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Cellular Networking Perspectives

David Crowe’s Wireless Telecom Magazine Articles

Q2 2005 Issue

General Mobile Radio Service (GMRS)

You’ve seen them at amusement parks, on ski hills, out camping and at the CNE – families doing their own thing but keeping in touch through walkie-talkie like radios. A few years ago these would have been Family Radio Service (FRS) phones, but increasingly the more powerful and functional GMRS (General Mobile Radio Service) radios are being seen. In fact, even before these radios were legal in Canada, American families were probably bringing them innocently across the border.

GMRS has been available in the US for several years. Consumer demand pushed Industry Canada to recognize the inevitable and allow their use here, although with more restrictions. The restricted service introduced in 2004 is designed to enhance its applicability for family communications, reduce its desirability for unintended uses and, perhaps most importantly of all, reduce the impact on previously licensed users of this spectrum.

The radios are similar to those used for private radio services by businesses, government and public safety agencies. Most are solid, well-built devices, not the flimsy walkie-talkies of our youth which barely had more range than two tin cans and a string. Despite their similarity to mobiles used for work, the GMRS frequencies are reserved for purely personal communications (the US FCC actually limits it to “an adult and their immediate family members, including a spouse, children, parents, grandparents, aunts, uncles, nephews, nieces, and in-laws,” implying that even family friends are outside the scope). The use of this radio system for business or other purposes is discouraged, although it is difficult to enforce this. In large U.S. cities, such as New York, business users of GMRS and FRS have been a significant nuisance. By trying to save money by obtaining a cheaper ‘private’ radio system, they end up overloading the system and making it unworkable for its intended users.

How GMRS Works

GMRS is a ‘push to talk’ radio system, with mobiles operating in ‘simplex’ mode on a single frequency (unlike cellular which uses ‘duplex’ mode, requiring one frequency to transmit and another to receive). A mobile is normally in receive mode, but when the ‘push to talk’ button is pressed, it stops receiving and starts transmitting.

Power is all important with radio systems, and one of the benefits of GMRS is that it usually operates with at least double the power available with FRS radios (0.5 Watts). In the United States, GMRS power can be as high as 4 watts for a handheld device (and much higher for repeaters and base stations), but in Canada it is limited to 2 watts, which will reduce the likelihood of interference between GMRS groups in crowded places and will allow a battery life of more than a day under normal usage conditions. FRS radios rarely reach 2 km, but GMRS can reach three to four times as far under ideal circumstances. Since communications are line-of-sight, the number of objects visible at the level of the radio is a reasonable indicator of the difficulties faced by the radio in transmitting. The range of mobiles will be reduced in difficult terrain, such as hilly areas and urban centers with high-rise buildings.

Now that 2-watt radios are approved in the Canada, the GMRS Alliance (GMRSA) is working with Electro-Federation Canada to investigate the approval of 5-watt mobiles. Before this can be approved, both radio interference and human safety issues have to be examined by Industry Canada and its advisory boards.

GMRS has similarities not only with FRS, but also with CB (Citizen’s Band) radio which has become famous for its association with truckers and infamous for its pollution by foul language. CB operates at much lower frequencies, 26-27 MHz, using AM (Amplitude Modulation) instead of FM (Frequency Modulation). This makes CB more prone to ‘skip,’ causing interference between very distant mobiles. These extraordinarily long-distance interferences only occur with FM under unusual atmospheric conditions. Most of the time, because it is ‘line-of-sight’ communications, FM provides reasonably consistent coverage in a specific area.

Like FRS and CB, but unlike cellular, GMRS has manual channel allocation. There is no network to assign a different (idle) channel to each user. This means that users need to respect other people, communicating only when the channel they are using is free. Alternatively, the users can change to a different, less busy channel, but each radio in the group will have to do this at the same time.

To reduce cross talk, many GMRS radios transmit a special tone while a person is talking. Radios are designed to mute when a different tone is received, meaning that they will not hear the conversations of other groups on the channel they are using (but it does not mean that they can use the channel at the same time).

GMRS is designed only for radio-to-radio communications. It is illegal in both the United States and Canada, for example, to connect a base station or mobile into the public telephone network. This restriction is to ensure that the airwaves do not get over-saturated by people using these phones as cellular-like devices with free airtime.

GMRS is also not to be used for packet data systems, but data complementary to its main use for voice communications is allowed. Mobiles can provide text messaging, for example, or other types of data that are initiated by a mobile user (not automatically). The only automatic data mechanism allowed is an automatic response by GPS-equipped mobiles to a query for their location. No matter what kind of data is used, the mobiles are limited to transmissions that last no more than 1 second, and to no more than one transmission every 30 seconds.

