Abstract—Jamming is a very effective denial-of-service attack that renders most higher-layer security mechanisms moot—yet it is often ignored in WSN design. We show that an interrupt jamming attack is simple to perpetrate in software using a MICAz mote, is energy efficient and stealthy for the jammer, and completely disrupts communication. Solutions are needed to mitigate this insider threat even if more powerful attackers are not thwarted. We present DEEJAM, a novel MAC-layer protocol for defeating stealthy jammers with IEEE 802.15.4-based hardware, to address this problematic area. It layers four defensive mechanisms to hide communication from a jammer, evade its search, and reduce its impact. Given the difficulty of modeling the physical layer accurately in simulation, we evaluate DEEJAM instead on the MICAz mote. We show the performance of the protocol against successively more complex attacks: interrupt jamming, activity jamming, scan jamming, and pulse jamming. Results show that DEEJAM defeats the otherwise devastating interrupt jammer, and achieves a packet delivery ratio of 88 % in the presence of a pulse jammer. To the best of our knowledge, this work is the first to confront multiple types of jamming on common WSN hardware with solutions that are shown empirically to enable continued communication despite an ongoing attack. I.

Most currently deployed sensor networks use the same channel to communicate information among nodes. This is a source of great inefficiency as it poorly utilizes the available wireless spectrum. This paper takes advantage of radio capabilities of MicaZ motes that can communicate on multiple frequencies as specified in the 802.15.4 standard. We consider the case of a data collection sensor network where multiple base-stations are responsible for draining data from sensor nodes. A key question becomes how to assign nodes to wireless channels such that network throughput is maximized. The problem is reduced to one of load balancing. A control theoretical approach is used to design a self-regulating load-balancing algorithm that maximizes total network throughput. It is evaluated both in simulation and on an experimental testbed. The results demonstrate a significant performance improvement. It is shown that a control theory approach is indeed needed to guarantee stability in data collection networks and prevent undue oscillation of nodes among different wireless channels upon dynamic changes in load conditions.

RACNet is a sensor network for monitoring a data center’s environmental conditions. The high spatial and temporal fidelity measurements that RACNet provides can be used to improve the data center’s safety and energy efficiency. RACNet overcomes the network’s large scale and density and the data center’s harsh RF environment to achieve data yields of 99 % or higher over a wide range of network sizes and sampling frequencies. It does so through a novel Wireless Reliable Acquisition Protocol (WRAP). WRAP decouples topology control from data collection and implements a token passing mechanism to provide network-wide arbitration. This congestion avoidance philosophy is conceptually different from existing congestion control algorithms that retroactively respond to congestion. Furthermore, WRAP adaptively distributes nodes among multiple frequency channels to balance load and lower data latency. Results from two testbeds and an ongoing production data center deployment indicate that RACNet outperforms previous data collection systems, especially as network load increases.

Abstract—We analyze the performance limits of data dissemination with multi-channel, single radio sensors. We formulate the problem of minimizing the average delay of data dissemination as a stochastic shortest path problem and show that, for an arbitrary topology network, an optimal control policy can be found in a finite number of steps, using value iteration or Dijsktra’s algorithm. However, the computational complexity of this solution is generally prohibitive. We thus focus on two special classes of network topologies of practical interest, namely single-hop clusters and multi-hop cluster trees. For these topologies, we derive the structure of policies that achieve an average delay within a factor 1+ɛ of the optimal average delay, in networks with large number of nodes. Through simulation, we show that these policies perform close to optimal even for networks with small and moderate numbers of nodes. Our analysis and simulations reveal that multichannel data dissemination policies lead to a drastic reduction in the average delay, up to a factor as large as the total number of channels available, even though each node can communicate over only one channel at any point of time. Finally, we present the foundations of a methodology, based on extreme value theory, allowing the implementation of our near-optimal dissemination policies with minimal overhead. I.

