IoT devices can be deployed almost anywhere, but they usually need to be connected to other IoT devices, either through the Internet or local area networks. For such communications, many IoT devices make use of wireless communications, whose coverage is key: if no coverage is available, an IoT device becomes isolated. This can happen both indoors (e.g., large buildings, industrial warehouses) or outdoors (e.g., rural areas, cities). To tackle such an issue, opportunistic networks can be useful, since they use gateways to provide services to IoT devices when they are in range (i.e., IoT devices take the opportunity of having a nearby gateway to exchange data or to use a computing service). Moreover, opportunistic networks can provide Edge Computing capabilities, thus creating Opportunistic Edge Computing (OEC) systems, which deploy smart gateways able to perform certain tasks faster than a remote Cloud. This article presents a novel decentralized OEC system based on Bluetooth 5 IoT nodes whose latency is evaluated to determine the feasibility of using it in practical applications. The obtained results indicate that, for the selected scenario, the average end-to-end latency is relatively low (736 ms), but it is impacted by factors such as the location of the bootstrap node, the smart gateway hardware or the use of high-security mechanisms.

There are more and more IoT devices that need to be interconnected with each other to perform compute-intensive tasks due to their limitations in terms of storage, computing power and energy consumption. However, IoT devices encounter the problem of the lack of wireless connectivity in places where they are deployed or where they are traveling through. A solution to this problem consists in the use of opportunistic systems, which provide connectivity and processing resources efficiently by reducing remote communications to the cloud. Opportunistic networks are considered useful both in IoT scenarios where the cloud becomes saturated (e.g., due to an excessive amount of concurrent communications or to Denial-of-Service (DoS) attacks), as well as in those areas where wireless communications coverage is not available, such as it frequently occurs in rural areas or during natural disasters, wars or when other factors cause network outages. This paper presents the design of a novel opportunistic Edge Computing system based on the use of Bluetooth 5 and Single Board Computers (SBCs). To illustrate the performance and feasibility of the proposed system, latency tests are presented. For such latency tests, an experimental testbed was built by communicating two separate IoT networks (each network consisted of an IoT node and an opportunistic Edge Computing gateway). The tests calculated the time of message propagation from one end node to another. The obtained results show that the developed system obtains latencies between 850 and 1200ms, depending on the scenario, which make the solution viable for many application scenarios with low latency requirements.

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