@phdthesis {47, title = {Generaci{\'o}n y correlaci{\'o}n eficiente de c{\'o}digos binarios derivados de conjuntos de secuencias complementarias para sistemas ultras{\'o}nicos}, volume = {PhD.}, year = {2009}, month = {03/2009}, pages = {347}, school = {University of Alcal{\'a}}, type = {PhD.}, address = {Alcal{\'a} de Henares}, abstract = {
In this thesis, current and new CDMA encoding schemes are evaluated for their application in ultrasonic sensory systems based on the determination of times-of-flight. Proper encoding improves the performance of such systems in terms of noise immunity, capability of simultaneous measurements and precision in the distance measurements. Important applications include encoded ultrasonic signals, such as obstacle detection, local positioning in ubiquitous computing or non-destructive testing. Furthermore, other fields such as radar, cipher cryptology or communications systems, also demand codes with favourable correlation properties.
The thesis can be divided into three major parts. The first looks at the aperiodic correlation properties of the most promising current binary codes, and proposes novel encoding schemes. The second deals with the design of efficient generation and correlation algorithms that notably decrease the number of operations necessary for the generation or detection of the codes. Finally, in the last part, the application of the codes in a local positioning system is discussed.
After a detailed analysis of various binary codes, including the generalized orthogonal LS and T-ZCZ recently discovered, a selection of those subsets with lower aperiodic auto-correlation sidelobes and aperiodic cross correlation values is given. Also, the partial aperiodic correlation properties of the chosen codes nearly eliminates the blind area that appears in ultrasonic sensory systems when the same transducer works as emitter and as receiver.
An important contribution presented in this thesis is a new generation algorithm of T-ZCZ pairs derived from a construction of complementary sets of sequences (CSS) recently proposed. These pairs have three zero correlation zones in the sum of their aperiodic correlation functions, and they overcome the restrictions of CSS in the number of sequences assigned to every emitter. The proposed T-ZCZ codes have smaller zones with interferences and lower maximum bounds in these zones than previously proposed generation schemes for T-ZCZ codes. And most importantly, these new codes can be very efficiently generated and correlated, if compared to a straightforward implementation. The design of the efficient generation and correlation algorithms is also presented. The first one, allows for an easy simultaneous generation of all the generalized pairs in a family. The second one simultaneously performs the correlation of the input signal with each pair of the family.
The ideal correlation properties of CSS, and the fact that most generalized orthogonal codes are derived from them, suggest that more effort has to be invested in these codes. This thesis proposes a modification of the efficient generation and correlation algorithms of these codes to achieve a generic implementation on a configurable architecture, capable to operate in real time and to be adapted to requirements from different applications. This implementation is the basis of novel algorithms proposed for the efficient generation and correlation of LS codes, generated either from Golay pairs or from CSS. This fast correlator, together with the zero correlation zone that LS codes exhibit, make them a good choice for quasi-synchronous applications.
Finally, the definition of an ultrasonic local positioning system has been explained. It makes it possible to verify the performance of the various encoding schemes used in the thesis, as well as the proposed efficient algorithms.
}, attachments = {https://geintra-uah.org/system/files/tesis_abstract_carmen_fuentes.pdf , https://geintra-uah.org/system/files/Part_I._MC_1-250_0.pdf , https://geintra-uah.org/system/files/Part_II._MC_251-345_0.pdf}, author = {Mar{\'\i}a del Carmen Perez}, editor = {Ure{\~n}a, J. and {\'A}lvaro Hern{\'a}ndez} }