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IDEA: Integrated Data and Energy Access for Wireless Sensor Networks (April 2015 - March 2020)
Client:Project Sponsor- NSF
- We will research methods for sharing the channel for the charging and data communication functions in the network, while addressing the challenges posed by phase variance and the constructive and destructive interference of energy signals in space.
- We will propose new routing metrics and protocols for creating energy paths, which will charge only selected sensors to ensure data delivery to the sink occurs timely over these pathways. It will yield concrete insights on the relationship between the number of ETs, their placement, the network lifetime, and the data communication capacity given the energy transfer requests within the network.
- We will answer fundamental questions on how much energy can be obtained through indoor ETs, as well as outdoors from the ambient RF environment in the TV band, leading to the creation of spatial-temporal energy maps.
- We will transform the concept of RF harvesting sensors to a platform for network deployment through a testbed of software-defined radio ETs and circuit designs for RF harvesting boards.
Key Intellectual Merits:
1. Software-Defined Wireless Energy Beamforming: We developed and demonstrated a software-defined solution for wirelessly charging the sensors using RF energy. Here, the actions of more than one energy transmitter (ET) were synchronized in phase and frequency in realtime using periodic feedback from the target sensor, but without any common clock reference. The controller selected the optimal subset of ETs to satisfy the energy request from a given sensor, which cooperatively beamform RF energy towards that sensor.
Fig. 1. Prototyping distributed energy beamfomring with USRPs.
Fig. 2. Architecture of software-defined energy beamforming.
Fig. 3(a) Network architecture of HYDRA where sensors are powered by joint adhoc beamforming from multiple energy transmitters (ETs) and ambient energy sources.
Fig. 3(b) Average received power density at various locations in the Boston area, from ambient sources as well as when the maximum energy harvesting yield source is intelligently chosen through the so called 'cognitive EH' approach.
U. Muncuk, S. Mohanti, K. Alemdar, M Y. Naderi, K. R Chowdhury, “Software-defined Wireless Charging of Internet of Things using Distributed Beamforming," ACM SenSys 2016 - The ACM Conference on Embedded Networked Sensor Systems, Stanford, CA, USA, November 2016. PDF
K. Chowdhury, and M.Y. Naderi, “Distributed Wireless Charging System and Method", Patent No. 62/308298.
2. Simultaneous Wireless Energy Transfer and Communication: When data communication and RF energy recharging occur in-band, sharing the RF medium and devoting separate access times for both operations raises architectural and protocol level challenges. We developed a method of concurrent transmission of data and energy to solve this problem, allowing ETs to transmit energy and sensors to transmit data in the sameband synchronously. Our key idea concerned devising a physical layer modulation scheme that allows the data transmitting node to introduce variations in the envelope of the energy signal at the intended recipient. We implemented a proof-of-concept receiver, modeled and validated through extensive experimentation. We also designed a new physical layer mechanism for guaranteed successful delivery of information in a point-to-point link.
Fig. 4. Energy management functions at the sensor, with the harvested energy budget feeding both the sensing as well as future transmission needs.
R. G. Cid-Fuentes, M. Y. Naderi, S. Basagni, K. Chowdhury, A. Cabellos-Aparicio, E. Alarcon, "On Signaling Power: Communications over Wireless Energy", IEEE INFOCOM 2016, San Francisco, CA, USA. PDF
R. G. Cid-Fuentes, M.Y. Naderi, S. Basagni, K. R. Chowdhury, A. Cabellos-Aparicio and E. Alarcón, "An All-Digital Receiver for Low Power, Low Bit-Rate Applications Using Simultaneous Wireless Information and Power Transmission", IEEE ISCAS 2016, Montreal, Canada, May 2016. PDF
3. Wake-Up Receiver & Token Identification using Energy Harvesting: The existing passive wake-up receivers (WuRxs) are radio frequency identification (RFID) tag based, which incur high cost and complexity. In this activity, we studied cost-effective and long-range WuRx solutions for range-based wake-up (RW) as well as directed wake-up (DW). In particular, we considered the case of an RF energy harvesting wireless sensor node and investigate how a low-cost WuRx can be built using an RF energy harvester available at the node.
Fig. 5. Prototype of EH-based passive wake-up receiver.
Fig. 6. (a) Touch energy harvester's schematic, (b) PCB design and token’s schematic.
