Modeling TCP in a multi-rate multi-user CDMA system

Abstract

Modern CDMA wireless channels support multiple transmission rates, which can be dynamically assigned to users based on traffic demand. However, in practice, assignment of high rate channels comes with the penalty of increased power as well as smaller orthogonal codes, which constrains their assignment to only a subset of active users. This motivates the need to carefully control high rate channel assignments so as to minimize power and achieve fairness among users. In this work, we propose a simple class of channel allocation policies to achieve this goal for TCP sessions. We develop an analytical model that explicitly captures both TCP dynamics and the impact of multiple users contending for a shared resource to evaluate the performance of the allocation policy. The model is shown to be accurate by comparing against ns-2 simulations and its utility demonstrated in computing the minimum number of required high rate channels to minimize contention. © IFIP International Federation for Information Processing 2007.