- History of Cellular Telecommunication
Cellular Telecommunication has a rather long history. The first commercial wireless telecommunication system was MRS (Mobile Radio Service) which the U.S. Detroit Police Department mobilized in 1921. For MRS, 2㎒ transceivers were mounted in vehicles. The first publicly opened system was Citizen's Band Radio with 40 channels on 27㎒ band.
Mobile telecommunication system rapidly grew from the 1960s. FCC in 1974 secured 806㎒-947㎒ band for mobile telecommunication system by removing unused UHF TV channel. In April 1981 FCC accepted the concept of cellular telecommunication, and in November 1982 it authorized the service on 800㎒ frequency band (824~849㎒ for mobile transmission and 869~894㎒ for base station transmission). FCC authorized analogue mobile telecommunication with voice FM (Frequency Modulation) and FSK(Frequency Shift Keying) signaling. As the result, Bell Lab's AMPS (Advanced Mobile Phone System) entered the stage. AMPS's each of 832 channels' bandwidth is 30KHz.
- Concept of Cell
A base transceiver station's span of coverage is called a cell. Usually hexagon shapes are used better to show how the system is laid out. Each BTS has a unique frequency not to be interfered from adjacent cells. The actual cell shape is more or less round, and has various forms according to its surrounding terrain and subscriber density.
- Cell Types
Cells are classified into Umbrella Cells (100km range, for satellite mobile), Hyper Cells (20km range, for rural area), Macro Cells (1~20km range, for highways and suburban areas), Micro Cells (50m~300m, for cities and urban areas) and Pico Cells (within 100m range, for in-building mobile). Since GSM900 and DCS1800's maximum ranges are 35km and 10km respectively, umbrella cells are not used in GSM networks. The other four types are all used in GSM networks.
- Cellular System Architecture
Every cellular base transceiver station has a powerful receiver and transmitter, a controller and an antenna. Usually hexagon shapes are used better to show how the system is laid out, the actual cell has various forms. Base stations have omni antennas or 120 degree antennas and employ sector antennas when focusing the power to a specific direction or increasing the capacity. A mobile phones is consists of a low-power transmitter and receiver, an antenna and a microprocessor control unit.
If during a connection the base station's signal becomes weak, the mobile phone moves to another channel. This is called handoff. The user will not perceive the handoff, but it gives the data communication critical effects. Each mobile phone has ESN (Electronic Serial Number) and MIN (Mobile Identification Number) to be authenticated every time it tries a connection.
- What is PCS?
PCS the same digital mobile telecommunications service except using different frequency band (800㎒ for cellular and 1.7GHz for PCS). Similar case is TV broadcasting: VHF is using 30㎒~300㎒, while UHF is using 300㎒~3GHz. The idea for PCS (Personal Communications Services) was that the people can communicate 'any kind' of information at 'anytime', 'anywhere'. In PCS system, each user is provided with UPT (Universal Personal Telecommunication) Number, a personal number, then the user roams freely all around the world, but the system was not realized because of a conflict between Europe and the U.S.
- Cellular versus PCS
▶ Transmission distance: Stable communication is secured by a long-distance transmission. Owing to a long-distance transmission quality, 800㎒ frequency can cover a wide range. 1.7GHz is not capable to cover a wide range due to a short-distance transmission quality.
▶ Radio Wave Diffraction: When a radio wave passes a barrier's end, the wave diffracts around the object. High diffraction capability of 800㎒ aids wave dispersion, and the lower diffraction capability of 1.7GHz produce blind spots.
▶ Radio Wave Transmissivity: High transmissivity aids radio wave to penetrate into buildings and mountain areas. Unlike 1.7GHz, higher transmissivity of 800㎒ radio wave suffer less affects from obstacles, such as high-rise buildings and mountainous terrain. Although PCS providers ads the high frequency ensures a quality services, but the there is no relationship between high frequency and a quality service. 800㎒ frequency band, suitable for mobile telecommunication, was all used up. So PCS's using 1.7GHz band is not because the band is good for a multimedia service, but because there was no alternative.
- System setup cost for PCS and Cellular system
Because PCS needs smaller range micro cells (50m~300m), while cellular communication is based on macro cells (1~20km range), PCS needs more base stations. However, the small size of its base stations, lower installation and space maintaining costs make PCS system cheaper to set up a network.
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