Electronica

Systems that characterize the state of an entity or object are very important in the "smart spaces" and "ubiquitous computing"; this information is usually known as the entity's "context". Those applications, which describe or characterize these entities and interact with it, are often referred as "contextaware computing". One of the most important information is the position of an object with the purpose of offering the most suitable services to him. The mechanisms and techniques that determine these space relations are named "location"; and the computing applications, based on the position, are called "location-aware computing". This article presents an indoor localization system in order to make a relative positioning among entities, fixed or mobile, without use an external infrastructure and only using acoustic transducers for their use in ubiquitous computing applications. Also, an analysis of the positioning algorithm, based on multidimensional scaling technique (MDS), is carried out in order to verify the errors in the position estimation when there are errors in the mechanism of ranging distances.

Some sensor systems are characterized by multiple simultaneous aperiodic emissions, with low signal-to-noise ratio and asynchronous detection. In these systems, complementary sets of sequences can be used to encode emissions, due to their suitable auto-correlation and cross-correlation properties. The transmission of a complementary set can be accomplished by interleaving the sequences of the set, generating a macro-sequence which is easily transmitted by a BPSK modulation. The detection of the macrosequence can be performed by means of efficient correlation algorithms with a notably decreased computational load and hardware complexity. This work presents a new hardware design in configurable logic of an efficient correlator for macrosequences generated from complementary sets of sequences. A generic implementation has been achieved, so the configuration can be changed according to the requirements of the application. The developed correlator has been tested in an ultrasonic pulse compression system in which real-time is needed. However, it is applicable in any multi-sensor or communication system where the goal is to make simultaneous emissions from different independent sources, minimizing mutual interference.

In this work, the performance of an acoustic relative metric Multidimensional Scaling Technique (MDS) [5]. This positioning system is studied, by a Monte-Carlo analysis, with algorithm allows to obtain a geometric configuration of the aim of determining the obtained accuracy and precision. The considerd objects in the smallest number of dimensions, only system has been designed in order to be used in the relative using the distances measured among them. Nevertheless, the positioning estimation of mobile objects which are not restricted data collected by ranging mechanism are usually influenced to a particular environment and cannot depend on any external infrastructure. In the proposed system, the spatial relations

The design of advanced sonar modules implies the use of more and more complex processing algorithms, in order to obtain as much information as possible from the environment. The use of simultaneous emission and reception techniques in certain transducers, that form an ultrasonic sensorial module, allows to increase the benefits and the performance of this type of systems. These developments make possible to obtain more information for every ultrasonic emission, diminishing the scanning time and improving the interpretation and usefulness of the obtained results. These techniques are usually based on the encoding of the ultrasonic emission, so the received signals can be correlated in order to search for possible echoes. As a consequence, the computational complexity necessary to carry out the implementation of the new algorithms increases considerably. The analysis of possible computing platforms for the real-time processing of the new algorithms becomes a task of great importance. In this work, some computing architectures are analysed and compared, in order to determine which scheme is most suitable for the ultrasonic signal processing.

A prototype of an ultrasonic transducer based on electromechanical film (EMFi) is presented, as well as its electronic driving and receiving blocks. The electromechanical film provides a wide bandwidth response, showing enough of a level of sensitivity to allow echo-pulse measurement in the most frequency ranges for robotics applications. Emission patterns are obtained, verifying the correspondence between experimental data and the theoretical piston model. Experimental results show that the EMFi-based transducer can be used as a broadband ultrasonic transducer, allowing transmission from 20 to 200 kHz. The wide bandwidth provided by the transducer is a remarkable advantage for sensor systems using encoded ultrasonic signals with wideband modulation schemes, which require considerably more bandwidth than what conventional transducers allow. In this way, main lobes can be discriminated more easily from sidelobes and crosstalk interference can be reduced.

The present work shows a local positioning system (LPS) for mobile robots (MR) using simultaneous emissions in the ultrasonic beacons. In order to solve the problem of the simultaneous emission of the ultrasonic beacons, the well-known technique called direct sequence code division multiple access (DS-CDMA) is used. This technique modulates the ultrasonic signal (50 kHz) with a 127-bit Gold code for even beacon. In this way, it is possible to detect the arrival time of the code, by earning out the simultaneous correlations with the assigned codes to each beacon. For determining the absolute position, the triangulation technique uses the time difference-of-arrival (TDOA) obtained between a reference beacon and the others. Using this method, certain errors, derived from the delay in the firing of the beacons and the response times of the ultrasonic transducers, are avoided. The existence of a synchronism in the emission of the beacons, that guarantees a periodic and simultaneous emission in all of them, is required, not being necessary to know the emission instant in the mobile robot. This is particularly useful in environments where several robots can coexist

This paper presents three novel methods to efficiently generate and correlate sequence pairs with three zero correlation zones in the sum of their aperiodic correlation functions. These sequences have achieved great importance in communications systems when the maximum transmission delay is less than the length of these zones, because the multiple access interference (MAI) and the intersymbol interference (ISI) can be removed. The proposed algorithms are based on the properties of complementary sets of sequences (CSS) and they offer an efficient hardware implementation of the corresponding generators and correlators that reduces the total number of operations to be performed in comparison with straightforward implementations. That makes possible real-time operation as well as the use of very long sequences.

