1660 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 51, no. 12, december 2004 Ultrasonic Ranging Sensor using Simultaneous Emissions from Different Transducers ´ Alvaro Hern´ andez, Jes´ us Ure˜ na, Juan J. Garc´ ıa, Manuel Mazo, Member, IEEE, Daniel Hernanz, Jean-Pierre D´ erutin, and Jocelyn S´ erot Abstract—In recent applications based on ultrasound, several ultrasonic transducers have been geometrically and electronically associated to constitute a global sensor. There are several different methods used to process the ultrasonic signals obtained from these transducers. In this work, mul- timode techniques using Golay complementary sequences are proposed for processing the ultrasonic signal. The sys- tem increases scan rate, precision, and reliability. It is also capable of echo discrimination, allowing simultaneous mea- surements to be made and detection of the same obstacle by different transducers without cross-talk problems. The real-time implementation of the algorithm is presented on a field-programmable gate array (FPGA) device. I. Introduction C lassical processing techniques used in ultrasonic transducers for mobile robots are based in time-of- flight (TOF) measurement. One isolated transducer is ex- cited by a squared signal and then the system waits for possible echoes. Detection is normally performed by in- tegrating and threshold-crossing the received signal. The problems with this mode of operation are well-known and referenced in previous works [1]–[4]: • Measurements must be carried out independently for each transducer. The transducers cannot be excited simultaneously to avoid cross-talk problems. It takes a long time to perform an environmental scan, as it must be sequential. • Furthermore, after a pulse is emitted, the signal is re- ceived by only one transducer (usually the same one that emitted the pulse), which means the probability of certain obstacles not being detected due to specular reflections is relatively high. • Measured distance precision is reduced. It may be enough for some applications, but not for processing measurements from different transducers in more so- phisticated systems. In these systems it is possible to determine reception angles, or perform reflector clas- Manuscript received February 12, 2003; accepted July 2, 2004. This work was supported by the Spanish Ministry of Science and Tech- nology under Grants COO1999-AX049 and HF2000-0017. ´ A. Hern´andez, J. Ure˜ na, J. J. Garc´ ıa, M. Mazo, and D. Hernanz arewith the Electronics Department, University of Alcal´a, Alcal´ade Henares, 28806 Madrid, Spain (e-mail: alvaro@depeca.uah.es). J. P. D´ erutin and J. S´ erot are with LASMEA Laboratory (U.M.R. 6602 C.N.R.S.), Blaise Pascal University, 63177 Aubi` ere Cedex, France. Fig. 1. Sonar sensor composed of four ultrasonic transducers. sification (i.e., walls, edges, corners) and mapping, if TOF have enough precision and reliability. In this work, a new low-level processing technique for ultrasonic signals, which overcomes most of the problems mentioned in the previous paragraphs, and its implemen- tation on a configurable device are presented. The follow- ing section introduces the proposed sonar system, which is suitable for use in mobile robots. Section III contains an explanation of the low-level algorithm, analyzing its re- quirements and constraints. Hardware implementation is illustrated in Section IV. Section V describes the results obtained, and, finally, some conclusions are discussed in Section VI. II. Ultrasonic Sensor Module The sensor configuration used can be seen in Fig. 1. It is the geometrical association of four transducers. Every two transducers constitutes a “vector sensor,” able to measure distances and reception angles [5]. These transducers are very close to each other to minimize correspondence prob- lems and to confirm the reception of echoes from the same reflector by both transducers [5], [6]. In Fig. 1, P is a pos- sible reflector detected by the four transducers (r 1 , r 2 , r 3 , and r 4 ). This sensor configuration type and its use have been described in [6], [7] in order to classify different reflector types. If it is desirable to improve the capability of these sensors, it is important to achieve the following features: • Simultaneous reception of the reflected signal by all the transducers (E/R1, R2, R3 and E/R4). In this way, four TOF measurements can be combined in high-level algorithms from just one emission. Further- more, the probability of obstacle detection is increased 0885–3010/$20.00 c  2004 IEEE