Energy Saving in Bluetooth 4.0 Wireless Locks Connected via Mobile Phone to the Internet

Abstract

In a modern environment users are more dependant on their ability to use their mobile phone for nearly everything. They communicate with almost any device and those devices provide nearly limitless access to for instance a watch or in new applications, a lock. Issues encountered with these devices are the almost always lack the ability to keep functioning for extended periods of time while having high transfer speeds and not a lot of space to store batteries. We present a means to keep a device operating for years with high transfer speeds in Bluetooth low energy connections, while functioning for year on end while connecting to a smartphone for access to the internet. To keep the solution working, high transfer speeds and minimal delays are needed as people are not willing to wait for extensive periods for a lock to open. This has to be done while operating for years with minimal space requirements. Our design uses the the Bluetooth low energy (LE) specification to keep the device connected to the mobile phone. The phone is connected to both the device (a lock) via Bluetooth LE and the internet. While the Bluetooth LE specification is low power, it is still considerably wasteful if high transfer speeds are used. As the internet connections of mobile phones are still considerably slow (even HSDPA) in response time, we can use this in our advantage to save power. The delays in these connections can be used to put the device to sleep. We also maintain full compatibility with the Bluetooth LE standard and keep high transfer speed when needed. Our solution provides the best transfer speed combined with the lower power consumption of low transfer rates. This is done by dynamically throttling the delays between each radio wakeup event. The method is tested for different delays expected in connection types like GPRS, UMTS and HSDPA. As a result device is able to operate for over 35% longer and save 144% power per message exchange without significant additional delays and without compromising the Bluetooth specification. It is also possible to use the technique without any low level access to the link layer which is preferable since it is not always possible to get access to the Bluetooth stack.