Branch : Computer Science and Engineering
Subject : Wireless Communication
AMPS and ETACS System
Introduction:
AMPS and ETACS are two initially used cellular system and these system use frequency modulation. In AMPS the maximum deviation of the FM modulator is ± 12 kHz
AMPS System:
- In the United States, transmissions from mobiles to base stations (reverse link) use frequencies between 824 MHz and 849 MHz, while base stations transmit to mobiles (forward link) using frequencies between 869 MHz and 894 MHz
- For AMPS, the maximum deviation of the FM modulator is ± 12 kHz
- The control channel transmissions and blank-and burst data streams are transmitted at 10 kbps for AMPS
- These wideband data streams have a maximum frequency deviation of ±8 kHz for AMPS,
- AMPS cellular radio systems generally have tall towers which support several receiving antennas and have transmitting antennas which typically radiate a few hundred watts of effective radiated power
- Each base station typically has one control channel transmitter, one control channel receiver, and eight or more FM duplex voice channels.
- Each base station in the AMPS system continuously transmits digital FSK data on the forward control channel (FCC) at all times so that idle cellular subscriber units can lock onto the strongest FCC wherever they are
- In the U.S. AMPS system, there are twenty-one control channels for each of the two service providers in each market, and these control channels are standardized throughout the country.
- In each U.S. cellular market, the non-wire line service provider (the "A” provider") is assigned an odd system identification number (SID) and the wire line service provider (the "B" provider) is assigned an even SID.
- The SID is transmitted once every 0.8 seconds on each FCC, along with other overhead data which reports the status of the cellular system
ETACS System:
- ETACS uses 890 MHz to 915 MHz for the reverse link and 935 MHz to 960 MHz for the forward link.
- For ETACS, the maximum deviation of the FM modulator is ± 10 kHz
- The control channel transmissions and blank-and burst data streams are transmitted at 8 kbps for ETACS
- These wideband data streams have a maximum frequency deviation ±6.4 kHz for ETACS,
- ETACS cellular radio systems generally have tall towers which support several receiving antennas and have transmitting antennas which typically radiate a few hundred watts of effective radiated power
- Each base station typically has one control channel transmitter, one control channel receiver, and eight or more FM duplex voice channels.
- ETACS supports forty-two control channels for a single provider.
- Thus any cellular telephone in the system only needs to scan a limited number of control channels to find the best serving base station
- For ETACS, area identification numbers (AID) are used instead of SID, and ETACS subscriber units are able to access any control or voice channel in the standard