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Cellular/PCS, Wireless Data Technical Issues

Cellular/PCS, Wireless Data Technical Issues. COMT 391 Wireless. Overview. Cell Layout Site Survey Signaling Mobile Operation. System Block Diagram Cellular/PCS. forward. Mobile. BTS. BSC. MTSO. PSTN. reverse. Data Bases. BTS Base Tranceiver Station BSC Base Station Controller

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Cellular/PCS, Wireless Data Technical Issues

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  1. Cellular/PCS, Wireless Data Technical Issues COMT 391 Wireless

  2. Overview • Cell Layout • Site Survey • Signaling • Mobile Operation

  3. System Block DiagramCellular/PCS forward Mobile BTS BSC MTSO PSTN reverse Data Bases BTS Base Tranceiver Station BSC Base Station Controller MTSO Mobile Telephone Switching Office Radio Link Bearer Trunk Signaling Trunk

  4. Frequency Reuse Pattern

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

  6. AMPS cont. • 832 channels (2 frequencies per channel) • Forward: 869-894 MHz • Reverse: 824-849MHz • Forward/Reverse Spacing: 45MHz • Adjacent Channel Spacing: 30kHz • 21 Control Channels per group • Cell Sizes: 2-20km

  7. Antenna Placement - high • Good Coverage • Co-Channel Interference Problems

  8. Buildings as Boundaries • Cell Limits Defined • Possible Adjacent Channel Interference

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

  10. 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

  11. Call Setup from Mobile • Mobile receives AC numbers over PC • Mobile finds the strongest AC • Mobile signals (dials) over the AC to the Base Station and the MTSO • MTSO transmits the Bearer Channel No.

  12. Mobile-Originated Call, AMPS Mobile BTS BSC MTSO PSTN RCC MIN, ESN, dialed no validation FCC Ch No, SAT code, Power SAT FVC SAT RVC FVC Conversation RVC

  13. 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 sends voice channel number to mobile

  14. 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.

  15. Call Handoff cont… • Current base station at MTSO command sends signal to mobile giving the new channel assignment. • Mobile tunes to the new channel. • Previous base station clears the call path.

  16. Mobile Handset • ESN - Electronic Serial Number • Programmable NAM (Number Assignment Module) • Contains among other things • System ID • First control channel to scan • System selection preferences • MIN (Mobile Identification Number)

  17. 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

  18. Hand-Off MS MS BS BS MTSO

  19. Roaming MTSO Mobile MTSO Mobile Mobile Mobile Mobile Mobile Mobile Mobile Mobile

  20. Roaming Details MS BS Request MTSO MTSO Response HLR HLR VLR Current Location Temporary Directory Number Billing Information Service Profile

  21. Intersystem Hand-Off MS MS BS BS MTSO MTSO

  22. The “Shoe-Lace” Effect MS BS BS BS BS BS BS BS BS MS

  23. Multi-System Tandem MS MS BS BS MTSO MTSO MTSO MTSO MTSO

  24. The “Trombone” Effect MS BS MTSO MTSO Fixed Station

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

  26. Classes of Standards • Analog Cellular • FDMA - Frequency Division Multiple Access • Digital Cellular • FDMA • TDMA - Time Division Multiple Access • CDMA - Code Division Multiple Access

  27. Frequency Frequency Time Time Frequency Time Access Methods FDMA TDMA CDMA

  28. Standards Content • Frequency Bands • Channel Assignments • Voice Encoding • Access Method and Frame Structure • Signaling Structure

  29. Wireless LAN • Short range • Single channel (“half-duplex”) • Packet-based • Signaling packets • Bearer packets • Authentication against back-end data base

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