# Extending the Coverage of IEEE 802.15.4z HRP UWB Ranging
## 1 Introduction  
Ultra-wideband (UWB) technology has gained attention in various fields due to its potential for precise distance measurement and ranging. In particular, high-rate pulse repetition frequency (HRP) UWB, defined in the IEEE 802.15.4z standard, has recently become prominent for enabling centimeter-level ranging accuracy between UWB devices [1, 2]. This UWB technology first appeared as short-range wireless personal area network (WPAN) technology in the early 2000s. It was standardized by the IEEE 802.15.4 committee, a WPAN standardization organization, and was announced as the IEEE 802.15.4a standard in 2007. However, UWB technology has not been widely adopted as WPAN communication technology due to competing technologies such as Wi-Fi and Bluetooth [3, 4]. However, with the increasing demand for location-based services in the IoT, smart factories, and other applications, UWB technology has been re-evaluated for its advantage of being able to measure the distance between UWB devices in addition to providing wireless communication. Since Apple's iPhone 11 in 2019, which launched a service that informs users of the locations of nearby UWB devices, most smartphones released by Samsung, Apple, and Google on the market today have integrated HRP UWB technology. In addition, automobile companies such as Hyundai Motors are also introducing UWB smart keys [5, 6]. Following this trend, HRP UWB technology has continued to improve its performance with the announcement of the IEEE 802.15.4z standard in 2020, and the IEEE 802.15.4 ab standardization work is currently in progress [5, 6, 7, 8, 9, 10]. Since HRP UWB ranging was originally introduced as a short-range precision ranging solution and not a long-range communication solution, there has been no meaningful attempt to expand the ranging coverage. Moreover, since HRP UWB ranging has been mainly applied to smartphones, its function has been limited to measuring the exact distance between nearby UWB devices after pairing via Bluetooth. Most smartphones first recognize UWB devices through Bluetooth pairing before performing UWB ranging to reduce power consumption in UWB ranging operation. As a result, HRP UWB ranging was constrained to several tens of meters, equivalent to the Bluetooth communication range. This trend is also true for HRP UWB applications other than smartphones. Most of the existing studies on IEEE 802.15.4z HRP UWB investigated by the authors have focused on improving the ranging accuracy, ensuring communication robustness, and mitigating interference with Wi-Fi 6E [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. Table 1 summarizes the operation ranges reported in prior studies, with most commercially available modules (e.g., Qorvo's DWM1000, DW3000, and DW3120; NXP's SR150 and SR040; and Spark's SR1010 and SR1020) being limited to approximately 50 or 100 m.  
Nevertheless, for IEEE 802.15.4z UWB technology to be widely used beyond smartphones and smart keys, it must be able to measure the distance between UWB devices that are hundreds of meters apart. If a longer operating range is possible beyond the current operating range limit of tens of meters, then HRP UWB communication technology can be widely used in various fields such as logistics, smart factories, and smart cities. In an effort to achieve this, alternative approaches such as hybrid localization schemes combining UWB ranging with inertial measurements [28] or control-based estimation methods [29] have been proposed. These methods have demonstrated effectiveness in mitigating packet loss and maintaining tracking continuity under degraded link conditions. Although hybrid localization schemes and sensor fusion techniques have shown promise in mitigating ranging failures under degraded conditions, they inherently introduce additional complexity, cost, and energy consumption to the system.