# Measurement and Analysis of RSS Using Bluetooth Mesh Network for Localization Applications
## 1 Introduction
Furthermore, BLE location service solutions depend on the RSS measurements on three widely spaced advertising channels that may be associated with different gains and multipath fading effects [5]. The RSS measurement data of BLE without channel information may statistically follow a multimodel distribution, making it hard to model the distance-power relation accurately. Thus, the research presented in this paper is formulated with two main objectives:  
* Experimentally study RSS measurements using BLE devices to better understand the key factors that may impact the performance of BLE localization systems, including small-scale fading effects with BLE signals and channel model differences among widely spaced advertising channels, and
* Explore new design techniques by exploiting the unique features of BLE systems to improve the performance of the RSS-based BLE localization solutions, including time-frequency diversity offered by three widely spaced advertising channels and the Bluetooth mesh networking technology. To accomplish these objectives, in this research, we designed a RSS measurement system using multiple ESP32 BLE modules and the Bluetooth mesh networking technology, which is capable of exploiting the space, time, and frequency diversities in measurements. We have also designed a communication protocol to associate channel ID information to advertising messages to enable channel-aware multi-device RSS measurements. Such a custom designed communication protocol is necessary in this research since standard BLE devices do not report which advertising channel is used for publishing a specific message. In this paper, based on channel measurement and analysis, we demonstrate that small-scale fading effects introduce large random variations in RSS measurements, making RSS unreliable for localization purposes. Therefore, we proposed a six-receiver configuration and space-time-frequency diversity combining scheme, which can be used to more accurately correlate RSS measurements to the distance between transmitter and receiver, and thus to achieve improved performance with the RSS-based localization techniques. Performance improvements of the six-receiver configuration and diversity combining scheme, as compared to the conventional single receiver system, are studied by comparing the empirical path loss models derived from measurement data. More importantly, we show with the measurement and modeling results that the reduction in the fitting errors is achieved without differentiating the three advertising channels. Thus, it is possible to conveniently implement the proposed six-receiver configuration using commercially available BLE devices and the standard Bluetooth mesh networking protocol stack without the need to decode the channel ID information from received messages. Additionally, such a system can be easily converted to a Bluetooth mesh network-based localization system. Due to the multi-hop wireless mesh networking nature of the system, it is especially convenient to cover a large space with different topologies. In summary, the major contributions of this paper are listed below:  
* We have presented a general framework for experimentally characterizing RSS measurements using the Bluetooth mesh network-based measurement system. We have presented design details of the proposed measurement system in terms of system architecture, hardware design, and communication protocols. * We have proposed a six-receiver configuration and a space-time-frequency diversity combining scheme to reduce the residual linear regression fitting errors in path loss models. Such a reduction can lead to more accurate range or location estimation based on RSS measurements, which is fundamentally important for localization. The rest of the paper is organized as follows. In Section 2, we present a brief review of several related papers in the literature. Impacts of radio propagation channel characteristics on RSS measurements are discussed in Section 3.