## 5 Challenges and Perspectives
_Involving directional antennas in coping with other malicious attack type._ While the configuration of their radiation pattern can inherently mitigate the effects associated to eavesdropping or jamming, the directional antennas can be involved in identifying, mitigating or even eliminating the security risks associated to other malicious attacks using angular information (signal's direction of arrival). For this, the key word is \"localization\", so any malicious attack that can be addressed using localization-based techniques (_i.e._, position verification) can be a valid target for future research. Relevant examples in this context are the selective forwarding attack [68] or the Hello flood attack [69]. 2. _Using directional antenna-based localization mechanisms to detect security attacks on other localization schemes._ The WSN's localization infrastructure is susceptible to an assortment of malicious attacks [70] that can endanger the network's proper functioning. Effective localization schemes based on the use of GPS devices or lateration-based algorithms can be automatically validated using angulation-based approaches relying on intrinsic angular information provided by directional antennas. 3. _Eliminating the consequences of several attacks by benefiting from the longer transmission range of directional antennas._ A concrete example can be the case of sensor nodes or groups of sensor nodes isolated from the rest of the network due to various malicious attacks (e.g., jamming, node capturing attack, resource depletion attack, _etc._). In this kind of situation the nodes can find alternative paths to regain the connectivity to the rest of WSN by contacting nodes that are further away. 4. _Using sensor nodes with both directional and omnidirectional antennas to solve complex security issues inside WSN._ Such an approach could combine the potential advantages brought by the two antenna types. In this case, strategies to switch from one type of antenna to the other have to be design in order to maximize the WSN capability to timely discover and eliminate the security risks. 5. _Coordinating the mechanisms based on the use of directional antennas with other security related technique._ Coping with the increased diversity of security threats that affect wireless sensor networks, demands the use of a complex ensemble of methodologies and protocols. The integration of security mechanisms based on directional antennas in an overall security system it's not a simple task due to a series of factors including the power, communication and computational constraints, the heterogeneity of sensor nodes, the unattended or hostile nature of the WSN environment, _etc._
6. _Extending the research field by addressing the security problems of more complex versions of WSNs,_ where the sensor nodes are endorsed with mobility (e.g., mobile wireless sensor networks [71] or airborne wireless sensor networks [72]) or where the sensor nodes coexist with other wireless node types (wireless sensor and actuator networks [73] or even wireless sensor, actuator and robot networks [74]). 7. _Fusing information received from directional antennas and from other devices (e.g., sensors) for coping with security threats._ In many cases, the network nodes are able to obtain supplementary information that can be used to mitigate the security attack risks. Routing information, list of neighboring nodes together, locations and battery energy levels of neighboring nodes or successive sensor measurements are only few examples of information that can be utilized in this context to mitigate the security risks. For example, multimedia sensor nodes equipped with video and audio capture capabilities can fuse such information with the ones obtained from directional antennas to address security-related issues.