CSR固件蓝牙无线信号强度链路质量与超距离指示CS101514ANP3 RSSI Link Quality and OutofRange Indication

RSSI, Link Quality and Out-of-Range Indication

接收信号强度指示，链路质量和输出超量程指示

Application Note

应用笔记

Issue 3

问题3

Document History 文档历史

Trademarks, Patents and Licences 商标，专利及牌照

Unless otherwise stated, words and logos marked with ? or ? are trademarks registered or owned by CSR plc or its affiliates.

除非另有说明，文字及标志标有?或 ? 是注册商标或子公司拥有或CSR公司。 Bluetooth ? and the Bluetooth logos are trademarks owned by Bluetooth SIG, Inc. and licensed to CSR Other products, services and names used in this document may have been trademarked by their respective owners.

蓝牙 ? 和蓝牙标识是公司所拥有蓝牙技术联盟的商标和企业社会责任授权给其他的产品，服务和文件中使用这个名称可能是其各自所有者的商标。

The publication of this information does not imply that any licence is granted under any patent or other rights owned by CSR plc and/or its affiliates.

公布的资料，这并不意味着任何许可证并授予任何专利或由CSR公司拥有的其他权利/或它的分支机构。

CSR reserves the right to make technical changes to its products as part of its development programme.

CSR公司保留权利，可部分作为其发展方案的技术改变其产品。

While every care has been taken to ensure the accuracy of the contents of this document, CSR cannot accept responsibility for any errors.

虽然每个已经采取谨慎，以确保文件的准确性本的内容，企业社会责任不能接受任何错误的责任。

Life Support Policy and Use in Safety-critical Compliance 生命支持政策和使用中的安全关键合规

CSR's products are not authorised for use in life-support or safety-critical applications. CSR公司的产品不授权使用的应用程序生命支持或安全的关键。 Use in such applications is done at the sole discretion of the customer.

在这种应用是在做客户自行决定的。

CSR will not warrant the use of its devices in such applications. CSR公司将不能保证在这样的应用程序使用的设备。

商标，专利及牌照................................................................................................................... 3 1 Introduction .................................................................................................................................. 5 1简介 ............................................................................................................................................... 5

2 Receive Signal Strength Indicator (RSSI) .......................................................................... 6 2接收信号强度指示器（RSSI） ................................................................................................... 6

3 Link Quality ......................................................................................................................... 9 3链路质量 ....................................................................................................................................... 9

4 What BlueCore Does .......................................................................................................... 10 4 BlueCore做些什么 .................................................................................................................... 10

4.1 HCI_Read_RSSI ............................................................................................................. 10 4.1.1 19.x及更高版本生成 .................................................................................................... 11 4.1.2早于19.x生成 ............................................................................................................... 12 4.2 HCI_Read_Link_Quality ............................................................................................... 15 5范围探测器.......................................................................................................................... 17 6参考文献.............................................................................................................................. 18 术语和定义............................................................................................................................. 19

1 Introduction 1简介

The Bluetooth Specification includes two Host Controller Interface (HCI) commands that can retrieve information from a Bluetooth radio about the received signal.

蓝牙规范包括两个HCI（HCI）命令，可以检索从蓝牙无线电收到信号的信息。 The specification defines the returned information very loosely, leaving manufacturers the option to provide more accuracy if they choose.

该规范定义的返回信息非常松散，如果制造商想要更准确，那么会给他们提供更多的选择。

This document explains how these commands work and how this information can be used to provide a simple Out-of-Range indication.

本文件解释了如何将这些命令的工作，以及如何利用这些信息可以提供一个简单的超出距离指示。

CS-101514-ANP3 ? Cambridge Silicon Radio Limited 2002-2009 CS-101514-ANP3 ?剑桥硅广播有限公司2002-2009

This material is subject to CSR's non-disclosure agreement. 这种材料是受CSR公司的非公开协议。

2 Receive Signal Strength Indicator (RSSI)

2接收信号强度指示器（RSSI）

The HCI_Read_RSSI command returns, for a specified Asynchronous Connectionless (ACL) connection, a signed 8-bit integer giving values between -128 and +127.

HCI_Read_RSSI命令为指定的异步无连接（ACL）链路返回一个有符号的8位整数，该值在+127和-128之间。

The Bluetooth specification only defines the following details: 蓝牙规范只定义了以下细节：

? If the RSSI is within the Golden Receiver Range, HCI_Read_RSSI returns the zero. ?如果RSSI的值在黄金接收范围内，则HCI_Read_RSSI返回零。

? If the RSSI is below the Golden Receiver Range lower limit, HCI_Read_RSSI returns a negative value.

?如果RSSI的值低于黄金接收范围的下限，则HCI_Read_RSSI返回一个负值。 ? If the RSSI is above the Golden Receiver Range upper limit, HCI_Read_RSSI returns a positive value.

