There have been many complaints over the past years around Westmoreland County regarding deficiencies in radio communications’ systems. Complaints have centered around many aspects of their particular system such as, lack of wider area coverage, dead spots, no secure communications, lack of interoperability with other municipal agencies, need for telephone interconnect, instant call for emergency, identification of units (unit ID), future use of Automatic Vehicle Location (AVL), Mobile Data, etc. A well designed trunked radio network would address all of these issues and would correct them.
Early telephone communications were set up in what was called a party line where only one telephone line connected a series of telephones. Under the party line concept only one conversation could occur at a time, all other users had to wait until that conversation terminated before trying to make a call. Perhaps you had a party line in your home when you were younger. Do you remember how you could listen in to other calls by simply picking up the receiver on the telephone? Most two-way radio systems work the same way today. Radio users share one frequency and only one conversation can go on at a time. In addition, radio channels today are extremely crowded so you wind up with many, many more users on that same frequency when you go to use it. This becomes increasingly frustrating for the radio user.
“Trunking” is a concept originally developed by the telephone company to alleviate the congestion on the telephone lines. Multiple, private phone use today is due to trunking. When a person want to make a telephone call that person accesses one of these trunked lines to use for the duration of their call. When the call is over, that person gives up the telephone line so someone else can use it. Trunking improves on the party line approach by adding multiple telephone lines (trunks) which are assigned to the caller for exclusive use during the call. This allows multiple conversations to take place simultaneously.
Trunked radio systems are modeled on the telephone trunking idea. Through advancements in electronic microcomputer technology, radio systems were able to incorporate the advantages of the trunking concept into wireless communications. Therefore trunking systems provide an efficient method for large groups of radio users to share a limited number of RF channels.
Good question! Any radio network will perform satisfactorily if properly designed and engineered, taking into consideration the customers requirements of radio coverage; talking out to the units and the units talking back and the reliability of this coverage (on the street, in buildings, etc.); the types of radio units (portable and mobile radios, low power mobile data units); radio to radio coverage (whether the units are within sight of each other or on opposite ends of the county).
It’s important to understand that no wireless system will provide 100% coverage, 100% of the time. Factors such as terrain, atmospheric conditions, the movement of the user and nearby vehicles and objects all can effect the signal. What we are trying to do is to build a system which will provide a high level of coverage, generally 95% or better for mobiles and portables both indoors and out. Equally important as identifying where coverage is needed, is knowing where less may be enough so we do not build sites we don’t need.
The overall goal is to allow users to talk where they need to, when they need to, and to do as efficiently and cost effectively as we can.
Lots of things! Here are some of the features:
* Faster System Access
* Orderly Access on a busy system
* Emergency Call
* Priority levels for each individual unit
* Carry on a private conversation between two units or more
* Out-of-range Indication
* Secure Communications
* Wide-area unit-to-unit coverage
No, you don’t, but its the best band if you have the channels. Trunking can come in various shapes and sizes. There are, of course, 800 MHz trunked systems but other frequencies can be trunked as well including VHF-High Band, UHF and 900MHz channels.
The FCC has set aside certain frequencies in the 800 MHz band for exclusive use by Public Safety users. Since Westmoreland County is already licensed for ten (10) 800 MHz channels it makes sense to use these frequencies to establish a “state of the art” trunked radio system network.
Let’s explain it this way: All of the existing public safety radio systems in Westmoreland County are classified as conventional systems. A conventional system consists of a single repeater or simplex base station located at a site which provides the coverage needed to communicate within a given area. For example, a police department may have a repeater licensed for their use at a particular site. At that same site there may also be other base stations/repeaters being utilized by either another police agency, fire department, EMS or public works department. Ordinarily each of these stations would operate on a different frequency and, more than likely, a different frequency band. (You’ll also notice that the equipment is probably from different manufactures; some of it is old, some not so old. Timeliness of repairs, parts availability, frequency compatibility, etc. are all on-going issues at a site like this.) This makes it very difficult for departments to talk to one another via radio. A conventional system isn’t very “smart”, a radio user accesses the system simply by pushing their push-to-talk switch. There is no magic, the radio transmits and everyone who has that channel in their radio or scanner and is within range of the system hears that transmission.
A trunked radio system is considerably more sophisticated. Let’s look at the above scenario but in terms of trunking. We’re at the site looking at the equipment and it all looks the same! That’s because all of the repeaters are in the same frequency band, 800 MHz. But if you look closely you’ll see that they are all linked together, there may even be another box, which is not a radio station but, in fact, is a computer. Unlike conventional, this is an intelligent system! This system is “smart”! Where conventional is mainly hardware driven, trunking is software driven. The user possesses a radio that has a personality!
OK, let’s keep this simple! Let’s look again at the above scenario where we have a tower site with many repeaters being used by different agencies and departments. In a conventional repeater system, at peak user periods, the chances are that half of the repeaters will be so busy that an average wait of several minutes to gain access to a clear channel will be common. In a trunked system, users have access to all repeaters in the system as they are made available to all users. In addition, voice channels are assigned automatically, eliminating the need for the operator to monitor and wait for a clear channel.