An advanced adaptive sonar module is described, capable of being configured to different circumstances and distances according to reflectors found in the environment. Thanks to the sensory distribution, it is possible to identify three basic types of reflector (planes, edges and corners). Furthermore, a heuristic map of the environment is built. The proposed methods have been computationally optimized, and implemented in a real-time system based on a Field-Programmable Gate Array (FPGA) and a Digital Signal Processor (DSP). Results have been obtained in the detection, classification and mapping of obstacles; and finally testing has been carried out on a commercial vehicle.

The determination of the relative position among mobile objects or members of a robot team is a useful information when the systems are not restricted to a particular environment and they cannot depend on an external infrastructure to obtain their location information. The solution for this kind of problems cannot be divided and treated separately for each object. Therefore it is necessary to implement mechanisms that allow to simultaneously determine the spatial relations among objects not knowing their absolute location in the environment. After that, a positioning algorithm can be computed whose complexity depends on the number of observations made and the precision required in the system. In this work, the implementation of a relative positioning system is described where only acoustic emissions are made in order to obtain information about the other objects. These data are obtained by using simultaneous round-trip-time-of-flight measurements. Finally, using this information, the object positions are computed with a multidimensional scaling technique, and a closer solution is achieved with least-square algorithms.

In this article, a time-of-flight detection technique in the frequency domain is described for an ultrasonic Local Positioning System (LPS) based on encoded beacons. Beacon transmissions have been synchronized and become simultaneous by means of the DS-CDMA (Direct-Sequence Code Division Multiple Access) technique. Every beacon has been associated to a 255-bit Kasami code. The detection of signal arrival instant at the receiver, from which the distance to each beacon can be obtained, is based on the application of the Generalized Cross-Correlation (GCC), by using the cross-spectral density between the received signal and the sequence to be detected. Prior filtering to enhance the frequency components around the carrier frequency (40 kHz) has improved estimations when obtaining the correlation function maximum, which implies an improvement in distance measurement precision. Positioning has been achieved by using hyperbolic trilateration, based on the Time Differences of Arrival (TDOA) between a reference beacon and the others.

In those positioning systems based on the detection of acoustic signals, an accurate detection of the arrival times is crucial for a correct estimation of the distance between nodes, and therefore, for the precise estimation of the node that wants to be located. In order to obtain this arrival time more accurately, acoustic signals can be coded using pseudorandom noise, but these coded signals are still affected by underwater channel phenomena. In this work, the detection of spread-spectrum modulated signals is analyzed in underwater environments that are highly affected by multipath and reverberation. A spread-spectrum signal, which consist of a modulated Kasami code, has been emitted through two different pools, reaching a receiver where it has been captured after following several line-of-sight and nonline-of-sight paths. Then, a correlation process has been performed offline to provide information about the arrival times (times-of-flight) that form the multipath structure. These times-of-flight are compared with those provided by an underwater acoustic propagation model, in order to test the performance of this model and its capacity to predict the outcome of signal detection in underwater environments with a strong multipath and reverberation component. That way, the validated propagation model could be later used in future studies to predict the detection of spread-spectrum signals and the performance of systems that use them in these adverse environments.

This work presents the development of a Local Position-correlations with the codes associated to every beacon, in order ing System (LPS), based on the transmission of ultrasonic signals, to detect the DTOAs between the reference beacon and the which have been previously encoded by Loosely Synchronous (LS) others. As the mobile robot does not need to know the emission codes. The LPS consists of several ultrasonic emitters located at instant t known positions in the environment, and of a portable receiver sync he RF signal can be supressed (it iS enough a common that computes its position by measuring the Differences in Times synchronism among all the beacons). of Arrival (DTOA) between a reference emitter and the others. The effectiveness of these systems strongly depends on the LS codes exhibit an Interference Free Window (IFW) in the SS codes that codify the ultrasonic emissions. Those codes auto-correlation and cross-correlation functions. Therefore, if the relative time-offset of the codes are within the IFW, it is possible should provlde very low cross-correlation (CC) values to to have simultaneous emissions without interference, as well as to avoid the Multiple Access Interference (MAI); and very low reduce the multipath effect. auto-correlation (AC) sidelobes to reduce the Inter-Symbol-Interference (ISI). In absolute positioning with ultrasounds, KeVwords-Acoustic LPS, asynchronous detection, DS-CDMA, LS-several previous works use pseudo-random (PR) sequences: codes, IFW, ISI, MAI.

