## 2 Related Work
### Existing Defense Mechanisms against Jamming  
A well-known attack on wireless communication, namely jamming, interferes with the radio frequencies of nodes. An adversary can easily disrupt the entire network with less than \(N\) jamming nodes on an \(N\)-size network. The standard defense against jamming involves various forms of spread-spectrum communication, but the main device used for ubiquitous networking, sensor nodes, will likely be limited to single-frequency use because of its low-cost, low-power character [5]. Generally, research on jamming defenses is categorized as shown in Figure 2: _detection, competition, and evasion_. Detection using both PDR (Packet Delivery Ratio) and RSSI (Receive Strength Signal Indicator) on sensor networks is proposed [16], but the detection mechanism requiresthe following countermeasures until the jammer can be perfectly be eliminated. Competition approaches can be utilized with the control of transmission power or strong coding for error correction [17], but these methods are too energy-consuming to apply on sensor nodes. Recently, evasion approaches have attracted considerable attention, because complete prevention against jamming is hard to implement and the provision of continuous service is important in the existence of jammers. These evasion approaches can be classified according to the affected layer: _physical layer_, _link layer_, and _network layer_. Spread spectrum has long been used to resist jamming attacks in wireless unicast environments. [PERSON] _et al._[18, 19] designed a scheme for broadcast jamming mitigation based on spread spectrum, especially DS (Directed Sequence) and FH-CDMA (Frequency Hopping-Code Division Multiple Access), and a balanced binary key tree and showed theoretical justifications of designed scheme. Specially, frequency hopping spread spectrum is based on the share of a secret spreading key (or code) between devices prior to the start of their communication. [PERSON] _et al._[20] proposed establishment of jamming-resistant keys using uncoordinated frequency hopping based on the assumption that the attacker cannot jam all frequency channels on which the nodes communicate at the same. However, the utilization of spread spectrum as a defense against jamming on the physical layer can be too energy-consuming to be widely deployed in resource-constrained sensors. Figure 2: Existing jamming defenses and DMP. As evasion approaches on link layer, channel hopping utilizes the fact that there are a number of orthogonal radio channels. For example, a representative sensor standard, IEEE 802.15.4 (e.g., CC2420 radio in MICAz motes) has 16 channels. [PERSON] _et al._[21] proposed a proactive (periodic) channel hopping scheme, coordinated synchronously. Reactive channel hopping, whereby radios switch channels to escape jamming, has been proposed to mitigate jamming in wireless sensor networks [22], and it occurs after radio jamming is detected and causes the entire network or only the jammed region to switch to a different radio channel networks. [PERSON] _et al._[23] compared the proactive and reactive channel hopping schemes, and showed that reactive defense provides better jamming tolerance than a proactive one when considering communication availability. However, channel hopping is not sufficient for jamming defense, because the jammer can also change the jamming channel continuously and then it enlarges the channel switching overhead on nodes. As one of the evasion methods on network layer, spatial retreat [24] is limited to mobile environments. As an evasive method used after detecting jamming, JAM (Jammed Area Mapping) simply focused on a mapping service for the jamming area [8]. JAM uses a priority message to inform the node's neighbors of the attack detection, maps the jammed area as feedback for routing and reports to a base station for jamming localization. However, it takes time for the routing protocol to update the information, or for the base station to get the report and take follow-up measures.