not anywhere in Nova Scotia!

Repeater Systems

For users who need more range, to cover a whole town or small region, it is necessary to somehow relay the transmissions with some kind of booster in between the users. For this the usual configuration is with the use of a repeater. In most cases a user transmits on a frequency, let’s call it A, to an unattended receiver and tower on a high point of land. That signal is then simultaneously retransmitted out to the surrounding area on another frequency; let’s call it B, to the intended user or users, who of course have to be listening on frequency B. To reply, any one of these users replies on frequency A to the high up retransmitter, and the signal automatically goes out on frequency B back to the first user. The receiver and retransmitter located in the advantageous high spot is called a repeater because of course that is what it does. The frequency used to send to the repeater is commonly called the input or uplink frequency, and the one transmitted by it is called the repeater output or downlink frequency. This is the type of system used by countless government and public service agencies across the world, as well as commercial and industrial users, also countless.

A -------------------------------------> Repeater --------------------------------------------> B (receives on Freq 2)
transmits on Freq 1 transmits on Freq 2

THEN

A <------------------------------------- Repeater <------------------------------------------- B (transmits on Freq 1)
receives on Freq 2 receives on Freq 1

Frequency vs. Channel

In these repeater systems there are actually two frequencies in each channel. That is why it it is generally not correct to equate the terms “frequency” and “channel”. Even in simple one frequency usage there will generally be a difference, in that the frequency is described by its measurement in kiloHertz or MegaHertz, but the channel will have an “alias” description such as Channel 1 or Channel 22. Even our FM broadcast frequencies have corresponding channel numbers. For example 88.1 MHz is also Channel 201 of the FM broadcast band, but these channel numbers have never caught on like TV channels did, and, by the way, don’t go searching for lower channel numbers for FM because there aren’t any! And speaking of channel numbers, no one using those cheap GMRS radios ever uses the actual frequency of the channel they are on. If you are on Channel 1, that is what you say, not the actual frequency, which in that case is 462.5625 MHz. The average user of such radios should be very happy that channel numbers are used instead!

Linked Repeaters

If a company or agency wishes to have wider geographical coverage than that one tower and repeater can give, it is possible and common to have more repeaters and join them together with further links. In fact there can be a long chain of links to provide distant communications. Nova Scotia had at one time a network of such repeaters such that a user in Halifax could transmit as normal through the local repeater but send out particular tones that could allow the signal to go onwards via a link to a distant repeater anywhere in the province. This is still true in amateur radio so that a ham with a low power handheld radio in Cape Breton can link to a repeater in Shelburne, for example. Nowadays the links can be VHF, UHF, microwave, satellite, or even via the internet! That ham with a handheld might be heard speaking to someone in Germany or Australia!

Who Uses a Channel

Each of these methods generally means that one user or set of users such as a company or government department has a channel or a few channels set aside for them alone, as of course they want to be able to use them when they need them without having to wait for others to be done. An exception lies with those GMRS radios where there isn’t any assignment to particular people. For example, the local hardware store might purchase a set of those radios and decide to use Channel 21. The nearby school might also buy a set and they could independently decide also to use Channel 21, and you can imagine the troubles that might ensue. Of course it that happens one of the two can move to a different channel and it might all work out. [See my separate article on the use of GMRS radios.]

In the last several decades the use of the radio spectrum has become increasingly crowded, and the frequencies themselves have become hot commodities. Cell phones and similar devices (which are small two way radios) have eaten up tremendous swaths of the spectrum and continue to increase. This has led government regulators, the telecommunications industry, and users towards methods that make more efficient use of the radio spectrum.

In addition, in the public safety sphere, there has been a tremendous impetus to allow better interoperability. Interoperability means communications amongst various users who in normal times would be happy to have their own private system but in times of emergency incidents would like to talk to each other.

Trunked Radio

Both of these needs have increased the use of trunked radio. Trunked radio essentially is the shared use of a few radio channels by many users. For example in regular or “conventional” radio, there could be a hill with 25 repeaters, each used by a separate user, and each with its own channel, different from the others, and maybe on entirely separate radio bands. You would likely not see 25 different towers as one tower can hold several different repeaters. To clarify, the actual tower usually only has the antenna, with the repeater (receiver/transmitter) located below in a building of some kind.

In this article I will be using the words "trunk" and "trunked" interchangeably, as both are in common use.

