# Simultaneous Sampling Algorithm for Sensors Spread Over a Wide Area

Outline

One of the problems with our existing ultrasonic three-dimensional
measuring system was that sampling frequency decreased as the number of tagged
objects increased. This problem was caused by the time division method used
to control ultrasound transmission. In this research we developed a method of
sustaining a high sampling frequency when transmitters and receivers are positioned
over a wide area (36 m × 10 m), then tested our algorithm by conducting a simulation.
The results of the simulation showed that when sensors are fixed to the ceiling
at 1 m intervals, sampling is possible at an average of 40 Hz per tagged object
even with twenty transmitters spread around the room at a height of 1.5 m above
the floor.

Ultrasound Simultaneous Sampling Algorithm

1. Check ultrasound transmission priority level. If priority level is high, transmit
ultrasound. If priority level is low, raise the priority level by 1 and do
not transmit

2. Check for interference with transmitters at higher priority levels. If there is no interference, proceed to step 3. If there is interference, raise the priority level by 1 and do not transmit.

3. Check whether the transmitter’s location can be calculated using distance information from receivers that are able to receive ultrasound. If the location can be calculated, transmit ultrasound. If calculation is not possible, raise the priority level by 1.

2. Check for interference with transmitters at higher priority levels. If there is no interference, proceed to step 3. If there is interference, raise the priority level by 1 and do not transmit.

3. Check whether the transmitter’s location can be calculated using distance information from receivers that are able to receive ultrasound. If the location can be calculated, transmit ultrasound. If calculation is not possible, raise the priority level by 1.

Results of Simulations

The following figure shows the results of two simulations
that were performed. In the first, ultrasound was simultaneously transmitted
from 10 transmitters spread over a wide area (36 m × 10 m), and in the second,
20 transmitters were used. 360 receivers were positioned at 1 m intervals. With
10 transmitters, measurement was possible at approximately 50 Hz per transmitter,
and with 20 transmitters, calculation was possible at approximately 35 Hz.

The following graph compares the results from simulations for ultrasound transmission conducted using the time division method (conventional method), and the simultaneous sampling algorithm method. When using the time division method, sampling frequency decreases rapidly as the number of transmitters rises, making increasing the number of transmitters problematic. With the simultaneous sampling algorithm, sampling is possible at approximately 10 Hz per transmitter even when using 100 transmitters. Compared to the conventional method, it is possible to maintain a higher sampling frequency as the number of transmitters is increased.

References

- 相澤洋志, 西田佳史, 堀俊夫, 柿倉正義, "時分割式超音波３次元位置計測のための同時サンプリング手法," 日本機械学会 ロボティクス・メカトロニクス講演会'04講演論文集, 1A1-H-45(1)-(4), June 2004
- T. Hori, Y. Nishida, T. Kanade, K. Akiyama, "Improving Sampling Rate with Multiplexed Ultrasonic Emitters," in Proceedings of 2003 IEEE International Conference on Systems, Man and Cybernetics, pp.4522-4527, October 2003
- T. Hori, Y. Nishida, T. Kanade, K. Akiyama, "Multi-lateration for Multiplexed Ultrasonic Sensors," in Proceedings of 2003 IEEE International Conference on Sensors (Sensors 2003), Vol. 2, pp. 1219-1224, October 2003
- 西田佳史, 秋山賢治, 堀俊夫, 柿倉正義, ",超音波3次元位置計測のための冗長なセンサデータを用いた高速位置推定アルゴリズム," 日本機械学会 ロボティクス・メカトロニクス講演会'03講演論文集, 1P1-3F-E6(1)-(2), May 2003