1. EE359 – Lecture 10 Outline Announcements: Average Ps (Pb)
Midterm Nov. 7, 11-1, Covers Chp. 1-7
Open book/notes. More details soon.
Review session next week
Practice midterms will be posted
Average Ps (Pb)
Combined average and outage Ps
Ps due to Doppler and ISI
Introduction to Diversity

2. Review of Last Lecture Modulation Tradeoffs Amplitude/Phase Modulation
Constellations, Pulse Shaping, Differential
Error Probability for Amp/Phase Modulation
Performance metrics in fading
Outage, Average Ps , Combined outage and average Ps
Outage probability
Probability that Ps is above target
Equivalently, probability gs below target (in AWGN)

3. Average Ps Ps Ps t or d Ts Expected value of random variable Ps
Used when Tc~Ts
Error probability much higher than in AWGN alone
Alternate Q function approach greatly simplifies calculations (switch integral order, becomes Laplace Xfm)

4. Combined outage and average Ps
Ps(gs)
Ps(gs)
Pstarget
Ps(gs)
Used in combined shadowing and flat-fading
Ps varies slowly, locally determined by flat fading
Declare outage when Ps above target value

5. Doppler Effects
High doppler causes channel phase to decorrelate between symbols
Leads to an irreducible error floor for differential modulation
Increasing power does not reduce error
Error floor depends on BdTs

6. ISI Effects
Delay spread exceeding a symbol time causes ISI (self interference).
ISI leads to irreducible error floor
Increasing signal power increases ISI power
ISI requires that Ts>>Tm (Rs<<Bc) 1 2 3 4 5 Tm Ts

7. Introduction to Diversity
Basic Idea
Send same bits over independent fading paths
Independent fading paths obtained by time, space, frequency, or polarization diversity
Combine paths to mitigate fading effects Tb t
Multiple paths unlikely to fade simultaneously

8. Main Points Fading greatly increases average Ps .
Alternate Q function approach simplifies Ps calculation, especially its average value in fading (Laplace Xfm).
Doppler spread only impacts differential modulation causing an irreducible error floor at low data rates
Delay spread causes irreducible error floor or imposes rate limits
Need to combat flat and frequency-selective fading
Focus of the rest of the course.
Diversity combats flat-fading by combining independently fading paths.

9. Happy Halloween