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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 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
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
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
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
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
Results 1. • Implemented ANC algorithms • Synchronization algorithm in WSN • Principles of operation activeloudspeaker DSP board gateway mote sensor mote
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
Results 3. Data transmission methods Transmission of row data • 1.8 kHz sampling frequency on the motes • Synchronization of WSNDSP • 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)
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
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
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
Synchronization 2 Graph of the reception time of synchronization messages
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
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
Synchronization 5 Indirect proof for synchronization
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