蓝牙低能量技术入门指南

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"BLE介绍" 本文档主要涵盖了蓝牙低功耗技术（Bluetooth Low Energy，简称BLE），也称为Bluetooth Smart，是蓝牙技术联盟（SIG）推出的一种优化无线通信标准，特别适用于那些需要低功耗和短距离通信的物联网(IoT)设备。BLE的设计目标是减少功耗，同时保持足够的数据传输速度，使其成为可穿戴设备、健康监测器、智能家居设备和其他电池供电设备的理想选择。 BLE的基本框架包括以下关键组件和概念： 1. **中央设备(Central)**：通常由智能手机或电脑等主控设备担任，可以扫描并连接到周边的外设设备，即外围设备（Peripheral）。 2. **外围设备(Peripheral)**：通常是传感器或其他数据源，它们广播自己的服务并等待被中央设备发现和连接。 3. **服务(Service)**：在BLE中，服务是一组相关特性的集合，用于定义设备的功能。每个服务都有一个唯一的16位或128位UUID（通用唯一标识符）。 4. **特性(Characteristic)**：服务中的基本数据单元，用于数据交换。特性有自己的UUID，可以包含读、写、通知或指示等属性。 5. **广告(Advertising)**：BLE设备在未连接状态下可以广播广告包，包含设备名、服务UUID和其它相关信息，以供中央设备扫描发现。 6. **连接(Connection)**：一旦中央设备选择了一个外围设备，两者可以建立连接，进行更高效的数据传输。 7. **GATT（Generic Attribute Profile）**：BLE的核心协议，负责服务和特性的定义，以及中央与外围设备之间的数据交换。 8. **功耗管理**：BLE协议栈设计时考虑了低功耗，例如通过快速连接和断开、睡眠模式以及限制连续传输来减少电池消耗。 9. **安全性**：BLE支持加密和身份验证，以保护数据安全，防止未经授权的访问。 10. **兼容性**：BLE与传统蓝牙（Bluetooth Classic）在硬件层面上兼容，但协议栈和应用层不同，两者不能直接互操作，需要特定的适配层。 11. **应用示例**：BLE广泛应用于智能手表、运动追踪器、智能门锁、环境传感器、医疗设备等，为这些产品提供了简单、可靠的无线连接解决方案。 12. **开发工具**：有许多开发工具和库，如nRF5 SDK、Adafruit Bluefruit LE、Core Bluetooth (iOS) 和Android Bluetooth API等，方便开发者构建BLE应用。 13. **固件更新**：BLE设备通常支持通过空中下载(Over-the-Air, OTA)方式进行固件更新，以实现新功能或修复问题。蓝牙低功耗技术提供了一种高效、节能的无线通信方式，对于物联网应用的发展起到了关键作用。了解并掌握BLE的基本框架和工作原理，对于无论是入门还是高级用户，都是进入这个领域的必要步骤。

phenomenal growth in smartphones, tablets, and mobile computing. Early and active

adoption of BLE by mobile industry heavyweights like Apple and Samsung broke open

the doors for wider implementation of BLE.

Apple, in particular, has put significant effort into producing a reliable BLE stack and

publishing design guidelines around BLE. This, in turn, pushed silicon vendors to

commit their limited resources to the technology they felt was the most likely to succeed

or flourish in the long run, and the Apple stamp of approval is clearly a compelling

argument when you need to justify every research and development dollar invested.

While the mobile and tablet markets become increasingly mature and costs and margins

are decreasing, the need for connectivity with the outside world on these devices has a

huge growth potential, and it offers peripheral vendors a unique opportunity to provide

innovative solutions to problems people might not even realize that they have today.

So many benefits have converged around BLE, and the doors have been opened wide

for small, nimble product designers to gain access to a potentially massive market with

task-specific, creative, and innovative products on a relatively modest design budget.

You can purchase all-in-one radio-plus-microcontroller (system-on-chip) solutions

today for well under $2 per chip and in low volumes, which is well below the total overall

price point of similar wireless technologies such as WiFi, GSM, Zigbee, etc. And BLE

allows you to design viable products today that can talk to any modern mobile platform

using chips, tools, and standards that are easy to access.

