  The task of determining the physical coordinates of a target in indoor
environments is still a key factor for many applications including people and
robot navigation, user tracking, location-based advertising, augmented reality,
gaming, emergency response or ambient assisted living environments. Among the
different possibilities for indoor positioning, Acoustic Local Positioning
Systems (ALPS) have the potential for centimeter level positioning accuracy
with coverage distances up to tens of meters. In addition, acoustic transducers
are small, low cost and reliable thanks to the room constrained propagation of
these mechanical waves. Waveform design (coding and modulation) is usually
incorporated into these systems to facilitate the detection of the transmitted
signals at the receiver. The aperiodic correlation properties of the emitted
signals have a large impact on how the ALPS cope with common impairment factors
such as multipath propagation, multiple access interference, Doppler shifting,
near-far effect or ambient noise. This work analyzes three of the most
promising families of codes found in the literature for ALPS: Kasami codes,
Zadoff-Chu and Orthogonal Chirp signals. The performance of these codes is
evaluated in terms of time of arrival accuracy and characterized by means of
model simulation under realistic conditions and by means of experimental tests
in controlled environments. The results derived from this study can be of
interest for other applications based on spreading sequences, such as
underwater acoustic systems, ultrasonic imaging or even Code Division Multiple
Access (CDMA) communications systems.
