Mobile Telephone Service

The Mobile Telephone Service (MTS) is a pre-cellular VHF radio system that links to the Public Switched Telephone Network (PSTN). MTS was the radiotelephone equivalent of land dial phone service. As of 2012, only rural and wilderness areas were still using the system.

The Mobile Telephone Service was one of the earliest mobile telephone standards. It was operator assisted in both directions, meaning that if one were called from a land line the call would be routed to a mobile operator, who would route it to one's phone. Similarly, to make an outbound call one had to go through the mobile operator, who would ask for the mobile number and the number to be called, and would then place the call.

This service originated with the Bell System, and was first used in St. Louis on June 17, 1946. The original equipment weighed 80 pounds (36 kg), and there were initially only 3 channels for all the users in the metropolitan area, later more licenses were added bringing the total to 32 channels across 3 bands (See IMTS frequencies). This service was used at least into the 1980s in large portions of North America. [1] On October 2, 1946, Motorola communications equipment carried the first calls on Illinois Bell Telephone Company's new car radiotelephone service in Chicago.[2][3] Due to the small number of radio frequencies available, the service quickly reached capacity.

MTS was replaced by Improved Mobile Telephone Service (IMTS), introduced in 1964.

Channels

[MTS] uses 25 VHF radio channels in the United States and Canada. The channels are identified by pairs of letters taken from positions on a North American telephone dial that, when changed to digits, form (for 12-channel mobile sets) 55, 57, 95 and 97.

In the 1960s plan, the VHF high-band allocations provided for 11 channels in the United States: JL, YL, JP, YP, YJ, YK, JS, YS, YR, JK and JR. In Canada, two additional channels were available: JJ and JW.

12-Channel
Mobile 		ID 24-Channel
Mobile 		Base Station MHz
Transmit Receive
JJ 152.480 157.740
XJ 1 152.495 157.755
1 JL 2 152.510 157.770
XK 3 152.525 157.785
2 YL 4 152.540 157.800
XL 5 152.555 157.815
3 JP 6 152.570 157.830
XP 7 152.585 157.845
4 YP 8 152.600 157.860
XR 9 152.615 157.875
5 YJ 10 152.630 157.890
XS 11 152.645 157.905
6 YK 12 152.660 157.920
XT 13 152.675 157.935
7 JS 14 152.690 157.950
XU 15 152.705 157.965
8 YS 16 152.720 157.980
XV 17 152.735 157.995
9 YR 18 152.750 158.010
XW 19 152.765 158.025
10 JK 20 152.780 158.040
XX 21 152.795 158.055
11 JR 22 152.810 158.070
XY 23 152.825 158.085
12 JW 24 152.840 158.999

Frequency problems and elimination of the service

These channels are prone to network congestion and interference since a radio closer to the terminal will sometimes take over the channel due to having a more powerful signal. The service uses technology that has been manufacturer discontinued for more than three decades.

The driver for replacement in most of North America, particularly large cities, was congestion, the inability of the network to carry more than two dozen channels in a geographic area. Cellular service resolved this congestion problem very effectively, especially since cellular frequencies, typically UHF, do not reach as far as VHF frequencies and can therefore be reused. The ability of a cellular system to use signal strength to choose channels and split cells into smaller units also helps expand channel capacity.

The driver for replacement in remote areas, however, is not network congestion, but obsolescence. Because the equipment is no longer manufactured, companies still using the service must struggle to keep their equipment operating, either by cannibalising from retired equipment or improvising solutions. Due to insufficient traffic, cellular is not a cost-effective replacement. Currently, the only viable solution is satellite telephony, as the small number of "base stations" which orbit the planet serve large geographic regions as they pass over. Cost, however, has been an issue, and the replacement will become acceptable to VHF mobile customers gradually, as the cost of satellite telephony has been dropping and will continue to drop.

Many MTS frequencies are now used for local paging services. They are only found in some parts of rural North America, having been replaced in most areas by cellular service in the 1980s or later.

The service territory of Northwestel has only eliminated ten MTS locations since 2003; in the case of six sites, cellular is available and the company had to rent tower space for five sites, making them even more unprofitable; four other sites had near zero traffic. The remainder of the MTS network is still operating, though at a deficit, virtually blanketing the Yukon and northern British Columbia highway network, the western Great Slave Lake region, the Mackenzie River and the Mackenzie Delta. As noted above, cellular service is too costly to install in these areas due to a more limited signal reach, cellular sites are more complex technology, and they would still require the same logistical support, like electricity supplied from diesel generators, using barged-in fuel.

