Evaluation of Zadoff–Chu, Kasami, and Chirp-Based Encoding Schemes for Acoustic Local Positioning Systems

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 (ALPSs) 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 ALPSs cope with common impairment factors, such as multipath propagation, multiple access interference, Doppler shifting, near-far effect, or ambient noise. This article 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.