Applying Passive RFID System to Wireless Headphones for Extreme Low Power Consumption

Applying Passive RFID System to Wireless Headphonesfor Extreme Low Power Consumption June 11th, 2008 Joon Goo Lee, Dongha Jung, Jiho Chu, Seok Joong Hwang, Jong-Kook Kim, Seon Wook Kim School of Electrical Engineering, Korea University, Seoul, Korea Janam Ku Samsung Advanced Institute of Technology, Korea

Content RFID Research Motivation Design Possibility and Opportunity Extended Gen2 Features of the original Gen2 (ISO18000-6 Type C) Added new commands for massive transferring to tags Modified command and response: Write Added new state and State transition of the EGen2 EGen2 Prototype System Overall verification system EGen2 Sender System EGen2 Receiver System Performance Evaluation Conclusion

RFID : Radio Frequency IDentification • Identify objects from a distance by using a small IC with RF transponder • RFID system is made up of three components • Transponder or tag, Interrogator or Reader, and Application • Classification • SAW/Inductive/Modulated Backscatter/Active • Read Only/WORM/Reprogrammable/Read and Write • 125-135kHz/13.56MHz/UHF(300-1000MHz)/2.45GHz • Inductive/Electromagnetic (Narrowband, Spread Spectrum)

General Use of RFID Technology Inventory control Container/Pallet Tracking Access control Equipment/Personal Tracking (In hospital, prison, etc.) Product tracking through manufacturing, assembly,and supply chain Fleet maintenance Various services by using mobile RFID Most applications are related to logistics and security.

Motivation (1/2) When we use wireless communication device Power consumption limits its usage!!! What is the wireless communication method which consumeslowest power? The answer is Passive RFID!!

Motivation (2/2) A kind of energy harvesting technology is used in passive RFID system However, RFID system has been only applied for automatic data acquisition methods Because of relatively lower data rate, security problem,range of communication, power dissipation of memoryread/write, and so on What if a passive tag just bypasses the received data to other device, is it possible to use passive RFID technology for special purposes? Data transmission system without storing the data For an example, a headphone

Design Possibility and Opportunity (1/2) What kind of passive RFID protocol is sufficient? We need High data rate: NFC, ISO18000-6 Type C (Gen2) Long working range: ISO18000-6 series, ISO18000-3 Small size of device: ISO18000-6 series, ISO18000-3 ISO18000-6 Type C is the best for the first step Feasibility checking with Gen2 Friss transmission equation was used for the calculation of path loss Assumptions Reader transmits 10dBm power to tags Antenna gain of the reader is 6dBi and antenna gain of a tag is zero Efficiency of a tag rectenna is 80% Half of the rectified power is available to the digital parts of a tag

Design Possibility and Opportunity (2/2) The result of channel modeling for the passive RFID of 860~960MHz band from Friss equation and our assumptions • From the above result, voice data and low quality music transmission is enough with Gen2

Extended Gen2 (1/4) Features of the original Gen2 Uses UHF (860~960MHz) band, backscatter modulation Forward modulation: DSB-ASK, SSB-ASK or PR-ASK Backward modulation: ASK and/or PSK Data encoding: PIE for R2T, FM0 or Miller for T2R Operating range: Several meters (Depends on Reader’s Tx power) Tag size: Sufficiently small (It depends on antenna design) Data link frequency: Relatively high Forward: 26.7kHz~128kHz Backward: 40kHz~640kHz Supports multi-reader environment  Session concept Has 4 kinds of memory banks (One of them is EPC code) Error detect: CRC5 or CRC16

Extended Gen2 (2/4) Added new commands for massive transferring to tags Burst command format and description BurstAckVS command format and description and its response format

Extended Gen2 (3/4) Modified command and response: Write • Write command was modified for writing ShortID in temporal memory • After Select operation, issue Write command in Ready state • After setting Membank, WordPtr, and RN as zero, assign ShortID reader wants with lower 7bit ofData • After writing ShortID to temporal memory of Tag, the Tag responds CRC check result of Write command and written ShortID • There is no TREPLY (about 20ms)  Reduce the power consumptionof the Reader • Automatic ShortID initialization when tag is out of reading zone

