@article {871, title = {CDMA-based Acoustic Local Positioning System for Portable Devices with Multipath Cancellation}, journal = {Digital Signal Processing}, volume = {62}, year = {2017}, month = {03/2017}, pages = {38-51}, abstract = {
This paper presents an acoustic local positioning system (ALPS) suitable for indoor positioning
of portable devices such as smartphones or tablets, based on the transmission of high frequency
CDMA-coded signals from a fixed network of beacons. The main novelty of the proposed ALPS is
its capability to mitigate the effects of multipath propagation by performing an accurate estimation
of the Line-of-Sight Time-of-Flights (LOS-TOF) through the Matching Pursuit algorithm. Signal
detection, multipath cancellation and positioning estimation all take place within the portable device,
which provides a graphical representation of the updated position in less than a second. The
performance of the Matching Pursuit algorithm is analyzed in a real scenario and the results show
that the proposed method is capable to retrieve the multipath-free System Availability under strong
multipath conditions with SNR levels as low as 0 dB.
}, keywords = {compass, wsn}, issn = {1051-2004}, doi = {10.1016/j.dsp.2016.11.001}, author = {Fernando J. Alvarez and Teodoro Aguilera and R. L{\'o}pez-Valcarce} } @conference {809, title = {Multipath cancellation in broadband acoustic local positioning systems}, booktitle = {IEEE 9th International Symposium on Intelligent Signal Processing (WISP)}, year = {2015}, month = {05/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Siena, Italy}, abstract = {

This work proposes a novel method to estimate the Line-of-Sight Time-of-Flights (LOS-TOFs) in a broadband acoustic local positioning system (ALPS) with strong multipath interference. The proposed method is based on the Matching Pursuit channel estimation algorithm that provides a low complexity approximation to the Maximum Likelihood solution for sparse channels. A multichannel version of this algorithm has been implemented to estimate a minimum of three coefficients in the channel responses of a particular ALPS, composed of four beacons that perform the simultaneous emission of BPSK modulated 255-bit Kasami codes. A statistical analysis of performance has been carried out by using a set of test signals synthetically generated to simulate different positions and reflection coefficients of the environment. The results of this analysis show the enhanced capability of the proposed method to estimate the LOS-TOFs under strong multipath interference, with respect to that of a classical system based on correlation + thresholding.

}, keywords = {compass, wsn}, doi = {10.1109/WISP.2015.7139174}, author = {Fernando J. Alvarez and R. L{\'o}pez-Valcarce} }