Towards Scalable Backscatter Sensor Networks Aggelos Bletsas & - PowerPoint PPT Presentation

Towards Scalable Backscatter Sensor Networks Aggelos Bletsas & John N. Sahalos RadioCommunications Laboratory (RCL) Aristotle University of Thessaloniki, Greece Cost Assist Workshop – April 2008, Cyprus

Outline 1. Introduction to RFIDs: Market Incentives, Technology & Business Challenges 2. Introduction to Backscatter Sensor Networks 3. Improving BSN Scalability with Practical Reader Antennas 4. Conclusion and Future Work April 2008 RCL, Cost Assist Workshop 2

RFID: Panacea… RFID � antenna + microchip, laminated, printed or encapsulated, powered by battery or via magnetic, electric (NFC) or electromagnetic coupling. � …part of automatic identification technologies (bar codes, magnetic stripes, twisted wires) � 80’s: car parks, road tolls (vehicle) 90’s: smart cards (people, vehicle, animals) 00’s: large consumer goods (e.g. Gillette), supermarkets (e.g. Walmart) April 2008 RCL, Cost Assist Workshop 3

RFID: Panacea or Pain? � “An expensive technology with features no- one needs. A SOLUTION IN SEARCH FOR A PROBLEM”! � “barcodes with an extensive network of readers can do the job” [R. Platts, “RFID-Panacea or Pain”, IEEE Engineering Management Review, vol. 35, no 2, 2007] April 2008 RCL, Cost Assist Workshop 4

RFID Market Incentive Examples: Health � Hospital employees spend ~25-33% of their time searching for equipment and losing about 10% of their inventory annually (RTLS importance). � RFID could save a 200-bed hospital 600 K$ annually, from less shrinkage, fewer rentals, procurement planning, staff productivity [M. Glabman, “Room for tracking: RFID technology finds the way”, Materials Management in Health Care, May 2004] � USA FDA: ~500,000 deaths due to medical mistakes… … half of the drug errors are preventable … in paper-based environment errors approach 40% (39% at prescription, 12% at transcription, 11% dispensing )!!! [M. McGee, “Health-Care I.T. has a new face”, Information Week 988:16, 2004], [A. M. Wicks, J. K. Visich, S. Li, “RFID Applications in Hospital Environments”, Hospital Topics, vol. 84, no. 3, 2006] April 2008 RCL, Cost Assist Workshop 5

RFID Market Incentive Examples: Transportation � Airport luggage handling: M$ market… [interestingly, combination of RFID/Barcodes!] Example Airports: Hong Kong, Stockholm, Brussels, Zurich, San Francisco April 2008 RCL, Cost Assist Workshop 6

RFID Market Incentive Examples: Transportation � Airport luggage handling: M$ market….(well-known) � …airport delayed check-in, security & boarding: multi-M€ cost for European Economy! (not well-known) …think of reducing the delay from 30 min =>1 min in terms of fuel flight value! � Potential solution: RFID ticket(?) April 2008 RCL, Cost Assist Workshop 7

RFID Market Incentive Examples: Digital Supply Chain � Just-in time inventory control: reconcile what you have with what you think you have… [enormous business value] � Intel example: 0.25 M units valued at 50M$, lesson learned: “100% read accuracy is needed only at selected stations, which helps products moving” � Metro Group example: “highly satisfied customers from 34% => 54%” April 2008 RCL, Cost Assist Workshop 8

RFID Market Goals � RFID: 0.05€ - 0.2€ (100billions/year) � Passive RF Sensors: 0.1€ - 2€ (1 billion/year) � Polymer (Printable) Sensors: < 0.01€ [source: Heikki Seppa, Functional Environment Seminar, VTT May 2004] Emerging ideas: RFID + Sensors April 2008 RCL, Cost Assist Workshop 9

RFID Benefits & Risks Business Benefits Technology Benefits Tighter Partnerships Improved Data Accuracy Efficient Processes Increased Automation Labor Cost Reduction Real-time Inventory 0 20 40 60 80 100 0 20 40 60 80 100 Technology Risks Business Risks Lack of Standards Tag/Reader Cost No clear ROI Obsolete Standards Lack of Wide Industry Limited Read Ranges Adoption 0 20 40 60 80 100 0 20 40 60 80 100 [ComputerWorld Magazine, 2004], [M.L. Chuang, W. H. Shaw, “RFID: Integration Stages in Supply Chain Management”, IEEE Engineering Management Review, vol. 35, no. 2, 2007] April 2008 RCL, Cost Assist Workshop 10

