IIFAA technology exploration - non-sensing control car

IIFAA is the abbreviation of "Internal Internet Finance Authentication Alliance", established in 2015, and is committed to launching "financial-level, full-link, standardized" industry security solutions around identity authentication and biometric technology. Now The stage has covered more than 1.6 billion devices. As the main initiator of the IIFAA alliance, Ant Financial has actively explored authentication technologies in IoT scenarios in addition to mobile terminals, and has implemented them in scenarios such as digital car keys. This article introduces the common sensorless entry technology in the field of digital car keys, mainly including the industry status, technology development direction, problems encountered by the IIFAA team in the exploration and corresponding solutions.
digital car key
The change of the car key has gone through several stages as shown in the figure below, from the swing key (also called the work key), the mechanical key to the chip key and the remote control key. The development of the key, in addition to providing users with richer functions, has also significantly improved the security level of the key. With the development of the mobile Internet, digital car key technology represented by mobile phones is becoming more and more mature, and has a tendency to replace physical keys. Compared with physical keys, digital car keys have more functions, such as positioning, sharing, remote control of cars, etc., and have obvious advantages in user experience.
In addition to four-wheel vehicles, digital car keys are also applied to the field of two-wheel battery vehicles. Manufacturers such as Mavericks, No. 9, and Harrow regard vehicle intelligence as the main direction of their products. Based on the precipitation in security fields such as mobile phone biometric authentication, the IIFAA team launched a digital car key for four-wheeled vehicles in 2020, mainly for the scene of later modification of four-wheeled vehicles (referred to as: after-installation); in 2021, it cooperated with Yadea to launch The digital key solution for two-wheeled vehicles, and launched the "Yardi Zhixiang" mini program to help Yadea move towards intelligence; in 2022, the team will continue to deepen the field of digital car keys, and have made achievements in equipment certification, industry standardization, etc. Notable achievements. The left side of the picture below is the "Digital Car Key" applet for four-wheel vehicles, which is suitable for most mainstream models; models.
Feel free to enter the car
For mid-to-high-end four-wheel vehicles, sensorless entry has almost become a standard feature. When the user carries a mobile phone or a physical key around the vehicle, the vehicle terminal performs user authentication and distance judgment according to the near-field communication signal, and then automatically triggers the unlocking of the lock.
According to the development history, the underlying technology that non-sensing car entry relies on mainly includes three stages: radio frequency, Bluetooth and UWB. Physical keys that are still widely used at this stage are based on radio frequency signals for signal transmission; thanks to the low power characteristics of Bluetooth and the comprehensive coverage of mobile phones, digital keys are mainly based on Bluetooth for communication; in the future, with the support of mobile terminals, UWB will It is widely used in the field of non-inductive entry of digital keys.
RF insensitive
The physical keys of four-wheeled vehicles and two-wheeled vehicles, the bottom layer is based on 433MHz or 315MHz radio frequency signal for signal transmission, so it is also called radio frequency key. Due to the relatively high power consumption of the RF module, the processing modes of the RF non-sensing vehicle end are mainly divided into the following two types:
1. The base station unit in the vehicle continuously sends a low-frequency message coded at 125kHz to search for and wake up transponders within a certain range. All transponders within range of the signal are able to receive the message and verify the encoded data field. Once the transponder on the key is successfully identified, it will automatically send a radio frequency Keeloq coded message with a frequency of 433.92MHz. The base station unit at the vehicle end will decode it after receiving the message. If the identification is successful, the control command will be executed. The agency opens the door.
2. The base station unit in the vehicle is generally in a dormant state or a power-off state, and can only be woken up when a trigger event occurs. The trigger event is generally an infrared signal on the door handle or a micro switch activated by the door handle device. The owner has to touch the door to trigger the system, which opens the door.
The division of the vehicle sensing area is relatively simple, mainly divided into the door area and the trunk area:
The insensibility of the physical key has been verified by a large number of users in terms of user experience. However, due to the relatively low complexity of the encryption algorithm used, the probability of being compromised is high, and security is a potential risk.
Bluetooth senseless
Bluetooth-based digital keys have been developed rapidly in recent years. Compared with the sensorless function of physical keys, Bluetooth-based sensorless has been widely researched and applied.
The working principle of Bluetooth sensorless is shown in the figure below. The core includes two points: 1. Identity authentication based on digital key, 2. Distance measurement based on Bluetooth.
According to the number of Bluetooth modules (antennas) on the car and the differences in Bluetooth working modes, there are mainly multiple combinations of Bluetooth insensible, and there are corresponding application scenarios:
1. The number of antennas on the vehicle side
a. Single antenna: The positioning accuracy is low, and it can reach 1-2 meters in open space. It is suitable for two-wheeled vehicles and later modified four-wheeled vehicles (referred to as: after-installation).
b. Multi-antenna: High positioning accuracy, up to 0.3 meters. However, due to the limitations of cost and installation process, it is suitable for four-wheel vehicles with no sense of production line integration (abbreviation: pre-installation).
2. Mobile Bluetooth working mode
a. Keep alive: Through the keep alive of the mobile phone application, data transmission and Bluetooth working mode switching are performed. However, due to the high difficulty of keeping alive and the Bluetooth multi-pile positioning requires the Bluetooth on the mobile phone to turn on the slave mode (Slave) for Bluetooth broadcasting, it is mainly used in front-mounted four-wheel vehicles.
b. Pairing: Based on the Bluetooth HID protocol, it realizes the fast connection between the mobile phone and the car Bluetooth. Pairing does not require application keep-alive, so it cannot control the working mode of Bluetooth on the mobile phone side, and thus cannot transmit business data. Therefore, it is mainly applicable to single-bluetooth scenarios on the car and machine side, usually for two-wheeled vehicles and rear-mounted four-wheeled vehicles.
To sum up, the schemes adopted by two-wheeled vehicles and four-wheeled vehicles mainly have the following combinations:
front mounted four wheeler
Rear mounted four-wheeler
two wheeler
single antenna

