Key predistribution is a popular technique for key distribution in sensor networks. The schemes available in current literature using this approach are for nodes with no or limited mobility. In this paper we present two key predistribution based scheme for heterogeneous networks i.e. networks which consist of nodes which are stationary as well as highly mobile. The existing schemes make use of only one key pool to establish links between the staionary and the mobile nodes. This restricts the mobility of nodes to one specific network. If the same key pool is used in multiple networks, the compromise of keys in one network would lead to compromise of keys in all the networks. We present two different solutions to this problem. The first approach uses a separate disjoint key pool to establish links between the stationary and mobile nodes of the network. In the second approach we take a large key pool and segment it into smaller key pools. Each of these segments acts as the key pool for different stationary sensor networks. The mobile nodes get keys from the aggregate of all these segments. The aggregate key pool can have some segments which can be used for future deployments. We compare the two schemes and analyze their performance. The schemes only deal with secure key distribution between the mobile and stationary nodes. It is assumed that the stationary nodes of the sensor networks are securely connected.
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