10-401-07-BasebandTransmissionDetection-2

10-401-07-BasebandTransmissionDetection-2 - Essential...

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Baseband Transmission 1 EE 401 Digital Communications Essential Blocks:Digital Communication System Format Pulse Modulation Bandpass Modulation Transmitter Synchronization Format Detection Demodulation Sampling Receiver Channel 010100 0 T 2T 3T 4T 5T 6T 7T 8T 0 T 2T 3T 4T 5T 6T 7T
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Baseband Transmission 2 EE 401 Digital Communications Channel disturbances Noise Intersymbol interference (ISI) and distortion Transmitted (ideal) Received (distorted+noisy) voltage Time Time ISI
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Baseband Transmission 3 EE 401 Digital Communications Probability of bit error: A channel with equal conditional probabilities is called binary symmetric channel Average probability of symbol error P e = p 0 P e0 p 1 P e1 since p 0 = p 1 = 1 / 2 P e = P e0 = P e1 or P e = Q 2 E b N 0 (Bipolar signaling) Average bit error probability in binary signaling is dependent ONLY on the ratio of transmitted bit energy to the noise power spectral density Expressing E b = ST b ;T b = 1 / R; N 0 = N / W E b N 0 = S T b N / W = S N W R
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Baseband Transmission 4 EE 401 Digital Communications Evaluation of Q(x) Q x = 1 2 x exp − t 2 / 2 dt
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Baseband Demodulation/Detection 5 EE 401 Digital Communications Correlation, P B and signal energy Energy of the difference signal: E d = 0 T [ s 1 t − s 2 t ] 2 dt = E b E b 2 E b = 2 E b 1 − E b = 0 T s 1 2 t dt = 0 T s 2 2 t dt Probability of bit error P B = Q E d 2N 0 = Q E b 1 − N 0 Correlation of two signals ,s 1 t and s 2 t = 1 T 0 T s 1 t s 2 t dt where 1 ≤ 1 = cos
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Baseband Demodulation/Detection 6 EE 401 Digital Communications Binary signalling: Antipodal and orthogonal Antipodal Orthogonal -Antipodal(bipolar); θ = π ρ =− 1 P B = Q 2 E b N 0 -Orthogonal(unipolar); θ = π / 2 ρ = 0 P B = Q E b N 0 Maximizing the energy of the difference signal !
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7 EE 401 Digital Communications Orthogonal (Unipolar) signaling Orthogonal; θ = π / 2 ρ = 0 P B = Q E b N 0 0 binary for 0 0 ) ( 1 binary for 0 ) ( 2 1 T t t s T t A t s E d = A 2 T for ρ = 0 E b = A 2 T / 2 ; average for equally likely signals P B = Q E d 2N 0 = Q A 2 T 2N 0 = Q E b N 0 Correlator detector(Macthed filter) E d = 0 T [ s 1 t − s 2 t
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10-401-07-BasebandTransmissionDetection-2 - Essential...

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