The following technologies were used in 1G or First generation of Wireless Telecommunication Technology:
Advance Mobile Phone Service (AMPS), Nordic Mobile Telephone (NMT), Total Access Communication System (TACS).C-NETZ , Radio Telephone Mobile System (RTMS) ,Nippon Telephone and Telegraph (NTT) and later NTACS (Narrowband Total Access Communications System) and JTACS (Japanese Total Access Communication System)
Advance Mobile Phone Service (AMPS) The limitations in Improved Telephone System and increase in number of telephony user led to the advent of new concept known as Advance Mobile Phone System .Cellular radio technology was used in Advance Mobile Phone System. This technology would accommodate maximum users with high quality of mobile service. Advanced Mobile Phone System was allocated with a spectrum bandwidth of 40 MHz, it worked on the principles of seven reuse pattern with cell splitting and sectoring. Cell Splitting and sectoring were used to increase the cell capacity. All cells were connected to each other and to the Mobile Telephone Switching Office by optical fiber. In this system calls were not connected directly, the calls were transmitted to cell center and Mobile Telephone Switching Office. Single channel consist of two frequencies. Transmissions were done using forward channel (channel used for base to mobile transmission) and reverse channel(channel used for mobile to base transmission) were forward channel was allocated frequency ranging from 869 – 894 MHz and reverse channel was allocated frequency ranging from 824 – 849 MHz. Here users were not connected directly, whenever the user dials a telephone number from the mobile unit (mobile unit contains an antenna and transceiver), a send button should be pressed then the phone starts searching the channels for a strongest signals and the call is transmitted to cell site, cell site establishes a connection between the user and Mobile Telephone Switching Office (MTSO). MTSO processes the call and the call is setup between the users .While the call in still in process the Mobile Telephone Switching Office monitors the signal strength and if a greater signal strength in found in adjacent cell the call is transferred to that cell (This scenario occurs when the user in moving ahead area covered by one cell and nearing to the other cell). When the user had moved out completely from the cell the same channel which the user was using before is allotted to a new user. When same channel is used for different users it is known as frequency reuse. Here MTSO is the main part this system, it provides administration over the system, it controls call processing, it co ordinates the working of all cell sites, establish connection with telephone company offices, it maintains co ordination between all cell sites. It also handles billing activities.
Nordic Mobile Telephone (NMT)
NMT-450 was analog cellular telephony system which was first operated in Scandinavia on 1st October 1981. NMT-450 provided 220 channels using frequency band of 450 MHz .Each cell in NMT-450 was capable of covering a very large area. The telephone instruments were almost like other telephone set but were slightly heavier than others. NMT was the first full duplex cellular system that provides automated calling and international roaming. NMT used FDMA/FDD technique with the downlink frequency in the range of 463-467.5 MHz and uplink frequency in the range of 453 – 457.5 MHz .NMT was very popular and with the continuous increase in number of user lead to congestion in the network as the number of channels were limited. These limitations in resources lead to invent of NMT-900. NMT-900 was introduced in 1986 in Nordic countries. NMT-900 provided much more number of channels as compared to NMT-450. NMT-900 operates in the frequency range of 900 MHz. In NMT network the downlink frequency is in the range of 935 – 960 MHz and uplink frequency is in the range of 890 – 915 MHz. In NMT network cell sizes were in the range of 2Km – 30 Km.
NMT system consisted of four parts
1) Mobile Telephone Exchange (MTX)
2) Home location Register (HLR), integrated in MTX or sometimes as a separate node
3) Base Station (BS)
4) Mobile Station (MS)
Mobile Telephone Exchange (MTX) and Home location Register (HLR) are the main parts of the system which controls the working of the system and provides an interface to the Public Switched Telephone Network (PSTN). Base Station (BS) are connected to the Mobile Telephone Exchange (MTX) and are used to handle radio communication between the Mobile Station (MS).Base Station (BS) also controls the radio link Quality between the calls. Mobile Station (MS) can be installed in vehicles or can be hand-portable which is connected to the nearest Base Station (BS) over radio. In NMT network the Mobile Station (MS) connects to the nearest Base Station (BS) through radio, this Base Station (BS) is further connected to Mobile Telephone Exchange (MTX) and one Mobile Telephone Exchange (MTX) is connected to other Mobile Telephone Exchange (MTX) either by direct circuits or by PSTN.
