Performance Modeling of Multi-Rate HDR and its Effect on TCP Throughput

An interesting feature of the 3G cellular networks is their ability to support multiple data rates. Though the performance of TCP over wireless networks has been well studied, there is still no clear understanding on the expected throughput of TCP over multi-rate cellular systems. In this work, we consider a multi-rate system like High Data Rate (HDR) and represent the state space using a Markov chain. We calculate the state transition probabilities assuming transitions are possible between adjacent states only. We calculate the expected data rate conditioned to the initial state both analytically and through simulations. We use an M/G/l queuing model to capture the delay and TCP throughput for each of the initial states. We also illustrate how TCP throughput is affected by parameters like velocity, bit error rate, window size, TCP loss rate, and the underlying radio link protocol.