S2L13 & S2L14 - Mobile Phones Communication (Movement of mobile Phone:…
S2L13 & S2L14 - Mobile Phones Communication
First Generation Mobile Phone: Analog Voice
Used a single large transmitter on top of tall building with single channel for sending/receiving.
Due to small number of channels, had to wait for dial tone.
Due to large power of transmitter, adjacent systems had to be several kilometres apart to avoid interference
System coverage improved with AMPS.
Through use of relatively small cells and the reuse of transmission frequencies in nearby cell
While IMTS can have 100km accross can have one call on each frequency, AMPS may have 100 10km cells in same area with 10 to 15 calls on each frequency
Movement of mobile Phone: handoff
At any instant, each mobile is logically in one specific cell and under control of cell's base station.
If mobile fading, base station notices and queries surrounding stations how much power from it.
Base station transfers ownership to cell getting strongest signal, i.e, cell location of telephone.
Mobile informed of change and asked to switch to a new channel.
Process called handoff and takes about 300 ms
2 ways of performing handoff
In soft, the phone is acquired by new base station before previous one signs off. No loss of continuity. Downside: Phone needs to be ab;e to tune to two frequencies at the same time
Old station drops mobile phone before new one acquired it.
Call Management in AMPS: Registration
Each telephone in AMPS has 32-bit serial number and 10 digit phone number
When phone switched on, scans a preprogrammed list of control channels to find most powerful
Phone broadcasts 32-bit serial and 34-bit telephone number.
When base station hears announcement, it tells MTSO, which records new client
Performing/Making a Call
Phone transmits number to be called on its own id on the access channel
If collsision, try again later.
When base station gets request it informs MTSO.
If caller a customer, looks for an idle channel for a call
If one is found, channel number sent back on the control channel.
Receiving a Call
Al idle phones continuously listen to paging channel to detect messages directed at them
Packet is sent to callee's MTSO to find out location
A packet then sent to base station in its current cell which then sends broadcast on paging channel.
Called phone replies yes on access channel and switches to required channel for call
Uses same channel frequency so that one channel can be analog and adjacent ones digital
In D-AMPS 1/3 of the time mobile is neither sending or receiving
It uses these idle slots to measure line quality
When discovers signal fading, contact MTSO which can break connection for mobile phone to try tuno to stringer signal
Allows each station to transmit over entire frequency spectrum all the time