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1G CELLULAR SYSTEM :- AMPS
Transcript of 1G CELLULAR SYSTEM :- AMPS
AMPS in General :-
AMPS: Advanced Mobile Phone System Known as First Generation Wireless.
Analog channels of 30 KHz.
Uses Frequency Division Multiple Access
Uses frequency reuse – people in other cells can use your frequency without interference.
Introduced in 1983.
Must be supported by every wireless carrier until February, 2008.
On Star still uses AMPS.
In 2005, 15% of Alltel’s customers were still using AMPS.
Replaced by TDMA and now CDMA (all digital) technologies.
Cellular development didn’t start in earnest until 1984, until after the Bell breakup.
The FCC allocated space in the 800 MHz FM band.
824.04 to 848.97 MHz and 869.04 to 893.97 MHz are the ranges used.
Airphone, Nextel, SMR, and public emergency services take up the 849 – 869 MHz
Cellular phones take up 50 MHz total, which is quite a chunk.
FM broadcast takes up 20 MHz, from 88 MHz to 108 MHz with 133 stations to broadcast on with a channel of 150 KHz.
Cellular uses a channel that is 30 KHz wide.
Cell phone providers have agreed that only 21 frequency pairs can be control channels.
So, the cell phone must scan only 21 frequencies to find its control channel.
The control channels are called:
Forward control path: Base station to mobile
Reverse control path: Mobile to base station
So, there are actually 4 communication frequencies involved in cellular communications.
The control channel is no longer used once the mobile has been assigned a voice channel.
Signaling is done in band from then on out.
When you first turn your phone on, it does a self diagnostic check.
It then scans each of the 21 forward control channels (base station to cellular), camping on the strongest one.
The phone rescans every 7 seconds to make sure that this channel is still the strongest.
The mobile then decodes the data stream being sent by the base station.
Note: The data paths are actually digital. So, AMPS is actually a hybrid system, though the voice is analog.
The data stream has information on what network the phone is on.
Using this, the phone can decided if it is roaming.
Registration Data Stream :
The control data is passed digitally at a rate of 10, 000 bps.
But, because analog waves experience a lot of interference, everything is sent at least twice.
The actual data rate is on average 1200 bps.
Slow, but it gets the job done.
AMPS Review :
Uses 4 frequencies to make a phone call.
2 for control, 2 for voice.
Channels are 30 KHz wide.
Operates in the 800 MHz band.
The voice is analog.
Every carrier must support until February of 2008.