Post on 15-Jan-2016
description
COMT 391
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Cellular/PCS, Wireless Data Technical Issues
COMT 391 Wireless
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Overview
• Cell Layout• Site Survey• Signaling• Mobile Operation
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System Block DiagramCellular/PCS
Mobile BTS BSC MTSO PSTN
Data Bases
forward
reverse
BTS Base Tranceiver Station
BSC Base Station Controller
MTSOMobile Telephone Switching Office
Radio Link Bearer Trunk
Signaling Trunk
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Frequency Reuse Pattern
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Example: AMPS
• 50MHz spectrum• 30kHz per channel per direction• 832 total full-duplex channels• 4, 7, and 12 cell clusters used
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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
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Antenna Placement - high
• Good Coverage• Co-Channel Interference Problems
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Buildings as Boundaries
• Cell Limits Defined• Possible Adjacent Channel
Interference
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Interference
• Co-Channel Interference• Adjacent Channel Interference• Outside Sources
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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
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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.
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Mobile-Originated Call, AMPS
Mobile BTS BSC MTSO PSTN
RCC MIN, ESN, dialed no
validation
FCC Ch No, SAT code, Power
FVC SAT
RVC SAT
FVCRVC
Conversation
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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
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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.
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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.
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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)
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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
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Hand-Off
MTSO
BSBS
MSMS
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Roaming
Mobile
MTSO
Mobile
Mobile
Mobile
Mobile
MTSO
Mobile
Mobile
Mobile
Mobile
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Roaming Details
MTSO
BS
MS
MTSO
HLR
HLR VLR
Request
Response
Billing Information
Service Profile
Current Location
Temporary Directory Number
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Intersystem Hand-Off
MTSO
BSBS
MSMS
MTSO
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The “Shoe-Lace” Effect
BS
BS
BS
BS
BS
BS
BS
BS
MS
MS
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Multi-System Tandem
MTSO
BSBS
MSMS
MTSOMTSOMTSO
MTSO
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The “Trombone” Effect
MTSO
BS
MS
MTSO
Fixed Station
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Security/Fraud Issues
• Security– Privacy of Conversations– Denial of Service
• Fraud– Illegally obtained ESN/MINs– Roaming-related (“tumbling” ESNs)
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Classes of Standards
• Analog Cellular– FDMA - Frequency Division Multiple
Access
• Digital Cellular– FDMA– TDMA - Time Division Multiple Access– CDMA - Code Division Multiple Access
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Access MethodsFr
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TimeFr
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TimeFr
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Time
FDMA
TDMA
CDMA
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Standards Content
• Frequency Bands• Channel Assignments• Voice Encoding• Access Method and Frame
Structure• Signaling Structure
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Wireless LAN
• Short range• Single channel (“half-duplex”)• Packet-based
– Signaling packets– Bearer packets
• Authentication against back-end data base