  The high bandwidth demand of Internet applications has recently driven the
need of increasing the residential download speed. A practical solution to the
problem has been proposed aggregating the bandwidth of 802.11 Access Points
(APs) backhauls in range via 802.11 connections. Since 802.11 devices are
usually single-radio, the communication to multiple APs on different
radio-channels requires the introduction of a time-division multiple access
(TDMA) policy at the client station. Current investigation in this area
supposes that there is a sufficient number of TCP flows to saturate the
Asymmetric Digital Subscriber Line (ADSL) behind the APs. However, this may be
not guaranteed according to the user traffic pattern. As a consequence, a TDMA
policy introduces additional delays in the end-to-end transmissions that will
cause degradation of the TCP throughput and an under-utilization of the AP
backhauls. In this paper, we first perform an in-depth experimental analysis
with a customized 802.11 driver of how the usage of multi-AP TDMA affects the
observed Round-Trip-Time (RTT) of TCP flows. Then, we introduce a simple
analytical model that accurately predicts the TCP RTT when accessing the
wireless medium with a Multi-AP TDMA policy. Based on this model, we propose a
resource allocation algorithm that runs locally at the station and it greatly
reduces the observed TCP RTT with a very low computational cost. Our proposed
scheme can improve up to 1:5 times the aggregate throughput observed by the
station compared to state-of-the-art multi-AP TDMA allocations. We also show
that the throughput performance of the algorithm is very close to the
theoretical upper-bound in key simulation scenarios.
