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Testbed for Wireless Adaptive Signal Processing Systems

Testbed for Wireless Adaptive Signal Processing Systems. György Orosz, László Sujbert, Gábor Péceli Department of Measurement and Information Systems Budapest University of Technology and Economics , Hungary Instrumentation and Measurement Technology Conference – IMTC 2007

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Testbed for Wireless Adaptive Signal Processing Systems

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  1. Testbed for Wireless Adaptive Signal Processing Systems György Orosz, László Sujbert, Gábor Péceli Department of Measurement and Information Systems Budapest University of Technology and Economics, Hungary Instrumentation and MeasurementTechnology Conference – IMTC2007 Warsaw, Poland, May 1-3, 2007

  2. Wireless signal processing • Advantages of Wireless Sensor Networks (WSNs) • Easy to install • Flexible arrangement • Wireless signal processing • Difficulties of utilization of WSN: • Data loss • Undeterministic data transfer • Limit of the network bandwidth • Purpose of the testbed • Considerations in the design • Hardware structure • Adequate application • Realistic demands • Exploits the resources

  3. ANC as test application • Principles of Active Noise Control (ANC) • Why ANC? • Inherently MIMO systems: plenty of sensors • Plant: acoustic system • Scalable • Linear • Exist everywhere • Various algorithms: • No HW modification • Comparability of structures • Easy to build and cheap • Identification: characterization of signal path

  4. mote1 mote2 moteN DSP codec DSP board moteG gateway mote reference signal System configuration • Plant to be controlled: acoustic system • Noise sensing: Berkeley micaz motes • Actuators: active loudspeakers • Gateway: network  DSP • Signal processing: • DSP board • ADSP-21364 32 bit floating point • 8 analog output channels • 330 MHz • motes microphone

  5. Control signals sensors feedback signals sensor1 Wireless Network Signal processing MIMO plant sensor2 Sync. (WSN  DSP) sensorN •  Synchronization • Distributed signal processing Data transmission  Error handling  Signal processing Research fields related to the testbed • Signal processing adaptation to WSN • Synchronization • Data transmission • Effective algorithms • Data compression • Distributed signal processing

  6. Results 1. • Implemented ANC algorithms • Synchronization algorithm in WSN • Principles of operation activeloudspeaker DSP board gateway mote sensor mote

  7. mote2 mote3 mote1 mote4 gateway DSP : data messages : token : synchron message Results 2. • Deterministic network operation • Implicit synchronization messages • Synchronization with continuous data flow • No extra load for network Network topology

  8. Results 3. Data transmission methods Transmission of row data • 1.8 kHz sampling frequency on the motes • Synchronization of WSNDSP • LMS and observer based ANC algorithms • Bandwidth restriction: about 2-3 sensors Transformed domain data transmission • 1.8 kHz sampling frequency on the motes • Transmission of Fourier-coefficients • Increased number of sensors:8 sensors (expansion possible)

  9. Conclusions • Platform for testing wireless systems • Application: ANC • Components: • Berkeley micaz motes • ADSP-21364 floating point DSP • Main difficulties • Data transmission • Synchronization • Some codes and technical details available at • http://home.mit.bme.hu/~orosz/wireless

  10. Future work • Improvement of the website • http://home.mit.bme.hu/~orosz/wireless • Discover the limits of the system • Sensor network: bandwidth limit • DSP: computational and memory limits

  11. fquartz_ref reception time of the messages fquartz_2 IT IT Ndiv reference timer tuneable timer S/H controller Tloc – Ta referencemote mote to be synchronized Synchronization 1 Mechanism of the synchronization

  12. Synchronization 2 Graph of the reception time of synchronization messages

  13. tsamp_r tsend t moteref ∆tsend Send(packet) TSend Receive(packet) Tloc2 t motei tsamp_i trec Sampling time instants Synchronization 3 Tdiff = ∆tsend + TSend – Tloc2

  14. Tloc.ref: the reference value of Tloc.x_y that is the time difference between the sampling time instant and reception time of the synchronization message Ts reception time instant of the synchronization message Ts T1_a T2_a t a) Tloc.a_1= Tloc.ref Tloc.a_1 Tloc.a_2 T1_b T2_b t b) Tloc.b_1> Tloc.ref Tloc.b_1 Tloc.b_2 T2_c T1_c t c) Tloc.c_1< Tloc.ref Tloc.c_1 Tloc.c_2 T1_ref T2_ref Synchronization 4

  15. Synchronization 5 Indirect proof for synchronization

  16. t DSP t gateway t mote0 t mote1 t mote2 Twin_0 Twin_1 Twin_2 Twin_0 Tp Twin_i: time gap of ith mote Tp: one network period : data messages : synchronization messages Network timing

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