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Bluetooth Overview

  • Bluetooth Basics
  • Benefits of Bluetooth Technology
  • How Bluetooth Technology Works
  • Core System Architecture
  • Profile Overview

Bluetooth Basics

Bluetooth wireless technology is a short-range communications technology intended to replace the cables connecting portable and/or fixed devices while maintaining high levels of security.

  • The key features of Bluetooth technology are
    • Robustness
    • Low Power
    • Low Cost
  • The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other.
  • Any Bluetooth-enabled device can connect to other Bluetooth-enabled devices in proximity.
  • Bluetooth devices connect and communicate wirelessly through piconets.
  • Each device can simultaneously communicate with up to seven other devices within a single piconet. Each device can also belong to several piconets simultaneously.
  • Piconets are established dynamically and automatically as Bluetooth-enabled devices enter and leave radio proximity.
  • A fundamental Bluetooth wireless technology strength is the ability to simultaneously handle both data and voice transmissions.
  • This enables users to enjoy variety of innovative solutions such as:
    • A hands-free headset for voice calls
    • Printing and fax capabilities
    • Synchronizing PDA, laptop, and mobile phone applications

Specification Make-up

Unlike many other wireless standards, the Bluetooth wireless specification gives product developers both link layer and application layer definitions, which supports data and voice applications.

Spectrum

  • Bluetooth technology operates in the unlicensed industrial, scientific, and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec.
  • The 2.4 GHz ISM band is available and unlicensed in most countries.

Interference

  • Adaptive frequency hopping (AFH) capability was designed to reduce interference between wireless technologies sharing the 2.4 GHz spectrum.
  • AFH works within the spectrum to take advantage of the available frequency.
  • This adaptive hopping allows for more efficient transmission within the spectrum.
  • The signal hops among 79 frequencies at 1 MHz intervals.

Range

  • The operating range depends on the device class:
    • Class 3 radios (0 dBm)– have a range of up to 1 meter or 3 feet
    • Class 2 radios (4 dBm)– most commonly found in mobile devices – have a range of 10 meters or 30 feet
    • Class 1 radios (20 dBm)– used primarily in industrial use cases – have a range of 100 meters or 300 feet

Power

  • The most commonly used radio is Class 2 and uses 2.5 mW of power.
  • Bluetooth technology is designed to have very low power consumption.

Data Rate

  • 1 Mbps for Version 1.2
  • Up to 3 Mbps supported for Version 2.0/2.1 + EDR

How Bluetooth Technology Works

  • Overview of Operation
  • Core System Architecture
  • Communication Topology
  • Profiles Overview

Overview of Operation

  • The Bluetooth RF (physical layer) operates in the unlicensed ISM band at 2.4 GHz.
  • The system employs a frequency hop transceiver.
  • RF operation uses a shaped, binary frequency modulation.
  • The symbol rate is 1 Megasymbol per second (Msps) supporting the bit rate of 1 Megabit per second (Mbps) or, with Enhanced Data Rate, a gross air bit rate of 2 or 3Mb/s.
  • A physical radio channel is shared by a group of devices that are synchronized to a common clock and frequency hopping pattern.
  • One device provides the synchronization reference and is known as the master. All other devices are known as slaves.
  • A group of devices synchronized in this fashion form a piconet.
  • Devices in a piconet use a specific frequency hopping pattern.
  • The basic hopping pattern is a pseudo-random ordering of the 79 frequencies in the ISM band.
  • The hopping pattern may be adapted to exclude a portion of the frequencies that are used by interfering devices.
  • The adaptive hopping technique improves Bluetooth technology co-existence with static (non-hopping) ISM systems when these are co-located.
  • The physical channel is subdivided into time units known as slots.
  • Data is transmitted in packets that are positioned in these slots.
  • A number of consecutive slots may be allocated to a single packet.
  • Frequency hopping takes place between the transmission or reception of packets.
  • Above the physical channel there is a layering of links and channels and associated control protocols.
  • The hierarchy of channels and links from the physical channel upwards is
    • Physical channel
    • Physical link
    • Logical transport
    • Logical link
    • L2CAP channel
  • Within a physical channel, a physical link is formed between any two devices that transmit packets in either direction between them.
  • In a piconet physical channel, there are restrictions on which devices may form a physical link.
  • There is a physical link between each slave and the master.
  • Physical links are not formed directly between the slaves in a piconet.
  • The physical link is used as a transport for one or more logical links.
  • Traffic on logical links is multiplexed onto the physical link by occupying slots assigned by a scheduling function in the resource manager.
  • A control protocol for the baseband and physical layers is carried over logical links in addition to user data. This is the link manager protocol (LMP).
  • Devices that are active in a piconet have a default asynchronous connection-oriented logical transport that is used to transport the LMP protocol signaling. For historical reasons, this is known as the ACL logical transport.
  • The default ACL logical transport is the one that is created whenever a device joins a piconet.
  • The link manager function uses LMP to control the operation of devices in the piconet.
  • The LMP protocol is only carried on the default ACL logical transport and the default broadcast logical transport.
  • Above the baseband layer, the L2CAP layer provides a channel-based abstraction to applications and services.
  • It carries out segmentation and reassembly of application data and multiplexing and de-multiplexing of multiple channels over a shared logical link.
  • L2CAP has a protocol control channel that is carried over the default ACL logical transport.
  • Application data submitted to the L2CAP protocol may be carried on any logical link that supports the L2CAP protocol.

