Fine-grained acoustic positioning with compensation of CDMA interference

In this communication we study the accuracy of an acoustic positioning system operating in a robotic cell, and working in sequential (Time-Division Multiple Access, TDMA) and simultaneous (Code-Division Multiple Access, CDMA) operations. In normal room conditions, and operating in TDMA mode with 7 acoustic beacons and 32 bits long binary phase modulated signals, the system achieves a location accuracy (reproducibility) of 2 mm for 90% of measurements in the complete work area, and 1 mm repeatability over small areas and short periods of time. This performance is degraded in CDMA mode, as the interference between the emitted signals causes outliers in the times-of-flight (TOF) of the weaker signals, and, consequently, large positioning errors. We demonstrate that the application of signal processing algorithms that cancel Multiple Access (MAI) and Intersymbol (ISI) Interference effects manages to eliminate most of the TOF outliers, and, as a consequence, the system can nearly replicate the TDMA positioning accuracy in CDMA operation, with the advantage of higher position update rates.