Synchronous and Concurrent Transmissions for Consensus in Low-Power Wireless
Doktorsavhandling, 2019

With the emergence of the Internet of Things, autonomous vehicles and the Industry 4.0, the need for dependable yet adaptive network protocols is arising. Many of these applications build their operations on distributed consensus. For example, UAVs agree on maneuvers to execute, and industrial systems agree on set-points for actuators.
Moreover, such scenarios imply a dynamic network topology due to mobility and interference, for example. Many applications are mission- and safety-critical, too.
Failures could cost lives or precipitate economic losses.

In this thesis, we design, implement and evaluate network protocols as a step towards enabling a low-power, adaptive and dependable ubiquitous networking that enables consensus in the Internet of Things. We make four main contributions:

- We introduce Orchestra that addresses the challenge of bringing TSCH (Time Slotted Channel Hopping) to dynamic networks as envisioned in the Internet of Things. In Orchestra, nodes autonomously compute their local schedules and update automatically as the topology evolves without signaling overhead. Besides, it does not require a central or distributed scheduler. Instead, it relies on the existing network stack information to maintain the schedules.

- We present A2 : Agreement in the Air, a system that brings distributed consensus to low-power multihop networks. A2 introduces Synchrotron, a synchronous transmissions kernel that builds a robust mesh by exploiting the capture effect, frequency hopping with parallel channels, and link-layer security. A2 builds on top of this layer and enables the two- and three-phase commit protocols, and services such as group membership, hopping sequence distribution, and re-keying.

- We present Wireless Paxos, a fault-tolerant, network-wide consensus primitive for low-power wireless networks. It is a new variant of Paxos, a widely used consensus protocol, and is specifically designed to tackle the challenges of low-power wireless networks. By utilizing concurrent transmissions, it provides a dependable low-latency consensus.

- We present BlueFlood, a protocol that adapts concurrent transmissions to Bluetooth. The result is fast and efficient data dissemination in multihop Bluetooth networks. Moreover, BlueFlood floods can be reliably received by off-the-shelf Bluetooth devices such as smartphones, opening new applications of concurrent transmissions and seamless integration with existing technologies.




Capture Effect

Distributed Computing

Wireless Networks




Industrial Internet of Things


Concurrent Transmissions

HA2 (lecture hall), Hörsalsvägen 4, Campus Johanneberg, Chalmers.
Opponent: Kay Römer, Professor and Director, Institute of Technical Informatics, Graz University of Technology, Austria


Beshr Al Nahas

Chalmers, Data- och informationsteknik, Nätverk och system

Orchestra: Robust Mesh Networks Through Autonomously Scheduled TSCH

SenSys'15: Proceedings of the 13th ACM Conference on Embedded Networked Sensor Systems,; (2015)p. 337-350

Paper i proceeding

Network-wide Consensus Utilizing the Capture Effect in Low-power Wireless Networks

Proceedings of the Conference on Embedded Networked Sensor Systems (ACM SenSys),; (2017)

Paper i proceeding

Paxos Made Wireless: Consensus in the Air

; (2019)

Paper i proceeding

Computer systems are embedded around us to ease our everyday life, e.g., in elevators, cars, and airplanes. For example, a car embeds hundreds of control units that are connected through a wired network. Each of these units is responsible for a function, e.g., controlling and monitoring speed, brakes, or non-critical functions like entertainment. One side effect is that a car has over 1 km of wires to connect these subsystems. This complicates both manufacturing and maintenance.

Moreover, networked objects are everywhere in our lives. We have become so used to being always online that we feel nervous when we are not. Our laptops and cell phones are always connected to the Internet, and even our homes are connected, too: Alarms, security cameras and the smart grid which feeds our homes with electricity and sends our consumption and the grid status. Industrial giants like Cisco and Ericsson predict a growing connectivity and project 22 billion devices to be connected by 2024. If this connectivity trend lives up to the predictions, a variety of appliances will be connected either to each other’s only or the Internet – in what is called the Internet of Things (IoT) – to enable remote control and automatic actions. All of the aforementioned scenarios require connectivity, and with the envisioned higher degree of connectivity, e.g., that includes moving parts, we cannot imagine wires running all over the place. Therefore, we turn to wireless solutions.

Having a wireless solution entails the lack of access to a wired energy source; thus, we have a limited power source from a battery or an energy harvester, e.g., a solar cell. Moreover, with wireless solutions, we expect data losses and communication outages, due to interference from other technologies. Such a data loss could have a catastrophic impact if it happens in a critical system, as a wireless brake system in a car, for example.

In this thesis, we design, implement and evaluate dependable network protocols that cope with the challenge of achieving a dependable operation over low-power and lossy wireless links with limited energy sources and processing power.

Ultralåg fördröjning, effektsnåla trådlösa nät

Stiftelsen för Strategisk forskning (SSF), 2017-01-01 -- 2021-12-31.

AgreeOnIT: Lättvikts konsensus och distribuerat datakunskap i resursbegränsade sakernas Internet

Vetenskapsrådet (VR), 2019-01-01 -- 2022-12-31.

ChaosNet: Distributed Computing for Low-Power Wireless Networks

Vetenskapsrådet (VR), 2015-01-01 -- 2018-12-31.






Informations- och kommunikationsteknik


Innovation och entreprenörskap



Technical report D - School of Computer Science and Engineering, Chalmers University of Technology: 176D

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4647


Chalmers tekniska högskola

HA2 (lecture hall), Hörsalsvägen 4, Campus Johanneberg, Chalmers.

Opponent: Kay Römer, Professor and Director, Institute of Technical Informatics, Graz University of Technology, Austria

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