K. Kaushik, D. Mishra, S. De, K. R. Chowdhury, and W. Heinzelman, “Low-Cost Wake-Up Receiver for RF Energy Harvesting Wireless Sensor Networks,” IEEE Sensors Journal, vol. 16, no. 16, Aug. 2016. PDF
P. Nguyen, U. Muncuk, A. Ashok, K. R. Chowdhury, M. Gruteser, and T. Vu, “Battery-Free Identification Token for Touch Sensing Devices, ACM Conference on Embedded Networked Sensor Systems (SenSys), Stanford, CA, Nov. 2016. PDF
4. Medium Access for Energy Transmitters: We researched, what we call a 'Duty cycled random-phase Multiple Access (DRAMA)' scheme, for wireless RF power transmission. Our approach is based not only in handling the interferences of multiple ETs, but also to benefits from them to broaden the input power range of existing energy harvesters at the sensor nodes. For this, DRAMA relies on the fundamental assumption that efficiency is maximized when the input power varies in time as much as possible since the energy harvesters operate with increased efficiency as a function of the input power.
R.G. Cid-Fuentes, M.Y. Naderi, R. Doost, K.R. Chowdhury, A. Cabellos-Aparicio, E. Alarcon, "Leveraging Deliberately Generated Interferences for Multi-sensor Wireless RF Power Transmission", in Proc. IEEE GLOBECOM 2015, San Diego, CA, USA, Dec. 2015. PDF
5. Multi-band Ambient RF Energy Harvesting for Self-powered Sensors: We developed a multi-band adjustable circuit for harvesting from LTE 700MHZ, GSM 850MHZ, and ISM 900MHZ bands with one single circuit. To this end, we designed a tunable impedance matching network composed of off-the-shelf components, such as adjustable capacitors (i.e. trimmers) to adapt the impedance matching network configuration with the selected RF band using a single fabricated ambient RF energy harvesting circuit. Our circuit design is fabricated on the printed circuit board with comprehensive evaluations at each associated frequency to test the power conversion efficiency.
Fig. 7. (a) Overview of our adjustable ambient RF energy harvesting system, (b) Prototype of the circuit.
Fig. 8. (a) Battery-free communications setup with TI eZ430-RF2500 sensors that are powered with LTE signals, (b) Levels of average ambient harvested power at different Boston locations.
U. Muncuk, K. Alemdar, J. D. Sarode and K. R. Chowdhury, "Multi-band Ambient RF Energy Harvesting Circuit Design for Enabling Battery-less Sensors and IoTs," IEEE Internet of Things Journal, vol.5, no: 4, Aug. 2018 PDF
6. Over-the-air frequency and phase synchronization for energy beamforming. We designed and implemented TX and Rx circuits for real-time over-the-air synchronization called RFClock that is the core enabler of real-time distributed energy beamforming. We designed a Tx circuit that generates a two-tone signal at different frequencies (915 MHz, 925 MHz) separated by desired reference clock frequency (10 MHz). Additionally, we devised the Rx circuit that is capable of extracting the 10 MHz from the two-tone signal transmitted over the air. The received signal is then amplified by using low-noise-amplifier (LNA) without significantly degrading its signal-to-noise ratio. A bandpass filter, filters out the band of the two-tone signal and this filtered signal is divided in two, in order to perform the multiplication step of the signal by itself. The desired reference clock is extracted from the output of the mixer by filtering with a bandpass filter centered at the desired reference frequency. These Tx and Rx over-the-air synchronization circuits enable real-time beamforming with the elimination of on-host frequency and phase synchronizations that add significant time overheads.
Fig. 9. (a) Schematic of RFClock, (b) Prototype of the RFClock.
7. Wearable sensor charging with software-defined magnetic resonance-based transfer. There has been increased interest in the use of wearable sensors in everyday activities from hearing aids to the smartwatch. We aimed to leverage the existing surfaces as energy transmitter to charge these sensors and implemented a multi-coils system (both Tx and Rx) for charging wearable sensor using magnetic resonance energy transfer. We first built a software-controlled surface with 27-coils in 1-square foot that has only one power management circuit. This powers any inductive compatible wearable sensor as soon as it place of the surface. Then we built a distributed magnetic resonance beamforming system. In particular, we designed and fabricated a multi-coils current sensing circuit based on 1:1 PFD3215 transformer as shown in Figure 10. The current measured would be the one flowing through a power inductor inserted in series with the amplifier; the transformer acts as an insulator, being connected in parallel with the sensing inductor. Our configuration provides a lower sensor’s equivalent impedance and higher resolutions of the real-time current measurement.
