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Simultaneous Rate and Power Control in Multirate Multimedia CDMA Systems

Simultaneous Rate and Power Control in Multirate Multimedia CDMA Systems. By: Sunil Kandukuri and Stephen Boyd. Overview. The Problem System Model The Solution Simulation Results Conclusion. The Problem. Power and rate adaptation in a CDMA system

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Simultaneous Rate and Power Control in Multirate Multimedia CDMA Systems

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  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 Pi = power transmitted by mobile i Ri = 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, Cij • Gain of path between mobile i and base station, Li • Total interfering effect of mobile j on mobile i, Gij is

  7. System Model: Calculations

  8. System Model: QoS Formula • Probability of error is a function of i, formula depends on modulation scheme • Simplified Pe 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 1TP (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

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