Communication Topology

  • Piconet
  • Operational Procedures and Modes

Piconet

  • A piconet onsists of two or more devices that occupy the same physical channel.
  • The common (piconet) clock is identical to the Bluetooth clock of one of the devices in the piconet, known as the master.
  • The hopping sequence is derived from the master’s clock and the master’s Bluetooth device address.
  • All other devices are referred to as slaves.
  • A device that is a member of two or more piconets is said to be involved in a scatternet.

Operational Procedures and Modes

  • Inquiry (Discovering)
  • Paging (Connecting)

Inquiry (Discovering) Procedure

  • A Bluetooth-enabled device that tries to find other nearby devices actively sends inquiry requests.
  • Bluetooth-enabled devices that are available to be found send responses.

Paging (Connecting) Procedure

  • One device carries out the page (connection) procedure while the other is connectable (page scanning).
  • The page procedure is only responded to by one specified Bluetooth-enabled device.

RF and Baseband

  • RF channel
    • Frequency hopping, bandwidth occupancy, slot timing, TDD, and TDM
    • RF performance measures
    • Modulation and coding
  • Network topology
    • Piconet, scatternet, master, slave
    • Slot structure
  • Packet format
    • Access code, header, payload
    • Packet types
  • Connection establishment
    • Device discovery
    • Device connection
  • Low power modes
    • Sniff
    • sub-Sniff

RF Channel

  • 2.4 GHz frequency band
    • Unlicensed (subject to certain constraints on output power and spreading)
    • World-wide availability
    • Shared with 802.11b/g, cordless telephony, microwave ovens
    • Other bands (WAN, 802.11a, WiMax, UWB)
  • Time Division Duplexing (TDD)
    • Half duplex, i.e., for any given slot, either transmitter or receiving (not both)
    • Take turns transmitting and receiving
    • Implies a simpler radio architecture (single synthesizer can be shared)
  • Frequency hopping (spread spectrum)
    • 1 MHz channels, hopping randomly over 79 frequencies (2402 to 2480 MHz)
    • Hopping rate nominally 1600 Hz (hops every 625 us = 1 slot)
    • Imposes requirements on synthesizer design and packet format to be able to quickly retune and settle synthesizer (~100 us)
  • Requires network synchronization
    • Both transmitter and receiver need to be hopping on the same sequence
    • Both transmitter and receiver need to be time-synchronized so that they are hopping at the same time

RF Performance Measures

  • Receiver sensitivity
    • Defined by Bluetooth SIG as the minimum received signal power to achieve a bit error rate better than 10-3 (basic rate) or 10-4 (EDR)
    • Dirty transmitter defined in Bluetooth SIG test specification
    • Advertised sensitivity can be ambiguous
      • DQPSK sensitivity can be 2 dB better than GFSK sensitivity
      • Typical sensitivity (GFSK) is around -88 dBm
      • -70 dBm sensitivity is required by BT spec
  • Packet Error Rate (PER/LPR)
    • Not included as part of Bluetooth SIG test spec, but may included in Vendor’s internal requirements
    • LPR = missed access code, header error, other (only dependent on GFSK AC+HDR)
    • PER = includes LPR + payload CRC error
  • Transmitter Output Power
    • Bluetooth spec defines several transmit classes
      • Class 3: Output power ≤ 0 dBm
      • Class 2: -6 ≤ Output power ≤ +4 dBm
      • Class 1: 0 ≤ Output power ≤ +20 dBm (requires power control)

