A Study on Propagation Characteristics of Spread Spectrum Sound Waves Using a Band-Limited Ultrasonic Transducer

Abstract

Propagation characteristics and range experiments of spread spectrum 40kHz ultrasonic waves have been explored under band-limited frequency. Comparative experiments were conducted using two arrangements combining a broadband speaker and a microphone for the broadband case, and an all-purpose receiving transducer and the broadband speaker for the band-limited case. Under the broadband condition, range accuracy measurements and evaluation of signal discrimination in a code division multiple transmission were made demonstrating 0.034% (corresponding to about 7mm in range distance) of range accuracy for a full-scale distance of 21.6m, demonstrating high signal discrimination. The severely band-limited experiment improved accuracy from 0.084% for a distance of 8.4m to 0.063% for a greater distance of 14.4m using a longer M-sequence length by extending shift registers from 10-bit to 15-bit. These experimental results show promise in the intended application of ultrasonic spread spectra to local positioning systems.

Distance Measurement by Automatic Peak Detection for Indoor Positioning Using Spread Spectrum Ultrasonic Waves

“…Furthermore, we have discussed factors such as positioning errors in indoor environments 8) , and signal degradation with band-limited transducers 9) . These studies showed the …”

Measurement accuracy on indoor positioning system using spread spectrum ultrasonic waves

“…To reduce the distance error caused by band limitation of signal, we will use four transmitters and one receiver of wide bandwidth utilizing the same experimental method as it that was proposed by Yamane, et al [4].…”

“…However, the systems are generally said to be weak in noises, and take longer time because of utilizing the time-division multiplexed method according as objects they have to measure are increased. As a solution to overcome such demerits , the local positioning system (LPS) has been proposed which has the Code Division Multiple Access (CDMA) performance and the robustness in noises by using the signal of spread spectrum ultrasonic waves [4] [5]. To achieve the practical system architecture at low cost, we have conducted experiments utilizing transducers with narrow bandwidth and narrow directional characteristics.…”

“…To achieve the practical system architecture at low cost, we have conducted experiments utilizing transducers with narrow bandwidth and narrow directional characteristics. From the experiments in the paper [4], it has been known that the distance between a transmitter and a receiver can be measured at high accuracy by using narrow bandwidth transducers.…”

Real-Time Distance Measurement for Indoor Positioning System Using Spread Spectrum Ultrasonic Waves

“…However, these systems are generally said to be weak in terms of noise resistance, and to take a longer time to acquire data, because they utilize the time-division multiplexed method, which becomes more taxing as the number of objects to be measured is increased. To overcome these drawbacks, positioning systems with spread spectrum (SS) ultrasonic waves have been investigated (Hazas & Hopper, 2006), (Yamane et al, 2004), (Suzuki et al, 2009); they use code division multiple access (CDMA) methods and are more robust to noise, because they use spread spectrum ultrasonic signals. According to these studies, although the procedure of reception and positioning calculation is computed off-line, the systems are shown to be highly effective.…”