Recent work in sensor network energy optimization has shown that batch-andsend networks can significantly reduce network energy consumption. Batch-andsend networks rely on effective batch data transport protocols, but the throughput of state-of-the-art protocols is low. We present conditional immediate transmission, a novel packet forwarding mechanism, with which we achieve a 109 kbit/s raw data throughput over a 6-hop multi-channel 250 kbit/s 802.15.4 network; 97% of the theoretical upper bound. We show that packet copying is the bottleneck in high-throughput packet forwarding and that by moving packet copying off the critical path, we nearly double the end-to-end throughput. Our results can be seen as an upper bound on the achievable throughput over a single-route, multi-channel, multi-hop 802.15.4 network. While it might be possible to slightly improve our performance, we are sufficiently close to the theoretical upper bound for such work to be of limited value. Rather, our results suggests that other mechanisms, such as multi-route forwarding, may be fruitful way to further improve multi-hop throughput. 1

We analyze the performance limits of data dissemination with multi-channel, single radio sensors under random packet loss. We formulate the problem of minimizing the average delay of data dissemination as a stochastic shortest path problem and show that, for an arbitrary topology network, an optimal control policy can be found in a finite number of steps, using value iteration or Dijkstra’s algorithm. However, the computational complexity of this solution is generally prohibitive. We thus focus on two special classes of network topologies of practical interest, namely single-hop clusters and multi-hop cluster chains. For these topologies, we derive the structure of policies that achieve an asymptotically optimal average delay, in networks with large number of nodes. Our analysis reveals that a single radio in each node suffices to achieve performance gain directly proportional to the total number of channels available. Through simulation, we show that the derived policies perform close to optimal even for networks with small and moderate numbers of nodes and can be implemented with limited overhead.

Abstract. As many radio chips used in today’s sensor mote hardware can work at different frequencies, several multi-channel communication protocols have recently been proposed to improve network throughput and reduce packet loss for wireless sensor networks. However, existing work cannot utilize multiple channels to provide explicit guarantees for application-specified end-to-end communication delays, which are critical to many real-time applications such as surveillance and disaster response. In this paper, we propose MCRT, a multi-channel real-time communication protocol that features a flow-based channel allocation strategy. Because of the small number of orthogonal channels available in current mote hardware, MCRT allocates channels to network partitions formed based on many-to-one data flows. To achieve bounded end-to-end communication delay for every data flow, the channel allocation problem has been formulated as a constrained optimization problem and proved to be NP-complete. We then present the design of MCRT, which includes a channel allocation algorithm and a real-time packet forwarding strategy. Extensive simulation results based on a realistic radio model demonstrate that MCRT can effectively utilize multiple channels to reduce the number of deadlines missed in end-to-end communications. Our results also show that MCRT outperforms a state-of-the-art real-time protocol and two baseline multi-channel communication schemes. 1

Abstract — With the exciting progress of wireless sensor network (WSN) research, we envision that in 5-10 years, the world will be full of low power wireless sensor devices. Due to the independent design and development, together with the unexpected dynamics during deployment of co-existing networks and devices, the limited frequency spectrum will be extremely crowded. Plus, existing electric appliances like microwaves make the congestion even worse. This paper proposes to develop new suites of WSN protocols along three complementary dimensions: (1) to achieve high communication throughput within a single WSN, (2) to achieve multi-frequency functionality among overlapping but cooperative WSNs and (3) to resolve the crowded spectrum issue caused by any reason, such as random transmitting devices, other nearby sensor networks, or even co-existing electric appliances. I.

Developing and evaluating wireless protocols is challenging because it requires flexible network interface hardware, which is not readily available. In this paper, we present FlexMAC, a wireless protocol development and evaluation platform based on commodity hardware. FlexMAC targets CSMA wireless protocols and allows customization of functions such as backoff, retransmission, and packet timing. We describe our implementation of FlexMAC and quantify FlexMAC’s precision for 802.11b compared with commercial hardware implementations. The results show that FlexMAC’s performance is very close to that of hardware implementations. We also present two case studies that illustrate FlexMAC’s flexibility: the use of opportunistic relaying to boost throughput and an investigation of temporal and throughput fairness. We found that FlexMAC is a useful tool for conducting 802.11-style protocol research.

as one of guiding principles to architect sensor network systems.Wedemonstrateitsgenericapplicabilityandeffectivenessbyapplyingthisprincipletothreetypicalsensornetwork technologies,namely,localization(Spotlight),sensing(uSense)and communication(mNets).Thesetechnologieshaveverydissimilar features,representingawidespectrumofsystemdesignrequirements.Wehaveinvestedsignificantefforttodesign,implement andevaluateourtechniquesonTinyOS/Motetestbeds.Theresults fromseveralrunningsystemsindicatethatasymmetricfunction placementisapowerfulguidingprincipletoachieveefficiencyand high-performancesimultaneouslyinwirelesssensornetworks.At theend,weexamthesystemfeaturesthatdiscouragetheuseof asymmetricfunctionplacementandapproachestoaddressthem. I.