?如果RSSI的值高于黄金接收范围的上限，则HCI_Read_RSSI返回一个正值。 The Golden Receiver Range is the target signal strength at the receiver. 黄金接收范围是接收方理想的信号强度。

If the receiving device supports the optional RSSI feature, and the transmitting device supports Power Control, then the receiving device can send requests to the transmitting device for increases and decreases in transmitted power in an attempt to keep the received power within the Golden Range, See Transmit Power Control .

如果接收设备支持可选的RSSI功能且发送设备支持功率控制，那么接收设备可向发送设备发出请求，以增加或减少发射功率，使接收功率保持在黄金范围内，详情见传输功率控制。

The Golden Receiver Range is 20dB±6dB wide. 黄金接收范围是20dB±6dB。

The dynamic range for Transmit Power Control is typically 30dB. 发射功率控制的动态范围通常是30dB。

These figures combine to produce an RSSI dead band of 50dB: HCI_Read_RSSI returns a 0 whether the devices are far apart transmitting at maximum power with RSSI at the bottom of the Golden Range, or very close but transmitting at minimum power with RSSI at the top of the Golden Range.

这些数字相结合，产生的50dB的RSSI死区：HCI_Read_RSSI返回0无论设备相距较远，RSSI的最大功率传输在黄金范围的底部，或设备非常接近，RSSI的最小发射功率传输在黄金范围的顶部。

That is, in a Power Control link HCI_Read_RSSI can not report the difference between a device 10cm away and one that is 50m away, and does not take into account the complications of signal strength nodes and nulls created by multipath interference.

也就是说，在一个功率控制的链路HCI_Read_RSSI不能报告出距离10cm或距离50m的差别，并没有考虑节点的信号强度和多径干扰造成空值的合并症状。

The scale of the positive and negative values returned when RSSI is outside the Golden Receiver Range, is left up to the individual manufacturer.

RSSI在黄金接收范围外时所返回的正值或负值，是留给个别制造商。

The Bluetooth specification indicates these values are in dB, but allows any degree of accuracy, so there is nothing to prevent the returned values being restricted to -1, 0 and +1.

蓝牙规格显示这些值的单位是dB，但允许任何准确度，所以没有什么可阻止返回的值被限制为-1，0和1。

Some hardware may be limited in its ability to measure incoming signal strength and only be capable of recognising signals within, above or below the golden receiver range.

某些硬件可能会受到限制，它能够测量输入信号的强度，只有在信号被承认高于或低于黄金接收范围。

Other hardware may have more accurate measurement, but it is not possible to make much use of the information via the HCI command because of the limits the specification places on the return parameter and the effects of Transmit Power Control.

其他硬件可能有更准确的测量，但它无法通过HCI命令获得更多有用的信息，因为规范限制返回参数和影响发射功率控制。

In summary, the HCI_Read_RSSI is not particularly useful on its own. 总之，HCI_Read_RSSI本身不是特别有用的。

In later firmware, BlueCore can return a more accurate absolute RSSI value using a manufacturer specific command (BCCMD), see section 4.1.1.

在以后的固件中，BlueCore仅可以返回一个更准确绝对的RSSI值使用制造商特定的命令（BCCMD），见第4.1.1。

3 Link Quality

3链路质量

The HCI_Read_Link_Quality command returns, for a specified ACL connection, an 8-bit unsigned integer, giving values between 0 and 255.

HCI_Read_Link_Quality命令为指定的异步无连接（ACL）链路返回一个有符号的8位整数，该值在+127和-128之间。

The Bluetooth specification provides no guidance as to what this number means beyond “The higher the value, the better the link quality is. Each Bluetooth module vendor will determine how to measure the link quality”.

蓝牙规范提供了一切指导这个数字意味着超越“该值越高越好链接的质量。每个蓝牙模块的供应商将决定如何衡量链路质量”。 This means that for a host to make intelligent use of the Link Quality information it must understand what the parameter means for the hardware concerned.

这意味着，主机要智能的利用链路质量信息必须知道参数对硬件方面代表的意思。

4 What BlueCore Does

4 BlueCore做些什么

For BlueCore implementation of HCI_Read_RSSI and HCI_Read_Link_Quality, CSR has attempted to provide as much useful information to the host as possible.

CSR公司为BlueCore执行HCI_Read_RSSI和HCI_Read_Link_Quality，试图为主机提供尽可能多的有用信息。

4.1 HCI_Read_RSSI 4.1 HCI_Read_RSSI

The method of calculating the value returned by HCI_Read_RSSI was changed for the 19.x releases.

计算HCI_Read_RSSI返回值的方法已更改为19.x版本。 The following notes apply to both the old and new methods: 以下注释同时适用于旧的和新方法：

? In an attempt to compensate for the considerable fading which occurs in the Bluetooth frequency band, the RSSI value is averaged over multiple hop frequencies and heavily filtered.