Fig. 10. (a) first (b) second versions of magnetic resonance-based sensing circuits.
Fig. 11. COMSOL-based magnetic flux intensity results for (a) beamforming toward the surface center, and (b) beamforming toward the surface side.
8. City-scale WakeUp Radio Design using LTE Signals. We designed and demonstrated a wakeup radio control plane that allows fine-grained signaling for city-scale IoT deployments without installing any additional infrastructure, and called FreeIoT. We developed a novel encoding scheme that changes the spatial positioning of Almost Blank Subframes (ABS) within a standard LTE frame to convey control information. ABS was originally defined in the standard to allow coexistence between the macro-cell eNB and nearby small cells, which in our system leveraged as a side channel for IoT signaling. In addition, we implemented a session management protocol to maintain contextual information of the control signaling. This allows our system to handle situations where the control message may span multiple frames, or when the LTE operator temporarily reduces the number of ABS. Furthermore, we incorporated an error detection and correction mechanism to counter channel and fading errors. Finally, we demonstrated a proof of concept testbed to validate the operation of our system using a software-defined LTE eNB and custom-designed RF energy harvesting circuit interfaced with TI eZ430-RF2500 sensors.
Fig. 11. (a) LTE network with the eNB and a given small cell, with spectrum sharing through ABS subframes, (b) FreeIoT framework: The control/wake-up information is conveyed by the position of ABS within a standard LTE frame, (c) circuit schematic of FreeIoT receiver.
K. Sankhe, U. Muncuk, M. Y. Naderi, and K. R. Chowdhury, "Talking When No One is Listening: Piggybacking City-scale IoT Control Signals Over LTE,'' IEEE INFOCOM 2018, Hawaii, USA, Apr. 2018. PDF
K. Chowdhury, and M.Y. Naderi, "Method And Apparatus For Overlaying City-Scale IoT Control Signals Over LTE Cellular Networks." Patent No. 62/577,509.
9. WiFi Friendly Energy Delivery with Distributed Beamforming. High power radiation within the ISM band interferes with the packet reception for existing WiFi devices. We devised the first system that merges the RF energy transfer functions within a standards compliant 802.11 protocol to realize practical and WiFi-friendly Energy Delivery (WiFED). We designed and implemented a software-defined architecture composed of a centralized controller that coordinates the actions of multiple distributed energy transmitters (ETs), and then integrated specific features of 802.11 within sensor control plane for requesting and monitoring energy. Additionally, we devised a controller-driven bipartite matching-based algorithmic solution that assigns the appropriate number of ETs to energy requesting sensors for an efficient energy transfer process. We demonstrated our WiFi-friendly distributed energy transfer through a practical system in software-defined radio testbed and extensive simulations.
Fig. 12. WiFED architecture for energy delivery with distributed beamforming over the existing 802.11ac network.
S. Mohanti, E. Bozkaya, M. Y. Naderi, B. Canberk and K. R. Chowdhury, "WiFED: WiFi Friendly Energy Delivery with Distributed Beamforming,'' IEEE INFOCOM 2018, Hawaii, USA, Apr. 2018. (best paper award) PDF
We engaged in building an outreach program, where high school freshmen, sophomores, and juniors get early exposure to engineering in a day-long visit to the NU campus. For this event, we have developed an educational game that runs on the Google Nexus-`S' Android phone. Here, the students search for so-called "radio eggs" spread throughout the campus with the phone, which are actually beacon signals transmitted by pre-selected access points. The phone displays an "egg-found" message only when the signal strength is between -65 to -70 dBm. For lower magnitudes of signal strength, the phone hints at a nearby presence of the egg by changing the color to blue e.g., Bike stand. All identified eggs switch permanently to green with a strike-out. At the end of the activity, students have explained concepts of the exponential fall of signal strength, path loss in the wireless channel, device addressing through beacon exchanges, and factors impacting correct packet reception.
Fig. 13. Various events from interactive demonstrations to educational games.