Simultaneous excitation systems for ultrasonic indoor positioning

Ultrasonic technology is a tool in the area of indoor positioning systems (IPSs) and has been extensively used in many applications. In ultrasonic IPSs (UIPSs), the use of a chirp signal (in which the frequency varies with time) is widespread due to its capability to obtain high-range resolution through its timefrequency characteristic. It also provides an opportunity to design effective waveform diversity which has always been the key to mitigating multiple-access interference (MAI) in multi-user UIPSs. To explore this, we analyze the chirp signal from the signal design perspective, with the goal of developing a precise and efficient UIPS for multi-user environments. To achieve this, three waveform diversity design schemes are proposed in which all the benefits of the classical chirp, such as high-range resolution, are retained while all the transmitters can transmit chirp signals simultaneously. In each scheme, a linear chirp is divided into two linear sub-chirps with diverse durations and/or bandwidths. This process is optimized by selecting the concatenated sub-chirps that generate a waveform which has a high-range resolution and relatively low interference in the same scheme. Initially, the effectiveness of the proposed schemes is evaluated for five simultaneous excitation signals using several metrics and experimental results are then presented for the ultrasonic indoor positioning.