1 / 7

EE359 – Lecture 18 Outline

EE359 – Lecture 18 Outline. Announcements Today’s lecture will end ~10 minutes early Nima’s OH Thur moved to Sun 10am, Packard 3 rd floor HW due Sunday 5pm. No late HWs accepted Last HW will be assigned Friday, due 1+ week later Bonus lecture info

clay
Download Presentation

EE359 – Lecture 18 Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EE359 – Lecture 18 Outline • Announcements • Today’s lecture will end ~10 minutes early • Nima’s OH Thur moved to Sun 10am, Packard 3rd floor • HW due Sunday 5pm. No late HWs accepted • Last HW will be assigned Friday, due 1+ week later • Bonus lecture info • Final info (coverage, review, extra OHs, etc) given 12/5 • Review of Last Lecture • Fading across subcarriers in multicarrier • OFDM FFT Implementation • OFDM Design Issues

  2. Remainder of Course • Today: OFDM • Lecture will end around 10:35am • Dec. 5: Spread spectrum • Bonus lecture: Dec. 5 6-8pm, Hewlett 103 • Finish Spread Spectrum • Class summary • Advanced topics in wireless • Class Ends  • Except for final Dec. 14  • No lecture Dec. 7

  3. Review of Last Lecture • Sphere Decoder (near ML): • Only searches within a sphere of received symbol. • Other MIMO design issues • Space-Time Codes, Adaptive techniques, Limited FB • ISI Countermeasures • Equalization, multicarrier (OFDM), spread spectrum • Multicarrier Modulation • Breaks data into N substreams such that B/N<Bc • Substream modulated onto separate carriers • Overlapping substreams: Dfi=1/TN

  4. Fading Across Subcarriers • Leads to different BERS • Compensation techniques • Frequency equalization (noise enhancement) • Precoding • Coding across subcarriers • Adaptive loading (power and rate)

  5. cos(2pfct) cos(2pfct) LPF A/D D/A Serial To Parallel Converter x x FFT Implementation of OFDM • Use IFFT at TX to modulate symbols on each subcarrier • Cyclic prefix makes linear convolution of channel circular, so no interference between FFT blocks in RX processing • Reverse structure (with FFT) at receiver X0 x0 TX Add cyclic prefix and Parallel To Serial Convert R bps QAM Modulator IFFT XN-1 xN-1 RX Y0 y0 Remove cyclic prefix and Serial to Parallel Convert R bps QAM Modulator Parallel To Serial Convert FFT yN-1 YN-1

  6. OFDM Design Issues • Timing/frequency offset: • Impacts subcarrier orthogonality; self-interference • Peak-to-Average Power Ratio (PAPR) • Adding subcarrier signals creates large signal peaks • Different fading across subcarriers • Same mitigation techniques as in MCM: Precoding to invert fading, coding across subcarriers, and adaptative loading over time most common • MIMO/OFDM • Apply OFDM across each spatial dimension • Can adapt across space, time, and frequency

  7. Main Points • Subcarrier fading degrades MCM performance • Compensate through precoding (channel inversion), coding across subcarriers, or adaptation • OFDM efficiently implemented using IFFTs/FFTs • Block size depends on data rate relative to delay spread • OFDM challenges: • PAPR; timing/frequency offset; fading across subcarriers • 4G Cellular, Wimax, 802.11n all use OFDM+MIMO • Adapt across space, time, and frequency

More Related