This is basic information about the Bluetooth I summarize to minimize the effort of reading +2300 pages full specification of Bluetooth. To gain the complete understanding, you should refer the BLUETOOTH SPECIFICATION Version 4.0 from https://www.bluetooth.org.
Feel free to ask any question or open a discussion by comments down below of this article.
Bluetooth wireless technology is a short-range communications system intended to replace the cable(s) connecting portable and/or fixed electronic devices. The key features of the Bluetooth wireless technology are robustness, low power consumption, and low cost.
There are two forms of Bluetooth wireless technology systems: Basic Rate (BR) and Low Energy (LE). Both systems include device discovery, connection establishment, and connection mechanisms. The Basic Rate system includes optional Enhanced Data Rate (EDR) Alternate Media Access Control (MAC) and Physical (PHY) layer extensions. The Basic Rate system offers synchronous and asynchronous connections with data rates of 721.2 kbps for Basic Rate, 2.1 Mbps for Enhanced Data Rate and high-speed operation up to 24 Mbps with the 802.11 AMP. The LE system includes features designed to enable products that require lower current consumption, lower complexity and lower cost than BR/EDR. The LE system is also designed for use cases and applications with lower data rates and has lower duty cycles. Depending on the use case or application, one system including any optional parts may be more optimal than the other.
The Bluetooth core system consists of a Host and one or more Controllers. A Host is a logical entity defined as all of the layers below the non-core profiles and above the Host Controller Interface (HCI). A Controller is a logical entity defined as all of the layers below HCI. An implementation of the Host and Controller may contain the respective parts of the HCI. Two types of Controllers are defined in this version of the Core Specification: Primary Controllers and Secondary Controllers.
Here are the valid implementations of Bluetooth cores:
AMP is an Alternate MAC/PHY Controller including an 802.11 PAL (Protocol Adaptation Layer), 802.11 MAC and PHY, and optionally HCI.
Overview of BR/EDR Operation
– The Basic Rate / Enhanced Data Rate (BR/EDR) radio (physical layer or PHY) operates in the unlicensed ISM band at 2.4 GHz. Supporting the bit rate of 1Mbps for BR and 2Mbps or 3Mbps for EDR.
– The basic hopping pattern is a pseudo-random ordering of the 79 frequencies, separated by 1 MHz, in the ISM band.
– Bluetooth technology provides the effect of full duplex transmission through the use of a Time-Division Duplex (TDD) scheme.
Overview of Bluetooth Low Energy Operation
– LE employs two multiple access schemes: Frequency division multiple access (FDMA) and time division multiple access (TDMA). 40 physical channels, separated by 2 MHz, are used in the FDMA scheme.
– The hopping pattern used in LE is a pseudo-random ordering of the 37 frequencies in the ISM band.
– Devices that transmit advertising packets on the advertising PHY channels are referred to as advertisers. Devices that receive advertising on the advertising channels without the intention to connect to the advertising device are referred to as scanners.
– The scanner may make a request to the advertiser on the same advertising PHY channel which may be followed by a response from the advertiser on the same advertising PHY channel
– Devices that need to form a connection to another device listen for connectable advertising packets. Such devices are initiators.
Core System Architecture
The Bluetooth Core system consists of a Host, a Primary Controller and zero or more Secondary Controllers. A minimal implementation of the Bluetooth BR/EDR core system covers the four lowest layers and associated protocols defined by the Bluetooth specification as well as one common service layer protocol; the Service Discovery Protocol (SDP) and the overall profile requirements are specified in the Generic Access Profile (GAP). The BR/EDR Core system includes support of Alternate MAC/PHYs (AMPs) including an AMPManager Protocol and Protocol Adaptation Layers (PALs) supporting externally referenced MAC/PHYs. A minimal implementation of a Bluetooth LE only core system covers the four lowest layers and associated protocols defined by the Bluetooth specification as well as two common service layer protocols; the Security Manager (SM) and Attribute Protocol (ATT) and the overall profile requirements are specified in the Generic Attribute Profile (GATT) and Generic Access Profile (GAP).
