FM Ambient backscattering for Low Power, Low-Cost Communication and Sensing

Nowadays, the explosive growth of Internet-of-Things-related applications has required the design of low-cost and low-power wireless sensors. Although backscatter radio communication is a mature technology used in radio frequency identification (RFID) applications, ambient backscattering is a novel approach taking advantage of ambient signals to simplify wireless system topologies to just a sensor node and a receiver circuit eliminating the need for a dedicated carrier source. This work introduces a novel wireless tag and receiver system that utilizes broadcast frequency modulated (FM) signals for backscatter communication. The proposed proof-of-concept tag comprises of an ultra-low-power microcontroller (MCU) and a radio frequency front-end for wireless communication. The MCU an accumulate data from multiple sensors through an analog-to-digital converter, while it transmits the information back to the receiver through the front-end by means of backscattering. The front-end uses a) binaty On-Off keying modulation and FM0 encoding and b) spectrally efficient 4-pulse amplitude modulation (4-PAM) on ambient FM station signals. The receiver consists of a commercial low-cost software defined radio which downconverts the received signal to baseband and decodes it using a suitable signal processing algorithm. The prototype tag was also tested in a real-time indoor laboratory deployment. Operation over a 5 m tag-reader distance was demonstrated by backscattering information while the FM station antenna was 34 Km way from the experimentation setup. For case a) the bit rate of was 147 bps with power consumption 220 uA (ADC on) and 3.6 uA (ADC off). For case b) low bit rate of 328 bps and power consumption 232 uA (ADC on) and 16 uA (ADC off).
Download Files.

Backscatter Wireless Sensor Network

Modern agriculture applications necessitate cheap, effective, low-maintenance and low-cost wireless telemetry for various environmental parameters, such as soil moisture, air humidity and temperature in the vicinity of multiple plants within the same field. Such continuous and dense environmental monitoring is critical for optimal crop management techniques and water saving. Thus, wireless sensor network (WSN) technologies for micro-climate monitoring in extended areas, are indispensable within this topic. Conventional WSNs consist of a large number of nodes, forming a (possibly mesh architecture) network in order to transfer monitored environmental data to a base station. Each node typically employs a Marconi-type radio, controlled by a micro-controller unit (MCU) and the sensors. However, large-scale deployments of conventional WSN technology are not common, due to power consumption, cost and maintenance complexity. In order to address such constraints, scatter radio has recently started to be exploited in wireless sensing and particularly for the development of WSNs. Scatter radio communication is known from 1948 and today, is exploited in the RFID industry. Communication is implemented with an antenna, a control circuit and a radio frequency (RF) switch between them. While scatter-radio principles have been restricted to communication ranges of up to a few meters, a novel scatter radio sensor network (WSN) for soil moisture (%SM) measurements was developed. A low-cost (6 Euro per sensor), low-power (in the order of 200 uW per sensor), with high communication range (in the order of 250 meter), scatter radio sensor network was designed and implemented, for soil moisture monitoring at multiple locations. The network utilizes analog frequency modulation (FM) in a bistatic network architecture (i.e., the emitter and reader are not co-located), while the sensors operate simultaneously, using frequency division multiple access (FDMA). In contrast to prior art, this work utilizes an ultra-low cost software-defined radio reader (RTL-SDR), offers custom micro-strip capacitive sensing with simple calibration, as well as modulation pulses for each scatter radio sensor with 50% duty cycle; the latter is necessary for scalable network designs. Overall root mean squared error (RMSE) below 1% is observed, even for ranges of 250 m. This is another small (but concrete) step for the adoption of scatter radio technology as a key enabling technology for scalable, large-scale, low-power and cost environmental sensor networking. Digital scatter sensor nodes were also designed and build in-house, in Telecom Lab. The digital nodes project is leading by my classmate Konstantinos Tountas. The nodes consist of three separate circuit boards: the communication "scatter radio" board, the power-board and the sensor board. The scatter communication board consisted of a Silabs C8051F930 MCU, a RF Transistor, and a oscillating crystal, was designed and implemented by Konstantinos Tountas. My contribution was on the design and the fabrication of the voltage source selection circuit, choosing between a solar panel and a coin battery. Also i was working on sensing part, a board containing multiple sensors (plant signal, illuminance, temperature, plant electrical potential, soil moisture and air humidity) was constructed. The sensed data are encoded with a linear block code and are transmitted by means of reflection to a USRP SDR receiver. The topology of the system is the bistatic, the emitter and reader are not co-located and the tag is in the middle.