Modulation

  • GFSK = Gaussian Frequency Shift Keying
    • Symbol rate is 1 Msymbol/second
    • Each symbol contains one bit of information (either 1 or 0)
    • Information is conveyed in the instantaneous frequency of the signal
      • ‘1’ = +160 kHz
      • ‘0’ = -160 kHz
  • π/4-DQPSK = π/4-Rotated Differential QuadraturePhase Shift Keying
    • Symbol rate is 1 Msymbol/second
    • Each symbol contains two bits of information (either 00, 01, 10, or 11)
    • Information is conveyed in phase differences between successive symbols (4 possibilities)
  • D8PSK = Differential 8-Phase Shift Keying
    • Symbol rate is 1 Msymbol/second
    • Each symbol contains three bits of information (either 000, 001, 010, etc)
    • Information is conveyed in phase differences between successive symbols (8 possibilities)

Coding

  • Coding increases robustness of the transmission
    • Decreases SNR requirement to achieve a desired bit error rate
    • Increases range
    • Does not require retransmission
      • All the work is done in the receiver
      • Error correction is performed before CRC check
  • Coding works by adding controlled redundancy to the information stream
    • Code rate = information bits / transmitted bits
  • Bluetooth uses R=1/3 repetition code and R=2/3 Hamming code

Network Topology

  • Piconet
    • It consists of a single master and one or more slaves (up to seven slaves)
    • Point-to-point, or point-to-multipoint
    • Master controls the physical channel which is shared by all devices
      • Hopping sequence is based on the master’s LAP and clock
      • Burst timing is based on the master’s clock
      • The physical channel ideally isolates nearby piconets from one another
  • Any particular device can take on either the master or slave role
  • Scatternet
    • A device can participate in two or more piconets (time division multiplexed)
    • Each piconet has its own hopping sequence.
    • There can only be a single master in each piconet

Core Architectural Blocks

  • Channel Manager
  • L2CAP Resource Manager
  • Device Manager
  • Link Manager
  • Baseband Resource Manager
  • Link Controller
  • RF

Channel Manager

  • Responsible for creating, managing, and destroying L2CAP channels for the transport of service protocols and application data streams.
  • Uses the L2CAP protocol to interact with a channel manager on a remote (peer) device to create these L2CAP channels and connect their endpoints to the appropriate entities.
  • The channel manager interacts with its local link manager to create new logical links.

L2CAP Resource Manager

  • Responsible for managing the ordering of submission of PDU fragments to the baseband
  • Required because
    • The architectural model does not assume that the Bluetooth controller has limitless buffering
    • The HCI is a pipe of infinite bandwidth

Device Manager

  • Functional block in the baseband that controls the general behavior of the Bluetooth enabled device
  • Responsible for all operation of the Bluetooth system that is not directly related to data transport

Link Manager

  • Responsible for the creation, modification, and release of logical links
  • Achieves this by communicating with the link manager in remote Bluetooth devices using the link management protocol (LMP)
  • The LMP allows the creation of new logical links and logical transports between devices when required

Baseband Resource Manager

  • Responsible for all access to the radio medium
  • It has two main functions:
    • A scheduler that grants time on the physical channels to all of the entities that have negotiated an access contract
    • Negotiate access contracts with these entities. An access contract is effectively a commitment to deliver a certain QoS that is required in order to provide a user application with an expected performance

Link Controller

  • Responsible for the encoding and decoding of Bluetooth packets from the data payload and parameters related to the physical channel, logical transport, and logical link
  • Carries out the link control protocol signaling which is used to communicate flow control and acknowledgement and retransmission request signals

RF

  • Responsible for transmitting and receiving packets of information on the physical channel.
  • Transforms a stream of data to and from the physical channel and the baseband into required formats

Profiles Overview

  • To use Bluetooth wireless technology, a device must be able to interpret certain Bluetooth profiles.
  • The profiles define the possible applications.
  • Bluetooth profiles are general behaviors through which Bluetooth-enabled devices communicate with other devices.
  • Bluetooth technology defines a wide range of profiles that describe many different types of use cases.
  • At a minimum, each profile specification contains information on the following topics:
    • Dependencies on other profiles
    • Suggested user interface formats
    • Specific parts of the Bluetooth protocol stack used by the profile
    • Several Commom Profiles

BT 4.0 Overview

  • What is BT low-energy technology?
  • BR/EDR vs. LE
  • How to achieve ultra-low power
  • BT low-energy architecture
    • Physical layer descriptions

What is BT Low-Energy Technology?