Link Manager, Link Controller, and BR/EDR Radio blocks comprise a BR/EDR Controller. An AMP PAL, AMP MAC, and AMP PHY comprise an AMP Controller. Link Manager, Link Controller and LE Radio blocks comprise an LE Controller. L2CAP, SDP and GAP blocks comprise a BR/EDR Host. L2CAP, SMP, Attribute protocol, GAP and Generic Attribute Profile (GATT) blocks comprise an LE Host. A BR/EDR/LE Host combines the set of blocks from each respective Host.
Communication Topology and Operation
Anytime a link is created using the BR/EDR Controller it is within the context of a piconet. A piconet consists of two or more devices that occupy the same BR/EDR physical channel.
This demonstrates a number of the architectural features. Device A is a master in a piconet (represented by the shaded area, and known as piconet A) with devices B, C, D and E as slaves. Two other piconets are shown: a) one piconet with device F as master (known as piconet F) and devices E, G and H as slaves and b) one piconet with device D as master (known as piconet D) and device J as a slave.
This demonstrates a number of the LE architectural features. Device A is a master in a piconet (represented by the shaded area, and known as piconet A) with devices B and C as slaves, unlike BR/EDR the slaves do not share a common physical channel with the master. Each slave communicates on a separate physical channel with the master. One other piconet is shown with device F as master (known as piconet F) and device G as a slave. There are three other broadcast groups shown: a) device D is an advertiser and device A is also an initiator (known as broadcast group D), b) device E is a scanner and device C is also an advertiser (known as broadcast group C), c) device H is an advertiser and devices I and J are scanners (known as broadcast group H).
Bluetooth Application Architecture
Application interoperability in the Bluetooth system is accomplished by Bluetooth profiles. Bluetooth profiles define the required functions and features of each layer in the Bluetooth system from the PHY to L2CAP and any other protocols outside of the Core specification. The profile defines the vertical interactions between the layers as well as the peer-to-peer interactions of specific layers between devices.
Generic Access Profile
– The Bluetooth system defines a base profile which all Bluetooth devices implement. This profile is the Generic Access Profile (GAP), which defines the basic requirements of a Bluetooth device.
– For BR/EDR, it defines a Bluetooth device to include the Radio, Baseband, Link Manager, L2CAP, and the service discovery protocol functionality. GAP defines a single role with functionality that may be present in each device.
– For LE, it defines the Physical Layer, Link Layer, L2CAP, Security Manager, Attribute Protocol and Generic Attribute Profile. GAP defines four specific roles: Broadcaster, Observer, Peripheral, and Central. The Broadcaster role is optimized for transmitter only applications. Devices supporting the broadcaster role use advertising to broadcast data. The broadcaster role does not support connections. The Observer role is optimized for receive only applications. Devices supporting the observer role are the complementary device for a broadcaster and receives broadcast data contained in advertisements. The observer role does not support connections. The Peripheral role is optimized for devices that support a single connection and is less complex than central devices. Devices supporting the peripheral role only require Controllers that support the Controller’s slave role. The Central role supports multiple connections and is the initiator for all connections with devices in the peripheral role.
Since all Bluetooth devices are required to implement GAP, any additional profiles implemented by a Bluetooth device become supersets of GAP. A top level profile that describes application interoperability is called an Application Profile.
GATT-BASED Profile Hierarchy
The GATT Profile specifies the structure in which profile data is exchanged. This structure defines basic elements such as services and characteristics, used in a profile.
– A service is a collection of data and associated behaviors to accomplish a particular function or feature of a device or portions of a device. A service may reference other primary or secondary services and/or a set of characteristics that make up the service.
– There are two types of services: primary and secondary. A primary service is a service that provides the primary functionality of a device. A secondary service is a service that provides the auxiliary functionality of a device and is referenced from at least one primary service on the device.
– Services may be used in one or more profiles.