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08-IntroductionToDigitalModulation - Digital Communication...

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Introduction to Digital Modulation Instructor: M.A. Ingram ECE4823 Digital Communication Transmitter User Interface Encoder Modulator RF Front End antenna bits 0110 more bits 011001 waveforms (symbols) Frequency up-conversion and amplification A simplified block diagram: interleaver Digital Communications Receiver A simplified block diagram: User Interface Decoder Demodulator RF Front End antenna bits 0110 “soft detections” of coded bits 011001 waveforms (faded symbols plus noise) Low-noise amplification and frequency down-conversion deinterleaver Symbols In each symbol period, T s , a digital modulator maps N coded bits word to a transmitted waveform from a set of M=2 N possible waveforms Each waveform corresponds to an information symbol, x n For Binary symbols, N=1 Detection The job of the receiver is to determine which symbols were sent and to reconstruct the bit stream that created them Definitions Bit Rate (bits per sec or bps) Bandwidth Efficiency (bps/Hz) where B is the bandwidth occupied by the signal S T N R / = B R B / = η
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Shannon Theorem In a non-fading channel, the maximum bandwidth efficiency, or Shannon Capacity is SNR = signal-to-noise ratio ( ) SNR MAX B + = 1 log 2 η Pulses A symbol period, T s , suggests a localization in time Localization in frequency is also
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