Which technologies were used in 0G or Mobile Radio Telephone system ?
The following technologies were used in 0G or Mobile Radio Telephone System 1) Push to talk 2) Mobile Telephone System (MTS) 3)Improved Mobile Telephone Service (IMTS) 4) Advanced Mobile Telephone System (AMTS) systems 5) MTD (Mobile telephony system D) 6) OLT (Offentlig Landmobile Telefoni or Public Land Mobile Telephony).
Push-to-talk (PTT) also referred as Press-to-Transmit provides half duplex communications to the two way radio i.e. only one person will speak at a time and other should hear. Here a button was used to switch different operations i.e. when a person wants to speak the button should be pressed; this enabled the transmitter and the receiver gets disabled automatically. Button should be released when they are done. Similarly the listener presses the button to reply; hence it was named as push to talk. Push-to-talk (PTT) also supports group calling i.e. one person can speak with many other persons of the same group. In this system only one large transmitter with single channel was used for both sending and receiving.
Example: At the airport, the air traffic controller uses one radio frequency to speak to all the pilots under him, in such a way all other pilots are aware of all the aircrafts position at that moment.
Mobile telephone system (MTS) was introduced in United States in 1946. Mobile telephone system used transceivers, these transceivers were too large to carry, so they were placed in vehicles .Mobile telephone system (MTS) was an analog system using half duplex mode of communication (voice signals can either be transmitted or received at an instance of time).In MTS system the entire land was divided into sections where each section had a Base station with a single high power transmitter which controls all the operations of that section. All the base stations in every section used the same frequency, so in order to avoid radio interference the base stations needed to be far away from each other. MTS used Push To Talk (PPT) technique. It used a PPT switch to turn on/off the transceiver. Pressing the PPT switch would turned on the transmitter and releasing the switch would turn on the receiver and the transmitter would automatically get off. When the user needs to make a call the callers need to make a call to the MTS operator where the operator would ask for the Mobile subscriber number and would find an idle channel for transmitting the call to the mobile terminal. The calls in MTS were switched manually. The major drawback of MTS was congestion as only three channels were provided that means only three voice calls would be made at a time in a specific sector.
Improved Mobile Telephone Service (IMTS) was an advance version of MTS (Mobile telephone service). IMTS was the first full duplex system (voice signals can be transmitted and received at the same time), two way communications were supported. Push to talk system was eradicated which was the prime factor of MTS. The main advantage of IMTS was that it supports direct dialing i.e. the user can directly call PSTN (Public switched telephone network) rather than calling operator. IMTS used transmitter of 200 watt, this high powered transmitter was placed on a hill top to cover the entire town or city (covered area is referred as cell).In IMTS Bandwidth was narrowed to attain more number of frequencies. Using IMTS each call needed two radio channels one channel to transmit and one of receive. Only 33 channels were available with operating frequencies Roaming was not support due to lack in number of channels. As the high powered transmitters and same frequency were used neighboring cell had to be far away from each other in order to avoid interference. Fading is one of the major problems of Improved Mobile Telephone Service (IMTS).
Mobile telephone System A: Mobile telephone System A was the first telephone system in Sweden which was developed by Sture Lauhren and Ragnar Berglund at Swedish Telecom. In 1956 MTA started of with its commercial services. It was the first automatic mobile telephone system in the world which provides direct calling i.e. the user can dial and get a call from the other telephone user without the telephone operator’s support. This system had 125 subscribers; this system was mostly used by banks, industries, government offices, various agencies and transport companies etc. The drawback of this system were the telephone size was bulky , call setting time was more , the system was bit complex so using the system was difficult. With these limitation this system was demolish in 1969.
Mobile telephone System B: Mobile telephone System B was the modified version of Mobile telephone System A developed by Berglund. In 1965 MTB started of with its commercial services in Stockholm. The Swedish Telecom company gave the mobile telephones on rent to the subscribers. The call could only be made up to three minutes, after three minutes the call becomes noisy and had to be disconnected. This system had 600 subscribers. MTB was demolished in 1983.
Mobile telephone System D: Mobile telephone System D also known as Mobiltelefonisystem D in Swedish was introduced in 1971 in Sweden. This system worked on the frequency band of 450 MHz. This system had 80 radio channels and 110 radio base stations. More than 700 operators were used in this system. To make a call the user need to know the location of the other end user i.e. the other subscriber (to whom the call was to be received) so that the operator could transfer the call to the nearest radio base station. This network had 20,000 subscribers. MTD was also used in Denmark and in Norway and allowed roaming facility within the Scandinavian countries. This System was demolished in 1987.
OLT (Offentlig Landmobile Telefoni or Public Land Mobile Telephony):Public terrestrial mobile telephone service also known as Norwegian for Offentlig Landmobil Telefoni (OLT) was the first manual mobile telephone system. OLT was launched by Televerket in 1966. The OLT network works on VHF band 160MHz where Frequency modulation technique is used on 160 -162 MHz (Mobile Unit) and 168-170 MHz (Base Station). The Major parts of country didnot have coverage but in 1981 it had 30,000 subscribers which made it the world’s largest network of that time. Each user was allotted five digit number. Mobile used for this network were mostly Half duplex (voice signals can either be transmitted or received at a time) except few expensive mobiles. These Expensive mobiles were full duplex (voice signals can be transmitted and received at the same time).The main drawback of OLT system was anybody could hear the conversation and with the increase in number of subscribers the service went short of capacity.