Imperial College London

Laksh Bhatia

Faculty of EngineeringDepartment of Computing

Research Postgraduate



laksh.bhatia16 Website




254ACE ExtensionSouth Kensington Campus





Publication Type

12 results found

Heggo M, Bhatia L, McCann J, 2022, RFTacho: Non-intrusive RF monitoring of rotating machines, The International Conference on Information Processing in Sensor Networks (IPSN) 2022

Measuring rotation speed is essential to many engineering applications; it elicits faults undetectable by vibration monitoring alone and enhances the vibration signal analysis of rotating machines. Optical, magnetic or mechanical Tachometers are currently state-of-art. Their limitations are they require line-of-sight, direct access to the rotating object. This paper proposes RFTacho, a rotation speed measurement system that leverages novel hardware and signal processing algorithms to produce highly accurate readings conveniently. RFTacho uses RF Orbital Angular Momentum (OAM) waves to measure rotation speed of multiple machines simultaneously with no requirements from the machine’s properties. OAM antennas allow it to operate in high-scattering environments, commonly found in industries, as they are resilient to de-polarization compared to linearly polarized antennas. RFTacho achieves this by using two novel signal processing algorithms to extract therotation speed of several rotating objects simultaneously amidst noise arising from high-scattering environments, non-line-of-sight scenarios and dynamic environmental conditions with a resolution of 1𝑟𝑝𝑚. We test RFTacho on several real-world machines like fans, motors, air conditioners. Results show that RFTacho has avg. error of < 0.5% compared to ground truth. We demonstrate RFTacho’s simultaneous multiple-object measurement capability that other tachometers do not have. Initial experiments show that RFTacho can measure speeds as high as 7000 rpm (theoretically 60000 rpm) with high resiliency at different coverage distances and orientation angles, requiring only 150 mW transmit power while operating in the 5 GHz license-exempt band. RFTacho is the first RF-based sensing system that combines OAM waves and novel processing approaches to measure the rotation speed of multiple machines simultaneously in a non-intrusive way.

Conference paper

Heggo M, Bhatia L, McCann J, 2021, Cognisense: A contactless rotation speed measurement system, The 19th ACM Conference on Embedded Networked Sensor Systems, Pages: 341-348

Several engineering applications require reliable rotation speed measurement for their correct functioning. The rotation speed measurements can be used to enhance the machines’ vibration signalanalysis and can also elicit faults undetectable by vibration monitoringalone. The current state of the art sensors for rotation speed measurement are optical, magnetic and mechanical tachometers. Thesesensors require line-of-sight and direct access to the machine which limits their use-cases. In this demo, we showcase Cognisense, an RF-based hardware-software sensing system that uses Orbital AngularMomentum (OAM) waves to accurately measure a machine’s rotation speed. Cognisense uses a novel compact patch antenna in a monostatic radar configuration capable of transmitting and receiving OAM waves in the 5GHz license-exempt band. The demo will show Cognisense working on machines with varied numbers of blades, sizes and materials. We will also present how Cognisense operates reliably in non-line-of-sight scenarios where traditional tachometers fail. We demonstrate how Cognisense works well in high-scattering scenarios and is not impacted by the material of rotor blades. Unlike optical tachometers that require one to face the machine head-on, Our demo will also show Cognisense performing reliably in the presence of a tilt angle between the system and the machine which is not possible with optical tachometers.

Conference paper

Bhatia L, Chen P-Y, Breza M, Zhao C, McCann Jet al., 2021, IRONWAN: increasing reliability of overlapping networks in LoRaWAN, IEEE Internet of Things Journal, ISSN: 2327-4662