In a trunked system there will be several channels (frequency pairs) available at one tower. Let’s say there are 5 channels. This can be used by many more than 5 users due to the fact that in at least normal times, each individual user is actually using the system on the air quite infrequently, or if frequent, for few seconds at a time. This means that generally speaking they can share the channels. Something like this has been done well back in time but in those cases several users shared just one channel, and while it worked, it did mean that User 5 might have to wait for User 14 to finish an interchange before they could use the channel. They did have tones and indicators to not only stop one user from hearing the other’s transmissions, but also to indicate when the channel was available.

In a trunked system, with the use of several channels each user can employ any of the channels. Figuring out which one to go to would be a challenge to any user wanting quick “pick up the mike” communications. In trunking there is computer control such that the site is monitored constantly and signals are sent out to all the users’ equipment in order to direct them to an available channel. The actual person with the equipment does not have to do anything whatsoever… his or her radio goes automatically to one of the clear channels and so do the radios of everyone else in his or her group. So let’s say it is Acme Garbage Company. When the driver of Truck 4 wants to talk to dispatch or anyone else in the Acme Garbage user group, he or she presses the push to talk (PTT) button on the mike. The computer controller (system controller) immediately determines that Channel X is available and “tells” that particular radio, and all the other ones in that group of users, to go to Channel X, and that is where they go. Only the Acme Garbage radios go there. This all happens between the instant the user presses the PTT and the instant he or she commences speaking! In fact it is necessary in trunk radio to pause just slightly before speaking to ensure all of this has happened otherwise the first syllable or two will be lost. In the short time between Truck 4 transmitting and the dispatcher or other truck replying, the system can reset and assign a different channel. In that ensuing time, the controller could have assigned the first channel to another active user, let’s say the fire department. This is all happening without the individual user having to know anything about the system, or even knowing his communications are jumping around on and off various channels.

Channel vs Talk Group

In fact this jumping around from one channel to another has led to confusion over the word “channel”. In radio generally, a channel equals a frequency (simplex) or a frequency pair (if a repeater is used). The problem is that a user would say that setting his or her radio to a setting that allows speaking to let’s say the dispatcher is setting it to a particular channel, but in trunk radio that can and does bounce around various actual frequencies. That is why in trunked radio it is usual and normal to refer to the radio setting and the group of users on it as a “talk group”. So Acme Garbage will have at least one talk group. The Acme talk group is what is bounced around by the controller to various actual radio channels. Having said that, it is quite common for trunk radio users to still think of their talk group as their channel, even though it is really not one radio channel. A talk group is therefore sometimes considered to be, and referred to as, a “virtual channel”.

Site Trunking

What has been described above is “site trunking”, meaning that this is happening at one tower with several different frequencies. Typically in Nova Scotia one trunk radio site will have three to twelve voice channels, depending on local demand. There also must be another channel called the control channel or data channel that is constantly sending out instructions to all the radios in its coverage area, and receiving signals back. For example in the case above when the garbage truck driver pressed the PTT, the request for service went out on the control channel to the site and onwards to the computer system controller, which immediately sent a signal back to the radio to tell it what voice channel to go to. This is lightning fast! As intended, site trunking allows many users to utilize one set of channels on one tower. Naturally there does exist a possibility that simultaneous needs can outnumber the availability of repeaters, and in this case someone will have to wait. In many jurisdictions, including Nova Scotia, a priority order is established. For example the ambulance service will take priority over Acme Garbage.

Multi-Site Trunking

Many or most trunk systems actually have more than one site and in fact can have scores of sites, as does the Nova Scotia provincial system. In a multi-site system there is one computerized system for the whole system… that is why it is called the system controller!

Affiliation

When a radio in the system is turned on by Person Z it will be on a particular talk group. The radio cannot be on without being on a talk group. Some users only have one talk group so that is pretty straight-forward, but some have many to choose from. The ambulance service for Nova Scotia has perhaps fifty different talk groups or channels! So the radio is turned on. It sends out a signal saying to the controller that it is turned on and what talk group it is set to. This signal is received via one of the sites, unless there is not any site in range. The radio will usually connect via the strongest signal site, which may be the closest one, but not necessarily if terrain or buildings affect the signals, or if the best one is completely busy. The radio is then considered to have “affiliated” to that site, and therefore the talk group the radio is set to will be connected by the central controller to that site. This will mean that if someone else somewhere in the system begins to speak on that talk group, those words will be sent out on the local site to our Person Z and anyone else in Z’s group of users, and through any other site that has a radio on that talk group affiliated. It will not normally be sent out via a site that does not have anyone on that talk group affiliated to it. That way the use of that talk group does not tie up the whole system but rather just some of the sites, and in fact only one, if all the users happen to be affiliated to just one site.

