Optimizing TCP Performance in Multi-AP Residential Broadband Connections via Minislot Access

The high bandwidth demand of Internet applications has recently driven the need of increasing the residential download speed. A practical solution to the problem is to aggregate the bandwidth of 802.11 access points (APs) backhauls in range. Since 802.11 devices are usually single radio, the communication to APs on different radio channels requires a time-division multiple access (TDMA) policy at the client station. With an in-depth experimental analysis and a customized 802.11 driver, in this paper, we show that the usage of multi-AP TDMA policy may cause degradation of the TCP throughput and an underutilization of the AP backhauls. We then introduce a simple analytical model that accurately predicts the TCP round-trip time (RTT) with a multi-AP TDMA policy and propose a resource allocation algorithm to reduce the observed TCP RTT with a very low computational cost. Our proposed scheme runs locally at the client station and improves the aggregate throughput up to 1.5 times compared to state-of-the-art allocations. We finally show that the throughput achieved by our algorithm is very close to the theoretical upper bound in key simulation scenarios. 1. Introduction Asymmetric digital subscriber line (ADSL) has become the “de-facto” standard for residential broadband access to the Internet. In addition, the density of ADSL deployments with 802.11 wireless local area network (WLAN) connectivity tends to be high, especially in urban areas [1]. The interplay between these two technologies introduces interesting technical challenges and opportunities that can be exploited. First, WLAN access rates are typically an order of magnitude higher than the bottleneck of the end-to-end path, which is either the ADSL [2] or the backbone [3]. Second, the set of ADSL links in the neighborhood are generally underutilized [2]. As a consequence, there is a potential to bundle the access points (APs) backhaul bandwidth via 802.11 connections. However, (i) APs usually operate on independent radio channel, and (ii) users typically connect to these APs with single-radio commodity 802.11 cards. Because a single-radio card cannot simultaneously connect to more than one AP, it has been proposed to rely on the standard 802.11 power saving (PS) mode to implement a time-division multiple access (TDMA) policy. Stations spend enough time to either collect all the bandwidth from each AP [4] or to provide a fair sharing of the aggregated resources [5] by sequentially cycling through the APs in a round-robin fashion [6]. Unfortunately, multi-AP TDMA policies hurt the throughput