This paper introduces the opensensor platform. The idea behind the opensensor is to build an open source wireless sensor platform. All relevant information to build, to program and to teach the opensensor is freely available. The opensensor platform can be used for all kind of wireless sensor network research, but in this paper the focus is on contextual information retrieval for the mobile phone. After introducing and motivating the opensensor platform, some first examples and projects for contextual information retrieval are introduced.

Abstract-Reliable data retrieval from a sensor network can require a temporal distributed data storage of the measured data among all motes. This is the case when a sink of information, or a gateway, is only occasionally present in the network. We consider a network consisting of a set of motes that in order to save energy independently of each other go into offline mode, switching theirs radios off. We propose a cooperative mechanism for distributed data storage that allows complete data retrieval with high probability. Reliable data retrieval is crucial for data-critical applications. Reliability is achieved by introducing redundancy in the system by applying ReedSolomon scheme for data encoding. This solution can tolerate the situation where a certain number of devices in the sensor cluster is unavailable at the moment of information retrieval. A probabilistic analytical model is developed to investigate the performance of the proposed algorithm. This model is verified by simulation and prototype testing. Prototyping is done on the OpenSensor platform developed at Aalborg University. Performance results indicate that the proposed cooperative data distribution method outperforms the non-cooperative one.

Abstract-In this paper we investigate three different MAC protocols based on CSMA/CA in terms of throughput and channel access delay. The investigation is based on analytical models and real implementations on a testbed developed for this purpose. While the first MAC approach is alike IEEE802.11, the other two approaches are based on packet aggregation per node and on cooperative approaches. It can be shown that the two novel MAC schemes are increasing the throughput compared to the standard CSMA/CA approach, but only the cooperative approach is resulting in lower channel access delays.

No abstract

No abstract