## 5 Emerging Challenges and Opportunities  
In this section, we will point to some technical challenges and opportunities for future emergency response systems and discuss related technical progress that has been made. Table 3 summarises the pros and cons of emerging technologies and open research problems from different perspectives. Emerging technologies for heterogeneous network integration emphasize compliance with standardds that open an opportunity to integrate WSNs with other networks. However, current technologies still rely on gateway nodes to transfer data. Since opportunistic networking is at the confluence of _ad hoc_ networking and disruption tolerant networks, this recent technology requires a more seamless networking environment to allow intermittent communications between any pair of devices at any time and place. Since emerging sensing devices are equipped with multiple types of wireless interfaces (for example, a smartphone has 3G, WiFi and Bluetooth interfaces), a device may belong to multiple types of networks at the same time. Network virtualisation for devices will then choose the best communication network for conveying data seamlessly based on urgency, available bandwidth and communication cost. On the other hand, instead of node-centric networks, knowledge-centric network designs are needed to advance towards distributed intelligence. Thus, knowledge-driven solutions will steer collaboration between several networks to integrate knowledge extracted from diverse data sources. Regarding security, emerging technologies can offer secure communications between devices only when they have the same sensing signature. This approach facilitates automatic authentication between devices and secure pairing of devices in physical proximity. However, these technologies aim at device-level information sharing rather than content-level information sharing. Once devices authenticate each other, complete trust between devices may expose the system to malicious attacks (e.g., drop-all behavior, random RF jamming and dissemination of false information) [57] in an opportunistic networking environment. Thus, the security of opportunistic communications becomes an open issue in emergencies. Regarding privacy, emerging technologies pull service content to avoid pushing private information, so as to keep private data sets separate from public data. Although these technologies provide system-defined privacy to isolate personal private data, user-defined privacy and multi-level privacy are not provided, and activity inferences are a risk to personal privacy. As emergency response systems must rely on diverse data sources, there are important open issues on knowledge inference in connection with trust, security and privacy. While emerging technologies pay attention to mobile sensing systems incorporated with cloud-enabled decision systems, they can also take advantage of information contributed by the crowd to find out the knowledge behind a huge amounts of sensing information. Only scalable decision-making models or bio-inspired approaches [58] are able to handle such a huge amount of data, and emerging technologies must pay attention to data optimisation and to migrating the computation between physical/virtual machines. Although a simple learning process can suffice in certain cases (e.g., identification of user mobility using GPS data only), more complex learning and inference from human activity is needed using different ambient signatures including audio, location and social network information. However, as these technologies only consider one-way knowledge flow from data from the sources to the back-end cloud, a novel two-way knowledge feedback loop from cloud to clients may facilitate not only knowledge discovery, but also sensing optimization. Designing participatory sensing and collaborative sensing models [59] is also a challenging problem. The control of sensing with one or more groups of people, devices, networks and systems may contribute a single piece of location information or a summary [60].