Existing code update protocols for reprogramming nodes in a sensor network are either unsuitable or inefficient when used in a mobile environment. The prohibitive factor of uncertainty about a node’s location due to their continuous movement coupled with the obvious constraint of a node’s limited resources, pose daunting challenges to the design of an effective code dissemination protocol for mobile sensor networks. In this work, we have designed an energy efficient, multihop reprogramming protocol for mobile sensor networks. Without making any assumptions on the location of nodes, this protocol uses the LQI and RSSI measurements of received packets to estimate link qualities and relative distances with neighbors in order to select the best node for code exchange. The protocol is based on a probabilistic broadcast paradigm with the mobile nodes smoothly modifying their advertisement transmission rates based on the dynamic changes in network density, thereby saving valuable energy. Contrary to previous protocols, this protocol downloads pages regardless of their order, thus, exploiting the mobility of the nodes and facilitating a fast transfer of the code.

While multi-hop broadcast based dissemination protocols, such as Trickle, Deluge and MNP, have gained tremendous popularity as a means for fast and convenient propagation of data/code in large scale wireless sensor networks, they can, unfortunately, serve as potential platforms for the spread of malware if the security is breached. To understand the vulnerability of such protocols and design defense mechanisms against piggy-backed virus attacks, it is critical to investigate the propagation process of these protocols in terms of their speed and reachability. In this work, we have proposed a general framework based on the principles of epidemic theory, for vulnerability analysis of current broadcast protocols in wireless sensor networks. In particular, we develop a common mathematical model for the propagation that incorporates important parameters derived from the communication patterns of the protocol under test. Based on this model, we analyze the propagation rate and the extent of spread of a data/malware over typical broadcast protocols proposed in the literature. The overall result is an approximate but convenient tool to characterize a broadcast protocol in terms of its data dissemination performance and also its vulnerability to malware propagation. 

Motivated by recently surfacing viruses that can spread over the air interfaces, in this work, we investigate the potentially disastrous threat of node compromise spreading in wireless sensor networks. Originating from a single infected node, we assume such a compromise can propagate to other sensor nodes via communication and pre-established mutual trust. We focus on the possible epidemic breakout of such propagations where the whole network may fall victim to the attack. Based on epidemic theory, we model and analyze this spreading process and identify key factors determining potential outbreaks. In particular, we perform our study on random graphs precisely constructed according to the parameters of the network, such as distance, key sharing constrained communication and node recovery, thereby reflecting the true characteristics therein. Moreover, a comparative study of the epidemic propagation is performed based on the effects of two types of sensor deployment strategies, viz., uniform random and group based deployment. The analytical results provide deep insights in designing potential defense strategies against this threat. Furthermore, through extensive simulations, we validate the model and perform investigations on the system dynamics. Our analysis and simulation results indicate that the uniform random deployment is more vulnerable to an epidemic outbreak than the group based deployment strategy.

Architecture and Protocol for Object Distribution and Tracking using RFID tags

A completely visible Pervasive Transaction Environment where it is possible to link all related distributions of physical objects and trace their mobility through their entire life process, has been elusive. With the emergence of Radio Frequency Identification (RFID) based object tags, it is now practicable to automatically collect information pertaining to the object’s place, time, transaction, etc. In this work, we proposed a mobility management architecture alongwith an application layer protocol for pervasive real-time tracking of object distribution. Subsequently, we expose an example application, i.e., Object Recall, based on RFArch and present efficient algorithms for performing the recall of RFID tagged objects that were previously distributed but turned out defective. We also perform a mathematical analysis of the distribution and recall process in a transaction network and get a stochastic estimate of the average spread of object distributions and the number of recall messages required. 

Secure Data aggregation in Wireless Sensor Networks

In-network processing presents a critical challenge for data authentication in wireless sensor networks (WSNs). Current schemes relying on Message Authentication Code (MAC) cannot provide natural support for this operation since even a slight modification to the data invalidates the MAC. In this work, based on the concepts of digital watermarking, we propose an end-to-end, statistical approach for data authentication that provides inherent support for in-network processing. In this scheme, authentication information is modulated as a watermark and superposed onto the sensory data at the nodes. The watermarked data can be aggregated by the intermediate nodes without incurring any en-route checking. Upon reception of the sensory data, the data sink is able to authenticate the data by validating the watermark, detecting whether the data has been illegitimately altered. In this way, the aggregation-survivable authentication information is only added at the sources and checked by the data sink, without any involvement of intermediate nodes. Moreover, the simple operation of watermark embedding and complex operation of watermark detection provide a natural solution of function partitioning between the resource limited sensor nodes and resource abundant data sink.
In addition, the watermark can be embedded in both the spatial and temporal domains to provide the flexibility between the detection time and detection granularity.

Wei Zhang, Pradip De, Yonghe Liu, and Sajal K. Das, "Secure Data Aggregation in Wireless Sensor Networks : A Watermark Based Authentication Supportive Approach", journal paper under review.

There has been an increasing demand for bandwidth-intensive services in mobile devices, such as streaming video and music, which bring about a paradigm shift in wireless cellular network architectures. Although various coding and modulation schemes are being adopted to address these requirements, a critical area of modification is the existing wireless network infrastructure, in particular, the backhaul architecture. Not only is it required to support high data rates, but also the hierarchical backhaul
topology needs to yield to a highly flexible and easily reconfigurable mesh network architecture to support new technologies and smaller cell sites. Based on the well-known Petersen graph, we propose a novel architecture, named PeterNet, for such a backhaul cellular network that connects the wireless base stations to the core network in a mesh topology using Free Space Optical (FSO) links. While our proposed architecture effectively leverages the benefits of a FSO connection, namely low cost deployment and high optical bandwidth, we prove, using important properties of the Petersen Graph, that this scalable topology also helps overcome the fundamental limitations of FSO technology like low link reliability under changing
weather conditions. The analysis shows an overall carrier-class reliability for the backhaul network in the order of four 9’s (99.99%) and five 9’s (99.999%). Furthermore, our architecture is not only deployable at the Base Transceiver Station level, but can also be extended to connect the Base Station Controllers at a higher level, thus providing a hierarchy of PeterNets
with the same properties.

Samik Ghosh, Pradip De, Kalyan Basu, and Sajal K. Das, "PeterNet : An Emergent Technology Based Radio Access Network Architecture for Next Generation Cellular Wireless Systems", in proceedings of The International Conference on Broadband Communications, Networks, and Systems (BroadNets) 2004. [pdf]