Related Media:

Crete is an island with fertile land and temperate climate, which favors almost any kind of crops. For many years, agriculture and livestock underlies the economic life of the island and that is an incentive for producing products of excellent quality (like olive oil, excellent selections of wines, vegetables like “Stamnagathi”). Additionally having such products as raw material, people of our island created unique traditional goods (such as “Graviera” Cheese, “Kaltsouni” Pie, roasted barley bread known as “Paksimadi”). Based on our previous observations and given the fact that the last decade the number of visitors on the island has increased significantly, we set as our target to give farmers, animal breeders and traditional products producers of Crete, referring next as producers, the opportunity of direct selling of their products to the visitors, using technological solutions. The idea is to develop a web-based application for producers and a smartphone application for visitors (designed for Android/iOS based devices), which will be interconnected through a central data exchange system. In more detail, the producers using an easy to use Web-Based environment will create an account in our system. After that, they will be able to register online their products with their prices and other necessary information like photographs of their products and a precise location of supplying (using exact coordinates). Then, the system operators will come in contact with them, in order to validate the registered data and check the prices to ensure good competition. On the other hand, visitors using a user friendly application on their smartphones, they can search for information about available local products in their close area using a predefined radius of search and with the support of their devices location services (GPS, Network Assisted Localization). The available locations of the found products will get pin-pointed on Google Maps. After that, our users will choose a desired pin and the application will present all the relevant information about the producer and his products. As final step, if a user wants to buy a product, he will only have to declare interest through his smartphone in order to inform the producer. The development and implementation of the proposed system will be very useful, especially for the producers but also for the visitors of the island as well as for the Greek state. The producers will have the opportunity to sell their products as retailers at very affordable prices. Additionally, visitors will have the ability to buy traditional and quality products at lower prices than the market average and finally the Greek State will earn positive reputation from the promotion of Greek products inside and outside the Hellenic borders.

Related Media:

Olive oil is very healthy fat obtained from the olive, a traditional tree crop of the Mediterranean Basin. The oil is produced by pressing fresh olives. It is commonly used in cooking and cosmetics. Here in Crete the cultivation of the olive tree is deeply rooted in the tradition of the island. The trees are perfectly adapted in the climate and soils of the island and this is the secret of producing an excellent oil. Nowadays, the main threat for olives is olive fruit fly, a species of fruit fly which feeds inside the fruit, destroying the pulp. The olive fly problem is treated by detection, monitoring and management. When it comes to detect and monitoring the olive fly, being vigilant, diligent and systematic is critical as fly population can multiply rapidly. In Crete, Greek government has appointed agriculturists to monitor populations in the spring with McPhail traps. When traps indicate that population is increasing in early summer, agriculturists give instruction to workshops to apply bait sprays. The traps are placed in different places throughout the region of Crete. The first application happens a week or two before pit hardening and it re-applies every 5 to 6 weeks during summer. The idea is to create and develop an Agriculture wireless Sensor Board (single node). Having this node and a pc/smartphone application, agriculturists or producers can monitor olive fly populations plus different environmental parameters from their houses without visiting the olive fields. Thus the system will be useful for preventing possible plagues with timely sprays. Nodes will be installed throughout the region of Crete along with McPhail traps which are already placed and will be created a large Wireless Sensor Network. Each node consists of a McPhail trap, a camera and a printed circuit board. Camera will receive a picture inside the trap and through image processing will estimate the number of dead olive flies. In addition, there will be sensors able to measure ambient temperature/humidity, atmospheric pressure, solar radiation, soil temperature and soil moisture. Each node can integrate a GPS that delivers accurate position of it. Node will be sleeping most of the time in order to save energy. After some hours wakes up, collects data from the sensors, implements the wireless communication via GSM/3G technology, send the collected information to a base station and goes again to sleep mode. Each node can be powered with rechargeable lithium batteries and a solar panel, making the system completely autonomous. Using Google Maps application at a pc/smartphone and an internet connection, the user will be able to watch the node position and the collected real-time data from any place in the world. Purpose of this project is to anticipate olive threats, to minimize time consumption and money, as well as maximize agriculture results. Finally the system may be useful for irrigation system manage as well as for agriculturists in research, i.e. to create statistical prediction models.