Suppose a PSTN (Public Network) user wants to call a mobile user then the connection has to setup between the MTX (Mobile Telephone Exchange) and the Public Network or PSTN.
This MTX can also be called as MTX G (Gateway MTX). This MTX G contains all the information about other MTX connected to it. The MTX G will find in which MTX is the Mobile Station exists (The information about all the mobile station under one MTX is found in subscriber register). Once the MTX H (Home MTX) where the mobile station exists is found a connection is made between the MTX G and MTX H. Now the Radio Connection is setup between the Base Station (Which is nearest to the Mobile Station) and the MTX and the communication can be done. As NTM is a Full Duplex System both the receiver and the caller can hear and talk to each other simultaneously. The main disadvantage of NMT was any one can listen to call with the scanner device as the voice traffic was not encrypted. In order to avoid this later manufactured scanner were made in such a way that the NMT bands were inaccessible but again it is easy to reprogram scanner to access the NMT bands or old scanners which can access NMT bands were easily available in market so the call is not secure. Later Analog encryption technique was included in NMT networks which worked on principle of two band audio frequency inversion. In this if both the mobile stations supports encryption they can turn it on before speaking and the audio (conversation) gets encrypted before transmission from mobile station to base Station . Here even if the base station does not support encryption the audio can easily be transmitted to the other Mobile station. And this encrypted data cannot be listened by scanner thus preventing the listening of calls through scanners. The encryptions system can easily decrypted using digital devices hence security of data is the major concern. The main disadvantage of NMT were low calling capacity , limited spectrum , poor data communication support and lack of privacy.
Total Access Communication System (TACS)
TACS was the first generation analog cellular technology which operates in 900 MHz frequency and provides 1000 channels. The main aim of this technology was to accommodate large number of users in a network (i.e. it was focusing on capacity instead of coverage).TACS is derived from AMPS (Advance Mobile Phone Service) Technology. It also supported roaming facilities and provides full duplex communication (caller can speak and hear at the same time) . It was first introduced in United Kingdom and later was used by Ireland and other European countries. This system was also used in Japan named as JTACS (Japanese Total Access Communication System). This system was very efficient and economical for the countries with high density of population. This system required large number of cells which can provide coverage to small town (small area) with less powerful transmitters. In United Kingdom the uplink frequency of TACS system was in the range of 890 MHz – 915 MHz and the Downlink frequency was in the range of 935 MHz – 960 MHz. The bandwidth of each channel is of 25 KHz. In this system two channels were required for a telephone conversation. So out of 1000 channels, 300 channels were assigned to Vodafone and 300 channels were assigned to Cellnet. Out of those 300 channels which were assigned to both operators 277 channels were used for speech, 21 channels were control channels and rest 2 channels were guard channels which acts as a guard in between two operators. Bandwidth was divided using FDMA (Frequency Division Multiple Access) Technique which supported single simplex voice channels. In telephonic conversion one frequency is used for sending and other frequency is used for receiving data (Full duplex communication). With the increase in popularity of this system more channels were added to it and the system was then known as Extended Total Access Communication System (ETACS).In ETACS additional downlink (range 917MHz- 933 MHz) and uplink (890 MHz – 915 MHZ) frequencies were allocated.320 additional channels were allocated to both the cellular operators for speech channels. The main drawbacks of this system were limited capacity because of inefficiencies of analog voice transport and limited services because of analog signaling. Due to these drawbacks ETACS was replaced by other more efficient systems like GSM (Second Generation of wireless telecommunication technology).
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(For C-NETZ Reference taken from the book Der Telefon-Ratgeber (The Phone Guide )- Page 124 written by Fritz Jörn)