LoRaWAN deployments follow an ad-hoc deployment model that has organically led to overlapping communication networks, sharing the wireless spectrum, and completely unaware of each other. LoRaWAN uses ALOHA-style communication where it is almost impossible to schedule transmission between networks belonging to different owners properly. The inability to schedule overlapping networks will cause inter-network interference, which will increase node-to-gateway message losses and gateway-to-node acknowledgement failures. This problem is likely to get worse as the number of LoRaWAN networks increase. In response to this problem, we propose IRONWAN, a wireless overlay network that shares communication resources without modifications to underlying protocols. It utilises the broadcast nature of radio communication and enables gateway-to-gateway communication to facilitate the search for failed messages and transmit failed acknowledgements already received and cached in overlapping network’s gateways. IRONWAN uses two novel algorithms, a Real-time Message Inter-arrival Predictor, to highlight when a server has not received an expected uplink message. The Interference Predictor ensures that extra gateway-to-gateway communication does not negatively impact communication bandwidth. We evaluate IRONWAN on a 1000-node simulator with up to ten gateways and a 10-node testbed with 2-gateways. Results show that IRONWAN can achieve up to 12% higher packet delivery ratio (PDR) and total messages received per node while increasing the minimum PDR by up to 28%. These improvements save up to 50% node’s energy. Finally, we demonstrate that IRONWAN has comparable performance to an optimal solution (wired, centralised) but with 2-32 times lower communication costs. IRONWAN also has up to 14% better PDR when compared to FLIP, a wired-distributed gateway-to-gateway protocol in certain scenarios.

Journal article

Chen P-Y, Bhatia L, Kolcun R, Boyle D, McCann Jet al., 2021, Contact-aware opportunistic data forwarding in disconnected LoRaWAN mobile networks, 40th IEEE International Conference on Distributed Computing Systems, Publisher: IEEE, Pages: 574-583

LoRaWAN is one of the leading Low Power WideArea Network (LPWAN) architectures. It was originally designedfor systems consisting of static sensor or Internet of Things (IoT)devices and static gateways. It was recently updated to introducenew features such as nano-second timestamps which open upapplications to enable LoRaWAN to be adopted for mobile devicetracking and localisation. In such mobile scenarios, devices couldtemporarily lose communication with the gateways because ofinterference from obstacles or deep fading, causing throughputreduction and delays in data transmission. To overcome thisproblem, we propose a new data forwarding scheme. Instead ofholding the data until the next contact with gateways, devices canforward their data to nearby devices that have a higher probabil-ity of being in contact with gateways. We propose a new networkmetric called Real-Time Contact-Aware Expected TransmissionCount (RCA-ETX) to model this contact probability in real-time. Without making any assumption on mobility models, thismetric exploits data transmission delays to model complex devicemobility. We also extend RCA-ETX with a throughput-optimalstochastic backpressure routing scheme and propose Real-TimeOpportunistic Backpressure Collection (ROBC), a protocol tocounter the stochastic behaviours resulting from the dynamicsassociated with mobility. To apply our approaches seamlesslyto LoRaWAN-enabled devices, we further propose two newLaRaWAN classes, namely Modified Class-C and Queue-basedClass-A. Both of them are compatible with LoRaWAN Class-Adevices. Our data-driven experiments, based on the London busnetwork, show that our approaches can reduce data transmissiondelays up to25%and provide a53%throughput improvementin data transfer performance.

Conference paper

Bhatia L, Tomic I, Fu A, Breza M, McCann Jet al., 2021, Control communication co-design for wide area cyber-physical systems, ACM Transactions on Cyber-Physical Systems, Vol: 5, Pages: 1-27, ISSN: 2378-962X

Wide Area Cyber-Physical Systems (WA-CPSs) are a class of control systems that integrate low-powered sensors, heterogeneous actuators and computer controllers into large infrastructure that span multi-kilometre distances. Current wireless communication technologies are incapable of meeting the communication requirements of range and bounded delays needed for the control of WA-CPSs. To solve this problem, we use a Control-Communication Co-design approach for WA-CPSs, that we refer to as the C3 approach, to design a novel Low-Power Wide Area (LPWA) MAC protocol called Ctrl-MAC and its associated event-triggered controller that can guarantee the closed-loop stability of a WA-CPS. This is the first paper to show that LPWA wireless communication technologies can support the control of WA-CPSs. LPWA technologies are designed to support one-way communication for monitoring and are not appropriate for control. We present this work using an example of a water distribution network application which we evaluate both through a co-simulator(modelling both physical and cyber subsystems) and test bed deployments. Our evaluation demonstrates full control stability, with up to 50% better packet delivery ratios and 80% less average end-to-end delays when compared to a state of the art LPWA technology. We also evaluate our scheme against an idealised, wired,centralised, control architecture and show that the controller maintains stability and the overshoots remain within bounds.

