Digital Carier Modulation, Exams of Marketing

Download Digital Carier Modulation and more Exams Marketing in PDF only on Docsity! Lecture 16: Digital Carier Modulation John M Pauly November 15, 2021 Digital Carrier Modulation Lecture topics I Eye diagrams I Pulse amplitude modulation (PAM) I Binary digital modulation I Amplitude shift keying (ASK) I Frequency shift keying (FSK) I Phase shift keying (PSK) I Example of a high-speed 8b/10b serial link Based on lecture notes from John Gill Polar Signaling with Raised Cosine Transform (r = 0.5) Last time we talked about Nyquist pulses. These were designed to be zero at the adjacent samples, but (1 + r) times wider in bandwidth than a sinc. The timing sensitivity is less than Tb, and the noise sensitivity increases roughly linearly with timing error. P (f) =  1 |f | < 1 4Rb 1 2 ( 1− sinπ ( f − 1 2Rb Rb )) ||f | − 1 2Rb| < 1 2Rb 0 |f | > 3 4Rb Polar Signaling with Raised Cosine Transform (r = 0.5) The pulse corresponding to P (f) is p(t) = sinc(πRbt) cos(πrRbt) 1− 4r2R2 b t 2 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 −1.5 −1 −0.5 0 0.5 1 1.5 Eye Diagram Measurements I Maximum opening affects noise margin I Slope of signal determines sensitivity to timing jitter I Level crossing timing jitter affects clock extraction I Area of opening is also related to noise margin PAM Eye Diagram I The eye diagram for 4-level PAM using Nyquist r = 0.5 pulses looks like this I Timing is even more critical I The noise sensitivity is increased by a factor of 4, since each eye is 1/4 the height. ISDN Power Spectrum I Power of 4-ary signaling: R0 = 1 4((−3) 2 + (−1)2 + 12 + 32) = 1 4 · 20 = 5 . If digital values are independent, Rn = 0 for n 6= 0. I Thus PSD is Sy(f) = 5 Ts |Px(f)|2 , I The PSD is the same as binary signaling. I More bits use more power. I We’ll return to M-ary signaling next class. Digital Carrier Modulation I In class so far we’ve just talked about baseband modulation of digital signals I Ethernet I Fiber I USB I As you’ve seen in the labs, the same ideas work for sending bits over a carrier, such as RF I We’ll look at several simple ways to encode bits on a carrier I On-Off Keying (OOK) I Phase-Shift Keying (PSK) I Frequency Shift Keying (FSK) I These are designed to be simple to generate, and simple to decode. Phase Shift Keying (PSK) I Binary PSK is the same as polar ASK. M-ary versions are next time. Carrier t Message t Transmited Signal t I Usually use an integer number of cycles of an offset frequency, and modulate that up to the carrier I Phase changes at zero crossing to minimize bandwidth I Detection generally must be synchronous, since the envelope is constant Example: BPSK31 I One PSK methods that is easy to decode is BPSK31, widely used in amateur radio. I A ”1” is a constant phase interval , and a ”0” is sent with a phase inversion. I The shaped pulses minimize the bandwidth I After demodulating to baseband, lowpass filter follow by an envelope detector will decode the bits. Figure from Wikipedia Frequency Shift (FSK) I Binary FSK uses two frequencies for 1 and zero. M-ary will be next time. Carrier t Transmited Signal t Message t I Usually integer numbers of cycles of each offset frequency, so that they are orthogonal I Easy to receive, can be done with filters and an envelope detector (see this week’s lab!). Does not need to be synchronous. Differential PSK (DPSK) I Differential PSK encodes the bits as the phase difference between two PSK pulses. I ”1” is a change of phase, and ”0” is the same phase. I This doesn’t need a synchronous receiver! The signal is its own reference. Example: A High-Speed Serial Link I Transport data from a receive array in an MR scanner wirelessly I Approximately 500 Mbps data rate I At most 1 m distance I Carrier in 3.2 or 5 GHz band This is work by Greig Scott from the Stanford MRSRL A High-Speed Serial Link System I Antenna and preamp pick up signal, demodulated, digitized to 16 bits I Data is serialized using 8b/10b encoding, and modulated and transmitted with OOK I Receiver envelope detects and deserializes the bits 8b/10b Eye Diagram, 3.2 GHz Carrier 3.2 GHz Biquad pair Lose Lock 8b/10b Waveforms, 5 GHz Carrier stays lacked 8b/10b Eye Diagram, 5 GHz Carrier Stays Locked