Bluetooth

Harrison Dempsey, Prateek Jain, Jeremy Maurice, Oliver Miles

Outline: What we’re going to tell you

I. Brief overview of wireless technologiesII. What is Bluetooth? Why do we use it?

III. Specification overview - radio band, range, and power

IV. Bluetooth ProfilesV. Data transfer - Packets and Frequency Hopping

VI. Networks - Pairing and Piconets

2https://nksoldes2015.com/explore/notepad-clipart/

Why do we communicate wirelessly? In general...

Advantages

● More convenient than wires● Sometimes the only option (Ex. long

range, mobile devices)

Disadvantages

● Slower (latency, bandwidth)● Power consumption/battery life

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Here are a few of our options.

● Low power, low bandwidth○ ZigBee○ BLE (Bluetooth Low Energy)

● Moderate power, moderate bandwidth○ Bluetooth

● High power, high bandwidth○ WiFi○ WiMax/RF

Each option has its strengths and weaknesses… let’s look at Bluetooth.

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Background

● Harald “Bluetooth” Gormsson○ King who united Denmark in the 10th century

● Bluetooth Special Interest Group (1994)○ Ericsson, Nokia, IBM, Toshiba, Intel, and more○ Wanted to create a unified standard to exchange

data over short distances○ Initial goal

■ Replace wires■ “Unite devices”

5http://daniel-mccloskey.deviantart.com/art/Harald-Bluetooth-644300366

What is Bluetooth?

● Convenient connections between devices - “piconet”

● Ubiquitous● Common uses

○ Device control○ File transfer

6https://vestavialibrary.org/bluetooth-upgrade-more-speed-greater-range/

In general, Bluetooth finds a useful middle ground:Advantages

● Data transfer bit rate is high enough to perform complex activities ○ Ex. streaming/transmitting

audio with relatively low latency

● Simple pairing process● Commonplace, cheap, standardized

○ Bluetooth Profiles● Moderate power consumption,

range

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Disadvantages

● Security○ Blueborne - BT stack vulnerabilities

allowed for devices to be compromised without being paired

● Interference○ 2.4 GHz

Why do we use Bluetooth?

(https://learn.sparkfun.com/tutorials/bluetooth-basics/wireless-comparison) 8

Specification

● Uses the 2.4 Ghz Industrial, Scientific, and Medical (ISM) radio band○ Goes from 2.402 Ghz to 2.48 Ghz○ 79 one Mhz channels

● 1600 ‘hops’ per second - 625 μsec per hop○ ~200 μsec used for synchronization

● Time Domain Duplex○ Every other hop is assigned to either the master or slave transmission

● Uses frequency hopping to mitigate interference○ Changes frequency for each hop

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Range and Power of Bluetooth Devices

● Class 1 - Laptops / Desktops / Industrial Applications○ 100mW Transmit Power Limit○ Typical range: ~100 m○ Generally requires power isolation to prevent interference

● Class 2 - Phones / Headsets○ 2.5mW Transmit Power Limit○ Typical range: ~10 m

● Class 3 - Extremely low power devices○ 1mW Transmit Power Limit○ Typical Range: ~1 m

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Bluetooth ProfilesWhat is a Bluetooth profile?

● A specification for a type of Bluetooth device defined by Bluetooth SIG○ Defines how the device uses the Bluetooth protocol- which parts of the stack are used?○ Ex. Is the device an audio device? Input device?○ A device can support multiple profiles

● Different profiles for different types of data

Why are Bluetooth profiles important?

● Devices are compatible if they support the same profiles○ Standardized implementation- a device is guaranteed compatibility with other devices of the

same profile.11

Commonly Used Bluetooth Profiles and Examples

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● Audio○ Hands-Free Profile and Headset

Profile■ Hands-free calling■ Earpieces

○ A/V Remote Control Profile■ Car Audio System

○ Advanced Audio Distribution Profile■ Headphones, Microphones

● Device Communication○ Serial Port Profile

■ Communication between Arduino devices

○ Human Interface Device■ Keyboards, mice, game

controllers

Example: Bluetooth Profiles in Google Nexus/Pixel phones

13https://support.google.com/nexus/answer/6048862?hl=en

Packet Timing

● Time Division Duplex (TDD)○ Master and slave alternate

transmitting and receiving○ Master transmits during

even-numbered slots○ Slave transmits during

odd-numbered slots

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http://sna.csie.ndhu.edu.tw/~cnyang/PDF/bt_tut.pdf

Packet Structure● Access Code used for

packet identification● Header contains

device address, type of transmission, etc.