?蓝牙频带在试图为大量衰减做补偿时，RSSI的值平均超过在多跳频和重过滤时。 Despite this, there are radio environments where this value will underestimate the true RSSI. 尽管如此，在有广播的环境下，这个值会低估真实的RSSI。

The filtering causes the value to respond slowly when data is not being transmitted on a link. 过滤导致该值的响应速度很慢，在链接上没有数据传送时。

The value freezes when the link is in hold mode and is very sluggish when the link is in sniff or park mode.

该值是冻结时，链路是处在保持模式，该值非常缓慢时，链路是处在呼吸模式或待机模式。

? The RSSI measurement is not calibrated or tested on a per-chip basis and CSR makes no warranty about its accuracy.

?RSSI的测量不是校验或测试每个芯片的基准，CSR对其准确性不作任何保证。 Users should establish for themselves whether this command meets their requirements. 用户应自己建立能满足其需求的命令。

4.1.1 19.x and Later Builds 4.1.1 19.x及更高版本生成

In 19.x and later builds, the firmware measures the RSSI value on a particular ACL link and provides an absolute RSSI indication, available using the RSSI_ACL BCCMD, see BCCMD Commands .

在19.x及更高版本，固件测量ACL链路的RSSI，并提供一个绝对的RSSI指示，可使用BCCMD命令RSSI_ACL，见BCCMD命令。

This value is still unlikely to be useful as a general range indication, because of the dynamic range introduced by power control, and environmental factors like fading.

此值仍是不太可能作为一个有用的一般范围指示，由于动态范围引入功率控制和环境因素，像衰减。

The value returned by HCI_Read_RSSI is taken from the absolute value, with the Golden Receiver Range applied as a deadband, returning the number of dBm by which the RSSI is above or below the Golden Range.

由HCI_Read_RSSI返回的值是绝对值，黄金接收范围应用在死区，返回值为dBm，其中的RSSI是高于或低于黄金范围。

When the HCI_Read_RSSI value is zero, the RSSI is within the Golden Range. 当HCI_Read_RSSI值为零，则RSSI处在黄金范围内。

The accuracy of both these values is expected to be ±4 dBm. 该值的精确度期望在±4dBm。

The measurement saturates when the absolute RSSI value reaches about -20 dBm (the saturation value from HCI_Read_RSSI varies from IC to IC).

当绝对RSSI的值达到约-20 dBm时，测量饱和。（HCI_Read_RSSI的饱和值变化根据IC和IC不同）。 The value returned is compensated for temperature, but may vary from device to device owing to differences in manufacture.

返回的值是温度补偿，但可能会有所不同，由于不同制造商的不同设备的差异。 In designs which have a fixed path loss between BlueCore and the antenna, this loss can be compensated for using PSKEY_RSSI_CORRECTION.

在设计中有一个固定的路径损失在BlueCore和天线之间，这种损失可以使用PSKEY_RSSI_CORRECTION得到补偿。

This affects all RSSI values reported by BlueCore. 这会影响所有出自BlueCore的RSSI值。

4.1.2 Pre 19.x Builds 4.1.2早于19.x生成

In builds before 19.x, a much cruder RSSI estimate is available. 在早于19.x生成，提供了一个很粗糙的RSSI。 The firmware behaves as follows: 该固件的行为如下：

? When the RSSI is above the Golden Range, the firmware returns a positive number. ?当RSSI在黄金范围以上时，固件返回一个正数。

The value is an approximation of the dB between the top of the Golden Range and the RSSI.

该值是一个近似的dB在黄金范围的顶部与RSSI之间。

The value is very crude: it can be ± 5dB from the real value, there is no guarantee that a constant RSSI results in a constant return value, and thus there is no guarantee that the mapping from RSSI to the returned value is monotonic.

该值是很粗糙：它可能与真正的值相差±5dB，它不保证恒定RSSI的结果是恒定返回的，因此也不能保证，从RSSI的映射到返回的值是单调的。

? When the RSSI is within the Golden Range, the firmware returns zero. ?当RSSI在黄金范围之内，固件返回零。

? When the RSSI is below the Golden Range, the firmware returns a negative number. ?当RSSI低于黄金范围，固件返回一个负数。

The value is an approximation of the dB between the RSSI and the bottom of the Golden Range.

该值是一个近似的dB在黄金范围的底部与RSSI之间。 The value is less accurate than for positive values. 该值小于准确的正值。

It can be more than ± 5dB from the real value, there is no guarantee that a constant RSSI results in a constant return, thus there is no guarantee that the mapping from RSSI to the returned value is monotonic, and the value clips at a minimum of approximately –10dB.