Extended Gen2 (4/4) Added new state : Data The state transition diagram of the EGen2 tag Fully compatible with original Gen2

Extended Gen2 (appendix) Supported communication methods and their procedure with EGen2 protocol 1. Broadcast Send Burst command with ShortID=0000000b All tags in the reading zone process the Burst and BurstAckVS commands When retransmission is unnecessary, reader omits setting ShortID 2. Multicast Procedure i) Inventory (Recognizing TagID) ii) Assert SL flag of wanting tag iii) Assign a unique ShortID to the tag iv) Choose wanting tags by repeating ii)~iii) Send Burst command with ShortID!=0000000b SL assertedtags process Burst andBurstAckVS 3. P2P Procedure i), ii), iii) are same as Multicast procedure iv) Send Burst command with ShortID=the unique ShortID The tag which has the unique ShortID processes Burst andBurstAckVS

Overall verification system Sender was modified from an original Gen2 tag reader EGen2 tag in receiver was extended from an original Gen2 tag Audio signal sampling rate was 14kHz and resolution of eachsample was 8-bit EGen2 Prototype System (1/5)

EGen2 Prototype System (2/5) EGen2 Sender System Software processes the modified protocol Command packet generation and response packet processing are done in hardware Audio sampler was added to RFID reader for audio transmission Analog part was omitted for fast verification 20

EGen2 Prototype System (3/5) EGen2 Receiver System (1/3) EGen2 tag is for wireless communication The rest parts are tag peripheral system for processing bypassed data from theEGen2 tag 21

EGen2 Prototype System (4/5) EGen2 Receiver System (2/3) EGen2 Tag architecture EGen2 tag was extended from the Gen2 tag which satisfies EPC Class-1 Generation-2 UHF (860~960MHz) RFID Protocol 1.1.0 version A power management unit generates 7 local clocks with clock-gating scheme and differentiates each clock phase to minimize the peak current We assumed that an analog front-end provides clock of 1.28MHz or 1.92MHz 22

EGen2 Prototype System (5/5) EGen2 Receiver System (3/3) Hardware Scheduler for low power Minimizing power consumption of receiver system by changingthe CPU’s power mode After AVR finishing the system initialization job as a general processor, the AVR changes its power mode to ‘Power-down Mode’ or‘Power-save mode’ H/W Scheduler wakes up AVR by using external interrupt andresumes a job with the AVR

Performance Evaluation (1/2) Measurement Setup We didn’t analyze the sender Gate level simulator was used for EGen2 tag and tag peripheral system Synopsys Design Compiler and Synopsys VCS under Anam CMOS 0.18um technology We used Prime Compiler with 25% toggle rate for the EGen2 tag power estimation The number of gates and the power consumption of tag components except for EEPROM* Gate increase: 3.5% Power increase: 3.8% Available distance: 1.8m • *: It is acceptable because EGen2 tag just bypasses the received data to tag peripheral system without writing the data into EEPROM

Performance Evaluation (2/2) Tag peripheral system Consists of AVR, DAC, hardware system which includes DAC FIFO, two wrappers and a communication unit The DAC FIFO consists of 8-bit 256 entries: 12K gates The rest of the hardware system: 5K gates The power consumption of the hardware system was 44uW When wake-up duty of AVR processor was 1% (1% active, 99% power save), 614uW was consumed

Conclusion • Contribution • EGen2 protocol • EGen2 is a ultra low power wireless communication protocol which is based on passive RFID technology • Feasibility of new use of passive RFID systems with EGen2 protocol • Digital parts of EGen2 tag consume 3.33 ㎼ (25% toggle rate) when the tag receives audio data from a sender • Prototype system by adding new hardware modules to the Gen2 reader and tag for our proposal • Proposal of a hardware control interface, an inter-IP communication unit, and a hardware IP scheduler in order to achieve the low power consumption of whole receiver system

Q&A

Applying Passive RFID System to Wireless Headphones for Extreme Low Power Consumption