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Simultaneous Rate and Power Control in Multirate Multimedia CDMA Systems By: Sunil Kandukuri and Stephen Boyd
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Overview The Problem System Model The Solution Simulation Results Conclusion
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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
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System Model: General Single cell CDMA Uplink multiple access channel Different channel gains System supports multiple rates
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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
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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
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System Model: Calculations
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System Model: QoS Formula Probability of error is a function of i, formula depends on modulation scheme Simplified P e expression QoS formula
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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
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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
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The Solution: Algorithm Minimize 1 T P (sum of powers) Subject to Can also add constraints such as
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Simulation Results Sum of powers transmitted vs interference
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Simulation Results QoS vs. interference
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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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