CASE STUDY SNAPSHOT
Customer : Tier 1 engaged in manufacture of components and accessories to automotive OEMsSize : 51-200
Project vertical : Automotive
Challenge : Remote keyless entry system with battery powered secure key fob development
Solution : Design and develop a DA14531 BLE SoC based vehicle key-fob
Services Availed : Embedded Software Design, Embedded Hardware Design,
Tools and Technologies :
- BLE Module: DA14531
- Programming Languages: C and Assembly
- Software Development: Keil-IDE and Arm compiler, Smart Snippets, Smart Bond Flash
INTRODUCTION
One of our service distributors introduced a Tier 1 who was in need of a design house for secure key fob development - remote keyless entry system with lock and unlock features. As with a typical key fob, the vehicle should be able to be unlocked by pressing the unlock button on the vehicle without the driver taking it out of packet and also by pressing the key in the key fob. On top of this, the Tier 1 and their 2-wheeler OEM wanted a dual mechanism where the vehicle lock/unlock feature has to be managed with a key fob as well as the user's mobile based key fob.
CHALLENGE
While there is radio based key fob solutions that typically operate in 315 MHz/434 MHz frequency range, this is not compatible with mobile phones. Thus, the key fob being designed should be compatible to both Android and iOS phones generally used by the customers. The second challenge is the need to achieve 2 years of battery life on a single coin cell battery as anything less than that will be too tedious for the users. Finally, the remote key less entry system should be highly secure and resilient against malicious attacks.
SOLUTION
Embien decided to use the one of the popular communication technologies – Bluetooth Low Energy – BLE that is supported by both Android and iOS. While the vehicle side of the design was managed by Tier 1, our team developed the key fob side of it. Running on top of the GATT profile, custom services and characteristics were defined and developed to support lock, unlock, and search features.
For the vehicle unit to support mobile interface/remote keyless entry, it had to be intelligent to act in both peripheral as well as in central mode. By default, both the vehicle and key fob act as peripherals. When the user presses the unlock button in the vehicle, it immediately switches to central mode and authenticates the key fob in vicinity. Similarly, when he unlocks the vehicle by pressing the button on the key fob, the key fob takes over as central and commands the vehicle. Based on various considerations, it was decided to go for Renesas DA14531 based design for the secure key fob development. It is an ultra-low power device with an added advantage of needing only very few external passives conserving valuable real estate for the small key fob application. Our embedded hardware design team worked on the design and came up with the small form factor to fit in the standard enclosure.
Key Fob - Block Diagram
A unique pairing mechanism was provided to match the key fob with vehicle by using vehicle ID. Our developers did a deep analysis and understood the battery discharge characteristics to calculate the lifetime of a battery and designed the firmware to keep the key fob in sleep state as much as possible. It was placed in peripheral state with its advertising times optimized for the best possible batter life.
To conserve the battery life, and with RF power being a major factor, our team dynamically handled the transmit power (TX) depending on the key usage. When the Find-Vehicle was being used, higher transmission power was utilized and the rest of the time reduced RF power to cover only shorter distances. The MCU was put to deep sleep mode to optimize the power usage of the device to achieve battery power for more than two years.
To enable vehicle access to remote keyless entry system only within 2 meters of the key fob, RSSI value was used to measure the distance between the key fob and cluster. Since the RSSI value fluctuates, multiple filters were used to reduce the noise and find the distance between key fob and vehicle. By default, both the vehicle and key fob were in peripheral state. Once the user presses the button either in key fob or on the vehicle, the respective device changes to central role and connects with the other device and exchanges the packets.
If the battery is less than 15%, then the key fob will send a notification at the end of the connection with vehicle to be indicated to the user over cluster interface. For security and battery-saving purposes, the key fob will go into deep sleep mode after two days of no valid connection. For every connection had a timeout associated for that session and connection automatically terminated on timeout.
For the remote keyless entry system, we addressed the secure communication requirement using the Long-Term Key (LTK) generated during the pairing time. PIN based pairing and other security mechanisms were added to further strengthen the resilience of the secure key fob. The firmware itself was protected by secure features of the MCU to prevent unauthorized access or tampering.
BENEFITS
With the support of our product engineering services, the customer was quickly able to come up with the secure BLE key fob product. Some of the benefits we offered to the customers were:
- Turnkey development in small key fob form factor.
- Mobile App enabled remote keyless entry design.
- Highly secure key fob with multiple layers of security.
- Secure Firmware validation to ensure confidentiality, integrity, and authenticity before even running.
- Optimized power consumption for longer battery life.
- Complete power profiling done along with detailed reports.
CONCLUSION
Embien helped the customer to add value to his offering to the end customer. With mobile based key fob, the design was unique and helped differentiate them from their competition. With the support of our embedded design services team and their expertise on ultra-low power design, the customer was able to complete the Secure key fob development in a short period of time and start serial production.