Communication Technology Laboratory Wireless Communication Group Wireless Personal Area Network:...

Communication Technology LaboratoryWireless Communication Group

Wireless Personal Area Network: Bluetooth

Outline

• Overview of Bluetooth• Physical Layer• Baseband Layer• Protocol Layers• Bluetooth Smart

2Communication Technology LaboratoryWireless Communication Group

Bluetooth

• Bluetooth is a wireless technology standard for exchanging data over short distances – ISM band from 2.4 to

2.485 GHz– fixed and mobile devices – building personal area

networks(PANs)• First proposed by telecom vendor

Ericsson in 1994• Originally conceived as a wireless

alternative to RS-232 data cables


• Audio and data peripherals– Headsets, Speakers, …– Keyboards, Cameras,

Printers, …

• Intelligent devices– Cellular phones, laptops, …

• Embedded applications– Cars, Industrial systems, …

Bluetooth Special Interest Group (source: Wikipedia)

• Bluetooth is managed by the Bluetooth Special Interest Group (SIG),

– founded in 1998 by a group of companies

– more than 20,000 member companies as of 2014

– Bluetooth was standardized as IEEE 802.15.1, but the standard is no longer maintained.

• The SIG oversees the development of the specification, manages the qualification program, and protects the trademarks.

• Bluetooth trademark subject to qualification of product by SIG

• Patents only licensed to qualified products

• Bluetooth Core Specification Working Group produces mainly 4 kinds of specifications

– The Bluetooth Core Specification, release cycle is typically a few years in between

– Core Specification Addendum (CSA), release cycle can be as tight as a few times per year

– Core Specification Supplements (CSS), can be released very quickly

– Errata



Bluetooth Characteristics

• Unlicensed 2.4 GHz radio band: ISM (industrial, scientific, medical) band – available worldwide Gross data rate of 1 Mbit/s (EDR: 3Mbit/s, HS: 24Mbit/s) Basic 10m range extended to 100m with amplifiers TDMA-TDD-Slow Frequency Hopping spread spectrum

• Supports up to 8 devices in a piconet (1 master and 7 slaves) Piconets can combine to form scatternets

• Mixed voice/data connections possible

• Encryption

• Extremely small

• Ubiquitous radio link


OSI and Bluetooth Protocol

L2CAP: logical link control and adaptation protocol

RFCOMM: emulates RS232 serial traffic over L2CAP

TCS: telephony control protocol specification

SDP: service discovery protocol


Bluetooth Core System Architecture

• Resource manager– managing the ordering of submission of

data fragments, scheduling• Channel manager

– create, manage, destroy L2CAP channels• Link manager (LM)

– create, modify, release logical links– update parameters of physical links

• Baseband resource manager: access to radio medium

– scheduler– negotiate QoS– realign time slots

• Link controller (LC)– encoding/decoding of data packets– carries out the link control protocol (LCP)

signalling• Device manager: all operations not related

directly to data transport– Inquiry

• Radio frequency (RF) – transmit and receive packets on the

physical channel

Bluetooth core system architecture

HCI: host controller interface

L2CAP: logical link control and adaptation protocol


Communication Topology: Bluetooth Piconet

• Collection of devices connected in an ad hoc

fashion

• One unit will act as master

– Sets clock and frequency hopping pattern

– Can connect to 7 active or 255 inactive (parked) slaves

– Determines bit rate allocated to each slave

• Unique frequency hopping pattern/ID

• All devices participating in the piconet are synchronized to a common clock and hopping sequence.

• Slaves can communicate only with the master and not with other slaves.

Master

Slave 1

Unit C

Unit D

Unit BSlave 2

Slave 3

Unit A

Unit E


Communication Topology: Bluetooth Scatternet

• A device may participate concurrently in two or more piconets on time-division multiplexing (TDM) basis.

• A device can be both master and slave.

• A device can never be a master of more than one piconet.

• Two or more piconets that include one or more devices participating in more than one piconet form a scatternet.

Master A

Slave A1

Common slave

Slave A2

Master BSlave B1

Slave B2Slave B3

Outline




Frequency Hopping

• When the piconet is established, the Master Clock (CLK) is communicated

to the slaves.

• Devices in a piconet use a specific frequency hopping pattern, which is

determined by fields in the device address and the clock of the master.

• The basic hopping pattern is a pseudo-random ordering of the 79

frequencies in the ISM band.

• Adaptive Frequency Hopping (AFH) is used to improve the performance of

physical links in the presence of interference as well as reducing the

interference caused by physical links on other devices in the ISM band.

– AFH uses less than the full 79 frequencies that the basic piconet uses.


Time Slots

• The basic piconet physical channel is divided into time slots, each 625 μs in

length.

• A time division duplex (TDD) scheme is used where master and slave

alternatively transmit.

• The packet start should be aligned with the slot start. Packets may extend

over up to five time slots.


RX/TX Timing in Multislave Configuration


Modulation

• The operating band is divided into 1 MHz spaced channels each signalling

data at 1 M Symbols per second.

