Modeling of power-controlled interference-limited wireless channels

This paper proposes an approach for efficient modeling of wireless channels that exhibit interference limitation and are subjected to fast power control. The approach is specifically intended for DS-CDMA systems, where multiple access interference (MAI) is the main limitation to system capacity, and fast closed loop power control is adopted to compensate for rapid variations of both user signal and interference strength. The model relies on Markov chains, by which we aim at representing the behavior of various components that may contribute to link level performance as seen from a single user perspective: fading on the user channel, total interference strength, transmitted power. The method we propose includes the following steps: (1) simulation of realistic (either power-based or SIR (signal-to-interference ratio)-based) closed-loop power control algorithms; (2) statistical analysis of samples of relevant processes (e.g. SIR) for a "reference user", that returns the order of the Markov chain and related transition probabilities. For various settings of parameters of the power control algorithm, numerical results are reported in terms of second order statistics of the "residual" SIR fluctuations, as obtained from simulations and from the Markov model. In this context, it is seen that a first order model may not be able to capture satisfactorily the intended channel behavior.