蓝牙室内定位

早在蓝牙 5.1 发布之前，蓝牙低能耗技术已经成为室内定位应用的领先解决方案。基本方法是使用蓝牙接收器（包括智能手机中的蓝牙接收器）测量来自固定信标的蓝牙信号的信号强度 (RSSI)。或者，固定锚点可以测量由移动设备（也称“标签”）发送的蓝牙信号的信号强度。这些基于信号强度的方法通常可以达到数米的精度级别，并且已经用于确定室内有无资产或人员。

在认识到市场对更精确的室内定位解决方案的日益增长需求之后，Bluetooth SIG 于 2019 年 1 月发布了蓝牙 5.1，其中蓝牙寻向功能是其主要功能。通过使用一系列多天线锚点，蓝牙寻向功能可用于在信号覆盖的室内环境中以三角法测量移动设备或标签的精确位置。

基于蓝牙 5.1 的室内定位技术可以实现米级精度。遵守 Bluetooth SIG 定义的标准可确保设备使用的消息格式在供应商之间兼容。此外，蓝牙技术广泛用于面向大众市场和小众应用的互联设备中，因此有望促进用户对室内定位解决方案的采用。

“跟随我”寻向功能演示

摄像头根据移动标签的射频信号到达锚点的角度来跟踪移动标签。

蓝牙 5.1 之前的蓝牙定位

下面的插图演示了蓝牙 5.1 之前的蓝牙低功耗技术如何广泛用于室内环境。这其中包括工业、商业和零售场所，以及博物馆等文化场所。在左侧，携带蓝牙设备的客户端和一个蓝牙锚点位于房间内，蓝牙锚点用于接收来自移动设备的广播消息。在右侧，房间内配备了多个蓝牙锚点。这两种方法都利用 RSSI 来测量所接收信号的强度。

在只有一个蓝牙锚点的情况下，客户端可以大致处于锚点的一定距离范围内。这种方法已被用于实施接近解决方案，以检测客户端是否进入了目标区域，包括购物中心或博物馆。当存在多个蓝牙锚点时，可以使用诸如三角测量之类的复杂算法来更准确地确定客户端相对于锚点的位置。

具有寻向功能的蓝牙定位技术

如引言中所述，蓝牙寻向功能可用于确定无线信号在移动客户端与一个或多个固定锚点之间的传播方向。蓝牙已经开发了两种解决方案架构，一种架构基于无线信号在锚点处的到达角 (AoA)，另一种架构基于无线信号在锚点处的离去角 (AoD)。

寻向功能 - 到达角 (AoA)

在 AoA 的情况下，移动资产配备了可发射蓝牙寻向信号（包含恒定频率扩展数据包 (CTE)）的标签。在这种情形下，使用基于网络的引擎根据由天线阵列进行的测量来确定传入信号的角度。如下所示，当移动客户端发射的信号到达各个天线（构成锚点的多天线阵列）时，会相对于其余各项存在轻微的相移。假设信号传播一个平面波，则可以使用每个天线上观测到的微小相位差来计算信号的到达角。

使用相位差来推导到达角。改编自 Bluetooth SIG

AoA 可以用于实施实时定位服务 (RTLS) 或跟踪用例。

寻向功能 – 离去角 (AoD)

在 AoD 的情况下，移动客户端接收由一个或多个天线阵列发射的蓝牙寻向信号。在这种情形下，移动客户端使用输入信号的测量值来计算信号离开天线阵列的方向。如果使用 AoD，当锚点天线阵列的每个元件发射的寻向信号到达客户端时，会相对于其余各项存在轻微的相位差。利用天线阵列的几何信息，客户端可以根据测得的相位差来计算信号离开天线阵列的角度。

使用相位差来推导离去角。改编自 Bluetooth SIG

AoD 可用于实现导航和寻路用例。

使用单一锚点寻向

室内定位设置可以使用配备多天线阵列的单一锚点。举例来说，此设置可用于确定移动客户端位于固定锚点的哪一侧。

使用多个锚点寻向

对于在精度方面有着更高要求的用例，可以使用多个配备多天线阵列的静态锚点来满足其需要。在这种情况下，可以使用来自多个锚点的传入或传出信号的角度并确定它们相交的位置，通过三角测量法精确计算资产的位置。

室内定位演示

定位引擎利用移动标签的射频信号在四个固定锚点的到达角，实时计算移动设备的精确位置，并在屏幕上显示出来。

 用例

通过检测角度，可以确定人在电梯的哪一侧。利用此信息，建筑物的门禁系统仅在人员接近电梯时才打开电梯门，从而提高安全性。

在工厂环境中，室内定位和追踪功能可以帮助连续定位和追踪多个资产，因此促进了自动化并提高了效率。

u-blox 解决方案

最新的 u-blox 蓝牙模块支持蓝牙 5.1 和寻向功能，包括：

The camera follows the mobile tag based on the angle of arrival of its RF signal at the anchor point.

