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 (蓝牙 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, 到达角度 (aoa) and Angle of Departure (AOD) technologies were added. Combined with triangulation positioning, it achieved sub-meter-level accuracy. 然而, 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. 另外, 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. 此外, 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. 在此过程中, 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 (接收的信号强度指示器). 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 (例如。, triggering alerts when a person approaches).

Accuracy Advantages of Channel Sounding

• 高精度: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) 技术.
• 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 低能量 (BLE) 基于硅实验室EFR32BG22芯片的汽车水平SOC模块, 适用于汽车钥匙系统, 车内传感器网络系统, 汽车控制系统, 板载诊断系统. 它已集成了服务器/客户端, 多连接, 高速吞吐量传输功能, 高性能, 低功耗特性，旨在确保出色的连接稳定性, transmission reliability.

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

A highly integrated Bluetooth 6.0 低能量 (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 (pep) and Remote Keyless Entry (rke)), Battery Management Systems (BMS), car-sharing, autonomous parking, cable replacement, and smartphone connectivity applications. 它支持差距, 到/山羊, 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