Method for managing data in a wireless sensor network

#1. Field of the Invention

#The present invention relates to and in particular to a method for managing data in a preferably non real-time sensor network.

#2. Description of the Related Art

#FIG. 1 is a diagram showing a schematic depiction of a group of a sensor network consisting of four clusters;

#FIG. 2 is a diagram showing a schematic depiction of a hierarchical group formation within a sensor network;

#FIG. 3 is a diagram showing a schematic depiction of a continuous data query; and

#FIG. 1 shows—schematically—a part of a sensor network with a multitude of sensor nodes Si. After deployment of the sensor nodes Si in an area to be monitored, clusters Q have been formed by means of the LEACH protocol, wherein in FIG. 1 a total of clusters Qz−1, Qz, Qz+1 and Qz+2 is depicted. Within each cluster, one of the sensor nodes Si has been elected—also by means of the LEACH protocol—as aggregator node AQ. The election of an aggregator node AQ within a cluster Q is always repeated anew after a pre-configurable period of time, i.e. an epoch. As it is clearly evident from FIG. 1, every cluster Q has all in all 9 sensor nodes Si, wherein the sensor node acting as aggregator node AQ is depicted as dark dot. The four clusters Q being neighbors to each other, are—according to the invention—arranged in a group. According to the invention, the arrows represent the data flow within the group. In every epoch the sensor nodes Si encrypt their sensed measured values ai by a symmetric, additively homomorphic privacy homomorphism PHS and send the encrypted values s=Ek (ai) to the aggregator node AQ chosen for the epoch of their cluster Q. The aggregator nodes AQ add the received encrypted values s and store the consequently resulting value az (for cluster Qz) persistently. In addition, every aggregator node AQ sends the stored value to the aggregator node AQ which is the neighbor cluster Q of its group in clockwise direction, where the value is also stored persistently. To give a concrete example, the aggregator node AQz of cluster Qz stores the value az of its own cluster Qz and in addition the value az−1 of the cluster Qz−1 neighboring cluster Qz in clockwise direction.

#FIG. 2 shows the application of the method according to the invention on two hierarchy levels. Concretely, four groups of the kind depicted in FIG. 1 are combined to a superordinated group. The data flow follows on a superordinated hierarchy level the same method as described in the context with FIG. 1.

#FIG. 3 shows—schematically—the process of continuous data query as well as a corresponding response scheme. At an arbitrary point in time, the reader R, for example a laptop has come near to the network in order to request specific data. For this purpose, the reader R sends out a radio signal that comprises the moment in time, i.e. concretely the epoch in which the requested data was sensed, as well as the region where the data was sensed. Since every sensor node Si knows to which cluster Q it belongs to, it is possible to forward the request only to those clusters Q whose aggregator nodes AQ possess the relevant information. Depending on the transmission distance of the aggregator nodes AQ, or the distance between the aggregator nodes AQ and reader R, respectively, the aggregator node AQ sends the relevant data—encrypted—either directly or—as depicted in the right part of FIG. 3—multi-hop over sensor node Si acting as forwarding node Fi.