## 2 Wireless Communication Technology  
Wireless localization is based on the transmission and reception of analog/digital signals composed of overlapping radio waves. Wireless communication has evolved with varying considerations such as frequency band and network capacity, tailored to specific applications and unique attributes. With the continued development of various wireless communication technologies, they are also being utilized in various applications, as is evident in the localization field [6]. In addition to the GNSS technologies such as GPS and Galileo that are already utilized for outdoor localization, there is an increasing demand for indoor localization due to the inefficacy of GNSS technology in such environments. Related research is being conducted to utilize various wireless communication technologies for effective indoor localization, and some of the commercially available wireless communication technologies include Wi-Fi, ultra-wideband (UWB), Bluetooth, and Zigbee, as shown in Table 1.  
Wi-Fi-based localization uses existing access points (APs) to estimate the location of a device. Initially, the target space was divided into multiple cells, and the received signal strength indicator (RSSI) collected in each cell was used to construct a radio frequency map. Recently, round trip time (RTT) information has been utilized to overcome localization  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Nominal Range** & **Maximum Signal Rate** & **Operating Frequency** \\ \hline Wi-Fi & 100–500 m & 10 Gbps & 2.4 GHz; 5 GHz; 6 GHz \\ \hline UWB & 30–100 m & 480 Mbps & 3.1–10.6 GHz \\ \hline Bluetooth & 10–100 m & 3 Mbps & 2.4 GHz \\ \hline Zigbee & 10–100 m & 250 Kbps & 915 MHz; 2.4 GHz \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of wireless communication technologies for indoor localization.  
errors. Using existing wireless local area networks (WLANs) offers the advantage of cost-effective initial infrastructure deployment. However, a corresponding drawback emerges as errors can be caused by path loss, and the initial connection time is long due to the security process, authentication protocols, and concurrent wireless frequency congestion.  
UWB [7] is a technology that uses very short pulses over a wide frequency band, resulting in reduced interference between pulse signals and good penetration ability, allowing for more precise and sophisticated localization. It has the advantage of being suitable for next-generation localization technology and the ability to transmit large amounts of data with low power. However, there is a drawback that it must solve the interference problems caused by overlapping with the bandwidth of Wi-Fi and Bluetooth, which are currently widely used.  
Bluetooth and Zigbee [8] are low-cost communication systems used for indoor localization. Bluetooth uses multiple beacons as anchors to estimate the location, while Zigbee determines the location by using the signal strength of the transmitted signal from a reference node and the received signal at a tag. Bluetooth is economically favorable due to its low cost, the mass production of chipsets, and low power consumption during operation. Zigbee is strategically designed to prioritize low data transmission, resulting in minimized network wait times and efficient power consumption. However, this design choice does come with the trade-off of comparatively slower data transmission speeds. Consequently, devices interconnected via Zigbee benefit from shortened waiting intervals while communicating with each other or with a central hub. This streamlined process facilitates swift connection establishment, effective exchange of small data payloads, and rapid responsiveness to commands or inquiries. Nevertheless, it is worth noting that both Bluetooth and Zigbee share a notable limitation in terms of signal resolution, which is an aspect warranting consideration.