The channels are assigned to users on a talkgroup basis, not as dedicated channels. When a user needs to talk, he presses his PTT and the system assigns an unused channel to that talkgroup and all other users on that group are directed to that channel/talkgroup pair – automatically. The main difference between dedicated channels and assignable talkgroups is that the number of talkgroups is not limited to the number of physical channels. Even though the County will probably have a maximum of 10 channels at a site, the number of talkgroups in the system can exceed 10, in fact hundreds can be defined. Obviously, not every talk group can be active at once. Since the talkgroups are defined by software and not hardware, they can be added or deleted from the system as needed through programming, without the need to buy new base stations or license new channels.
Unfortunately not, trunking is an entirely different animal. Because of the sophistication of the call processing, new trunked radio units would have to be purchased to use on this system.
At this time, due to budgetary constraints, no changes are being made to the paging network, and the 800 MHz trunked radio system will not effect this. In addition, no pager units are being made which operate on 800 MHz systems, and they aren’t anticipated in the future, according to the major vendors. After the 800 MHz system is up and running, a next step will be to upgrade the paging network to consolidate it on one band, either UHF or VHF where equipment is readily and competitively available.
It all depends on what you mean by “expensive”. Yes, you will pay more for most trunked units than you would for conventional units but you are getting a better system. Pound for pound the additional features of a trunked system outweigh the extra cost.
Glad you asked! Let’s start with Fayette County. They are currently using an 800 MHz trunked radio system for police, fire and EMS. Allegheny, Armstrong and Beaver County have applied for or are licensed on 800 MHz trunked radio frequencies and are evaluating plans to implement their own county wide trunked networks in the future. It’s not hard to envision, in the not too distant future, a high technology radio network encompassing Southwestern Pennsylvania. As of this time, Butler and Washington County are continuing to use conventional radio systems.
How will trunking help?
Trunking is mobile data friendly and can be designed to handle any number of units. Because frequencies in the 800 MHz band are protected, you are assured of having a clear channel for data communications. Additionally, units will have access to the Commonwealth’s CLEAN system along with potential access to resident and remote databases. Also, NCIC 2000’s new capabilities will be available such as, mugshots, fingerprinting, access to new Federal Databases and linkage fields (providing the ability to associate multiple records with the same criminal or the same crime.)
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What is the length of the migration period from the existing to trunking system? |
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The County intends to support and dispatch existing conventional systems until at least January 1, 2006. |
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| Q: |
Presently we have what we refer to as a private channel. Will we have this capability with 800 MHz? |
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Yes. |
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| Q: |
At its implementation, will we be able to choose the manufacturer or make of our radios? |
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Probably not as each system is proprietary and radios only work on systems from the same vendor. |
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If the answer to the above question is no, will we ever be able to choose the make? |
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Perhaps. If the selected vendor enters into licensing agreements with other manufacturer, other equipment choices may be available in the future. |
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| Q: |
After the conclusion of the migration period, will be able to communicate directly with other agencies that are not necessarily converting to 800 MHz ( such as DCNR, PSP) without having to utilize two radios ( in other words, will the county utilize conventional interface?) |
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Yes, there will be a conventional interface but it is not anticipated that permanent patches between the 800 MHz and conventional systems will be used. Therefore a separate radio may be needed to talk to other systems. |
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| Q: |
How many new towers will be erected with the 800 MHz system? |
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That will depend on the selected vendors design. It is estimated that between 9 and 12 sites will be needed. |
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| Q: |
How many channels do you plan on having? |
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The County has ten (10) 800 MHz channels licensed for use in the system plus the two (2) existing detective channels which can be incorporated later. |
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| Q: |
What will the price of the radios be? |
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Pricing is not available yet, but user radios are anticipated to cost between $1000 and $3500 at list pricing, before discounts. |
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| Q: |
Will the County be able to develop a contract purchasing plan to assist us in acquiring radios? |
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Yes, this has been included in the specification. |
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Will the County guarantee that service will be equitable between different services and/or agencies. |
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Yes. |
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Will there be enough channels to avoid “wait tones”? |
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During normal conditions, yes. During very busy periods, or upon equipment failure, some busies are to be expected. |
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Will we have encryption capabilities? |
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Yes, optional on digital radios. Analog radios will not support encryption. |
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| Q: |
Will the system be set for MDT usage? |
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Yes, as a future application. |
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| Q: |
If a site fails, will we be able to utilize another site even with multiple failures? |
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Yes, the back bone system will be fault tolerant with no single point of failure. |
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| Q: |
What is the direct unit to unit communications capability, without using a repeater? |
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Unit to unit talk-around capability will be supported. |
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Will there be a multi-site controller? |
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Probably. This is a final design issue depending upon which vendor is selected. |
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| Q: |
Has the Fayette County 800 MHz trunking experience been reviewed? |
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Yes. |
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| Q: |
Would it be advisable for us to retain some of our current high band radios? |
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That will be up to each agency depending upon its needs. One of the main objectives of the system is to get everyone on the same platform so only one radio is needed. |
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| Q: |
Will we be able to program our own radios? |
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Technically, yes. This and other system administration issues remain to be worked out during system implementation. |
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