Bluetooth location prior to Bluetooth 5.1

The illustrations below demonstrate how Bluetooth low energy technology prior to Bluetooth 5.1 is commonly used in indoor environments. These include industrial, commercial, and retail locations, as well as cultural venues such as museums. To the left, a client carrying a Bluetooth-enabled device is located inside a room with a Bluetooth anchor that receives advertising messages from the mobile device. To the right, the room is equipped with multiple anchors. Both approaches leverage the RSSI, a measurement of the strength with which the signal is received.

In the case with only one Bluetooth anchor node, the client can be roughly located within a certain distance of the anchor. This approach has been used to implement proximity solutions that detect whether a client has entered a target area, e.g. in a shopping center or a museum. When several Bluetooth anchors are present, complex algorithms such as trilateration can be used to more accurately determine the client’s position relative to the anchors.

Bluetooth positioning with direction finding

As outlined in the introduction, Bluetooth direction finding makes it possible to determine the direction that radio signals travel between the mobile client and one or several fixed anchor points. Bluetooth has developed two solution architectures, one based on the radio signal’s angle of arrival (AoA) at the anchor point, the other based on its angle of departure (AoD).

Direction finding – Angle of arrival (AoA)

In the case of AoA, the mobile asset is equipped with a tag that transmits a Bluetooth direction finding signal, which includes a constant tone extension packet (CTE). In this scenario, measurements made by the antenna arrays are used to determine the angle of the incoming signals using a network-based engine. As illustrated below, the signals transmitted by the mobile client reach the individual antennas that comprise the anchor’s multi-antenna array with a slight phase shift relative to the rest. Assuming that the signal propagates a planar wave, the slight phase differences observed at each antenna can be used to calculate its angle of arrival.

Using phase differences to derive the angle of arrival. Adapted from Bluetooth SIG

AoA can be used to implement real-time location services (RTLS) or tracking use cases.

Direction finding – Angle of departure (AoD)

In the case of AoD, the mobile client receives Bluetooth direction finding signals transmitted by one or several antenna arrays. In this case, the mobile client uses measurements of the incoming signal to compute the signal’s direction of departure from the antenna array. Using AoD, the direction finding signals transmitted by each element of the anchor’s antenna array reach the client with a slight phase difference relative to the rest. With information on the geometry of the antenna arrays, the client can calculate the angle of departure of the signal from the antenna array using the measured phase differences.

Using phase differences to derive the angle of departure. Adapted from Bluetooth SIG

AoD can be used to implement navigation and wayfinding use cases.

Direction finding with a single anchor

An indoor positioning setup may use a single anchor featuring a multi-antenna array. This setup can be used to determine, for example, on which side of a fixed anchor node the mobile client is located.

Direction finding with multiple anchors

Multiple static anchors featuring multi-antenna arrays can be used to meet the needs of use cases with more demanding requirements in terms of accuracy. In this case, the position of an asset can be calculated accurately through triangulation, using the angle of the incoming or outgoing signals from several anchors and determining where they intersect.

Indoor positioning demo

Using the angle of arrival of the mobile tag's RF signal at four fixed anchor points, the positioning engine calculates the precise position of the moving device in real-time and displays it on the screen.

 Use cases

Indoor positioning solutions serve a broad range of use cases including logistics, healthcare, manufacturing, retail, and in warehouses and smart buildings.

Angle detection makes it possible to determine on which side of the elevator a person is located. A building’s entrance control system can use this information to only open the elevator's doors when the person is directly approaching them, increasing security.

In factory environments, indoor positioning and tracking can help continuously locate and track multiple assets, facilitating automation, and improving efficiency.

u-blox solutions

Bluetooth 5.1 and direction finding are supported by the latest u-blox Bluetooth modules including: