Digital Modulation - Vodafone Chair Mobile Communications Systems
Digital Modulation - Vodafone Chair Mobile Communications Systems
Digital Modulation - Vodafone Chair Mobile Communications Systems
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<strong>Vodafone</strong> <strong>Chair</strong> <strong>Mobile</strong> <strong>Communications</strong> <strong>Systems</strong>, Prof. Dr.-Ing. G. Fettweis chair<br />
Introduction to <strong>Communications</strong>:<br />
<strong>Digital</strong> <strong>Modulation</strong><br />
Eye Diagram and BPSK Transmission<br />
Prof. Dr.-Ing. Gerhard Fettweis<br />
<strong>Chair</strong> <strong>Mobile</strong> <strong>Communications</strong> <strong>Systems</strong>, TU Dresden
<strong>Digital</strong> Data Transmission (1)<br />
Transmit Filter<br />
Block diagram of the transmitter for transmitting<br />
digital data over a baseband channel<br />
Pulses of different symbols don’t overlap<br />
Ideal channel with infinite bandwidth (rectangular pulses!) can<br />
accommodate baseband transmission without signal distortion<br />
Error-free signal reconstruction possible<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 2
<strong>Digital</strong> Data Transmission (2)<br />
Transmit Filter<br />
Transmission over band-limited channel:<br />
Use a pulse shape with better localization in the frequency domain!<br />
Consequence:<br />
Each received pulse is affected by adjacent pulses.<br />
Inter-symbol interference (ISI)!<br />
ISI is a major source of bit errors at the receiver!<br />
Pulse shapes at transmitter and receiver have to be chosen carefully<br />
to minimize ISI (e. g. root-raised cosine pulses).<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 3
Visualization of Pulse Shape Properties<br />
Filtered signal<br />
Eye Diagram:<br />
Signal form viewed within one symbol interval<br />
Contributions from many overlapping pulses<br />
Horizontal and vertical aperture affects system performance<br />
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Raised Cosine filter, r = 0.5 Raised Cosine filter, r = 1<br />
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chair<br />
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TU Dresden, Gerhard Fettweis Slide 4<br />
Filtered signal<br />
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BPSK Transmission over Noisy Channel<br />
BPSK Transmission over Noisy Channel<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 5
Baseband Transmission: System Model<br />
Transmit Filter Receive Filter<br />
Baseband equivalent transmission<br />
Transmitted signal has lowpass characteristics<br />
Channel is modelled as an AWGN channel<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 6
Eye Diagram: Noise Influence<br />
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Eye pattern: α=1, noise free<br />
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Presence of the noise causes closing of the eye.<br />
For low SNR, the eye is closed.<br />
Decision errors are made at the receiver.<br />
chair<br />
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TU Dresden, Gerhard Fettweis Slide 7<br />
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Eye pattern: α=1, SNR=12dB<br />
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BPSK Transmission: Noiseless Channel<br />
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Eye pattern: α=1, noise free<br />
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Grayscale picture of Barkhausenbau, TU Dresden<br />
Intensity of a pixel is encoded with n=8 bits<br />
Channel is noiseless and nondispersive: Error-free transmission<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 8
BPSK Transmission over AWGN Channel<br />
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Eye pattern: α=1, SNR=4dB<br />
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chair<br />
TU Dresden, Gerhard Fettweis Slide 9
BPSK Transmission over AWGN Channel<br />
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Eye pattern: α=1, SNR=0dB<br />
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Bad quality of the received picture<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 10
BPSK Transmission over AWGN Channel<br />
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Eye pattern: α=1, SNR=-6dB<br />
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<br />
Details are unrecognizable<br />
chair<br />
TU Dresden, Gerhard Fettweis Slide 11