Signal coding and pulse compression provide indoor sonars [5][6][7]. However, a new problem arises in ultrasonic systems with the capability to obtain accurate this case. It is well known from outdoor acoustics that measurements that are nearly independent of the conditions of atmospheric turbulence causes random fluctuations in the operation. This property, together with the high robustness to amplitude and the phase of traveling sound waves [8]. noise also achived with these techniques, are making possible the Depending on how much the shape of the transmitted signals development of high reliability systems intended for outdoor is modified by this effect, they could not be properly operation. However, these systems must face new problems not .

Positioning systems in underwater environments constitute a relatively new field of research that is gaining increasing interest in recent days. These systems are useful to locate buoys that are monitoring the environment, as well as Remotely Operated Vehicles (ROVs) or Autonomous Underwater Vehicles (AUVs). An acoustic relative positioning system is presented in this work, based solely on pseudorandom coded acoustic signals emitted underwater and detected by matched filtering processes. One of the buoys acts as the master node, emitting its code through a hydrophone, which will be received by the other buoys. These buoys will after reply with their own code, obtaining the round-trip times of flight (RTOF) for each pair of buoys. Once the RTOFs are obtained, the distances between them can be computed knowing the sound speed value, and from them the positions are calculated by means of the Multidimensional Scaling technique (MDS). Different codes are studied, being the performance criteria the average error between the real and estimated distances. This performance is evaluated using a ray-tracing propagation model, which takes into account the transmission loss due to different phenomena, as well as the dynamic effect of wind-generated waves.

This paper presents a characterization of an underwater positioning system based on surface nodes equipped with GPS and acoustic transducers. The positioning system calculates the coordinates of an underwater vehicle in one of the surface nodes or beacons, by the emission, detection, and reply of acoustic encoded signals. The characterization of the system has been performed by means of a statistical study, considering different numbers of beacons, beacons' position and physical phenomena, such as noise, multipath, and Doppler spread. The error propagation caused by these phenomena and the geometrical configuration of the system has been quantitatively assessed in different positioning algorithms, based on trilateration and iterative procedures. The results show how the different phenomena affect the vehicle estimated position errors for the different positioning algorithms. In addition, the obtained errors inside the projected area of the beacons are ∼1 m or lower, rising to a few meters for the worst case scenario, showing the feasibility of the acoustic positioning system.

Systems that characterize the state of an entity or object are very important in the "smart spaces" and "ubiquitous computing"; this information is usually known as the entity's "context". Those applications, which describe or characterize these entities and interact with it, are often referred as "contextaware computing". One of the most important information is the position of an object with the purpose of offering the most suitable services to him. The mechanisms and techniques that determine these space relations are named "location"; and the computing applications, based on the position, are called "location-aware computing". This article presents an indoor localization system in order to make a relative positioning among entities, fixed or mobile, without use an external infrastructure and only using acoustic transducers for their use in ubiquitous computing applications. Also, an analysis of the positioning algorithm, based on multidimensional scaling technique (MDS), is carried out in order to verify the errors in the position estimation when there are errors in the mechanism of ranging distances.

In relative positioning systems, with the aim of estimating object positions, distances among them are computed in a cooperative way, usually by measuring times-of-flight from the signals that they emit. These emissions are often synchronized with additional signals or suitable hardware that acts as a temporal reference. In this paper, a ranging system is presented where only acoustic emissions are used to compute the distances between objects or nodes. Thus, an organization and operation algorithm is proposed, which provides a temporal reference to the acoustic emissions carried out by every node. In this way, distances are computed by determining the temporal relation between a request of emission from a coordinator node and the corresponding answers emitted by the other nodes. In order to simultaneously detect the acoustic emissions, the signals are encoded with complementary set of sequences allowing multisensory operation and accepting low signal-to-noise conditions. With this measurement scheme, additional signals and high accuracy clocks often used for synchronization can be eliminated, thus reducing hardware complexity, power consumptions, and possible interferences with other systems (i.e. if radio frequency signals are used). The simulation and experimental results show that subcentimeter accuracy can be obtained with the proposed ranging scheme.

This paper presents three novel methods to efficiently generate and correlate sequence pairs with three zero correlation zones in the sum of their aperiodic correlation functions. These sequences have achieved great importance in communications systems when the maximum transmission delay is less than the length of these zones, because the multiple access interference (MAI) and the intersymbol interference (ISI) can be removed. The proposed algorithms are based on the properties of complementary sets of sequences (CSS) and they offer an efficient hardware implementation of the corresponding generators and correlators that reduces the total number of operations to be performed in comparison with straightforward implementations. That makes possible real-time operation as well as the use of very long sequences.