  • BT low-energy technology is a global standard, very low-power wireless technology.
  • BT low-energy technology enables devices with coin cell batteries to be wirelessly connected to standard BT enabled devices.
  • A BT low-energy stack can work standalone (LE single-mode) or work with a BR/EDR stack (dual-mode).

BR/EDR vs. LE

Technical specifications BR/EDR LE
Radio frequency 2.4 GHz 2.4 GHz
Distance/range 10 meters (class 2) 10 meters (class 2)
Over-the-air data rate 1–3 Mbps 1Mbps
Technical specifications BR/EDR LE
Application throughput 0.7–2.1 Mbps 0.2 Mbps
Active slaves in piconet 7 > 4 billion, in theory
Security 64-bit/128-bit and application layer user defined 128-bit and application layer user defined
Technical specifications BR/EDR LE
Robustness Adaptive fast frequency hopping, FEC, fast ACK Adaptive fast frequency hopping
Latency (from a nonconnected state) 100 ms <6ms
Government regulation Worldwide The same as BR/EDR
Technical specifications BR/EDR LE
Certification body BT SiG The same as BR/EDR
Voice capable Yes No
Network topology scatternet Star(single)
Power consumption 1 as the reference 0.01 to 0.5 (depending on the use case)
Service discovery Yes The same as BR/EDR
Technical specifications BR/EDR LE
Profile concept Yes The same as BR/EDR
Primary use cases Mobile phones, gaming, headsets, stereo audio streaming, automotive, PCs, etc. Mobile phones, gaming, automotive, PCs, watches, sports and fitness, healthcare, home electronics, automation, industrial, etc.

How to Achieve Ultimate Low Power

  • Lower standby time (i.e., lower duty cycle)
    • Only three channels are used for advertising (vs. 16 to 32 channels for BR/EDR).
    • RF is on for 0.6 to 1.2 ms (vs. 22.5 ms for BR/EDR).
  • Faster connection (i.e., able to send data quicker)
    • The devices can connect in 3 ms (vs. > 100 ms for BR/EDR).
  • Lower peak power
    • BT low-energy technology uses relaxed RF parameters.
      • GFSK modulation index is increased to 0.45–0.55 (vs. 0.28–0.35 for BR)
      • Allows better range/robustness
    • Packet length restricted
      • Together with GFSK, gives lowest complexity transmitter/receiver
      • Provides lower peak power

BT Low Energy Architecture

  • Physical layer: transmits/receives bits
  • Link layer: packets and control
  • HCI: interface between host and controller
  • L2CAP: multiplexer
  • Attribute protocol: protocol for accessing data
  • Attribute profile: how are things organized
  • Device profiles: applications

Physical Layer – Channels

  • 2.4 GHz ISM band transceiver
    • Divided into 40 RF channels
    • 2 MHz channel spacing
  • Advertising channels
    • Used to broadcast data
    • Connectable
    • Discoverable
    • Three fixed channels (Ch37 = 2402 MHz, Ch38 = 2426 MHz, and Ch39 = 2480 MHz)
  • Data channels
    • Used to send application data
    • Adaptively frequency hopped
    • 37 dynamic channels

Physical Layer – Modulation

  • GFSK modulation
    • Gaussian frequency shift keying
    • Bit time product BT = 0.5
    • Modulation index = 0.5
  • Can be combined with BR/EDR RF in a dual-mode device
    • BT low energy additional cost on dual-mode is almost $0

What is BT HS Technology?

  • The BT HS technology has the capability to switch over to an 802.11 radio for fast data transfer.
  • The BT core is able to dynamically select the right controller, BR/EDR or AMP, under the L2CAP layer for any job.
  • BR/EDR, the primary controller, is used to perform discovery, association, connection establishment, and connection maintenance.
  • AMP, the secondary controller, is used for fast data transfer; up to 24 Mbps throughput rate.
  • In addition, mobile devices, including BT 3.0, will realize increased power savings due to enhanced built-in power control.
  • BT 3.0 + HS is completely backwards compatible with older BT devices, and still uses the same protocols for establishing connections.

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