Perhaps one of the less visible key factors contributing to the success of BLE is that it

was designed to serve as an extensible framework to exchange data. This is a funda‐

mental difference with classic Bluetooth, which focused on a strict set of use cases. BLE,

on the other hand, was conceived to allow anyone with an idea and a bunch of data

points coming from an accessory to realize it without having to know a huge amount

about the underlying technology. The smartphone vendors understood the value of this

proposition early on, and they provided flexible and relatively low-level APIs to give

mobile application developers the freedom to use the BLE framework in any way they

see fit.

Devices that talk to smartphones or tablets also offer another easy-to-underestimate

advantage for product designers: they have an unusually low barrier to adoption. Users

are already accustomed to using the handsets or tablets in their possession, which means

the burden of learning a new UI is limited, as long as we respect the rich visual language

that people have grown accustomed to in the platforms they use.

With a relatively easy-to-understand data model, no intrusive licensing costs, no fees

to access the core specs, and a lean overall protocol stack, it should be clear why platform

designers and mobile vendors see a winner in BLE.

2 | Chapter 1: Introduction

The Specification

In June 2010, the Bluetooth SIG introduced Bluetooth Low Energy with version 4.0 of

the Bluetooth Core Specfication. The specification had been several years in the making

and most of the controversial sections and decisions were finally ironed out by the

companies involved in the development process, with a few additional concerns left to

be dealt with in subsequent updates of the specification.

The first such major update, Bluetooth 4.1, was released in December 2013 and is the

current reference for anyone looking to develop BLE products. Althought the basic

building blocks, procedures, and concepts remained intact, this release also introduced

multiple changes and improvements to smooth the experience of the user.

As with all Bluetooth specifications, 4.1 is backwards compatible with 4.0, ensuring the

correct interoperability among devices implementing different specification versions.

The specifications allow developers to release and qualify products against either of the

versions (until deprecated), although the rapid adoption of new specification releases

and the fact that the 4.1 version standardizes several common practices among devices

makes it recommendable to target the latest available one.

Unless otherwise noted, this book uses the Bluetooth 4.1 specification as reference.

Wherever necessary, and especially when mentioning a noteworthy change or addition,

we will clarify when the previous 4.0 specification does not cover a particular area.

To obtain the latest adopted version of the Bluetooth specification, see the Bluetooth

SIG’s Specification Adopted Documents page.

Configurations

The Bluetooth specification covers both classic Bluetooth (the well-known wireless

standard that has been commonplace in many consumer devices for a number of years

now) and Bluetooth Low Energy (the new, highly optimized wireless standard intro‐

duced in 4.0). Those two wireless communication standards are not directly compati‐

ble and Bluetooth devices qualified on any specification version prior to 4.0 cannot

communicate in any way with a BLE device. The on-air protocol, the upper protocol

layers, and the applications are different and incompatible between the two technolo‐

gies.

Based on Specification Support

Table 1-1 shows the wireless technologies implemented for the three main device types

on the market today.

The Specification | 3

More and more BR/EDR devices entering the market include BLE as well, and the trend

is expected to continue as single-mode BLE sensors become more ubiquitous. Those

dual-mode devices can forward the data obtained from a single-mode BLE device to

the internet using their GSM or WiFi radios, a feature that is becoming more and more

common as more BLE sensors enter the market.

Based on Chip Count

Chapter 2 introduces and discusses the several protocol layers that constitute the Blue‐

tooth protocol stack, but for now it suffices to outline the three main building blocks

of every Bluetooth device:

Application

The user application interfacing with the Bluetooth protocol stack to cover a par‐

ticular use case.

Host

The upper layers of the Bluetooth protocol stack.

Controller

The lower layers of the Bluetooth protocol stack, including the radio.

Additionally, the specification provides a standard communications protocol between

the host and the controller—the Host Controller Interface (HCI)—to allow interoper‐

ability between hosts and controllers produced by different companies.

These layers can be implemented in a single integrated circuit (IC) or chip, or they can

be split in several ICs connected through a communication layer (UART, USB, SPI, or

other).

These are the three most common configurations found in commercially available

products today:

SoC (system on chip)

A single IC runs the application, the host, and the controller.

Dual IC over HCI

One IC runs the application and the host and communicates using HCI with a

second IC running the controller. The advantage of this approach is that, since HCI

is defined by the Bluetooth specification, any host can be combined with any con‐

troller, regardless of the manufacturer.

Dual IC with connectivity device

One IC runs the application and communicates using a propietary protocol with a

second IC running both the host and the controller. Since the specification does

not include such a protocol, the application must be adapted to the specific protocol

of the chosen vendor.

Configurations | 5

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