Bluetooth Harrison Dempsey, Prateek Jain, Jeremy Maurice, Oliver - - PowerPoint PPT Presentation

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Bluetooth Harrison Dempsey, Prateek Jain, Jeremy Maurice, Oliver - - PowerPoint PPT Presentation

Mar 05, 2024 416 likes •698 views

Bluetooth Harrison Dempsey, Prateek Jain, Jeremy Maurice, Oliver Miles Outline: What were going to tell you I. Brief overview of wireless technologies II. What is Bluetooth? Why do we use it? III. Specification overview - radio band,

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Bluetooth

Harrison Dempsey, Prateek Jain, Jeremy Maurice, Oliver Miles

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Outline: What we’re going to tell you

I. Brief overview of wireless technologies II. What is Bluetooth? Why do we use it? III. Specification overview - radio band, range, and power IV. Bluetooth Profiles V. Data transfer - Packets and Frequency Hopping VI. Networks - Pairing and Piconets

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

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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

3

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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.

4

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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”

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

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What is Bluetooth?

  • Convenient connections

between devices - “piconet”

  • Ubiquitous
  • Common uses

○ Device control ○ File transfer

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

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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

7

Disadvantages

  • Security

○

Blueborne - BT stack vulnerabilities allowed for devices to be compromised without being paired

  • Interference

○

2.4 GHz

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Why do we use Bluetooth?

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

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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

10

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Bluetooth Profiles

What 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.

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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

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Example:

Bluetooth Profiles in Google Nexus/Pixel phones

13

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

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Packet Timing

  • Time Division Duplex (TDD)

○ Master and slave alternate transmitting and receiving ○ Master transmits during even-numbered slots ○ Slave transmits during

  • dd-numbered slots

14

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

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Packet Structure

  • Access Code used for

packet identification

  • Header contains

device address, type

  • f transmission, etc.
  • Payload contains data

transmission

15

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

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Packets

  • Packets can be 1, 3,
  • r 5 “hops” long
  • Analogous to the

“burst” feature of the AHB

16

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

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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

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

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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 and

Adaptation Protocol (L2CAP)

○ Interface with host controller

https://www.engineersgarage.com/articles/bluetooth-protocol-basics-working 19

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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

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

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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

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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

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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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25

Questions?

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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

26

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