TCP performance in WCDMA-based cellular wireless IP networks

The performance of TCP (transmission control protocol) is evaluated for downlink data transmission in a cellular WCDMA (wideband code division multiple access) network where variable rate transmission is supported at the RLC (radio link control)/MAC (medium access control) level. A simple rate search procedure (based on the number of simultaneous TCP connections and the channel condition) is proposed for the RLC/MAC level transmission rate selection for downlink data transmission. The dynamic rate variation is assumed to be achieved by using single-code transmission with variable spreading factor, where the spreading factor varies inversely with the transmission rate. A novel 'mean-sense' approach to calculate intercell interference in such an environment is developed assuming homogeneous traffic load (in terms of active TCP connections) in different cells. The impact of the different physical layer, RLC/MAC layer and TCP parameters on the end-to-end throughput performance are investigated by simulating the system dynamics under multiple concurrent TCP connections.