1 / 9

EE359 – Lecture 9 Outline

EE359 – Lecture 9 Outline. Announcements: Project proposals due this Friday at 5pm Midterm will likely be @ Nov. 10, 6-8pm. HWs will be due Friday 5pm SHARP going forward Linear Modulation Review Linear Modulation Performance in AWGN Q-Function representations

glynn
Download Presentation

EE359 – Lecture 9 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 9 Outline • Announcements: • Project proposals due this Friday at 5pm • Midterm will likely be @ Nov. 10, 6-8pm. • HWs will be due Friday 5pm SHARP going forward • Linear Modulation Review • Linear Modulation Performance in AWGN • Q-Function representations • Probability of error in fading • Outage probability • Average Ps (Pb)

  2. 1 g g0 g Review of Last Lecture • Capacity in Flat-Fading: g known at TX/RX • Optimal Rate and Power Adaptation • Channel Inversion and Truncated Inversion • Received SNR constant; Capacity is Blog2(1+s) above an outage level associated with truncation • Capacity of ISI channels • Water-filling of power over freq; or time and freq. • Capacity of ISI Channels Waterfilling

  3. Our focus Passband Modulation Tradeoffs • Want high rates, high spectral efficiency, high power efficiency, robust to channel, cheap. • Amplitude/Phase Modulation (MPSK,MQAM) • Information encoded in amplitude/phase • More spectrally efficient than frequency modulation • Issues: differential encoding, pulse shaping, bit mapping. • Frequency Modulation (FSK) • Information encoded in frequency • Continuous phase (CPFSK) special case of FM • Bandwidth determined by Carson’s rule (pulse shaping) • More robust to channel and amplifier nonlinearities

  4. Amplitude/Phase Modulation • Signal over ith symbol period: • Pulse shape g(t) typically Nyquist • Signal constellation defined by (si1,si2) pairs • Can be differentially encoded • M values for (si1,si2)log2 M bits per symbol • Ps depends on • Minimum distance dmin (depends on gs) • # of nearest neighbors aM • Approximate expression:

  5. Alternate Q Function Representation • Traditional Q function representation • Infinite integrand • Argument in integral limits • New representation (Craig’93) • Leads to closed form solution for Ps in PSK • Very useful in fading and diversity analysis

  6. Linear Modulation in Fading • In fading gsand therefore Psrandom • Performance metrics: • Outage probability: p(Ps>Ptarget)=p(g<gtarget) • Average Ps , Ps: • Combined outage and average Ps (next lecture)

  7. Ts Outage Ps Ps(target) t or d Outage Probability • Probability that Ps is above target • Equivalently, probability gs below target • Used when Tc>>Ts

  8. Average Ps • Expected value of random variable Ps • Used when Tc~Ts • Error probability much higher than in AWGN alone • Alternate Q function approach: • Simplifies calculations (Get a Laplace Xfm) Ts Ps Ps t or d

  9. Main Points • Linear modulation more spectrally efficient but less robust than nonlinear modulation • Psapproximation in AWGN: • Alternate Q function representation simplifies calculations • In fading Psis a random variable, characterized by average value, outage, or combined outage/average • Outage probability based on target SNR in AWGN. • Fading greatly increases average Ps .

More Related