Bluetooth® Low Energy Technology for Car Access Systems

The automotive industry is undergoing a major transformation to meet consumer demand to replace car keys with smartphones. With the popularity of "phone as key" technology, you no longer need a traditional key card and can use your phone to operate the "Passive Entry/Passive Start" (PEPS) system. The leading advantage of Bluetooth® low energy technology is that it is a versatile technology that can be widely used in smartphones.

Figure 1: Bluetooth low energy PEPS architecture in a car. The number of satellite modules may vary depending on system requirements. 

Figure 1 shows a typical architecture of a low-power Bluetooth PEPS in a car, using the "phone as a key" technology. In this architecture, there is a central smart key module and nine satellite modules. The central smart key module communicates with the mobile key, and the satellite modules can passively monitor the Bluetooth low energy connection between the central module and the smartphone. TI's automotive low-power Bluetooth® car access satellite node reference design describes how to implement this node design. 

Although there are many wireless technologies striving to achieve the "phone as a key" solution, Bluetooth low energy technology has become the most ideal choice due to the following advantages:

Low power consumption – As more and more electronic devices are used in cars, the power consumption budget of modern connected cars is shrinking, especially when the ignition switch is turned off. Therefore, low power consumption has become one of the key requirements for the design of car access control systems. Since car access control systems involve multiple nodes, the power consumption of each node has a greater impact on the entire system. Bluetooth Low Energy (BLE) technology has become an ideal choice for such always-on applications due to its low power consumption characteristics.

Accuracy – Since car access systems are often exposed to various RF environments such as crowded cities and underground garages, in order to ensure their reliability and accuracy in these places, the system must be robust to multipath propagation effects. Multiple low-energy Bluetooth anchor points in car access systems can solve this problem by fusing different data such as received signal strength indication (RSSI), angle of arrival (AoA), and phase ranging collected from multiple anchor points. In addition, multiple passive anchor points (or nodes) also increase the confidence of the measurement. Therefore, low-power Bluetooth technology not only meets the required accuracy in RF environments, but also improves the reliability of car access applications.

Wide application – Another challenge in designing a “phone as key” solution is to ensure interoperability between the car access system and a variety of smartphones. According to the latest Bluetooth market information in 2019, 100% of new smartphones support Bluetooth technology. With the widespread application of low-power Bluetooth technology in the industry, it has become the industry standard for smartphone real-time location systems (RTLS). The direction finding function introduced in the latest Bluetooth standard has further strengthened low-power Bluetooth technology and has become a key technology for realizing positioning applications such as “phone as key” and PEPS.

The potential of Bluetooth Low Energy technology to enhance the user experience of car access systems is unlimited. Users can walk to the car and unlock it with their smartphone key. The car can automatically adapt to the user's preferences, such as the position of mirrors, seats, steering wheels and head-up displays, based on a custom digital profile. With a car access system based on Bluetooth Low Energy technology, the car can also use a variety of secure ranging and positioning technologies to locate the authorized mobile phone in the car, adding another safety measure before unlocking the door and starting the car. In addition, users can create digital keys for friends and family, and create temporary digital keys for valet parking staff to make car sharing more convenient.

With TI's CC2640R2F-Q1 wireless microcontroller, you can apply Bluetooth low energy technology to car access systems to replace traditional car keys.