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 Measurement Technology Conference – IMTC 2007 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.  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 System configuration mote 1 mote G DSP board reference signal gateway mote codec DSP mote 2 mote N microphone

5. Research fields related to the testbed  Signal processing adaptation to WSN  Synchronization  Data transmission Effective algorithms Data compression  Distributed signal processing MIMO plant sensor 1 sensor 2 sensor N Wireless Network Wireless Network Signal processing Control signals feedback signalssensors  Synchronization  Distributed signal processing Data transmission  Error handling  Signal processing Sync. (WSN  DSP)

6. Results 1.  Implemented ANC algorithms  Synchronization algorithm in WSN Principles of operation sensor mote DSP board gateway mote active loudspeaker

7. Results 2.  Deterministic network operation  Implicit synchronization messages Synchronization with continuous data flow No extra load for network DSP mote 2 mote 3 gateway mote 1 mote 4 : data messages : token : synchron message 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

12. Synchronization 1 Mechanism of the synchronization reference timer S/H controller tuneable timer – TaTa T loc IT f quartz_2 f quartz_ref N div reception time of the messages reference mote mote to be synchronized

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

14. Synchronization 3 T diff = ∆t send + T Send – T loc2 Send(packet) Receive(packet) mote ref mote i Sampling time instants t send t rec T Send t samp_r t samp_i t t T loc2 ∆t send

15. Synchronization 4 t t t TsTs T 1_a T 1_b T 1_c T 2_a T 2_b T 2_c T 1_ref T 2_ref TsTs T loc.a_1 T loc.b_1 T loc.c_1 T loc.a_2 T loc.b_2 T loc.c_2 a) b) c) T loc.a_1 = T loc.ref T loc.b_1 > T loc.ref T loc.c_1 < T loc.ref T loc.ref : the reference value of T loc.x_y that is the time difference between the sampling time instant and reception time of the synchronization message reception time instant of the synchronization message

16. Synchronization 5 Indirect proof for synchronization

17. Network timing t t t t t TpTp DSP gateway mote 0 mote 1 mote 2 T win_0 T win_1 T win_2 T win_0 T win_i : time gap of i th mote T p : one network period : data messages : synchronization messages