Increasing the Energy Efficiency and Responsiveness of Bluetooth Low Energy (BLE)

19.02.2018
MA-Endpräsentation: Tobias Renzler - Betreuer: Carlo Boano / Michael Spörk - 14:00 Uhr

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The low-power consumption and low-cost of Bluetooth Low Energy (BLE) devices raised the popularity of BLE over the past years. Nowadays, BLE is supported by most consumer electronic devices and it is an integral part in everyday application domains. Because it is used in a wide range of applications, the specific requirements of BLE applications are largely different. Furthermore, requirements may change over time and may be user dependent, having an adverse impact on the energy efficiency and responsiveness of BLE. The community is aware of changing application requirements over time: several runtime adaptation techniques for device discovery and connection management are indeed available in the literature. However, to date, there is no work that targets the influence of user behavior on the device discovery process of BLE. This thesis focuses on making the device discovery process more energy efficient and responsive. It does so by introducing two novel concepts: Adaptive Advertising and Range Extender. To find the appropriate trade-off and adapt it at runtime, Adaptive Advertising is introduced. The latter adapts the advertising interval of a BLE advertiser at runtime, according to a daily schedule, based on user behavior. To increase the responsiveness of BLE even further, the concept of Range Extender is introduced. The latter informs BLE devices about the presence of other nearby BLE devices by establishing a temporary or permanent connection. Both Adaptive Advertising and Range Extender are generic such that they can be used in different application scenarios. To outline the benefits of both approaches they are evaluated according to a real world application: the Nuki Smart Lock. The implementation of Adaptive Advertising takes place on the Cypress CY8C4248LQI-BL483 chip. An experimental evaluation shows that the energy consumption and the mean device discovery latency can be decreased by 50%. The Range Extender is implemented on Nordic Semiconductor’s nRF52 radio chip using the real-time operating system Zephyr. In both Temporary and Permanent Connection mode, the connection partner could be notified in a mean time of less than two seconds. After a successful notification the connection partner may adapt its advertising interval. This reduces the device discovery time of other potential connection partners, depending on the currently used advertising interval, by more than 95%.