• Binary GFSK (Gaussian Frequency Shift Keying) is used as the modulation

scheme. Therefore, 1 M symbols per second results in data rate of 1 Mbit/s.

• Version 2.0 + Enhanced Data Rate (EDR): 3 Mbit/s

– a combination of GFSK and Phase Shift Keying modulation (PSK)

– two variants, π/4-DQPSK and 8DPSK.

– EDR can provide a lower power consumption through a reduced duty cycle.

• Version 3.0 + High Speed (HS): provides theoretical data transfer

speeds of up to 24 Mbit/s– Bluetooth link is used for negotiation and establishment

– high data rate traffic is carried over a collocated WiFi link.


Transmit Power

• Basic 10m range (with 0 dBm transmit power)

• Extended 100m range (20 dBm transmit power)

• Power classes:– Class 1

▫ Minimum output power: 1 mW (0 dBm)▫ Maximum output power: 100 mW (20 dBm)

– Class 2▫ Minimum output power: 0.25 mW (-6 dBm)▫ Maximum output power: 2.5 mW (4 dBm)

– Class 3▫ Minimum output power: N/A▫ Maximum output power: 1 mW (0 dBm)

• RSSI (Radio Signal Strength Indicator)-based power control

Outline




Baseband

• The OSI Physical (PHY) layer is represented by the radio and the

baseband. Furthermore, the baseband specifies the medium access control

layer.

• The baseband specifies the lower level operations at the bit and packet

levels, e.g., forward error correction (FEC) operations, encryption, cyclic

redundancy check (CRC) calculations, Automatic Repeat Request (ARQ)

Protocol.

• The baseband adds addressing and link control field to the raw payload

data.


Packet Structure

• General packet format

• All packets include the channel access code (CAC). This is used to identify communications on a particular physical channel and to exclude or ignore packets on a different physical channel that happens to be using the same RF carrier in physical proximity.

• Packet Types– High-quality Voice packets: HV1, HV2, HV3– Mixed data/voice packet: DV– Data–medium rate packets: DM1, DM3, DM5– Data–high rate packets: DH1, DH3, DH5, AUX1– Baseband control packets: NULL, POLL, ID, FHS

Channel Access Code

Header Payload


Data Rates

Packet type FECSymmetric max. rate (kbit/s)

Asymmetric max. rate (kbit/s)

DM1 2/3 108.8 108.8 108.8

DH1 No 172.8 172.8 172.8

DM3 2/3 258.1 387.2 54.4

DH3 No 390.4 585.6 86.4

DM5 2/3 286.7 477.8 36.3

DH5 No 433.9 723.2 57.6

AUX1 No 185.6 185.6 185.6


Error Protection

• Data error protection– Forward Error Correction (FEC)

• 1/3 FEC: Repeat each bit 3 times

• 2/3 FEC: (15,10) shortened Hamming code

– Automatic Repeat Request (ARQ)

– Cyclic Redundancy Check (CRC)• Header Error Check (HEC)

• Payload CRC

• Encryption User information can be protected by encryption of the packet payload; the

access code and the packet header shall never be encrypted.

• Whitening Before transmission, both the header and the payload shall be scrambled with a

data whitening word in order to randomize the data.


Physical Channels

• Two devices which are in the communication range of each other, need to tune their transceivers to the same RF at the same time to communicate.

• For communication a shared physical channel is used.

• Four physical channels are defined, each is optimized and used for a different purpose.

– Two of the physical channels (i.e., the basic and adapted piconet physical

channels) are used for communication between connected devices and are

associated with a specific piconet.

– The remaining physical channels are used for discovering devices (i.e., the inquiry

scan physical channel) and for connecting devices (i.e., the page scan physical

channel).


Physical Channels

• A device can use only one of the physical channels at any given time.

• To support multiple concurrent operations, the device uses TDM between

the channels.

• Whenever a device is synchronized to the timing, frequency, and access

code of a physical channel, it is said to be connected to this channel.

• All physical channels use frequency hopping, i.e. they change the

frequency periodically to reduce the effects of interference and for

regulatory reasons.

Outline




Logical Links and Transports

• A variety of logical links are available to support different application data

transport requirements. Each logical link is associated with a logical

transport, which has a number of characteristics.

• These characteristics include flow control, acknowledgement, repeat

mechanisms, sequence numbering, and scheduling behavior.

• Between master and slave(s), different types of logical transports may be

established.


Logical Transports

Five logical transports have been defined:

• Synchronous logical transport

1. Synchronous connection-oriented (SCO) link

– Symmetric, point-to-point link between the master and a specific slave

– Reserves slots on the physical channel and can, therefore, be considered as a circuit-

switched connection

– SCO packets are never retransmitted.

