COMT 3911 Cellular and PCS Technical Issues COMT 391

2 Overview Cell Layout Signaling Mobile Handset Operation

COMT 3913 North American AMPS system 50MHz spectrum 30kHz per channel per direction 832 total full-duplex channels 4, 7, and 12 cell clusters used

COMT 3914 Antenna Placement - high Good Coverage Co-Channel Interference Problems

COMT 3915 Buildings as Boundaries Cell Limits Defined Possible Adjacent Channel Interference

COMT 3916 Interference Co-Channel Interference Adjacent Channel Interference Outside Sources

COMT 3917 Signaling Channels Dedicated Control Channels (CC) –Mobile will scan for the strongest control channel when first switched on –System Identification –Number of Paging and Access Channels Paging Channels (PC) –Used to Initiate Calls to a Mobile Access Channels (AC) –Used to Initiate Calls from a Mobile

COMT 3918 Call Setup from Mobile Mobile receives AC number over PC User dialed digits are stored in the Mobile Mobile finds the strongest AC Mobile sends the dialed digits over the AC to the Base Station and the MTSO MTSO transmits the Voice Channel No.

COMT 3919 Call Setup From Mobile cont… Mobile tunes to the selected voice channel Mobile loops the supervisory audio tone (shows voice channel active) MTSO sends digits to the PSTN PSTN completes call

COMT Call Setup to Mobile PSTN delivers call to MTSO MTSO transmits Mobile ID over all Paging Channels Mobile acknowledges on the strongest Access Channel MTSO selects the voice channel to use MTSO starts supervisory tone and sends voice channel number to mobile

COMT Setup to Mobile Cont. Mobile loops the supervisory tone MTSO instructs mobile to begin ringing Mobile rings and sends 10kHz alert tone to the MTSO Alert tone stops when mobile picks up, MTSO completes call connection

COMT Speech Channel Control Signals (AMPS) Signaling Tone (10kHz) from Mobile to MTSO –Alerting –Flash-hook, disconnect, etc. Supervisory Audio Tones (6kHz+/- 30Hz) (there are three of these) –Base Station to Mobile, looped back by the mobile

COMT Call Handoff Base Stations monitor the signal strength If strength drops below hand-off level, all base stations are asked to look for the mobile; strongest becomes new BS MTSO instructs the new base station to activate a voice channel to receive the handoff; BS starts transmitting the Supervisory Audio Tone.

COMT Call Handoff cont… Current base station at MTSO command sends signal to mobile giving the new channel assignment. Mobile send a signaling tone burst, and tunes to the new channel. Previous base station clears the call path.

COMT Mobile Handset ESN - Electronic Serial Number Programmable NAM (Number Assignment Module) Contains among other things –System ID –First control channel to scan –A/B system selection –MIN (Mobile Identification Number)

COMT Mobile Identification Number MIN1 - Mobile System Id (3 digits) –US: Area Code –International: Mobil Carrier Identifcation MIN2 - Station Number –US: NXX and line number –International: internal mobile number

COMT Roaming Mobile MTSO Mobile MTSO Mobile

COMT Security/Fraud Issues Security –Privacy of Conversations –Denial of Service Fraud –Illegally obtained ESN/MINs –Roaming-related (“tumbling” ESNs)

COMT Classes of Standards Analog Cellular –FDMA - Frequency Division Multiple Access Digital Cellular –FDMA –TDMA - Time Division Multiple Access –CDMA - Code Division Multiple Access

COMT Access Methods Frequency Time Frequency Time Frequency Time FDMA TDMA CDMA

COMT Standards Content Frequency Bands Channel Assignments Voice Encoding Access Method and Frame Structure Signaling Structure