# Measurement and Analysis of RSS Using Bluetooth Mesh Network for Localization Applications
## 1 Introduction  
Bluetooth low energy (BLE) was released as a part of the Bluetooth 4.0 standard in 2010. With its inherent power efficiency, BLE is ideally suited for applications requiring short bursts of wireless transmission over long term, low power, low data rate operations. As a result, BLE has become a premier short-range wireless connectivity technology for consumer mobile devices as well as for the emerging Internet of Things (IoT) developments for a wide range of applications [1, 2, 3, 4]. In the past few years, the BLE-based location service technology has become one of the fastest growing applications for Bluetooth. Industry forecasts now predict that over 400 million products in the Bluetooth location services area will be shipping per year by 2022 [3]. The success of BLE for location services is due in part to several new features that are enabled by the standard, including low-power beacons and fast scanning of advertisement packets. The new features have effectively addressed technical limitations of the Bluetooth Classic and offer some advantages over the more prevalent Wi-Fi-based solutions [5]. In addition, BLE is intended to provide considerably reduced power consumption and cost than the Bluetooth Classic while maintaining a similar communication range. The standard permits devices to implement either or both BLE and Bluetooth Classic subsystems. Thus, it is convenient to have location service-specific systems designed using BLE and to adjust the deployment density and complexity to meet location service requirements. In contrast,when location services are designed as an add-on feature of an existing system such as Wi-Fi, system design and deployment will be constrained to meet the primary application requirements of the existing system. For example, BLE beacons are not constrained to provide uniform communication coverage, while Wi-Fi access points are deployed primarily for wireless communication with minimal coverage overlap [5]. In general, BLE localization solutions are designed based on the same principles as being used by the Wi-Fi-based systems. When two BLE devices are within the range of direct wireless communication, received signal strength (RSS) measurements at the physical layer can be used to estimate the distance or proximity between the two devices [6, 7]. Such a capability can be used to develop location services involving only two BLE devices. For example, in item finding solutions, small, battery-powered BLE tags are attached to objects that may be easily misplaced such as keys and wallet, and then one can use a smartphone to listen for the beacon signals coming from the tags, measure RSS, estimate distance, and finally locate the item [3]. In some other applications, many BLE devices need to be deployed throughout the operating environment to provide a more sophisticated infrastructure support for location services. Current systems can typically provide meter-level accuracies (about 1 to 10 m), while the exact accuracy in a specific application scenario depends on the deployment density of the infrastructure devices and the characteristics of the operating environment [3, 5]. Radio signals have an attenuation rate of 20 dB per decade of distance when propagating in free space [8], which makes it straightforward to estimate the distance from transmitter to receiver by measuring RSS. However, in multipath environments, instantaneous measurements of radio signal RSS suffer from random fluctuations due to the combined effects of path loss, shadowing, and small-scale fading. As a result, radio signal RSS-based localization solutions have poor performance in multipath environments. In addition, BLE signals are more susceptible to small-scale fading effects than Wi-Fi signals due to the narrower signal bandwidth of BLE. The BLE and Wi-Fi systems both operate in the unlicensed ISM band at 2.4 GHz, but with different channel bandwidth. BLE systems transmit signals over 2 MHz-wide channels, while the channel bandwidth of Wi-Fi is 20 MHz.