蓝牙HFP协议规范 v1.7.2：无线音频与车载设备交互

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"HFP_v1.7.2.pdf 是一份关于蓝牙 Hands-Free Profile (HFP) 的最新协议文档，由 Bluetooth SIG 准备并修订至 v1.7.2 版本，发布日期为2019年1月21日。此文档主要由音频、电话和汽车工作组编撰，旨在定义一套功能，使得移动电话可以与蓝牙连接的手持设备（如车载装置或蓝牙耳机）配合使用，提供无线的远程控制和语音连接。遵循此规范的设备能确保与支持此 profile 的蓝牙移动电话之间的互操作性。文档还包含了从 v1.7.0 至 v1.7.2 的版本历史记录，详细列举了各版本间的变更内容。" 蓝牙Hands-Free Profile (HFP) 规范是蓝牙技术中一个重要的组成部分，主要用于实现移动电话与各种蓝牙设备（如车载套件、蓝牙耳机等）之间的无线通信。该协议定义了一系列接口和功能，使得这些设备能够方便地进行语音通话，同时还能对移动电话进行遥控操作，如接听/挂断电话、音量调节等。在HFP v1.7.2 中，可能包含以下关键特性与改进： 1. 提高了音频质量：通过优化传输算法和错误纠正机制，确保了语音通话的清晰度和稳定性。 2. 支持更多的音频编码格式：可能增加了对AAC、aptX等高质量音频编码的支持，以满足不同设备和场景的需求。 3. 增强的电源管理：可能引入了更智能的电源控制策略，以延长蓝牙设备的电池寿命。 4. 用户体验优化：可能包含了更快的连接速度、更低的延迟以及更稳定的连接状态。 5. 兼容性增强：通过更新规范，确保新旧设备之间能够更好地协同工作，减少兼容性问题。 6. 安全性提升：可能增强了数据加密和身份验证机制，以保护用户隐私和通话安全。版本历史记录中，从 v1.7.0 到 v1.7.1 的变化可能涉及了一些小的修正和改进，而 v1.7.1 到 v1.7.2 的升级可能包括了更多的功能增强和问题修复。具体变更内容可能涉及到新增特性、错误修复、性能优化等，但具体内容需要查阅完整的协议文档才能得知。 HFP_v1.7.2.pdf 是蓝牙技术领域中关于HFP的重要参考资料，对于蓝牙设备制造商、开发者以及想要深入理解蓝牙音频通信的人员来说，具有很高的价值。它提供了详细的协议定义和实现指南，有助于确保蓝牙设备间的无缝协作和用户体验。

Hands-Free / Profile Specification

Bluetooth SIG Proprietary Page 16 of 134

Figure 2.2: Typical Hands-Free Use

The following roles are defined for this profile:

Audio Gateway (AG) – This is the device that is the gateway of the audio, both for input and output.

Typical devices acting as Audio Gateways are cellular phones.

Hands-Free unit (HF) – This is the device acting as the Audio Gateway’s remote audio input and output

mechanism. It also provides some remote control means.

These terms are used in the rest of this document to designate these roles.

2.3 User Requirements and Scenarios

The following rules apply to this profile:

a) The profile states the mandatory and optional features when the “Hands-Free Profile” is active in the

Audio Gateway and the Hands-Free unit.

b) The profile mandates the usage of CVSD for transmission of audio (over the Bluetooth link). The

resulting audio is monophonic, with a quality that, under normal circumstances, does not have

perceived audio degradation.

c) Between the Hands-Free unit and the Audio Gateway, only one Audio Connection per Service Level

Connection at a time is supported.

d) Both the Audio Gateway and the Hands-Free unit may initiate Audio Connection establishment and

release. Valid speech data shall exist on the Synchronous Connection in both directions after the

Audio Connection is established. Since it is only the AG that knows if wide band speech should be

used, it should always be the AG that establishes the Synchronous Connection with the required

codec.

e) Whenever an “Audio Connection” exists, a related “Service Level Connection” shall also exist.

f) The presence of a “Service Level Connection” shall not imply that an “Audio Connection” exists.

Releasing a “Service Level Connection” shall also release any existing “Audio Connection” related to

it.

2.4 Profile Fundamentals

If a LMP link is not already established between the Hands-Free unit and the Audio Gateway, the LMP

link shall be set up before any other procedure is performed.

There are no fixed master or slave roles in the profile.

The Audio Gateway and Hand-Free unit provide serial port emulation. For the serial port emulation,

RFCOMM (see [1]) is used. The serial port emulation is used to transport the user data including modem

control signals and AT command from the Hands-Free unit to the Audio Gateway. The AT commands are

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蓝牙HFP协议规范 v1.7.2：无线音频与车载设备交互

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