Evaluation of MAI Effect in Encoding Techniques for an Infrared Positioning System

Signal attenuation and multipath effect limit the behaviour of Global Navigation Satellite System (GNSS) in outdoor environments. Thus, there is a current trend on finding a centimetric accuracy three-dimension optical indoor positioning system using LEDs and photodiodes. There are several works that rely on encoding techniques to distinguish between transmitters. Due to the simultaneous reception, interferences between the cross-correlation signals may appear (Multiple Access Interference, MAI). In this way, the implemented encoding technique is crucial to remove the existent Multiple Access Interference (MAI) effect. In this work, Kasami, LS (Loosely Synchronized) and T-ZCZ (Three Zero-Correlation Zone) sequences with different lengths from 71 to 1024 bits have been analysed with the final goal of mitigating the MAI effect in the estimation of the receiver’s position. Simulations and experimental results, at a distance of 2m between transmitters and receiver, prove a better behaviour with the 1151-bit LS sequences achieving standard deviations below 0.25cm for plane XY and average absolute errors below 0.3 and 7.4cm in simulations and experimental tests, respectively.