GMRS has been allocated 15 channels at 462 MHz and a matching set at 467 MHz. The 462 MHz channels are used for most purposes, with the 467 MHz frequency range being reserved for transmission to a repeater. A repeater is a more powerful radio that receives a communication on a 467 MHz channel and retransmits a little bit later, at a significantly higher power (up to 50 watts), on the 462 MHz channel exactly 5 MHz lower. This can extend the mobile-to-mobile (actually, mobile-to-repeater-to-mobile) range up to 50 km. However, at present, repeaters are allowed in the United States but not in Canada.

The range of a GMRS mobile can also be extended with base stations for some applications. These allow mobile-to-base communications when all mobiles are in the range of the base station but not necessarily within range of each other. Base stations use the normal 462 MHz channels, but the same higher power as repeaters. However, their range is more limited because they do not have the same large antenna. These higher powers are, just like repeaters, not yet allowed in Canada.

Table 1: GMRS Frequencies
Channel Simplex Channels Transmit to Repeaters

1

462.5500 MHz

467.5500 MHz

2 (*)

462.5625

467.5625

3

462.5750

467.5750

4 (*)

462.5875

467.5875

5

462.6000

467.6000

6 (*)

462.6125

467.6125

7

462.6250

467.6250

8 (*)

462.6375

467.6375

9

462.6500

467.6500

10 (*)

462.6625

467.6625

11

462.6750

467.6750

12 (*)

462.6875

467.6875

13

462.7000

467.7000

14 (*)

462.7125

467.7125

15

462.7250

467.7250

* indicates that the channel pair is also used for FRS.

Canadian Problems

FRS and GMRS are not being introduced into virgin spectrum in Canada. Industry Canada previously had 127 licensees in this band, operating 108 base stations and 4,590 mobile devices. 65 of these users were determined to be critical users, according to Rob Morse, Project Manager with Electro-Federation Canada. This included cardiac monitoring equipment in several hospitals and radios used for communications by a number of fire departments. All but two of these have either had their radios retuned or, in a few cases, replaced, often choosing to move up to the 600 Mhz band. Other, less critical, users are not believed to be at great danger of interference. Some may simply purchase GMRS radios to replace their current equipment, since it is more compact and functional than their current equipment.

The retuning plan was essentially the same as one implemented for the FRS frequencies in 2000. Industry Canada required that distributors of radios work with the non-profit Electro-Federation Canada (EFC) to develop and fund the ‘retuning’ plan, to ensure a smooth transition of current users to other frequencies. The manufacturers are represented by the GMRSA, and currently nine major radio distributors in Canada are members. These companies are subsidizing the cost of moving others out of their new playing field.

Funding the retuning exercise gave the GMRSA members the exclusive right to sell GMRS radios for one year, to help them recoup the cost of the project. Future market entrants will also have to pay part of the retuning costs as they enter the market.

Table 2: GMRS Alliance Participants (March 2005)

AVS Technologies

Columbia Communications

Cosmo Communications Canada Inc.

Garmin International Inc.

Lectron Radio Sales Ltd.

Lenbrook Industries

Midland Radio Corporation

RadioShack Canada

Sonigem Products Inc.

Source: EFC


In the United States, a license costs US$80 and lasts for 5 years, but Canadians get a break and don’t have to pay license fees for GMRS. FRS is not licensed in either country. Even though a license is not required, consumers should be aware that all GMRS phones used in Canada must be certified for use here.

Canadian families will benefit from this newer radio system with more functionality than FRS. There is a danger, however, that the restrictions on its use will prove difficult to enforce, leading to a degradation in the usefulness of the service over time. Without license fees, it is unlikely that the government will be highly motivated to spend money monitoring transmissions for violations. Hopefully, this will not be one of those times when a few rotten eggs spoil the omelet for everyone.

Table 3: Useful GMRS Websites

Organization and Purpose

Website

Electro-Federation Canada (EFC)

www.electrofed.com

Industry Canada

Spectrum Management and Telecommunications
(Amendment 4 to RSS-210 for GMRS)

strategis.ic.gc.ca/epic/internet/
insmt-gst.nsf/en/sf08202e.html

Industry Canada

Spectrum Provisions for License-Exempt General Mobile Radio Service Products
at 462/467 MHz

www.strategis.ic.gc.ca/epic/internet/
insmt-gst.nsf/vwapj/sp462.PDF/$FILE/
sp462.PDF

Personal Radio Steering Group

www.provide.net/~prsg/wi-gmrs.htm

Personal Wireless Bulletin Board

www.popularwireless.com/cgi-bin/Ultimate.cgi

U.S. Federal Communications Commission (FCC)

wireless.fcc.gov/services/personal/generalmobile

About the Author

David Crowe is a wireless standards, numbering resource and technology consultant based in Calgary. He can be reached at David.Crowe@cnp-wireless.com.

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