1. EE359 – Lecture 13 Outline Annoucements Midterm announcements No HW this week (study for MT; HW due next week) Midterm review Introduction to adaptive modulation Variable-rate variable-power MQAM Optimal power and rate adaptation Finite constellation sets

2. Midterm Announcements Midterm Thur Nov. 7, 6-8pm, Thornton 110 Open book/notes (bring textbook/calculators) Covers Chapters 1-7 No computers Short review today OHs this week: Andrea: Tuesday 5-6pm and Wednesday 6-7pm Mainak: Mainak’s: Tues 6-7 pm, Packard 364, Wed 7-8pm Packard 106, Thurs 1:30-2:30 pm, Packard 106 No HW this week (new HW posted Thurs) Midterms from past 3 MTs posted, 10 pts for taking one and solns to all exams

3. Review of Last Lecture Maximal Ratio Combining MGF Approach for Performance of MRC Transmit diversity With channel knowledge, similar to receiver diversity, same array/diversity gain Without channel knowledge, can obtain diversity gain through Alamouti scheme over 2 consecutive symbols

4. Adaptive Modulation Change modulation relative to fading Parameters to adapt: Constellation size Transmit power Instantaneous BER Symbol time Coding rate/scheme Optimization criterion: Maximize throughput Minimize average power Minimize average BER Only 1-2 degrees of freedom needed for good performance

5. Variable-Rate Variable-Power MQAM Uncoded Data Bits Delay Point Selector M(  )-QAM Modulator Power: P(  ) To Channel  (t) log 2 M(  ) Bits One of the M(  ) Points BSPK 4-QAM 16-QAM Goal: Optimize P(  ) and M(  ) to maximize R=Elog[M(  )]

6. Optimization Formulation Adaptive MQAM: Rate for fixed BER Rate and Power Optimization Same maximization as for capacity, except for K=-1.5/ln(5BER).

7. Optimal Adaptive Scheme Power Adaptation Spectral Efficiency  kk  Equals capacity with effective power loss K=-1.5/ln(5BER).

8. Spectral Efficiency Can reduce gap by superimposing a trellis code

9. Constellation Restriction Restrict M D (  ) to {M 0 =0,…,M N }. Let M(  )=  /   *, where   * is later optimized. Set M D (  ) to max j M j : M j  M(  ). Region boundaries are  j =M j   *, j=0,…,N Power control maintains target BER M(  )=  /   *  00  1 =M 1  K * 22 33 0 M1M1 M2M2 Outage M1M1 M3M3 M2M2 M3M3 MD()MD()

10. Power Adaptation and Average Rate Power adaptation: Fixed BER within each region l E s /N 0 =(M j -1)/K l Channel inversion within a region Requires power increase when increasing M(  ) Average Rate

11. Efficiency in Rayleigh Fading Spectral Efficiency (bps/Hz) Average SNR (dB)

12. Main Points Adaptive modulation leverages fast fading to improve performance (throughput, BER, etc.) Adaptive MQAM uses capacity-achieving power and rate adaptation, with power penalty K. Comes within 5-6 dB of capacity Discretizing the constellation size results in negligible performance loss.