Some Notes on Cellular and
Personal Communication Systems
Mobile Telephone Service (MTS)
- Introduced in 1946.
- Single powerful transmitter.
- Used radio frequencies between 35 and 45 MHz.
- Required pushbutton to talk, release to listen.
- Operator required to connect to PSTN. Number not related to PSTN number.
- Caller needed mobile phone's number and location.
- Required heavy transmitter/receiver in car's trunk.
- Connected to car's battery.
- Pulse dialing.
Improved Mobile Telephone System (IMTS)
- Introduced in 1963, but required a decade to implement.
- Used radio frequencies between 454 and 512 MHz.
- Base transmitters were 100 to 200 W. Mobile transmitters were 20W.
- FDM provided only 12 channels in each city.
- Mobile phones could used any of several different frequencies.
- Connected to local Class 5 CO.
- Numbers corresponded to PSTN numbers.
Advanced Mobile Phone System (AMPS)
- Tested in late 1980s and implemented in 1983.
- Uses low lowered base and mobile transmitters (both 7 W).
- The mobile transmitters use frequencies 825 to 845 MHz and the
base units use frequencies 870 to 890 MHz.
- 728 Mobile Service Areas (MSAs) defined by FCC in US.
- MFJ assigned 2 Cellular carriers in each MSA for competition:
- A Carrier: Non-Wireline carrier
- B Carrier: Wireline carrier (like Ameritech)
- Each MSA carrier allocated 312 channels, 30 kHz each.
- Each MSA is divided into regions called cells. Ideally, they
are hexagon shaped. This allows 7-way frequency reuse.
- No adjoining cells use the same channels.
- Each cell can use up to 1/7 of available channels.
- To increase capacity, make the cells smaller.
- The Mobile Telephone Switching Office (MTSO)
- Interconnects the base stations of all cells in an area.
- Connects mobile network to wireline network.
- Handles
- Registration (determines which cell a mobile unit is in).
- Call Handoff (when a call fades, the MTSO determines the new
cell that the mobile unit has moved into).
- Roaming (mobile unit can gain service when it moves into a new
service area, but at a higher price).
Digital Advanced Mobile Phone System (DAMPS)
- Uses pulse code modulation (PCM) and
Time Division Multiplexing (TDM).
- Uses 825 to 895 MHz frequency band.
IS-54B Digital Cellular (TDMA)
- Voice is digitized at 8 Kbps.
- Each 30 kHz channel caries 3 voices.
- Security and encryption can be built in.
- Uses Code Division Multiple Access (CDMA)
- 0 and 1 in digital signal are represented by one
byte codes indicating bit value and channel number.
- Everyone transmits at the same time, special equipment
at the MTSO sorts it all out.
- Digital transmission with TDM allows more channels per
users per cell.
Personal Communications Systems (PCS)
- Combines voice and data services.
- Voice and/or caller id.
- Paging with numeric message.
- Email delivered to PCS device.
- Fax notification.
- Stock quotes.
- Sports scores.
- Weather reports.
- Web access.
- Intelligent network.
- Seamless inter-carrier signalling.
- Roaming to any area.
- Automatic user location and validation.
- Security and encryptation features.
- Uses different frequencies than cellular telephones.