WPI Precision Personnel Location System: Synchronization of Wireless Transceiver Units Vincent Amendolare Electrical and Computer Engineering Worcester Polytechnic Institute Worcester, Massachusetts June 2, 2009
WPI PPL Research Project December 1999, six firefighters died after becoming lost in a burning building Project goal to design a system to track indoor personnel in 3D 1 foot accuracy No pre-installed infrastructure Minimal setup 2
System Overview RF Approach Transmitter on personnel Receivers outside Position based on received signals Local coordinate system 3
System Concept and Display 4
Multicarrier Ranging Signal Sum of unmodulated carriers evenly spaced in frequency samples channel response Carriers may be placed around existing services Current system uses 70 carriers from 600-700MHz 5
Singular Value Array Reconciliation Tomography ( ART) Unique algorithm developed at WPI Estimates positions from our RF data Not based upon 1-D ranging and multilateralization like most approaches See references http://www.ece.wpi.edu/research/ppl/publications/ 6
ART Synchronization ART uses data from all receive antennas at once Fundamentally a TDOA approach Common constant time offset on all received data does not affect result Different time offsets on received data must be rectified somehow Accuracy of better than 0.5ns required 7
Previous System Architecture 8
Wireless Transceiver Units Transmit and Receive Functionality Crucial for Geometric Auto Configuration 4 receive channels with ADCs FPGA Onboard FFT Ethernet connectivity Used with 802.11 9
New System Architecture 10
Synchronization Now without co-located ADCs, the data captured is no longer synchronized New Scheme Coarse Synchronization Rate Synchronization Fine Synchronization 11
Coarse Synchronization When transceivers are turned on, they are grossly unsynchronized Coarse synchronization will align each transceivers clock within 20 microseconds 2 steps Signal Strength Training Signal Detection and Clock Reset 12
Coarse Sync Training
Coarse Sync Detection 14
Rate Synchronization New system architecture has separate ADCs with sample clocks that drift relative to each other Captured data has different unknown time offsets on each transceiver that change with time Violates ART requirements Solution: Stationary Reference Transmitter Frequencies interleaved with tracking transmitter(s) 15
Rate Synchronization 16
Rate Synchronization Ideal Received Signal: Signal Captured at t0: Key Symbol At some later time ti: Divide, then solve for time offset: 17
Rate Synchronization Signal from Tracking transmitter: Repair received data: Remaining time offset terms okay except last one, constant unknown time offset between transceivers 18
Fine Synchronization Need to solve for the constant time offsets between transceivers Small set of numbers Temporary Solution for Line of Sight case Place tracking transmitter at known location Assume ART result would be correct with correct set of time offsets Scan solution space to optimize ART metric 19
Fine Synchronization
System Test - Proof of Concept 21
System Performance 22
Conclusions Major Step towards system realization achieved by removing baseband cables Synchronization scheme devised Additional Reference Transmitter Full system test showed ideal performance Further work being done on Fine Synchronization problem to remove line of sight assumption 23
Indoor Location Workshop WPI hosting 4th annual workshop on Precision Indoor Personnel Location and Tracking for Emergency Responders in August 2009 in Worcester, Mass. www.ece.wpi.edu/research/ppl 24
WPI Precision Personnel Locator Acknowledgements The rest of the WPI PPL team Worcester Fire Department Thank you! Vincent Amendolare, vamend@wpi.edu www.ece.wpi.edu/research/ppl 25