# Bluetooth Communication Leveraging Ultra-Low Power Radio Design
## 1 Introduction  
Bluetooth Low-Energy (BLE) is the leading protocol for short-range, low power wireless communication networks [1]. Wireless short-range technologies like BLE support tens of meters of maximum distance between devices for a variety of applications including wireless sensor networks and the majority of the low-power devices used in the Internet of Things (IoT) (Figure 0(a)). The BLE standard has a competitive advantage over other IoT-compatible wireless technologies because of its ability to communicate directly with smart phones, computers and tablets. Since consumer electronics are ubiquitous, BLE-enabled IoT devices can be seamlessly connected to personal area networks without the need for additional wireless access points. The use cases for BLE have proven to be valuable in different IoT applications including medical health monitoring, automated emergency calls, smart tags, home automation and in-vehicle networks. For environmental and industrial monitoring systems, BLE beacon tags can also be used for indoor localization [2, 3], identification and tracking of objects and personnel. In such applications, the power consumption of the device is widely recognized as the limiting factor to scaling the number of battery-powered IoT devices [4]. Assuming a scenario where a billion devices are deployed with an expected battery lifetime of 1 year, this would result in replacing 2.7 million batteries each day. In reality, this unacceptable number imposes significant logistical burdens in operational deployments and reduces the utility of IoT devices in different sectors. Batteries represent a logistically prohibitive maintenance problem that requires a large maintenance workforce, presenting a daunting challenge for individual facilities where maintenance resources are already at capacity. Therefore, the battery is needed to last as long as the life of the product, which can be on the order of 10 years for an embedded device performing signal processing and wirelesscommunication [5]. Current battery lifetimes of BLE sensors are typically <1 year, far short of the 10-year target for other IoT protocols such as cellular narrowband IoT (NB-IoT) and LoRa devices. However, reducing the power consumption and the operating supply voltages enable the design of self-powered IoT devices in which energy harvesting technologies can be used to power the node from the environment [6]. One growing application in this field is body-powered wearable devices in mobile health technologies which allow remote and continuous health monitoring as shown in Figure 1b[7]. Another application in the industrial sector is in machine health monitoring (MHM), where self-powered ULP sensors can be deployed to observe specific abnormal patterns in the monitored physical/mechanical signals of a machine for early failure detection. Low-power operation facilitates harvesting of the machine's vibrational energy using piezo-electric materials to charge super-capacitors which are used to power the sensor [8]. Typically, the RF radio accounts for a significant portion of the aggregate power profile of the device. Thus, each data transmission operation performed by a battery-powered node shortens its subsequent lifetime, limiting the amount of data transmittable before needing to recharge/replace the battery. In a typical IoT application, it is reasonable to assume the radio consumes 60-90% of the operating power budget [9]. The active power for a single BLE packet transmission is usually several mWs, in addition to the startup energy of the frequency synthesizer and the crystal oscillator [10]. In order to extend the battery's lifetime, aggressive duty-cycling can be implemented [5]. This technique leads to a significant increase in the operational lifetime for battery-powered devices. Using the advertising interval (TI) defined as the time between two successive transmission events, the intended battery lifetime can be estimated (preferably >10 years).