Research Article On the Use of Perfect Sequences and Genetic Algorithms for Estimating the Indoor Location of Wireless Sensors M. Ferreira, 1,2 J. BagariT, 1,3 Jose M. Lanza-Gutierrez, 2,4 S. Priem-Mendes, 1,2 J. S. Pereira, 1,2,3 and Juan A. Gomez-Pulido 2,4 1 Polytechnic Institute of Leiria, School of Technology and Management, 2411-901 Leiria, Portugal 2 Center for Research in Informatics and Communications, Polytechnic Institute of Leiria, 2411-901 Leiria, Portugal 3 Instituto de Telecomunicac ¸˜ oes, Leiria Branch, 2411-901 Leiriah, Portugal 4 Department of Technologies of Computers and Communications, Polytechnic School, University of Extremadura, 10003 C´ aceres, Spain Correspondence should be addressed to M. Ferreira; marco.ferreira@ipleiria.pt Received 3 December 2014; Accepted 27 February 2015 Academic Editor: Kyung-Chang Lee Copyright © 2015 M. Ferreira et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Determining the indoor location is usually performed by using several sensors. Some of these sensors are fxed to a known location and either transmit or receive information that allows other sensors to estimate their own locations. Te estimation of the location can use information such as the time-of-arrival of the transmitted signals, or the received signal strength, among others. Major problems of indoor location include the interferences caused by the many obstacles in such cases, causing among others the signal multipath problem and the variation of the signal strength due to the many transmission media in the path from the emitter to the receiver. In this paper, the creation and usage of perfect sequences that eliminate the signal multipath problem are presented. It also shows the infuence of the positioning of the fxed sensors to the precision of the location estimation. Finally, genetic algorithms were used for searching the optimal location of these fxed sensors, therefore minimizing the location estimation error. 1. Introduction Te GPS (Global Positioning System) receivers work well in line-of-sight (LOS) conditions, meaning they cannot be used in an indoor scenario or locations in which there is limited LOS to the GPS satellites. Current GPS outdoor location accuracy is around 3 meters and is too high for most home automation purpose tasks. Additionally a GPS signal cannot be caught clearly in indoor scenarios. Te type and quality of measurements have a considerable efect on the performance of a positioning algorithm in a Wireless Sensor Network (WSN). Diferent types of mea- surements have been considered in the literature [1] for the positioning problem, for example, received signal strength (RSS), angle-of-arrival (AOA), time-of-arrival (TOA), and time-diference-of-arrival (TDOA). Te application of such techniques can be found in [2]. Since designing an estimator for the positioning problem strongly depends on the model of measurements, it is of great importance to use an accurate model for measurements. Te sensor nodes can be either stationary or moving. Tey might also be able to make more than one type of measurement. Our project started with RSS-based measurement because it is the only accepted measurement that does not sufer from NLOS conditions. Our real scenario work instance is a building with a considerable set of walls where a wireless sensor should be able to locate itself. Te performance of communication systems using Code Division Multiple Access (CDMA) and Orthogonal Fre- quency Division Multiple Access (OFDMA) is directly related to the coding sequence they use. Tese sequences should have a perfect autocorrelation and excellent cross-correlation properties for synchronization or code detection in noisy environments. Te importance of code detection accuracy in these coding sequences becomes evident when they are applied in WSN environments that have much interference. In this paper, the general issue of implementing an accurate Indoor Positioning System (IPS) will be tackled, Hindawi Publishing Corporation International Journal of Distributed Sensor Networks Volume 2015, Article ID 720574, 12 pages http://dx.doi.org/10.1155/2015/720574