Cellular and PCS Technical Issues

1
Cellular and PCS Technical Issues

• COMT 391

2
Overview

• Cell Layout
• Signaling
• Mobile Handset Operation

3
North American AMPS system

• 50MHz spectrum
• 30kHz per channel per direction
• 832 total full-duplex channels
• 4, 7, and 12 cell clusters used

4
Antenna Placement - high

• Good Coverage
• Co-Channel Interference Problems

5
Buildings as Boundaries

• Cell Limits Defined
• Possible Adjacent Channel Interference

6
Interference

• Co-Channel Interference
• Adjacent Channel Interference
• Outside Sources

7
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

8
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.

9
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

10
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

11
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

12
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

13
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.

14
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.

15
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)

16
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

17
Roaming
MTSO
Mobile
MTSO
Mobile
Mobile
Mobile
Mobile
Mobile
Mobile
Mobile
Mobile
18
Security/Fraud Issues

• Security
• Privacy of Conversations
• Denial of Service
• Fraud
• Illegally obtained ESN/MINs
• Roaming-related (tumbling ESNs)

19
Classes of Standards

• Analog Cellular
• FDMA - Frequency Division Multiple Access
• Digital Cellular
• FDMA
• TDMA - Time Division Multiple Access
• CDMA - Code Division Multiple Access

20
Access Methods
FDMA
TDMA
CDMA
21
Standards Content

• Frequency Bands
• Channel Assignments
• Voice Encoding
• Access Method and Frame Structure
• Signaling Structure