Operation

All calls were placed by a suitably equipped telephone operator.

Outgoing calls were placed when the operator connected to a base station (originally using a cord board, but by the 1990s could be done by dialing a code sequence from a TOPS position), then announced the call over the channel (giving the channel's name first), e.g.,

"Dawson Channel calling 2M-2368, 2M-2368, 2M-2368."

The page would usually be repeated twice more after a pause. The called party had to have their unit on and the volume set at a level that allowed them to notice a call and then listen to the called number. If the called party heard an incoming call, they would then use the microphone to announce they were receiving the call, and the operator would allow the two parties to speak, monitoring for the end of the call and marking a manual ticket for billing.

The format of such "voice-called" mobile customer numbers varied by jurisdiction. B.C. Tel, for example, used seven-character numbers starting with N or H, a digit (often 1), then five more digits for the individual customer. AGT in Alberta used seven-character numbers.

Soon enough, customer equipment, "selective call", was developed that had a built-in circuit that could be programmed to recognize a five-digit code as its own, in a manner similar to IMTS systems and crude compared to cellular phones. The phone company would assign the customer a number and the customer would have it programmed into the set by the phone company or by a dealer.

The operator would connect to the base station by cord board and key the five-digit number; in the 1990s, phone operators at TOPS positions would key the five digits after dialing the code to initiate the call and then identify the base station; a typical TOPS operator code would consist of a two digit sequence for voice-call or selective call, a three digit sequence for the base station, then the customer number.

The base station would signal the five digit sequence; any and all radios tuned to that base station would detect the sequence and compare it with their own; if it matched, the unit would signal its user with a bell or buzzer, and the user could then answer and announce the identity of their unit, similar to how a voice-call user would respond.

Calls from mobile units to a base station were started by signaling the operator by pressing the microphone button. The operator would plug into the channel (automated TOPS systems routed the incoming call through the normal queue), announce availability and the channel name, and the customer would identify their mobile number. (Security systems were sometimes adopted later to prevent fraud, by the customer giving a confidential number. In an automated connection to the operator, other radios on the base station could hear the transmission from the station, not what the radio user was transmitting.) The customer would then specify the details of their call, either to another mobile or to a landline number, which the operator would then place. The call was manually ticketed prior to the use of TOPS, and automatically ticketed if the mobile user was automatically connected to the TOPS operator.

Very few companies automated MTS to use TOPS as most were able to discontinue MTS services due to the reasons above: they could not meet the service demand except by switching to cellular. Northwestel was one company still offering MTS that tied the base stations into TOPS.

A variant of MTS used short-wave frequencies, and was known as High Frequency or High Frequency-Single Sideband, so named for using frequencies between 3 and 30 MHz. These services required far fewer base stations and were used to reach distant locations over vast territories. The drawback was that the frequencies were extremely noisy from various interference, and were subject to propagation problems due to time of day, mostly due to the sun's effect on the ionosphere. Northwestel, which discontinued the service shortly after 2000, could not tie this system into TOPS, and had to aurally monitor the channels using speakers to listen for incoming calls.

For billing purposes, many MTS base stations were identified with a very close-by rate center of an automatic exchange. However, if there was no nearby rate center, they became an "Other Place Point". Phone companies typically identified these, and single points such as an individual telephone in a rural area, using a six-digit combination of 88T-XXX, where T is a digit from 6 to 9, and X is any digit 0-9. For example, Fox Lake, Yukon Territory, was 889-949. This combination would serve the same purpose as the NANP area code and central office code, with its own latitudinal-longitudinal coordinates, to allow a distance to be calculated for rating of a call. This coding system, which was in its zenith of usage during the 1980s and 1990s, was rendered unusable when the North American Numbering Plan administrator withdrew the 88X codes for future use as toll free (e.g. 1-800-) services.

By the end of the 1990s, very few companies still had need of the Other Place Point codes, and other rating arrangements were made. For example, Northwestel would use the nearest exchange for calls to its mobile points from other phone companies, and would code the locations in its billing software for calls within the company's operating territory. The rate impact was negligible for calls over longer distances.

See also

References

  1. ↑ Regis J. Bates, Donald W. Gregory Voice & data communications handbook McGraw-Hill Professional, 2007 ISBN 0-07-226335-0 page 193
  2. ↑ Motorola First Car Radio Telephone
  3. ↑ History of Car Telephones 1946-1953

External links

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