Understanding and mitigating the impact of RF interference on 802.11 networks

Abstract

We study the impact on 802.11 networks of RF interference from devices such as Zigbee and cordless phones that increasingly crowd the 2.4GHz ISM band, and from devices such as wireless camera jammers and non-compliant 802.11 devices that seek to disrupt 802.11 operation. Our experiments show that commodity 802.11 equipment is surprisingly vulnerable to certain patterns of weak or narrow-band interference. This enables us to disrupt a link with an interfering signal whose power is 1000 times weaker than the victim's 802.11 signals, or to shut down a multiple AP, multiple channel managed network at a location with a single radio interferer. We identify several factors that lead to these vulnerabilities, ranging from MAC layer driver implementation strategies to PHY layer radio frequency implementation strategies. Our results further show that these factors are not overcome by simply changing 802.11 operational parameters (such as CCA threshold, rate and packet size) with the exception of frequency shifts. This leads us to explore rapid channel hopping as a strategy to withstand RF interference. We prototype a channel hopping design using PRISM NICs, and find that it can sustain throughput at levels of RF interference well above that needed to disrupt unmodified links, and at a reasonable cost in terms of switching overheads.

Persistent jamming in wireless local area networks: Attack and defense

“…Traditionally, channel hopping and link adaptation techniques have been developed as solutions that mitigate the effect of jamming [13,14,15,16,17,18,19]. Channel hopping techniques attempt to avoid jammed channels through changing the channel among the orthogonally available channel bands.…”

“…A pair of nodes using proactive channel hopping has a hopping sequence that periodically changes [14]. In a reactive channel hopping scheme, a node only switches to a different channel if it detects the presence of jamming signal [13,15,16,18]. If a coordinator or pair of nodes decides to switch channels, all other nodes in the network switch channels as well.…”

Exploiting programmable architectures for WiFi/ZigBee inter-technology cooperation

“…While most studies focus on the analysis of ZigBee performance degradation in the presence of WiFi interference, recently, it has been shown that significant throughput reductions can also be observed in WiFi networks [3,9]. Surprisingly, WiFi vulnerabilities arise despite the fact that many mechanisms have been included at the medium access control (MAC) and physical (PHY) layer to guarantee robustness to interference.…”

A software framework for alleviating the effects of MAC-aware jamming attacks in wireless access networks

“…A large body or prior studies employ frequency hopping (FH) techniques to overcome the presence of jammers [26][27][28]. Frequency hopping can be either proactive or reactive.…”

“…To the best of our knowledge, FIJI is the first system to examine the effects of implicit jamming on the overall performance of WLANs and mesh networks. Gummadi et al [26] find that 802.11 devices are vulnerable to specific patterns of narrow-band interference related to time recovery, dynamic range selection and PLCP-header processing. They show that due to these limitations, an intelligent jammer with a 1,000 times weaker signal (than that of the legitimate transceiver) can still corrupt the reception of packets.…”