## 1 Introduction
### Problem and Scope
[PERSON] and others optimized the main flow of the BeepBeep System and proposed the one-Beep System, which carries out two-way interaction at the beginning, develops acoustic anchors based on appropriate mobile devices, designs a new deployment scheme, and completes the deployment. All of the anchors must complete the acoustic signal sending and receiving processes in each localization loop on time. After the initial stage, the subsequent stage only needs to complete a single interaction process [16], which avoids the clock synchronization task that is difficult to implement on the Android platform. Essentially, the errors at the receiving terminal are not easy to handle and are more numerous than those in terminals based on TDOA. For this reason, the system designed in this manuscript does not adopt TOA as its core. As for TDOA, the key foundation is similar to that of TOA, but not the same. [PERSON]. previously proposed the ASSIST System [17]. Acoustic signals in the frequency band of 18-21 kHz are used as the localization signals, and TDOA is used actively. The positioning accuracy after measuring is 26 cm. However, active positioning suffers from obvious interference and increased power consumption and cannot support multi-user tasks simultaneously, which is not conducive to large-scale deployment. To make matters worse, it has a greater negative impact on NLOS situations. By contrast, the indoor acoustic signal positioning system [18] proposed by [PERSON] et al. greatly shortens the single positioning time cost by combining frequency division multiplexing and time division multiplexing technology, and the positioning error is within 10 cm. However, the anchors require a time synchronization part to support this arrangement, which makes the positioning accuracy heavily dependent on the clock synchronization accuracy between each anchor. Even if the clock synchronization calculation can be omitted through some clever process, revisions would still be expected over a large range. [PERSON] and others built an indoor localization system using multiple smartphones [11]. They applied a necessary reference anchor to implement the TDOA algorithm, and skillfully avoided the strict conditions of clock synchronization through simple but very effective mathematical processing. In addition, to cope with critical indoor temperature requirements for different situations, the influence on indoor temperature was also taken into account in the calculation process. The localization error of the enhanced system is within 25 cm. However, although the system flow and principles are unambiguous, the hardware used in this system is relatively expensive and may not be suitable for large-scale promotion in complex and flexible NLOS scenarios. [PERSON] et al. [22] sought to use an advanced particle swarm optimization (PSO) method to optimize a support vector machine (SVM) and achieve NLOS acoustic signal identification in the system based on indoor deployment situations. Then, the localization process was completed with the help of reliable peripherals or equipment according to a novel NLOS coping mechanism. Additionally, a new deployment scheme needed to be applied. Although the measured positioning accuracy can be within 20 cm, this method still faces many limitations in flexible NLOS scenarios. It can be seen from the aforementioned manuscripts that due to the functional limitations of hardware equipment, the system will have to handle some negative factors that cannot be completely avoided, such as clock synchronization error, some other accumulation error caused by multiple approximation paths in different steps or the calculation process, etc. At the same time, there may be an improper equipment layout scheme, which causes NLOS scenario to extremely restrict the indoor localization system. Furthermore, the NLOS scenario has already become the primary error source in the localization system based on acoustic signals in [7; 11; 19; 20; 21; 22]. To handle these shortcomings, a useful NLOS chirp signal solution is needed.