Throughput evaluation and enhancement of TCP clients in Wi-Fi hot spots

Abstract

In this paper we consider a Wi-Fi hot spot were M users are performing TCP downloads from Internet remote servers. Our study focuses on characterizing the way the TGP flow control mechanisms affect the MAC protocol operations, and identifying the main causes of the throughput limitations shown by the TCP traffic. In particular, we show that the TCP throughput is not limited by the collision events, but by i) the inability of the MAC protocol to assign a higher chance of accessing the channel to the hot spot Access Point than the mobile users, and ii) the interaction of flow control mechanisms used at the TCP layer and the contention avoidance scheme used at the MAC layer. We propose an extension to the MAC protocol that requires only modifications of the hot spot Access Points. Our proposed enhancement allows the Access Point to send bursts of TCP packets towards the hot spot clients. We design a resource allocation protocol aimed at maximizing the success probability of the uplink transmissions by dynamically adapting the burst size to the number of users' collisions and successful transmissions. Simulations confirm the improvements of the TCP throughput achieved by our enhanced MAC protocol. © IFIP International Federation for Information Processing 2004.