Enhancing Bluetooth TCP throughput via link layer packet adaptation

Abstract

TCP throughput limitations over wireless links have received considerable attention in the last few years. One of the problems is that TCP congestion control interprets packet losses as an indication of congestion, whereas in wireless links, losses could be due to transient link quality degradations. In this paper, we propose and study a link layer solution and evaluate its effects on TCP in the context of Bluetooth. We enhance the Bluetooth link layer to make use of channel state information and accordingly adapt the Bluetooth packet type to enhance TCP throughput We propose a simple analytical method to determine the optimal packet type for a given channel state by adding FEC support or changing packet size. Since wireless interfaces, such as 802.11 or Bluetooth, can provide information regarding the channel state using relevant APIs, this simple enhancement can easily be added to the link layer. We implemented this functionality in the Bluetooth link layer. Our simulation experiments show that the proposed adaptive packet type solution significantly improves TCP throughput. The throughput enhancement increases with the error rate. For high error rates close to 0.1%, the link layer enhanced with the adaptive scheme is able to maintain good TCP throughput, whereas throughput is almost zero when the adaptive scheme is not used.