Feedback Control and Coordination over Wireless Networks

“Is it possible to close feedback loops efficiently and reliably over dynamic wireless networks?”

Many modern computing systems interact with the physical world through sensing and actuating devices. The ability to close feedback loops among these devices over dynamic wireless multi-hop networks enables a new breed of powerful cyber-physical applications, but calls for concerted research contributions from the control and communication communities to meet the extraordinary dependability, adaptability, and efficiency requirements of these applications.

Our group is involved in making significant advances in this direction by demonstrating fast feedback control over low-power wireless multi-hop networks with provable guarantees on closed-loop stability (video 1, video 2), as well as unprecedented efficiency and flexibility in the use of limited resources by tightly integrating self-triggered control with real-time wireless communication.

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Dependable Wireless Communication with Synchronous Transmissions

“Can we exploit packet collisions rather than fighting against them?”

For decades, wireless communication protocols have been designed based on the assumption that a packet collision inevitably leads to a reception failure. As a result, most protocols rely on up-to-date information about the state of the network (e.g., its topology), enabling them to take decisions with the goal of avoiding collisions. However, wireless networks are often highly dynamic – their state can change quickly and unpredictably – which makes traditional wireless protocols brittle and inefficient.

Our group has taken pioneering steps to understanding, improving, and exploiting synchronous transmissions, a disruptive concept that takes advantage of packet collisions instead of trying to avoid them. Our research on communication primitives and protocols based on synchronous transmissions has solved problems that were thought to be extremely difficult or even impossible, for example, by designing efficient and reliable protocols that rely on no or very little network state.

Energy-harvesting and Batteryless Systems

“How do we power trillions of sensing devices?”

This is one of the key questions we need to answer as the number of sensors embedded in the environment around us or even inside our bodies continues to grow exponentially in the coming years. Powering the sensors from ambient energy rather than primary batteries, which have a large environmental footprint and require manual replacement, is an essential part of the answer. Another one is whether we can even do without rechargeable batteries, building reliable sensing systems based on devices that have no energy storage or only a small capacitor, which has negligible aging effects.

Our group is investigating new methods and tools for energy-harvesting and batteryless sensing systems including PreAct, a long-term energy-management algorithm that makes better use of available ambient energy, and Shepherd, the first testbed that can accurately record and replay high-resolution energy-harvesting traces synchronously across a set of distributed (batteryless) devices. 

Benchmarking and Reproducibility

The ability to rigorously compare different solutions and to faithfully reproduce experimental results is fundamental for establishing a scientific claim and advancing the state of the art. Unlike other fields of computing and communication, (low-power) wireless networking lacks well-defined benchmarks and the uncontrolled variability of the evaluation environment (e.g., a testbed) makes it difficult to quantitatively compare and reproduce experimental results.

Within the IoTBench initiative, our group strives to remedy these issues by investigating benchmarks and evaluation methodologies that promote comparability and reproducibility.