This chapter deals with PA model validation and comparison. In general PAs are complex dynamic systems that combine both short- and long-term memory effects with nonlinear phenomena. In contrast with linear systems with memory, where superposition holds and so any test signal can be used, or nonlinear systems with linear memory, where memory effects can be separately characterized and de-embedded to obtain a simple algebraic descriptive function, nonlinear dynamical systems must be \u2018locally\u2019 modeled and validated. Therefore, test signals and model comparison criteria must be carefully chosen to suit a particular set of typical operating conditions
