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EE104: Lecture 24 Outline

EE104: Lecture 24 Outline. Announcements Review of Last Lecture Passband Digital Modulation ASK, PSK, and FSK Modulation ASK and PSK Detection Noise Immunity Noise in ASK/PSK Probability of Bit Error (P b , BER). Announcements. HW 7 due Monday at 7pm (no late HWs)

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EE104: Lecture 24 Outline

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  1. EE104: Lecture 24 Outline • Announcements • Review of Last Lecture • Passband Digital Modulation • ASK, PSK, and FSK Modulation • ASK and PSK Detection • Noise Immunity • Noise in ASK/PSK • Probability of Bit Error (Pb, BER)

  2. Announcements • HW 7 due Monday at 7pm (no late HWs) • Solutions will be posted then. • Final Exam is Th., 3/20, 8:30am in Gates B03 (basement) • Exam is open book/notes, covers through Friday’s lecture. • Emphasis is on material after midterm, similar to practice finals • SCPD student must make remote arrangements w/me by this Friday • Practice finals posted on class website • 10 bonus points if turned in by 3/20 at 8:30am (Joice has solutions) • Final Review: Sunday 7-8pm (room TBD) • Extra Office Hours • My extra hours: M 4:30-6:30, TW 12-2, and by appointment • Jaron: W 6-8 (Bytes), Nikola: after review and T 5-7pm (101 Packard) • tbp forms available now from Joice (10 bonus points) • Will do at end of class Friday

  3. Review of Last Lecture • FM Detection • “Differentiator” and Envelope Detector • Zero Crossing Detector • Phase lock loop • Information as Bits • Baseband Digital Modulation • On-off Modulation • Polar Modulation • Pulse Shaping

  4. Passband Digital Modulation • General Form • Bits encoded in amplitude An, phase n, or frequency n=2p(fn-fc)t of s(t). • An and n(t) are constant over a bit time Tb • These values change every nTb

  5. ASK, PSK, and FSK 1 0 1 1 • Amplitude Shift Keying (ASK) • Phase Shift Keying (PSK) • Frequency Shift Keying m(t) AM Modulation 1 0 1 1 m(t) AM Modulation 1 0 1 1 FM Modulation

  6. r(nTb)+N DN r(nTb) ASK/PSK Demodulation • Similar to AM demodulation, but only need to choose between one of two values • Decision device determines which of r0 or r1 that r(iTb) is closest to • Noise immunity DN is half the distance between r0 and r1 • Bit errors occur when noise exceeds this immunity Decision Device nTb r1 “1” or “0” r(nTb) s(t)  r0 cos(2pfct)

  7. DN Noise in ASK/PSK N(t) nTb • Probability of bit error: Pb=p(|N(nTb)|>DN) • N(nTb) is a Gaussian RV: N~N(0,.25NoTb) • For x~N(0,1), Define Q(z)=p(x>z) • ASK: Pb=p(N>.25AcTb)=Q(.25TbAc2/N0)=Q(Eb/N0) • PSK: Pb= p(N>.5AcTb)=Q(.5TbAc2/N0)=Q(Eb/N0) • Eb is the average energy per bit. “1” or “0” r(nTb)+N(nTb) s(t) +  Channel cos(2pfct)

  8. Main Points • Digital passband modulation encodes binary bits into the amplitude, phase, or frequency of the carrier. • Decision device in receiver uses threshold to determine which bit was sent. • Noise immunity in receiver dictates how much noise is required to make a decision error (proportional to Ac and Tb) • White Gaussian noise process causes a Gaussian noise term to be added to the decision device input • Bit error probability with white noise is a function of the symbol energy to noise spectral density ratio.

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