Journal article

Bhatia L, Breza M, Marfievici R, McCann Jet al., 2020, Dataset: LoED: The LoRaWAN at the Edge dataset, The 3rd International SenSys+BuildSys Workshop on Data: Acquisition to Analysis, Publisher: ACM, Pages: 7-8

This paper presents the LoRaWAN at the Edge Dataset (LoED), an open LoRaWAN packet dataset collected at gateways. Real-world LoRaWAN datasets are important for repeatable sensor-network and communications research and evaluation as, if carefully collected, they provide realistic working assumptions. LoED data is collected from nine gateways over a four month period in a dense urban environment. The dataset contains packet header information and all physical layer properties reported by gateways such as the CRC, RSSI, SNR and spreading factor. Files are provided to analyse the data and get aggregated statistics. The dataset is available at:

Conference paper

Wang H, Zhou G, Bhatia L, Zhu Z, Li W, McCann Jet al., 2020, Energy-neutral and QoS-aware protocol in wireless sensor networks for health monitoring of hoisting systems, IEEE Transactions on Industrial Informatics, Vol: 16, Pages: 5543-5553, ISSN: 1551-3203

Hoisting equipment is core to many industrial systems and therefore their state of health significantly affects production lines and personnel safety; this is especially important in environments such as coal mines. The health of the hoisting system, can be estimated by deploying energy harvesting wireless sensor nodes that monitor the drum surface stress. In this network of sensor devices, it is very costly to send highly sampled data as it causes radio congestion and consumes energy. However, from our experience of sensing hoist systems, we note that the data observed at the upper surface of the hoist is significantly more indicative of the state of health of the whole system, compared with data sensed at the lower surface. Therefore, we need to take advantage of this to optimise the communications of sensor nodes. However, scarce energy can be collected for these devices from the hoist itself, along with the prioritised Quality of Service (QoS) requirements (throughput, delay) of monitoring signals, raises important challenges for energy management. In this paper, we use Lyapunov optimisation techniques and propose an Energy-neutral and QoS-aware Protocol (EQP), including duty cycling and network scheduling to solve it. Extensive simulations show that EQP helps sensor nodes realize consecutive monitoring, and achieve more than 38% utility gain compared with existing strategies.

Journal article

Tomic I, Breza MJ, Jackson G, Bhatia L, McCann JAet al., 2019, Design and evaluation of jamming resilient cyber-physical systems, IEEE International Conference on Cyber, Physical and Social Computing (CPSCom 2018), Publisher: IEEE

There is a growing movement to retrofit ageing,large scale infrastructures, such as water networks, with wirelesssensors and actuators. Next generation Cyber-Physical Systems(CPSs) are a tight integration of sensing, control, communication,computation and physical processes. The failure of any one ofthese components can cause a failure of the entire CPS. Thisrepresents a system design challenge to address these interde-pendencies. Wireless communication is unreliable and prone tocyber-attacks. An attack upon the wireless communication of CPSwould prevent the communication of up-to-date information fromthe physical process to the controller. A controller without up-to-date information is unable to meet system’s stability and perfor-mance guarantees. We focus on design approach to make CPSssecure and we evaluate their resilience to jamming attacks aimedat disrupting the system’s wireless communication. We considerclassic time-triggered control scheme and various resource-aware event-triggered control schemes. We evaluate these ona water network test-bed against three jamming strategies:constant, random, and protocol aware. Our test-bed results showthat all schemes are very susceptible to constant and randomjamming. We find that time-triggered control schemes are justas susceptible to protocol aware jamming, where some event-triggered control schemes are completely resilient to protocolaware jamming. Finally, we further enhance the resilience ofan event-triggered control scheme through the addition of adynamical estimator that estimates lost or corrupted data.

