Providing Common Time and Space in Distributed AV-Sensor Networks by Self-Calibration
Array audio-visual signal processing algorithms require time-synchronized capture of AV-data on distributed platforms. In addition, the geometry of the array of cameras, microphones, speakers and displays is often required. In this chapter we present a novel setup involving network of wireless computing platforms with sensors and actuators onboard, and algorithms that can provide both synchronized I/O and self-localization of the I/O devices in 3D space. The proposed algorithms synchronize input and output for a network of distributed multi-channel audio sensors and actuators connected to general purpose computing platforms (GPCs) such as laptops, PDAs and tablets. IEEE 802.11 wireless network is used to deliver the global clock to distributed GPCs, while the interrupt timestamping mechanism is employed to distribute the clock between I/O devices. Experimental results demonstrate a precision in A/D D/A synchronization precision better than 50 μs (a couple of samples at 48 kHz). We also present a novel algorithm to automatically determine the relative 3D positions of the sensors and actuators connected to GPCs. A closed form approximate solution is derived using the technique of metric multidimensional scaling, which is further refined by minimizing a non-linear error function. Our formulation and solution account for the errors in localization, due to lack of temporal synchronization among different platforms. The performance limit for the sensor positions is analyzed with respect to the number of sensors and actuators as well as their geometry. Simulation results are reported together with a discussion of the practical issues in a real-time system.
Keywordsdistributed sensor networks self-localizing sensor networks multichannel signal processing
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- 1.Elson, J., Girod, L., Estrin, D. (2000) Fine-grained network time synchronization using reference broadcasts. 5th Symposium on OS Design and Implementation.Google Scholar
- 2.Fancourt, C., Parra, L. (2001) The coherence function in blind source separation of convolutive mixtures of non-stationary signals. Proc IEEE Workshop on Neural Networks for Signal Processing, 303–312.Google Scholar
- 3.Gill, P., Murray, W., Wright, M. (1981) Practical Optimization.Google Scholar
- 4.Girod, L., Bychkovskiy, V., Elson, J., Estrin, D. (2002) Locating tiny sensors in time and space: A case study. Proc. International Conference on Computer Design.Google Scholar
- 7.Lienhart, R., Kozintsev, I., Wehr, S. (2003) Universal synchronization scheme for distributed audio-video capture on heterogeneous computing platforms. Proc 11th ACM Conf on Multimedia, 263–266.Google Scholar
- 8.Lienhart, R., Kozintsev, I., Wehr, S., Yeung, M. (2003) On the importance of exact synchronization for distributed audio processing. Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing.Google Scholar
- 10.Mock, M., Frings, R., Nett, E., Trikaliotis, S. (2000) Clock synchronization for wireless local area networks. IEEE 12th Euromicro Conference on Real-Time Systems (Euromicro RTS 2000), 183–189.Google Scholar
- 12.Press, H., Teukolsky, S., Vettring, W., Flannery, B. (1995) Numerical Recipes in C The Art of Scientific Computing. Cambridge University Press, 2 edition.Google Scholar
- 13.Raykar, V., Kozintsev, I., Lienhart, R. (2003) Self localization of acoustic sensors and actuators on distributed platforms. International Workshop on Multimedia Technologies in E-Learning and Collaboration (WOMTEC).Google Scholar
- 15.Sachar, J., Silverman, H., Patterson, W. (2002) Position calibration of large-aperture microphone arrays. Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, 1797–1800.Google Scholar
- 16.Savvides, A., Han, C, Srivastava, M. (2001) Dynamic fine-grained localization in ad-hoc wireless sensor networks. Proc. International Conference on Mobile Computing and Networking.Google Scholar
- 18.Van Trees, H. (2001) Detection, Estimation, and Modulation Theory, 1. Wiley-Interscience.Google Scholar