One advantage of a multi-site system is that there may be more than one site in range of a particular user radio. Back in the site trunking section I pointed out that it might happen that all the channels at the site are in use, and therefore someone wanting to use the site might get a busy signal. In a multi-site system that user would be automatically connected to another in-range site, so that in effect a busy signal should be extremely rare. In fact busy signals have occurred at times of major incidents when many many public service users want access at the same time, and this is one reason at least for good training in the use of the system, as seasoned observers and users have come to realize.

Handing off From Site to Site

The other aspect of multi-site trunking systems is that as a mobile user goes from location to location, the radio will disaffiliate from one site and go on to another one. It does not necessarily always go to another site as soon as the second site becomes stronger than the first. Instead it may stay on the first one until it becomes too weak to use, or rather meets a minimum criterion, and then switches to the next site.

Similarity to Cellular Telephone Service

If you are thinking that this sounds a little familiar, that is likely because you already know that this is how cell phone service works. In fact without going into the many differences that do in fact exist, the two types of systems do work quite similarly. In fact, for the user, the main differences are that in the telephone system you speak and listen at the same time and you do not have talk groups, but rather you connect to the land line system each time you dial or receive a call. By the way, remember way back when I referred to simplex and semi-duplex, now I can say that a telephone system in which you can talk and hear the other person at the same time, is referred to as a full-duplex configuration.

Trunked Radio in Nova Scotia and the Maritimes

There are several different varieties of trunk radio systems, differing by the particular technology. It is not the intent here to differentiate whatsoever. I do mean to describe the main system here in Nova Scotia. By that you will realize that there is more than one trunked radio system in this province but the ones not mentioned here are small in size and used only by commercial enterprises. There is an older style provincial trunked system in Prince Edward Island and as well trunked systems operating in and around both Moncton and Saint John, New Brunswick. The trunked system in operation in Fredericton is actually part of the Nova Scotia system described below. Commercial trunked systems are operated by such users as the Halifax Casino and Michelin Canada.

Nova Scotia Trunked Mobile Radio System (TMR)

Beginning in and around the turn of the century in 2000 the Nova Scotia government replaced its legacy conventional linked repeater system with what is called the Nova Scotia Trunked Mobile Radio System, usually referred to as the TMR. I must jump ahead to the present to tell you that in 2014 the TMR is being replaced by a similar but upgraded system referred to as TMR2, to be described farther down the page. This replacement will not be completed until 2015 and therefore I will speak of both here. Because the TMR is in the process of being replaced by TMR2 I will from this point refer to the existing system as TMR1.

TMR1 is a system made up of around 70 sites covering Nova Scotia and as well the Fredericton area of New Brunswick. It is owned and operated by Bell Aliant/Bell Mobility but principally under contract to the province of Nova Scotia. Some of the towers housing the repeaters do in fact belong to the government but most are Bell sites also used for the cellular service and for other purposes.

Users other than the province are accommodated by subsidiary or secondary contracts. This system provides what can be described as complete coverage of the province but in reality there are a few weak spots in populated areas, and several blank areas where the population is very low or non-existent. It serves the provincial government and as well the volunteer sector that is sponsored or assisted by the government such as EMO, Ground Search and Rescue, and volunteer fire departments. It also is used by many or all aspects of the federal government and by several municipalities, including the largest one, Halifax Regional Municipality. As of November 2014, one major user, the Emergency Health ambulance system, has left TMR behind and has migrated to the replacement system TMR2.

In theory at least all of these public sector users should have talk groups in their radios usable to speak to other public sector users. For example a snowplow operated by HRM should be able, if necessary, speak to a sheriff department vehicle located in Cumberland County. Things like this do not happen unless they have to, and even then only if all the parties involved know how to do it, and are allowed to do so by their respective dispatchers. This capability is extremely important, and it is used quite often in connection with major incidents such as searches and the occasional disaster or near-disaster situation. Having said that, there are also many instances of this capability not being taken advantage of, or of being done incorrectly or inefficiently.

Secondarily the TMR is also used by many commercial entities who use the system on a lower priority basis and do not have access to the mutual assistance and liaison talk groups just mentioned. Most of these users have one or two talk groups and can only talk to their own units.

Due to its size and capabilities for interoperability the TMR1 system was at its outset considered to be perhaps the best in Canada and one of the leaders in North America as a whole. It remains the envy of many states and provinces, but as time has gone on its actual hardware is becoming dated, with many advances since its inception. As well there is opportunity for improving on the already good interoperability practices and framework and on its geographical coverage.

TMR1 was originally intended to last for the first decade of the century but without an immediate replacement in sight, the contract between Bell and the provincial government was extended, so that today this system still operates as before.

