Ocelot´s Knapsack Calculations for Modeling Power Amplifier and Walsh Code Limits

We give a model for the performance impact on wireless systems of the limitations of certain resources, namely, the base-station power amplifier and the available OVSF codes. These limitations are readily modeled in the loss model formulation as a stochastic knapsack. A simple and well-known recurrence of Kaufman and Roberts allows the predictions of the model to be efficiently calculated. We discuss the assumptions and approximations we have made that allow the use of the model. We have included the model in Ocelot, an Alcatel-Lucent tool for modeling and optimizing cellular phone systems. The model is fast to compute, differentiable with respect to the relevant parameters, and able to model broad ranges of capacity and resource use. These conditions are critical to our application of optimization.