1. Simultaneous Rate and Power Control in Multirate Multimedia CDMA Systems By: Sunil Kandukuri and Stephen Boyd

2. Overview The Problem System Model The Solution Simulation Results Conclusion

3. The Problem Power and rate adaptation in a CDMA system Each user has a required QoS (a required effective data rate Goal: Minimize total transmit power

4. System Model: General Single cell CDMA Uplink multiple access channel Different channel gains System supports multiple rates

5. System Model: Parameters Parameters N = number of mobiles P i = power transmitted by mobile i R i = raw data rate of mobile i W = spread bandwidth QoS requirement of mobile i,  i, is the effective data rate

6. System Model: Interference Interference caused by one user on another represented by cross correlations between codes, C ij Gain of path between mobile i and base station, L i Total interfering effect of mobile j on mobile i, G ij is

7. System Model: Calculations

8. System Model: QoS Formula Probability of error is a function of  i, formula depends on modulation scheme Simplified P e expression QoS formula

9. The Solution Objective: Minimize the sum of powers of the mobiles subject to the QoS requirements of all mobiles Technique: Geometric programming Geometric programming – a non- convex optimization problem is cast as a convex optimization problem

10. The Solution Convex optimization –objective and constraints are all convex –Can obtain a global optimum or a proof that the set of specifications is infeasible –Efficient implementation

11. The Solution: Algorithm Minimize 1 T P (sum of powers) Subject to Can also add constraints such as

12. Simulation Results Sum of powers transmitted vs interference

13. Simulation Results QoS vs. interference

14. Summary For optimization objective and given constraints, paper showed an efficient technique Is this the “right” way to pose the problem –Good– practical QoS definition –Not so good – Minimizing “total” power