# Mobile Autonomous Sensing Unit (MASU): A Framework That Supports Distributed Pervasive Data Sensing
## 3 The MASU Framework  
The MASU framework supports opportunistic mobile collaborative sensing activities performed over dynamic and distributed communication scenarios that include both stable and unpredictable communication links. This framework is based on what we call MASU units (potentially mobile nodes), which are smartphones or other devices that run the MASU software infrastructure and interact among them in a peer-to-peer fashion. These nodes not only can work autonomously and perform independent sensing tasks, but also interact opportunistically with other units to perform collaborative sensing. In this sense, the framework allows nodes to act as both consumers and providers of sensing services while preserving their autonomy. The collaboration among a group of MASU units allows the provision of complex and high quality sensing services that could not be provided by individual sensing devices, due to limitations in their capabilities (e.g., CPU, memory, sensor quality, etc.) or to the high cost involved in the sensing tasks. For this reason, the interaction between various units enables a number of collaborative sensing services that are beneficial for the overall group of devices involved in terms of hardware resources, energy consumption and information quality. In order to model a variety of processes and services involved in a collaborative sensing activity, the MASU framework defines a number of roles played by different units. A role can be seen as a particular set of services provided and/or consumed by a specific unit. A MASU unit can play one or more roles within a collaborative sensing activity. Moreover, it can have various instances of the same type of role activated at the same time. A unit can also participate in a number of parallel collaborative sensing activities, interacting simultaneously with units that are part of different activities and playing the same or different roles in them. In other words, a MASU unit can be seen as an autonomous node playing one or more roles in various work sessions. Figure 1 shows an overview of the MASU work scenario, when two collaborative sensing activities are being performed among a group of units. It shows two different groups of units that, according to the roles played by them, provide and/or consume diverse services within the activity they are participating. In addition, one of the units is participating in both sensing activities so that it can contribute to and benefit from both of them. The process to conceive, develop and evaluate the MASU framework was inspired in the design science research approach [26], which is a problem solving process that involves seven steps (guidelines) for finding a solution to the stated problem (an information system). Following these guidelines we defined the MASU design (guideline 1) for addressing the pervasive sensing problem (guideline 2). We evaluated the performance and capability of such a design using simulations and also through an empirical test using a MASU-based application (guideline 3). The evaluation results indicated the framework was able to manage the device heterogeneity in a distributed way, considering various types of communication links among nodes; which represents a clear contribution for the development of pervasive sensing solutions (guideline 4). The MASU design was represented using contextualized component diagrams (guideline 5), and these design solutions were revised through periodic formal technical reviews [27] that helped us find effective solutions to the design challenges of the system (guideline 6). Finally, the design results were communicated to the technical audience involved in the MASU evaluation process in order to help them make an effective use of the framework (guideline 7). Figure 1: Overview of the MASU work scenario. The design evaluation methods used during the development of MASU were diverse; each one was chosen depending on the development stage of the product.