Cellular provides the only reliable global coverage available today. For truly remote regions without terrestrial tower deployment, compare with Satellite Communication.
Evolution of Cellular Network Technologies
- 1948: First commercial phone
- cell phones, 5,000 users, 30,000 calls weekly
- everyone shares the same signal
- 1965: improved mobile telephone service
- more spectrum
- full duplex (receive and transmit)
Early mobile networks were inefficient. There were a lot of overlap, and an active user could be anywhere in a 40-60 mile range of the transmit tower (giving exclusive access).
Each tower’s range is called a cell. In the early days, each tower had 12 frequencies at the same time.
Definition (Cell)
A cell is spatial division of coverage via cell towers.
- requires more infrastructure/towers
- needs logic to support handoff of a user between towers (harder for operators)
- there will be some overlap… so who gets the user?
- How often does handoff happen? Depends on the size of the cells.
This same idea reappears in Satellite Communication, where satellites effectively act like moving cells covering portions of the Earth.
1G
- AMPS - Advanced Mobile Phone Service (circa 1983)
- 1G is defined by analog voice channels and established digital control channel (handles the handoffs)
- single-user analog is not very efficient
- spectrum allocation is extremely scarce resource, therefore want to maximize efficiency of its use
- Deprecated
- killed off OnStar (used for emergency calls during car crashes)
- ADT home alarms
- AMPS died in early 2000s
Dual Tone Multi Frequency (DTMF) Signaling
- Switchboard operators used to physically plug wires to make connections
- Pulse dialing was used to make a phone number by sending specific pulses.
Handoff
- Base station detects weak signal
- Base station tells mobile about new, better tower
- Base station sends cutover trigger
- Cons:
- No “make before break” many drops
- Mobile has better estimates than base station
- Towers are in between hexagonal ranges, not in the center. Each antenna gets a beam formation to cover some pattern in a cell/hexagon.
- Overtime AMPS received more frequencies.
- divided bands into more blocks.
- 850 MHz
2G
- Deployed 1933
- Used TDMA to share AMPS channels
- each channel analog pair was 30 kHz
- digital compression gave 3 time slots per channel
- encrypted
AKA as TDMA, D-AMPS (Digital AMPS)
2G is a collection of second generation protocols. This is also true for later generations.
First sunset happened in 2008.
Global System for Mobile Communications (GSM)
- standard for 2G
- GSM meant phone for a while in parts of Europe
- GSMA is GSM Association
- 1987: 13 European countries sign accord to use one wireless standard
- GSM standard ratified
- Not much new in GSM, but many arbitrary design decisions
- Real innovation was indirection and interoperability.
- Indirection to talk to different towers by giving identity.
- Therefore needs to be interoperable between different towers.