lecture 7: channel capacity and multiplexing anders västberg [email protected] 08-790 44 55
TRANSCRIPT
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Lecture 7: Channel capacity and multiplexing
Anders Västberg
08-790 44 55
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Concepts
• Data rate
• Channel capacity
• Signal Bandwidth
• Channel Bandwidth
• Noise
• Error rate
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Bandwidth limited channelHartley’s law
MBC 2log2
C Channel capacity (bit/s)M Discrete LevelsB Channel bandwidth (Hz)
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Bandwidth limited and noisy channelShannon’s law
)1(log2 SNRBC
C Channel capacity (bit/s)SNR=P/N Signal to Noise ratio (not in dB!)B Channel bandwidth (Hz)
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Shannon’s Law
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Bandwidth and Capacity
2 4 6 8 1 0B k H z 1 0
2 0
3 0
4 0
5 0
6 0
C k b i t s
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Multiplexing• The signals of the different users are multiplexed at the transmitter
and then transmitted as one entity.• Examples of broadcast network:
• Radio and TV broadcast systems• Downlinks in a mobile cellular communication system• Downlinks in a satellite communication system
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Multiple Access
Examples of Multiple Access systems:•Uplink in a mobile cellular system•Uplink in a satellite communication system
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Multiplexing/Multiple Access
• Frequency division multiplexing (multiple access) (FDM/FDMA)– Channel bandwidth greater than signal
bandwidth
• Time division multiplexing (multiple access) (TDM/TDMA)– Channel capacity greater than signal data rate
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FDM/TDM
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Frequency divison multiplexing
Guard bandSignal bandwidth
|H(f)|
f
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Time divison multiplexing
• Bit interleaving
• Block interleaving
• Synchronous TDM– Time slots fixed and pre-assigned to sources
• Asynchronous TDM– Time given to sources with data to send
1 0 1 1 0 0 1 1
1 0 11 0 01 1
1
1
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Homework before F8
• Beskriv principen för DSSS?
• Vad är snabb och långsam FHSS?