multiple antennas

keep alive


This article will introduce single-antenna, multi-antenna, App keep-alive and pairing later in this article.
UWB senseless
concept introduction
UWB (Ultra Wideband) is a carrier-free communication technology that uses nanosecond to microsecond non-sinusoidal narrow pulses to transmit data. By transmitting extremely low-power signals over a wide spectrum, it can measure radio frequency very accurately. time-of-flight of the signal, enabling centimeter-accurate distance/position measurement.
Compared with WIFI and Bluetooth, UWB has been significantly improved in many aspects, especially in positioning accuracy, which has broad application prospects:
Application Scenario
As a new technology, UWB is only supported by some mobile phone models of Apple and at this stage. In terms of application scenarios, in 2021, Apple released Airtag that supports UWB technology. In August of the same year, released the "One Finger Link" function along with the mobile phone. The exploration of UWB technology by leading mobile phone manufacturers has driven more mobile phone manufacturers, equipment manufacturers, and automobile manufacturers to research UWB technology.
The left picture below shows that the iPhone 11 series is equipped with the U1 chip, and the right picture shows that the AirTag is equipped with the same chip.

The Mi Mix4 mobile phone is equipped with UWB technology, and it is applied to the Mijia IoT scene.
In 2021, the Car Connectivity Consortium (CCC) released the "Digital Car Key Version 3.0 Specification", which uses Bluetooth Low Energy (BLE) and Ultra Wideband (UWB) technologies as the basic technical solutions for non-sensing car entry. The general layout of UWB in the industry is shown in the figure below. The BLE module is responsible for communicating with the mobile phone, and wakes up the UWB modules on the mobile phone and the car to work. The UWB module performs high-precision positioning and notifies the car to unlock. operate.
key technology
The previous part gave a general introduction to the development history of sensorless car entry and related technologies. This part mainly introduces some problems and solutions encountered in the Bluetooth sensorless exploration. In the past two years, the team has covered rear-mounted four-wheelers, front-mounted four-wheelers, and two-wheelers in the business promotion, and therefore conducted in-depth research on all key technologies related to non-sensing, mainly including Bluetooth ranging, multi-Bluetooth (UWB) ranging, mobile App keep alive and Bluetooth pairing.
Single bluetooth ranging
The Bluetooth signal is in the 2.4G shared frequency band, which has a lot of interference, and the 12CM wavelength is easily blocked, so the distance measurement accuracy error through the Bluetooth signal is relatively large. According to the actual measurement, in an open place, the single Bluetooth ranging accuracy can reach 1-2 meters. When we realize non-sensing car entry based on single Bluetooth, there are two main innovations: fuzzy distance measurement based on signal strength RSSI and faster setting interaction.
ranging algorithm
There is an empirical formula for the conversion of Bluetooth signal strength RSSI and physical distance:
Calculation formula:
d = 10^((abs(RSSI) - A) / (10 * n))
d - the calculated distance
RSSI - Received Signal Strength (negative values)
A - Signal strength when the transmitter and receiver are separated by 1 meter
n — Environmental attenuation factor