● Payload contains data transmission

15http://www.ques10.com/p/2706/explain-the-frame-format-in-bluetooth-technology-1/

Packets

● Packets can be 1, 3, or 5 “hops” long

● Analogous to the “burst” feature of the AHB

16http://sna.csie.ndhu.edu.tw/~cnyang/PDF/bt_tut.pdf

Frequency Hopping

● The transmitter and the receiver communicate on changing frequency bands○ 79 frequency bands to choose from

● Master device dictates a changing frequency pattern that slave devices follow

● Designed this way to avoid interference with other devices on the ISM spectrum

● Makes data transfer harder to be intercepted

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Frequency Hopping

18https://www.youtube.com/watch?v=CkhA7s5GIGc

The Stack

● Multiple protocols work together for Bluetooth to work● The radio

○ Receive/transmit signals

● Baseband○ Error catching○ Physical linking to all layers

● Link Manager Protocol○ Controls linking between

devices with pairing

● Logical Link Control andAdaptation Protocol (L2CAP)○ Interface with host controller https://www.engineersgarage.com/articles/bluetooth-protocol-basics-working

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Pairing

● Devices make themselves discoverable ○ Identify themselves and their services via

profiles● Can only pair with devices supporting the same

profile● Bond for security and to enable reestablishing a

connection without user input ● Once connection is established and unique

passkeys are exchanged, devices can share data● Convenient replacement for wires, little user

config needed

20http://manuals.denon.com/WMS/DSB-200/EM/ENG/BONDSYaaimogad.html

Pairing Difficulties

● Time○ Pairing is slow

● Older bluetooth devices can take up to 10s to pair!● Newer versions can take up to 5s● Can often edit announcement interval at cost of increased power

○ Increase effective phone battery by broadcasting less frequently○ Could be broadcasting as frequently as every 6ms or as slow as once every 5s○ Can manage in software and disable checking until required by user

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Piconets

● Small local point to point networks● Each Bluetooth piconet can have 7 active

devices ○ 6 slaves and 1 master○ More devices can be connected in either

parked or hold mode and remain synchronized

● One master per piconet but can function as a slave in another piconet○ Forms scatter net○ Time division multiplexed between

piconets

http://sna.csie.ndhu.edu.tw/~cnyang/PDF/bt_tut.pdf 22

Summary: What we have told you

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I. Brief overview of wireless technologies ○ Wireless is convenient but has higher power consumption and is slower

II. What is Bluetooth? Why do we use it? ○ Standardized, cheap middle ground

III. Specification overview - radio band, range, and power ○ Moderate range, low-moderate power consumption

IV. Bluetooth Profiles ○ Profiles guarantee compatibility, different profiles for different types of data

V. Data transfer - Packets and Frequency Hopping○ Frequency hop to avoid interference

VI. Networks - Pairing and Piconets○ Up to 7 device to device connections

References● http://sna.csie.ndhu.edu.tw/~cnyang/PDF/bt_tut.pdf

● https://www.youtube.com/watch?v=sCMDIjbKLb0&t=2s

● http://large.stanford.edu/courses/2012/ph250/roth1/

● https://www.youtube.com/watch?v=CkhA7s5GIGc

● https://learn.sparkfun.com/tutorials/bluetooth-basics/how-bluetooth-works

● http://www.ques10.com/p/2706/explain-the-frame-format-in-bluetooth-technology-1/

● https://www.electronics-notes.com/articles/radio/pll-phase-locked-loop/tutorial-primer-basics.php

● https://www.link-labs.com/blog/types-of-wireless-technology

● https://go.armis.com/hubfs/BlueBorne%20Technical%20White%20Paper.pdf

● https://www.radio-electronics.com/info/wireless/bluetooth/networks-networking-connections-pairing.php

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Questions?

Header Structure

● AM_ADDR is the temporary address for active members of the piconet● TYPE tells the type of data transmission● FLOW/ARQN are for flow and acknowledgement● SEQN is the sequence number for packet ordering● HEC is an error check, packet is discarded if an error is found

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http://www.ques10.com/p/2706/explain-the-frame-format-in-bluetooth-technology-1/