Bluetooth BLE Module Vehicle Key Channel Sounding Application

What is Channel Sounding?

Channel Sounding refers to a process that involves transmitting specific sounding signals and receiving and analyzing the propagation characteristics of these signals in wireless channels. It is used to evaluate the quality, structure, and behavior of the channel.

In wireless communications, signals undergo severe changes before reaching the receiver, due to obstacles such as walls, multipath reflections, and device occlusion.

In the early stage (Bluetooth 4.0 and earlier versions), distance estimation was based on Received Signal Strength Indicator (RSSI) through signal attenuation, with an accuracy of approximately 3–5 meters. This technology was mainly used for basic positioning functions such as Find My. At that time, the frequency hopping technology adopted fixed sequences, resulting in limited anti-interference capability.

With the introduction of direction-finding technology in Bluetooth 5.0, Ankomstvinkel (Aoa) and Angle of Departure (AOD) technologies were added. Combined with triangulation positioning, it achieved sub-meter-level accuracy. Imidlertid, this solution relied on complex antenna arrays, leading to high hardware costs.

The newly released Bluetooth 6.0 incorporates Channel Sounding as a core feature. It enables bidirectional high-precision ranging through standardized protocols, supporting Phase-Based Ranging (PBR) and Round-Trip Time (RTT) with an accuracy of ±50 cm. I tillegg, it incorporates built-in security mechanisms to defend against relay attacks.

How Does Channel Sounding Work?

Channel sounding is a method for estimating distances between two devices, designated as the initiator and the reflector. They exchange information across 72 RF physical channels, with the initiator transmitting first, followed by the reflector’s response. This alternating transmission and reception enable precise distance measurements.

The technique employs Phase-Based Ranging (PBR) or Round-Trip Time (RTT) or both for accurate coordination across the 2.4 GHz spectrum.

It also supports one to four antenna paths to improve measurement accuracy and reliability.

• Round-Trip Time (RTT)

Round-trip time (RTT) in a communication channel refers to the duration a signal takes to travel from the initiator to the reflector and back again. By assessing the Time of Flight (ToF) – the time it takes for a packet to be exchanged between the initiator and the reflector – the distance can be estimated. To achieve this, both devices record the Time of Arrival (ToA) and the Time of Departure (ToD). Analyzing the differences between ToA and ToD for both the initiator and the reflector provides the data necessary for a reliable distance calculation. I tillegg, in terms of security, since time cannot be reversed, RTT is considered highly secure.

• Phase-Based Ranging (PBR)

Phase-Based Ranging (PBR) utilizes the principle of phase rotation in RF signals to determine distances. I denne prosessen, the initiator sends a signal with specific frequency and amplitude information, and the reflector measures the phase of this received signal before sending a response. By comparing the phase differences between the signals from both devices, their relative distance can be determined. PBR offers a significant security advantage, especially compared to methods like RSSI (Received Signal Strength Indicator). The complexity of manipulating phase information makes PBR a more secure technology for distance measurement.

Typical Applications of Channel Sounding

• Keyless Entry System:The on-board receiver detects the direction of the key fob and accurately determines whether it is inside or outside the vehicle.
• Industrial Asset Tracking:Enables precise localization of goods, AGV robots, forklifts, and other assets.
• Smart Door Locks/Access Control Systems:Automatically unlocks when the user approaches, and remains locked if the user’s direction is incorrect.
• Motion Recognition and Proximity Detection:Supports basic gesture recognition and safety protection scenarios (F.eks., triggering alerts when a person approaches).

Accuracy Advantages of Channel Sounding

• High Precision:Centimeter-level accuracy.
• Enhanced Security:Multi-layered security mechanisms, including RTT, DRBG and RTT attack detection.
• Wide Compatibility: Integrated into mainstream consumer-grade platform devices, eliminating the need for additional radio frequency (Rf) teknologier.
• Additional Benefits: Lower power consumption and potentially lower implementation costs.

Different Vehicle Key Technologies Comparison

Vehicle Key Solutions

• Feasycom Bluetooth BLE RSSI Vehicle Key Solution – FSC-BT3721V BLE Module

A small-size AEC-Q100 Bluetooth 5.3 Lav energi (Ble) automotive level SoC module based on Silicon Labs EFR32BG22 chip, suitable for car key system, In-bil sensor nettverkssystem, Automotive Control System, on-board diagnostic system. It has server/client integrated, multi-connection, high-speed throughput transmission function, high performance, low power consumption characteristics designed to ensure excellent connection stability, transmission reliability.

• Feasycom Bluetooth BLE Channel Sounding Vehicle Key Solution – FSC-BT2004TV BLE Module

A highly integrated Bluetooth 6.0 Lav energi (Ble) Channel Sounding low-power automotive level SoC module, it integrates the TI CC2745R10 chip compliant with the AEC-Q100 standard and is specifically designed for Bluetooth Low Energy (Ble) 6.0 automotive applications. Optimized for low-power wireless communications, the module leverages advanced Bluetooth 6.0 Channel Sounding technology, making it ideal for vehicle access systems (including Passive Entry/Passive Start (PEPS) and Remote Keyless Entry (RKE)), Battery Management Systems (BMS), car-sharing, autonomous parking, cable replacement, and smartphone connectivity applications. Det støtter gap, Til/geit, SMP and L2CAP profiles. The module comes with user-friendly firmware pre-installed, allowing developers to quickly integrate Bluetooth functionality via simple serial AT commands.

Typical Specification Comparison