It can be seen from the parameters that the error of this distance measurement will be relatively large, and the RSSI value of the Bluetooth signal is always in a state of jumping. For this reason, in engineering, only the RSSI signal is processed, and the processed RSSI value is used as the characteristic value of the distance. Through multiple optimizations, we found a smoothing algorithm with better effect, which can "cut peaks and suppress valleys" and better reflect the changing trend of signal strength.
The blue in the figure below is the actual Bluetooth signal strength, and the orange is the smoothed signal strength:
The smoothing algorithm of RSSI can be summarized into the following categories:
1. Clipping. Reduce the impact of signal mutations by limiting the range of signal changes
2. Median value. Sorting takes the middle value.
3. Arithmetic mean. Averaging over a certain amount of signal strength as the actual value
4. Median average. Take a set of queues to remove the maximum and minimum values, and then take the average.
According to the Bluetooth protocol, 20-50 signal strengths can be collected in 1 second, and the sampling frequency is high enough. Combining the characteristics of the above algorithms and the high-frequency sampling values of Bluetooth, we integrated a variety of algorithms in engineering, and the smoothing effect met expectations in actual measurements.
interactive optimization
Setting the lock opening and closing distance according to RSSI will cause great troubles for users in terms of interaction. Users don't know what the value of "-80" or "80" means, so we optimize the interaction. On the one hand, it guides the user to collect signal strength at a desired location to complete the setting of the unlocking position; on the other hand, it provides "far, middle and near" experience settings to meet the needs of users with different experiences:

Direction of development
In order to improve the ranging accuracy of Bluetooth, Bluetooth V5.1 introduces AoA and AoD high-precision positioning methods. AoA positioning is based on the angle of arrival, and AoD is based on the angle of departure. Due to the increase in the cost and process of Bluetooth modules, and the coverage of Bluetooth modules on mobile phones is not high enough, these two methods are still in the laboratory stage at this stage. With the support of more devices, the ranging accuracy of a single Bluetooth module will increase to the order of 10cm in the near future.

Multi-Bluetooth Ranging
The four-wheeled vehicles integrated with digital keys in the production line use multi-antenna modules for positioning. At this stage, the Bluetooth module is mainly used. With the popularization of UWB technology, it will replace Bluetooth and be more widely used.
Taking Ideal One as an example, the classic distribution of Bluetooth modules on the vehicle side is shown in the figure below, which is the so-called 1+5 mode. 1 Bluetooth antenna works in slave mode, continuously broadcasts Bluetooth, and is responsible for data interaction with the mobile phone. The A-pillar, B-pillar and the trunk are equipped with 5 Bluetooth antennas, which work in host mode and are responsible for monitoring the Bluetooth broadcast on the mobile phone side. The car terminal performs positioning based on the signals collected by the five Bluetooth broadcast modules.
During the promotion of our project, we will conduct research on UWB multi-pile positioning technology. After actual measurement, the accuracy can be 10-20CM, and it has been demonstrated in many exhibitions. Since multi-pile positioning is more research at the algorithm level, this part will not be expanded.

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