Inter-Provincial Trunked Radio Proposal

In the years leading up to the end of the first decade in 2010 discussions were convened among all three of the Maritime provinces with a view to an integrated trunk system covering all three provinces. This proposal reached a stage advanced enough that a complete list of sites was published and requests for proposals distributed to industry. While some specifics varied from province to province the basic idea was that the new system would be owned and operated by a joint crown corporation. It would replace the extensive conventional repeater networks operating on VHF and UHF in New Brunswick, the TMR in Nova Scotia, and the less advanced provincial trunk system in PEI, along with the RCMP’s conventional UHF repeater network in PEI. This proposal eventually fell apart due to cost constraints, principally in New Brunswick, but not before several new towers had been constructed in Nova Scotia.

TMR2

When the Maritimes proposal was ended, the Nova Scotia government elected to work towards a new system for that province alone. Eventually this resulted in a replacement trunk system operated by Bell for the province and generally referred to as TMR2. As of November 2014 this system is in place and one major user, EHS, has migrated to it. Others in the provincial sector will migrate over the ensuing months, so that by mid or late 2015, all the provincial users will have left TMR1 behind. Other TMR1 users such as HRM and the federal government will also migrate. TMR2 uses the newly opened 700 MHz band and is not allowed by Industry Canada to have commercial users, so this system will not have subsidiary users. The result will be that TMR1 will be left with just a few such users, and most likely will be shut down except perhaps in the higher volume areas around Halifax, but this is purely speculation.

TMR2 uses all of the same sites in Nova Scotia used by TMR1 except for one in Digby County, but it also has additional sites. As of its inception TMR2 has 86 fixed sites or towers, plus it also has a mobile site termed SOW (Site on Wheels) that can be deployed if necessary to wherever needed. TMR2, like TMR1, is connected together by fibreoptics and by microwave links. It is perhaps misleading to say it is directly connected together, because even if a user operating through a tower is speaking with someone using a nearby other tower, the signals in both directions are first sent to the central controller or “switch” in Halifax, as are all the control signals that designate channels as described above.

TMR2 is operating as a P25 Phase 1 system. You can look that up on-line, but it really isn’t relevant here at this level, other than to say that if you were intending to listen in on the system, you must have a radio receiver that can interpret digital signals. In other words you need a digital receiver. This is not the venue for me to talk about scanners but perhaps I need to say that you essentially need a modern digital trunktracking scanner to listen to TMR2. Additionally you will find that all or most of the law enforcement communications on TMR2 will be encrypted. This means that the communications can only be interpreted or deciphered by other allowed users in that group, and certainly cannot be deciphered by any scanner. The days in Nova Scotia of listening to the police are essentially gone or soon will be, other than in Cape Breton Regional Municipality and a few of the towns scattered around the province. Back to the comment about Phase 1 just above. This system is capable of operating as a Phase 2 P25 system but cannot do so unless all the user radios also are capable of doing so. If it ever does operate on Phase 2 you will need a TDMA capable digital scanner, some of which do exist.

For those of you reading this who are not particularly “into” radio and do not have a scanner, suffice it to say that TMR2 is a highly sophisticated radio system. It is one of the very most advanced in North America. It allows “clear as a bell” radio communications between almost anywhere in Nova Scotia, though even TMR2 is not perfect in difficult spots, whether geographical locations or building constraints. In addition to the technical considerations, the organization of the talk group system is well thought out and allows for enhanced cooperation among public service users throughout the province. This is not to say that all PS entities in Nova Scotia will be on TMR2. For example it is likely that the Kentville Police Department will continue to use its own system but it should have some capability to patch to TMR2 and link to other users. The vast majority of volunteer fire departments in the province have their own conventional radio systems and it can be expected that this will continue; however all of them will also have at least some TMR2 radios and it might be expected that as time goes on there will be a gradual migration to daily use of TMR2 by these departments. Good use of TMR2, especially when it comes to interoperability, depends to a great extent on good training!

If you think you might be interested in listening to the day to day or emergency communications of the TMR, TMR2 or any other radio system, have a look at my other pages on www.marscan.com and also check out the forum and data site www.scanmaritimes.com The latter is a site that you must join in order to access most of the content, but it is also where you can best discuss with seasoned scanner listeners. A more general forum and data site to check is www.radioreference.com that does have an Atlantic Canada section, but is the place to go on a myriad of radio topics.

As always, if you see mistakes or anything out of date or misleading in the above article, please contact me: marscan1 AT gmail.com Thanks.