María del Carmen Pérez

Efficient Correlator for LS Codes Generated from Orthogonal CSS

This paper presents a novel method to correlate loosely synchronized (LS) codes generated from mutually orthogonal complementary sets of sequences (CSS). The proposed correlator significantly reduces the total number of multiplications and additions to be performed, in comparison with straightforward correlators. This fast correlator, together with the interference free window that LS codes exhibit, make them a good choice for next generation of Wireless communications.

Multiband Waveform Design for an Ultrasonic Indoor Positioning System

In the last years, indoor positioning systems have become an ubiquitous part of smart spaces. The use of coded ultrasonic indoor positioning systems leads to accurate position estimation at reduced cost as the low propagation speed of sound allows the use of analog-to-digital converters at low sampling frequencies. In these systems, coding schemes play a key role in the accuracy and robustness of range estimation and, therefore, in positioning. Consequently, the careful selection and design of the appropriate transmitted waveform should be carried out. This paper introduces two novel multiband waveform synthesis applied to ultrasound-based indoor positioning systems and it compares their performance with current coding schemes used in such systems. Simulations and experimental tests show that some of the proposals effectively deal with several limitations of the previous transmitted waveforms in ultrasonic positioning systems.

Ultrasonic Multitransducer System for Classification and 3-D Location of Reflectors Based on PCA

This paper presents a system to classify and locate basic ultrasonic reflectors (plane, corner, and edge) in 3-D environments. The classification system is based on the principal-component-analysis (PCA) technique, using the time of flight (TOF) as the classification parameter. The system proposes a sensorial structure to simultaneously obtain up to 16 TOFs at every emission/scanning process. A particular and different macrosequence has been assigned to every transducer in the sensorial system to encode their emissions. These macrosequences, obtained from complementary sets of sequences, allow simultaneous emission and reception to be carried out with all the transducers for the same scanned environment. The set of obtained TOFs make it possible to identify the type of ultrasonic reflector, as well as its position in 3-D environments. The results achieved by the classification system are presented for both simulated and real data.

Recursive algorithm to directly obtain the sum of correlations in a CSS

This paper presents a new recursive algorithm to directly obtain the sum of the autocorrelation functions of the M sequences belonging to a Complementary Set of Sequences (M-CSS). The proposed algorithm allows a digital filter with only one stage to be obtained, what significantly reduces the total number of memory requirements, multiplications and additions to be performed in comparison with the use of M correlators, even when these correlators could have an efficient implementation. The use of this algorithm can be of great relevancy since there is an increasing interest in the use of CSS (or derived sequences such as Loosely Synchronized-LS-sequences or Zero Correlation Zone-ZCZ-sequences) in the field of communications and sensor systems.

Android application for indoor positioning of mobile devices using ultrasonic signals

In this paper we present an Android application, called LOCATE-US, that allows accurate indoor positioning of mobile devices by processing the ultrasonic signals coming from a local positioning system (LPS). The LPS operates around 41KHz, and an external hardware based on an ultrasonic microphone digitizes the incoming signals and send them to the mobile device, where they are processed by means of the proposed application. This allows the use of CDMA techniques and overcomes most of the problems to be faced at the 20-22kHz range available in current smartphones, which include audible artifacts and poor resolution. The proposed software allows each mobile device in the environment to compute its own position by means of hyperbolic trilateration and represents the trajectory in the device screen, for future Location Based Services applications. Experimental results show that the proposed application achieves centimeter accuracy and can execute all the data processing for the position estimation in a time less than 0.5s.

Ultrasonic signal acquisition module for smartphone indoor positioning

Smartphone capabilities can significantly enhance mobile and context-aware applications that depend on location information. Whereas outdoor Location Based Services (LBS) are highly developed thanks to GPS, indoor LBS still demand a positioning technology that provides accurate location data. In this paper, an ultrasonic signal acquisition module for fine-grained indoor positioning of portable devices, such as smartphones or tablets, is presented. It is based on a microcontroller that digitizes the signals coming from a set of ultrasonic beacons placed on the ceiling and transfers the data acquired through Bluetooth Wireless Technology to the smartphone, for their consequent processing. All ultrasonic beacons emit simultaneously, each one a different Kasami code which is BPSK modulated with a carrier frequency of 40kHz. At the reception, the proposed module, that can coexist with an unlimited number of receivers, digitizes the analog signal captured by an electret microphone and sends it to the smartphone. Then, the smartphone carries out the correlation of the received signal with the emitted codes and obtains its absolute position by hyperbolic trilateration. Test results show that the proposed system can achieve similar accuracies to conventional ultrasonic based local positioning systems, with the advantage of services of a smartphone.

Efficient filter for the generation/correlation of Golay binary sequence pairs

In this paper, a digital filter for the generation/correlation of binary Golay pairs of sequences of length 2Ni¾?10Mi¾?26PN, M and P are non-negative integers is proposed. It is carried out by means of a novel Golay kernel 26 decomposition, also introduced in this paper, combined with building blocks of Golay kernels 2 and 10, presented in previous works. The proposed filter has a similar architecture to the digital filter for the generation/correlation of Golay multilevel pairs of sequences, where the parameters at intermediate stages have to be adjusted to obtain Golay binary pairs of sequences in the final stage. Copyright

FPGA-Based Track Circuit for Railways Using Transmission Encoding

The current stage of railway transportation systems must deal with increased safety and reliability issues. A key point is improving occupancy track circuit performance and providing them with redundancy, higher noise immunity, and the capability to acquire additional information about the track section involved. This work proposes a novel track circuit based on the encoding of the electrical transmissions with Kasami codes. Track circuit emitters send signals coded with a known sequence that can be identified by the corresponding receivers using correlation techniques; these processes increase immunity to noise and changes in environmental conditions. An appropriate selection of orthogonal sequences for encoding, as well as different carrier frequencies for transmissions, allow simultaneous emissions and receptions without cross interference.

EMFi-Based Ultrasonic Sensory Array for 3D Localization of Reflectors Using Positioning Algorithms

This paper describes a first prototype of an airborne ultrasonic array that combines pulse-compression techniques with positioning algorithms in order to achieve accurate determination of the position of the reflectors placed in front of the array. The new sensory system is based on an array with four independently controlled emitters and a receiver. The emitters are made of ferroelectrets as active material, leveraging their features to produce broadband air-coupled ultrasonic transducers at low cost. The ultrasonic emissions are encoded with an orthogonal Kasami sequence for each transducer, making possible to transmit simultaneously from each one. Furthermore, one of the main novelties of the proposal is that reflectors are located by means of a spherical trilateration algorithm that uses the time-of-flight of the ultrasonic signals from each transmitter to the receiver, bounced back by the reflector.

Ultrasonic LPS adaptation for smartphones

In this paper we present a privacy-oriented Ultrasonic Local Positioning System (U-LPS) allowing users with portable devices, such as smartphones or tablets, to accurately determine their position in indoor environments. Indoor U-LPSs have been widely used to provide location information with centimeter or even sub-centimeter level accuracy at high rates. However, most of these systems demand specific hardware in the reception stage that cannot be used with current smartphones. Hence, the user cannot benefit from the versatility of services that these kind of devices offer. This work presents the design of an external device which translates the high frequency ultrasonic information emitted by a CDMA-based U-LPS, into a low frequency band understandable for the mobile phone by means of an analog multiplier. The output of the multiplier is connected to the smartphone or tablet using the Jack input connector as if it was a microphone. Then, the mobile device processes the low band frequency signals and estimates its position.