它可以比真实值超过±5dB值，并不能保证一个固定的RSSI返回结果是一个常数，因此没有保证的RSSI映射从到返回的值是单调的，值被截取在最小值近似于-10dB。 The graph below shows how the HCI_Read_RSSI return value might plot against actual received signal strength.

下面的图显示了如何让HCI_Read_RSSI返回实际可能接收到的信号强度。

The graph describes a possible behaviour only and is not guaranteed to match actual IC behaviour.

该图描述了一个仅是符合实际的可能行为，但不保证集成电路的行为。

图4.1：HCI_Read_RSSI值VS接收信号强度在固件19.x前

The Golden Receiver Range is visible between -60 and -40dBm. 黄金接收范围是可见的在-60dBm至-40dBm间。

In a Power Control Link, the transmitters would effectively widen this 20dB dead-band by adding its dynamic range.

在功率控制链路，发射方将有效扩大范围，并加入了20dB死区的动态范围。 In designs which have a fixed path loss between BlueCore and the antenna, this loss can be compensated for using PSKEY_RSSI_CORRECTION.

在设计中有一个固定的路径损失在BlueCore和天线之间，这种损失可以使用PSKEY_RSSI_CORRECTION得到补偿。

This affects only the RSSI values reported by Inquiry Response with RSSI events, not the HCI Read RSSI value.

这只会影响RSSI的值，根据报告查询响应具有RSSI的事件，而不是HCI读取RSSI值。

4.2 HCI_Read_Link_Quality

The HCI_Read_Link_Quality command returns a number that is directly equivalent to Bit Error Rate (BER) on the following scale.

HCI_Read_Link_Quality命令返回一个数字，它直接等同于误码率（BER）如下。 ? Between 0xff and 0xd7 each bit distance represents 0.0025% BER i.e: ? 在0xff和0xd7间，每个位的距离代表误码率0.0025％，即：

? Between 0x59 and 0x00 each bit distance represents 0.64% BER i.e: ? 在0x59和0x00间，每个位的距离代表误码率0.64％。即：

In general, a link with a BER between 0 and 0.1% is workable. 一般来说，一个连接的误码率介于0和0.1％间是可用的。 Trying to run a link with a BER above 1% will give poor results. 试图运行一个高于1％误码率的连接会得到恶劣的结果。

The scale below 215 (0xd7) is not fully characterised since results in this region are not stable and often indicate a link is dropping more packets than it is receiving.

上面的215（0xd7）是不完整的描述，因为这个结果并不稳定，往往表明链路会比接收时丢失更多的包。

Both measurements are averaged, exponentially, over a number of packets (between 5 and 20).

两种测量的平均，指数，超过一个包的数量（在5和20之间）。

Only packets that pass both access code and Header Error Correction (HEC) checks are counted. ACL packets from a device, and SCO packets from the same device, are both used to evaluate RSSI and Link Quality – both HCI commands accept only an ACL connection handle as an argument.

只有数据包通过接入码和信头差错控制（HEC）检查才有意义。ACL的数据包从一个设备，以及SCO的数据包从相同的设备，都用来评估RSSI和连接质量—两个HCI命令只能接受一个ACL连接句柄作为参数。

The measurements for devices that exchange a lot of packets will be more accurate than those that only exchange packets infrequently.

对设备测量的许多包的交换会比那些只有少量包的交换的准确。

Link Quality BER measurements are based on Forward Error Correction (FEC) failures (HEC, DM payload, HV1/2 payload). Information on dropped packets is not included for the simple reason that slave devices do not know when the master is going to transmit and so can not know if a packet has been dropped, or if one was simply not transmitted.

链路质量误码率的测量是基于前向纠错（FEC）的失败（HEC, DM payload, HV1/2 payload）。丢失数据包是不包含信息的，原因很简单，从设备不知道主设备在何时传送，所以无法知道数据包丢失，或者根本就没有数据包传送。

Although dropped packet information is available at a master, including it in Link Quality reports would imply different scales for master and slave devices, which doesn't make sense since, for many applications, the distinction is irrelevant once the connection is established.

虽然主设备可以知道丢失数据包信息，包括其链接的质量报告将意味着不同规模主、从设备，因为这是没有意义的，在许多应用中，一旦连接建立起来，区别是无关的。 This type of Link Quality is of far more use than RSSI in determining, for example, selecting an access point. The user does not care about the strength of the received signal, but its quality. 这种类型的连接质量是远远超过在决定中使用RSSI，例如，选择一个存取点。用户不关心所收到的信号强度，但关心质量。

5 Out Of Range Detector 5范围探测器

Although neither Link Quality, nor RSSI (or even a combination of the two) is suitable for range measurement the two can be used together to provide some useful information:

虽然链路质量和RSSI（即使是两个组合）都不适用于范围测量，但是它们一起使用会提供一些有用的信息：

6 Document References 6参考文献

Terms and Definitions 术语和定义

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