Characterization of the Near-Far problem in a CDMA-based acoustic localization system

In this work the Near-Far problem is characterized in the context of an acoustic local positioning system (ALPS). First, a simple energy normalization algorithm is presented to identify the Near-Far situation and also to resolve the signal detection in the case of non-overlapping receptions. Then, an improved signal interference cancellation (ISIC) algorithm is proposed to remove from the received signal most of the energy of the most powerful reception in case of overlapping receptions, thus allowing the detection of weaker signals. The performance of these algorithms has been first studied by simulating the behaviour of an ALPS with four beacons emitting BPSK-modulated Kasami codes installed in a rectangular anechoic chamber. The same study has been later conducted with signals acquired in a real scenario, using a third-generation iPad as the mobile node of the ALPS.