Optimization of Matched Chaotic Frequency Modulation Excitation Sequences for Multichannel Simultaneously Triggered Ultrasonic Ranging System

The matched spectrum and correlation characteristics are both important to realize the multichannel ultrasonic sensors working together. The spectrum matching can make full use of the bandwidth of the ultrasonic ranging system, and the good correlation characteristic can eliminate crosstalk among multichannel ultrasonic sensors triggering simultaneously. Linear frequency modulation (LFM) excitation sequences have been used as transmission signals for ultrasonic sensors. Due to the narrow bandwidth of the ultrasonic ranging system, the number of available LFM excitation sequences is limited. The chaotic frequency modulation (CFM) excitation sequences, which can generate more available excitation signals, are proposed in this paper. The nondominated sorting genetic algorithm-II is adopted to optimize both the spectrum and correlation characteristic of the CFM excitation sequences. After optimization, the CFM excitation sequences are spectrally matched to the ultrasonic ranging system as well as have best correlation characteristic. Real experiments have been implemented using an ultrasonic ranging system consisting of eight-channel SensComp 600 series electrostatic sensors excited with 2 ms CFM sequences. Experimental results show that spectra of the optimized CFM excitation sequences can match to the system and can work together without crosstalk. DOI: 10.4018/japuc.2012010101 2 International Journal of Advanced Pervasive and Ubiquitous Computing, 4(1), 1-16, January-March 2012 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. crosstalk phenomenon, where one ultrasonic sensor receives echoes transmitted by another ultrasonic sensor (Meng, Yao, & Wu, 2006). Usually, the ultrasonic receiver cannot judge whether the received echo is created from its own transmission or not, so false time-of-flight (TOF) measurement often occurs. In order to avoid ultrasonic crosstalk, most ultrasonic ranging system triggered their sensors sequentially (Hori, Nishida, Kanade, & Akiyama, 2003). which limit the work efficiency of the ultrasonic ranging system. To eliminate the ultrasonic crosstalk, some researchers adopted different code and modulation schemes constructing excitation sequence to assign each ultrasonic sensor a recognizable signature. Jörg and Berg (1998) first applied pseudorandom sequences to give each ultrasonic sensor a marker. A matched filter in the receiving circuit then identified the associated source sensor. Ureña, Mazo, García, Hernández, and Bueno (1999) used a 13-bit Barker code to construct their excitation sequences for ultrasonic sensors. While the available Barker codes limit their application. Golay codes (Hernández, Ureña, Hernanz, García, Mazo, Dérutin et al., 2003; Ding & Payne, 1990; Hernández, Ureña, García, Mazo, Hernanz, Dérutin, & Sérot, 2004; Alvarez, Ureña, Mazo, Hernandez, García, Jimenez, & Donato, 2004; Diaz, Ureña, Mazo, García, Bueno, & Hernández, 1999; Marziani, Ureña, Hernández, Mazo, Alvarez, García, & Donato, 2007) were applied in ultrasonic ranging system to avoid crosstalk and increase the signal to noise ratio (SNR). Chaotic codes (Fortuna, Frasca, & Rizzo, 2003; Yao, Meng, Li, & Lin, 2008) were also used to eliminate crosstalk in multichannel simultaneously triggered ultrasonic ranging System. Fortuna et al. (2003) exploited chaotic pulse position modulation (CPPM) to fire the ultrasonic sensor. Yao et al. (2008) proposed chaotic pulse position width modulation (CPPWM) excitation sequences as the transmission sequences of ultrasonic sensors. Nakahira, Kodama, Furuhashi, and Maeda (2005) used binary-coded frequency-shift keyed signals to drive ultrasonic sensors to eliminate crosstalk. Meng, Zhang, Liang, and Wang (2005) and Meng, Liang, and Li (2006) proposed pseudorandom frequency modulation and frequencyhopping pseudorandom pulse-width modulation sequences to excitation ultrasonic sensor, and the result of avoiding crosstalk was not good. The signals with linear frequency modulation (LFM) (Pollaskowski, 1994) were used as the transmission signals of ultrasonic sensors, which could avoid crosstalk. But the spectra of LFM excitation sequences are not totally matched to that of the ultrasonic ranging system. And the number of available LFM excitation sequences is limited because of the narrow bandwidth of the ultrasonic ranging system. In order to make the spectrum of excitation sequence match to that of the ultrasonic ranging system, Pollatowski and Ermert (1994) applied transmitter signals with a constant amplitude level and nonlinear frequency modulation. However, they did not research how to obtain the good correlation characteristics of the excitation sequences. Optimization techniques have also been applied to construct excitation sequences in multichannel ultrasonic ranging system. Griep, Ritcey, and Burlingame (1995) adopted a global optimization technique to select proper coding signal for multiple-user ultrasonic ranging system. Hikino, Belkerdid, and Malocha (2000) optimized PN sequences to reduce autocorrelation function’s side-lobe. Nakahira et al. (2005) used a combination of simulated annealing and hill climbing to minimize the peaks in the cross-correlation function as well as minimize the maximum side-lobe in the autocorrelation function. Meng, Lan, Yao, and Li (2009) applied a genetic algorithm (GA) to optimize short CPPM and pseudorandom PPM triggering sequences in order to improve correlation characteristics (i.e., minimize the side-lobe in the autocorrelation function and the peaks in the cross-correlation function). Yao et al. (2008) adopted nondominated sorting genetic algorithm II (NSGA-II) to optimize CPPWM excitation sequences in order to sharpen the autocorrelation and flatten the cross-correlation as well as to maximize echo energy. 14 more pages are available in the full version of this document, which may be purchased using the "Add to Cart" button on the product's webpage: www.igi-global.com/article/optimization-matched-chaoticfrequency-modulation/68801?camid=4v1 This title is available in InfoSci-Journals, InfoSci-Journal Disciplines Communications and Social Science. Recommend this product to your librarian: www.igi-global.com/e-resources/libraryrecommendation/?id=2