Conference paper

Bhatia L, Boyle D, McCann J, 2018, Aerial interactions with wireless sensors, The 16th ACM Conference on Embedded Networked Sensor Systems (SenSys 2018), Pages: 373-374

Sensing systems incorporating unmanned aerial vehicles have the potential to enable a host of hitherto impractical monitoring applications using wireless sensors in remote and extreme environments. Their use as data collection and power delivery agents can overcome challenges such as poor communications reliability in difficult RF environments and maintenance in areas dangerous for human operatives. Aerial interaction with wireless sensors presents some interesting new challenges, including selecting or designing appropriate communications protocols that must account for unique practicalities like the effects of velocity and altitude. This poster presents a practical evaluation of the effects of altitude when collecting sensor data using an unmanned aerial vehicle. We show that for an otherwise disconnected link over a long distance (70m), by increasing altitude (5m) the link is created and its signal strength continues to improve over tens of metres. This has interesting implications for protocol design and optimal aerial route planning.

Conference paper

Bhatia L, Tomic I, McCann J, 2018, LPWA-MAC - a low power wide area network MAC protocol for cyber-physical system, The 16th ACM Conference on Embedded Networked Sensor Systems (SenSys 2018), Publisher: ACM, Pages: 361-362

Low-Power Wide-Area Networks (LPWANs) are being successfully used for the monitoring of large-scale systems that are delay-tolerant and which have low-bandwidth requirements. The next step would be instrumenting these for the control of Cyber-Physical Systems (CPSs) distributed over large areas which require more bandwidth, bounded delays and higher reliability or at least more rigorous guarantees therein. This paper presents LPWA-MAC, a novel Low Power Wide-Area network MAC protocol, that ensures bounded end-to-end delays, high channel utility and supports many of the different traffic patterns and data-rates typical of CPS.

Conference paper

Tomic I, Bhatia L, Breza MJ, McCann JAet al., 2018, The limits of LoRaWAN in event-triggered wireless networked control systems, Control 2018: The 12th International UKACC Conference on Control, Publisher: IEEE

Wireless sensors and actuators offer benefits to largeindustrial control systems. The absence of wires for commu-nication reduces the deployment cost, maintenance effort, andprovides greater flexibility for sensor and actuator location andsystem architecture. These benefits come at a cost of a highprobability of communication delay or message loss due to theunreliability of radio-based communication. This unreliabilityposes a challenge to contemporary control systems that aredesigned with the assumption of instantaneous and reliable com-munication. Wireless sensors and actuators create a paradigmshift in engineering energy-efficient control schemes coupled withrobust communication schemes that can maintain system stabilityin the face of unreliable communication. This paper investigatesthe feasibility of using the low-power wide-area communicationprotocol LoRaWAN with an event-triggered control schemethrough modelling in Matlab. We show that LoRaWAN is capableof meeting the maximum delay and message loss requirements ofan event-triggered controller for certain classes of applications.We also expose the limitation in the use of LoRaWAN whenmessage size or communication range requirements increase orthe underlying physical system is exposed to significant externaldisturbances.

Conference paper

Breza M, Bhatia L, Tomic I, Fu A, Ikram W, Kongezos V, McCann JAet al., The Separator, a Two-Phase Oil and Water Gravity CPS Separator Testbed

Industrial Control Systems (ICS) are evolving with advances in newtechnology. The addition of wireless sensors and actuators and new controltechniques means that engineering practices from communication systems arebeing integrated into those used for control systems. The two are engineered invery different ways. Neither engineering approach is capable of accounting forthe subtle interactions and interdependence that occur when the two arecombined. This paper describes our first steps to bridge this gap, and push theboundaries of both computer communication system and control system design. Wepresent The Separator testbed, a Cyber-Physical testbed enabling our search fora suitable way to engineer systems that combine both computer networks andcontrol systems.

Journal article

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