Summary of RFID R&D Challenges 1. Read Range (frequency dependent) 2. Communication throughput (bps/sensor) 3. Scalability (number of RFID sensors) => anti-collision ability 4. Accuracy/Reading speed (number of sensors/sec): ~ 40 tags/sec current state of the art 5. Antenna size (as small as possible) 6. Packaging material & environment (affect reader/tag coupling) 7. Efficient tag manufacturing & programming 8. Tag/Reader Cost 9. Integration: addressing all (or most of) the above in an application! Integrated, Application-Driven Approach is needed. April 2008 RCL, Cost Assist Workshop 11

Range/Frequency Dependence Water/metal penetration increases… Range increases… Throughput/sensor increases… Backscatter Communication Near Field Communication (Electromagnetic Coupling) (Capacitive or Inductive Coupling) � ISM bands different across continents => need for flexible Readers… � SDR a valid solution… April 2008 RCL, Cost Assist Workshop 12

The Backscatter Sensor Networks (BSN) Approach Technology Risks Tag/Reader Cost Obsolete Standards Limited Read Ranges 0 20 40 60 80 100 RFID + Sensors => Sensor Networks via Backscatter = Backscatter Sensor Networks Cost => Commodity Hardware, Software-Defined Radio for Reader, Reader-less, ultra-low cost sensor ! Obsolete Standards => Software-defined reader! Range => Semi-passive (battery assisted)… battery already present for sensor electronics (e.g. humidity/CO2 sensor)… however, communication is achieved via backscatter only… low-bit rate for environmental sensing (e.g. plant monitoring in agricultural fields ) April 2008 RCL, Cost Assist Workshop 13

The Backscatter Sensor Networks (BSN) Approach � Ultra-low cost complexity tag/sensors � Unidirectional communication � Ultra-fast fading (changes within same symbol) [Unique] � Easy-to-debug, scalable implementation � trading off bit-rate for all the above… (environmental sensing does not need large bandwidth/sensor) April 2008 RCL, Cost Assist Workshop 14

The Backscatter Sensor Networks (BSN) Approach � Main problem in sensor networks: battery life is limited… � Backscatter sensor nodes require battery for modulation purposes and not for transmission/reception! April 2008 RCL, Cost Assist Workshop 15

The Backscatter Sensor Networks (BSN) Approach Hub (Reader) Sensor G. Vannucci, A. Bletsas and D. Leigh, "A Software-Defined Radio System for Backscatter Sensor Networks", IEEE Transactions on Wireless Communications (TWC), in press. April 2008 RCL, Cost Assist Workshop 16

Current RadioCommunications Lab Focus 1. Read Range (frequency dependent) 2. Communication throughput (bps/sensor) 3. Scalability (number of RFID sensors) => anti-collision ability 4. Reading speed (number of sensors/sec): ~ 40 tags/sec current state of the art 5. Antenna size (as small as possible) 6. Packaging material & environment (affect reader/tag coupling) 7. Efficient tag manufacturing & programming 8. Tag/Reader Cost 9. Integration: addressing all (or most of) the above in an application! April 2008 RCL, Cost Assist Workshop 17

Scalability of BSNs � For agricultural fields, sensor density is large (~1-1.5 sensor/m 2 )… � Large number N of sensors is needed… � Required bandwidth is proportional to N � … � Anti-collision performance depends on available bandwidth …tradeoff between anticollision performance and N (or bandwidth) April 2008 RCL, Cost Assist Workshop 18

Reader Antenna BSN Capacity Enhancement Beamforming antenna: Tag Collision occurs when tags close in modulating frequency AND close in geographical space… => Larger number of sensors for given bandwidth (compared to omni)! April 2008 RCL, Cost Assist Workshop 19

Collision Probability… Edge Collision probability is analytically derived as a function of reader antenna directivity April 2008 RCL, Cost Assist Workshop 20

Example: 8x8 Butler Matrix Reader Anti-collision Enhancement � Density: ~1.5 sensor/m 2 � Bandwidth Reduction (or Capacity Enhancement): ~2 � Results apply to passive tags as well… � Proposed Tag anti-collision assists alleviation of Reader Collision problem as well! April 2008 RCL, Cost Assist Workshop 21

Tag Antennas for BSNs � Experimentation with meander-type antennas, proposed in the literature for passive tags… � Battery-assisted tags: no need for power transfer => different problem… April 2008 RCL, Cost Assist Workshop 22

Tag Antennas for BSNs � Prototype… � Design… � Radar Cross Section can be increased compared to passive case (perfect matching). April 2008 RCL, Cost Assist Workshop 23

Experimentation � Carrier transmitted… � Tag modulating waveform… � Received (backscattered) waveform… April 2008 RCL, Cost Assist Workshop 24

Next Steps… � Augment Reader Antenna with Diversity Reception Techniques… � Experimental Testing indoors (many reflections) and outdoors… April 2008 RCL, Cost Assist Workshop 25