  Dense, unmanaged 802.11 deployments tempt saboteurs into launching jamming
attacks by injecting malicious interference. Nowadays, jammers can be portable
devices that transmit intermittently at low power in order to conserve energy.
In this paper, we first conduct extensive experiments on an indoor 802.11
network to assess the ability of two physical layer functions, rate adaptation
and power control, in mitigating jamming. In the presence of a jammer we find
that: (a) the use of popular rate adaptation algorithms can significantly
degrade network performance and, (b) appropriate tuning of the carrier sensing
threshold allows a transmitter to send packets even when being jammed and
enables a receiver capture the desired signal. Based on our findings, we build
ARES, an Anti-jamming REinforcement System, which tunes the parameters of rate
adaptation and power control to improve the performance in the presence of
jammers. ARES ensures that operations under benign conditions are unaffected.
To demonstrate the effectiveness and generality of ARES, we evaluate it in
three wireless testbeds: (a) an 802.11n WLAN with MIMO nodes, (b) an 802.11a/g
mesh network with mobile jammers and (c) an 802.11a WLAN. We observe that ARES
improves the network throughput across all testbeds by up to 150%.
