25-08-2017, 09:32 PM
NIPPON TELEPHONE
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INTRODUCTION
The worlds first cellular system was implemented by NIPPON TELEPHONE and telegraph company (NTT) in Japan . The system ,deployed in 1979 , uses 600 FM duplex channels (25 kHz for each one link) in the 800 MHz band. In Europe , the Nordic Mobile Telephone system (NMT) was developed in 1981 for the 450 MHz band and uses 25 KHz channel . The European Total Cellular System (ETACS) was deployed in 1985 and is virtually identical to the U.S. AMPS system , except that the smaller bandwidth channels result in a slight degradation of signal to noise ratio (SNR) and coverage range. In Germany , a cellular system called C-450 was introduced in 1985 .The first generation European cellular systems are generally incompatible with one another because of different frequencies and communication protocol used. These systems are are now being replaced by the PAN EUROPEAN DIGITAL CELLULAR STANDARD GSM (Global System for Mobile )which was deployed in 1990. in a new 900 MHz band which all of Europe dedicated for cellular system with modern network features.
PLANNING A CELLULAR SYSTEM
How to start planning
Assume that the construction permit for a cellular system in a particular market area is granted .the planning stage becomes critical.Agreat deal of money can be spent and yet poor service may be provided if we do not know how to create a good plan.First we have to determine two regulations-
REGULATIONS
The Federal regulations administered by FFC are the same throughout the United states . The state regulations may be different from state to state,each city and town may have its own
Building codes and zoning laws.Become familiar with the rules and regulations.The plan is workable.
SYSTEM FUNDAMENTAL DESIGN
The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity. It offered very high capacity in a limited spectrum allocation without any major technological changes. The cellular concept is a system level idea which calls for replacing a single , high power transmitter (large cell) with many low power transmitter (small cells), each providing coverage to only a small portion of the service area. Each base station is allocated a portion of the total number of channels available to the entire channel, and near by base stations are assigned different groups of channels. So that all the available channels are assigned to a relatively small number if base stations.
CELLULAR TELEPHONE SYSTEM
A cellular telephone system provides a wireless connection to the PSTN for any user location within radio range system.Cellular systems accommodate a large number of users within a large geographical area, within a large geographical area. High capacity is achieved by limiting the coverage of each base station transmitter to a small geographic area called CELL so that the same radio channels may be reused by another base station located some distance away. A sophisticated switching technique called a HAND OFF enables a call to proceed uninterrupted when the user moves from one cell to another cell.
The MOBILE SWITCHING CENTRE(MSC) is also called MOBILE TELEPHONE SWITCHING OFFICE(MTSO) since it is responsible for connecting all mobiles to the PSTN in a cellular system. Each mobile communicates via radio with one of the base stations and may be handed off to any number of base stations throughout the duration of a call.