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Final Exam Prep: Spread Spectrum, HW Announcements, and Review Sessions

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This lecture outlines key announcements for the final exam including the due date for Homework 8, bonus points for course evaluations, and project submission details. It covers essential topics like Direct Sequence Spread Spectrum, Interference Rejection, RAKE Receivers, and Multiuser Techniques. The final exam is on December 13 and will cover chapters 9, 10, 12, and portions of chapters 13. A practice exam will be available for bonus points. Office hours and review sessions are scheduled to aid in exam preparation.

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Final Exam Prep: Spread Spectrum, HW Announcements, and Review Sessions

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  1. EE359 – Lecture 19Outline • Announcements • Final Exam Announcements • HW 8 (last HW) due Friday 5pm (no late HWs) • 10 bonus points for course evaluations online • Projects due Dec. 6 • Direct Sequence Spread Spectrum • ISI and Inteference Rejection • Spreading Codes and Maximal Linear Codes • Synchronization • RAKE Receivers • Multiuser Spread Spectrum

  2. Final Exam Announcements • Final Friday, 12/13, 12:15-3:15 • Covers Chapters 9, 10, 12, 13.1-13.2 (+ earlier chps) • Similar format to MT, but longer: open book, notes. • Practice finals posted next week(10 bonus points) • Turn in to Pat or Mainakfor solns, by exam for bonus pts • Course summary Dec 6 12:30-2:05 here (pizza@noon) • Final review (Mainak) : Mon 12/9, 6 pm to 7 pm? • OHs next 3 weeks: • Me: next MTW by appt, 12/2 9-10am, 12/6 2-3pm, 12/9 by appt, 12/12 6:30-7:30pm (pls confirm), 12/13 9-10am, Skype • Mainak: Please respond to Piazza poll (see last slide)

  3. cos(2pfct) cos(2pfct) LPF A/D D/A Serial To Parallel Converter x x + Review of Last LectureFFT Implementation of OFDM X0 x0 n(t) TX R bps Add cyclic prefix and Parallel To Serial Convert • Design Issues • PAPR, frequency offset, fading, complexity • MIMO-OFDM • Pulse shaping v QAM Modulator IFFT h(t) + Pulse shaping XN-1 xN-1 m=sTm/Tsamp RX Y0 y0 Remove cyclic prefix and Serial to Parallel Convert R bps QAM Modulator Parallel To Serial Convert FFT yN-1 YN-1 Yi=HiXi+ni

  4. Tc Review of Last Lecture:Intro. to Spread Spectrum • Modulation that increases signal BW to combat narrowband interference and ISI • Also used as a multiple access technique • Two types: Frequency Hopping and DSSS • FH:Hops info. signals over a wide bandwidth • DSSS: modulates info signal by chip sequence S(f) s(t) sc(t) Sc(f) S(f)*Sc(f) 1/Tb 1/Tc Tb=KTc

  5. S(f) I(f) S(f) S(f)*Sc(f) I(f)*Sc(f) Despread Signal Receiver Input Info. Signal ISI and Interference Rejection • Narrowband Interference Rejection (1/K) • Multipath Rejection (Autocorrelation r(t)) aS(f) S(f)*Sc(f)[ad(t)+b(t-t)] S(f) brS’(f) Despread Signal Receiver Input Info. Signal

  6. 1 -Tc Tc -1 N Maximal Linear Codes • Autocorrelation determines ISI rejection • Ideally equals delta function • Maximal Linear Codes • No DC component • Large period (2n-1)Tc • Linear autocorrelation • Recorrelates every period • Short code for acquisition, longer for transmission • In SS receiver, autocorrelation taken over Tb • Poor cross correlation (bad for MAC)

  7. 1 -Tc Tc -1 2n-1 Synchronization • Adjusts delay of sc(t-t) to hit peak value of autocorrelation. • Typically synchronize to LOS component • Complicated by noise, interference, and MP • Synchronization offset of Dt leads to signal attenuation by r(Dt) r(Dt) Dt

  8. x x x RAKE Receiver • Multibranch receiver • Branches synchronized to different MP components • These components can be coherently combined • Use SC, MRC, or EGC Demod sc(t) y(t) ^ dk Diversity Combiner Demod sc(t-iTc) Demod sc(t-NTc)

  9. Multiuser DSSS • Each user assigned a unique spreading code; transmit simultaneously over same bandwidth • Interference between users mitigated by code cross correlation • In downlink, signal and interference have same received power • In uplink, “close” users drown out “far” users (a1>>a2: near-far problem) a a1 a2 a

  10. Main Points • Spread spectrum increases signal bandwidth above that required for information transmission • Benefits include ISI and interference rejection, multiuser technique • DSSS rejects ISI by code autocorrelation • Maximal linear codes have good autocorrelation properties but poor cross correlation • Synchronization depends on autocorrelation properties of spreading code. • RAKE receivers combine energy of all MP • Use same diversity combining techniques as before

  11. Proposed days/times for Mainak’s OHs, final review, and discussion Please respond to Piazza poll on this proposal 12/2 (8:30 am to 10:30 am): Discussion session for Homework 8 + Office hour (to replace Tuesday DH and Wednesday OH) 12/6 (11 am to 12 noon): OH (instead of Thursday OH) 12/9 (6 pm to 7 pm): Final review session 12/10 (7 pm to 8 pm): Extra 12/11 (7 pm to 8 pm): OH 12/12 (7 pm to 8 pm): OH

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