2. Extended synchronous connection-oriented (eSCO) link

– Symmetric or asymmetric, point-to-point link between the master and a specific slave

– Circuit-switched connection between the master and the slave


Logical Transports

3. Asynchronous logical transport (ACL) link

– Used to carry LMP and L2CAP control signalling and best effort asynchronous

user data

– In the slots not reserved for synchronous logical transports, the master may

exchange packets with any slave on a per-slot basis

– Packet-switched connection between the master and all active slaves

participating in the piconet

– The default link of active devices in a piconet

4. Active slave broadcast (ASB) logical transport

5. Parked slave broadcast (PSB) logical transport


Logical Transport Types


Link Controller

• The link controller protocol is responsible for maintaining a link once it has

been set up.

• The main tasks of the link controller include:

– Carrying out higher level operations like inquiry and paging

– Managing links with different devices

– Managing links with different piconets


Connection States

State diagram of link controller

HOLD SNIFF

• Standby– Only native clock running

• Inquiry– Discover co-located Bluetooth devices

• Page– Establish piconet– Include new devices in existing piconet

• Connection– Normal piconet operation– Max. 7 active slaves

• Park– Slaves, that are associated to a

piconet, but not active (rarely used)• Hold

– one time sleep period, keep active slave address (scatternet)

• Sniff– periodic sleep period, keep active slave

address (mouse, keyboard)


Connection Progress

This diagram shows a typical

progress through the states for a

Single connection.Inquiry

Page

Master

Response

Connection

(Master)

Inquiry

Scan

Page

Scan

Slave

Response

Connection

(Slave)

Inquiry

Response

Master Slave


Higher Layers of the Architecture

• Logical Link Layer Control and Adaptation Protocol (L2CAP)

Simple data link protocol on top of the baseband

– Connection-oriented and connectionless

– Protocol multiplexing

– Segmentation and reassembly

– Quality-of-Service (QoS) flow specification per connection (channel)

• Link Manager Protocol (LMP)

LMP allows: – Creation of new logical links and logical transports between devices when

required

– General control of link and transport attributes such as the enabling of

encryption on the logical transport

– Adapting of transmit power on the physical link, or the adjustment of QoS

settings for a logical link

Outline




Recent History of Bluetooth

• The Bluetooth Special Interest Group (SIG) is taken care of current and future versions of this industry standard

• For Bluetooth v1.1 and Bluetooth v1.2 there has been a colaboration with IEEE802.15.1– IEEE Standards 802.15.1-2002 and

802.15.1-2005

• Afterwards the IEEE Study Group 802.15.1b voted unanimously to discontinue the relation to Bluetooth SIG– later versions of Bluetooth did not

become IEEE standards

• Bluetooth v2.0 with optional Enhanced Data Rate (EDR) has been published in November 2004.– combination of GFSK and DPSK to

increase data rate to 3Mbps

• Bluetooth v2.1 + EDR (July 2007)– Secure simple pairing protocol speeds

up pairing procedure

• Bluetooth v3.0 + HS (high speed) published April 2009– alternate PHY based on WiFi used for

high data rate (up to 24Mbps)– UWB Multiband was candidate PHY

but was dropped due to IPR problems – Bluetooth PHY used for control

channels and medium rate traffic

• Bluetooth Smart (v4.0) published June 2010: Classic Bluetooth, Bluetooth+HS and Bluetooth Low Energy– low energy protocol originates from the

Wibree system (Nokia); – LE not compatible with other Bluetooth

modes

• Bluetooth v4.1 (December 2013)– incremental update

Bluetooth Low Energy (BLE, Smart Bluetooth)

• New low power design, no downward compatability to Classic Bluetooth (CB)

• To be used in sensor networks– sensors transmit short data

packets with a low duty cycle– support low latency– not optimized for streaming

data– asymmetric node complexity

(slave - master)• Reuse to as much as possible

Classic Bluetooth hardware

• Simplified physical layer as compared to Classic Bluetooth– three advertising channels

(CB uses 16 or 32 for Inquiry and Page) used for connection process

– 37x2MHz data channels (CB: 79x1MHz)

– increased modulation index of GMSK

• 3ms latency from nonconnected state (CB: >100ms)


Dual Mode Chipsets (Bluetooth Smart Ready) (www.csr.com)


Classic Bluetooth Versus Bluetooth Smart (source: Wikipedia)


Technical Specification Classic Bluetooth technology Bluetooth Smart technology

Distance/Range (theoretical max.)

100 m (330 ft) <100 m (<330 ft)

Over the air data rate 1–3 Mbit/s 1 Mbit/s

Application throughput 0.7–2.1 Mbit/s 0.27 Mbit/s

Active slaves 7 Not defined; implementation dependent

Security56/128-bit and application layer user defined

128-bit AES with Counter Mode CBC-MAC and application layer user defined

RobustnessAdaptive fast frequency hopping, FEC, fast ACK

Adaptive frequency hopping, Lazy Acknowledgement, 24-bit CRC, 32-bit Message Integrity Check

Latency (from a non-connected state)

Typically 100 ms 6 ms

Total time to send data (det.battery life)

100 ms 3 ms

Voice capable Yes No

Network topology Scatternet Scatternet

Power consumption 1 W as the reference 0.01 to 0.5 W (depending on use case)

Peak current consumption

<30 mA <15 mA

Service discovery Yes Yes

Profile concept Yes Yes

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