蓝牙 - 经典蓝牙物理信道介绍

物理信道有多种类型。所有蓝牙物理信道的特点都是一组物理层的频率与时间参数相结合，并受到空间因素的限制。对于基本的和经过调整的蓝牙组网(piconet)所用物理信道，跳频用于定期改变频率，以减少干扰影响，同时也是出于监管原因。

在 BR/EDR 核心系统中，对等(peer)设备使用共享物理信道进行通信。为此，它们的收发器需要同时调谐到相同的物理层频率，并且需要在彼此距离的合适范围内。由于射频载波的数量有限，而且许多蓝牙设备可能在同一空间和时间区域内独立运行，因此很有可能出现两个独立蓝牙设备的收发器调谐到相同射频载波的情况，从而导致物理信道碰撞。为了减少这种碰撞带来的不良影响，物理信道上的每次传输都以一个接入代码开始，该代码被设置为与设备的物理信道相关代码。该信道接入码是物理信道的属性。接入码存在于每个传输数据包的开头。接入码用于定时同步、偏移补偿、寻呼和查询。

定义了多个 BR/EDR 物理通道。每个通道都经过优化，用于不同的目的：

• 其中两个物理信道（基本 piconet 信道和适配 piconet 信道）用于连接设备之间的通信，并与特定 piconet 相关联。

• 其他 BR/EDR 物理信道用于发现（查询扫描信道）和连接（寻呼扫描信道）蓝牙设备。

• 设备使用同步扫描物理信道获取无连接从属广播物理链路的时序和频率信息，或恢复当前 piconet 时钟。

蓝牙设备在任何时候都只能使用一个 BR/EDR 物理通道。为了支持多个并发操作，设备在信道之间使用了时分复用技术。

A number of types of physical channel are defined. All Bluetooth physical channels are characterized by a set of PHY frequencies combined with temporal parameters and restricted by spatial considerations. For the basic and adapted piconet physical channels frequency hopping is used to change frequency periodically to reduce the effects of interference and for regulatory reasons.

In the BR/EDR core system, peer devices use a shared physical channel for communication. To achieve this their transceivers need to be tuned to the same PHY frequency at the same time, and they need to be within a nominal range of each other. Given that the number of RF carriers is limited and that many Bluetooth devices may be operating independently within the same spatial and temporal area there is a strong likelihood of two independent Bluetooth devices having their transceivers tuned to the same RF carrier, resulting in a physical channel collision. To mitigate the unwanted effects of this collision each transmission on a physical channel starts with an access code that is used as a correlation code by devices tuned to the physical channel. This channel access code is a property of the physical channel. The access code is present at the start of every transmitted packet. Access code is used for timing synchronization, offset compensation, paging and inquiry.

Several BR/EDR physical channels are defined. Each is optimized and used for a different purpose.

* Two of these physical channels (the basic piconet channel and adapted piconet channel) are used for communication between connected devices and are associated with a specific piconet.

* Other BR/EDR physical channels are used for discovering (the inquiry scan channel) and connecting (the page scan channel) Bluetooth devices.

* The synchronization scan physical channel is used by devices to obtain timing and frequency information about the Connectionless Slave Broadcast physical link or to recover the current piconet clock.

A Bluetooth device can only use one BR/EDR physical channel at any given time. In order to support multiple concurrent operations the device uses timedivision multiplexing between the channels.

基础组网信道 (Basic piconet channel)

在正常运行期间，基本piconet 通道用于连接设备之间的通信。

• 特点

1. 1. 基本 piconet 信道的特点是通过 PHY 信道进行伪随机序列跳转。跳转序列对 piconet 来说是唯一的，由主设备的蓝牙设备地址决定。跳转序列的相位由主设备的蓝牙时钟决定。所有参与 piconet 的蓝牙设备都与信道保持时间和跳频同步。

   2. 信道被划分为多个时隙，每个时隙对应一个物理层跳频。连续的跳频对应不同的物理层跳频。时隙根据 piconet 主站的蓝牙时钟编号。数据包由参与 piconet 的蓝牙设备传输，并以时隙边界为起点。每个数据包以信道访问代码开始，该代码来自 piconet 主设备的蓝牙设备地址。

   3. 在基本