BLE/Wifi/Lora

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# 181U Spring 2020
## Low Energy Wireless Communications (BLE and Lora)

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- 181U
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# Agenda

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* Battery powered devices require low-energy radio
* Bluetooth Low Energy -- short distance, medium throughput
* LoRa -- long distance, very-low throughput

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# Bluetooth Low Energy (BLE)

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* Based on IEEE 802.15.1
* Subset of Bluetooth 4.0
* Smart Mesh
* Wide OS support
* Used in smartphones, tablets, smart watches, ...

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# BLE Relationship to Bluetooth

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* New
   - efficient discovery/connection procedures
   - very short packets
   - asymmetric design for peripherals
   - client/server architecture
* Old
   - Reuse Bluetooth radio architecture
   - Reuse logical and physical transports

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# Basic Concepts

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* Everything has **State**
  - server devices expose their state

* Clients can use the state exposed on servers
  - read: e.g., get current temperature
  - write: e.g., increase set point temperature

* Servers can notify clients when state updates

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# Stack Architecture

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# Physical Layer

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* Uses 2.4 GHz ISM Band
   - Industrial Scientific Medical band
   - License Free – with certain rules
   - 2400 MHz to 2483.5 MHz
* Used by many other standards
   - IEEE 802.11, IEEE 802.15
   - and many proprietary radios

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# 40 Physical Channels

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# Phy Summary

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* 2.4 GHz GFSK
* 40 channels
   - 2 MHz channel spacing
   - 2402 MHz to 2480 MHz
* Range
   - 50m to further than 150 m

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# Link Layer

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* Link Layer State Machine
   - can have multiple state machines active in device
* Link Layer Channels
   - Advertising Channels & Data Channels
   - Advertising Packets & Data Packets
* Link Layer Control Procedures

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# Link Layer State Machine

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# Link Layer Channels

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* Advertising Channels
  - Advertising Channel Packets
  - Used for Discoverability / Connectability
  - Used for Broadcasting / Observing
* Data Channels
  - Data Channel Packets
  - Used to send application data in Connection

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# Link Layer Channels

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# Scanning

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(Passive scanning shown; another mode is active scanning)

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# Connections

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# Topology

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# Connections

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* Used to send application data
reliably, robustly
* Includes
  - ultra low power connection mode
  - adaptive frequency hopping
  - connection supervision timeout

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# Connection Events

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# Maximum Data Rate

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* Asymmetric Tx/Rx Packet Sequence
  - 328 + 150 + 80 + 150 = 708 μs
* Transmitting 27 octets of application data
  - ~305 kbps

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# Link Layer Encryption

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Uses AES 128 encryption block and CCM as defined by RFC 3610

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# Attribute Protocol

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# Attribute Protocol (ATT)

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* Client Server Architecture
  - servers have data
  - clients request data to/from servers
* Protocol Methods
  - request, response, command,
  - notification, indication, confirmation
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# Servers Expose Data Using Attributes

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* Attributes have values
  - array of octets
  - 0 to 512 octets in length
  - can be fixed or variable length

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# Attributes are Addressable

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* Each attribute has a “handle”
  - used to address an individual attribute by a client
* Clients use handles to address attributes
  - Read (0x0022) => 0x04 ; Read (0x0098) => 0x0802

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# Attributes are Typed

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* Attributes have a type
  - type is a «UUID», determines what the value means
* Types are defined by “Characteristic Specifications”
  - or Generic Access Profile or Generic Attribute Profile

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# Attributes are Typed (Example)

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* «Battery State»
* defined by “Battery State Characteristic” specification
  - enumerated value
      -0x04 = Discharging

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# Attribute Permissions

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* Attributes values may be:
  - readable / not readable
  - writeable / not writeable
  - readable & writeable / not readable & not writeable
* Attribute values may require:
  - authentication to read / write
  - authorization to read / write
  - encryption / pairing with sufficient strength to read /
write

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# Protocol Methods

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# Generic Attribute Protocol (GATT)

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BLE is complicated by many pre-defined *profiles*.  If you want to build a "standard" device (for example a thermostat), this simplifies the process.  Introducing a new type of device is *complicated*.

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# Generic Access Profile

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Generic access profile (and protocols) define the  ways clients and servers interact.

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# Building Applications -- Two Approaches

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* Use Standard Services
  - defined by Bluetooth SIG
  - includes lots of useful things
     - battery
     - heart rate
     - temperature
  - Great interoperability
  - Vast “app” ecosystem

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* Define Your Own Service
  - using 128-bit UUIDs
  - you can do what you want
     - motor controls
     - custom sensors
     - calibration
  - Closed ecosystems
  - Few supporting apps

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# The Energy-Range Tradeoff

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BLE is low energy, but limited range (10's of meters)

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# LoRa and SigFox Offer an alternative

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These technologies trade bit-rate for range.  Very useful for slowly changing sensors.

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# Link Budget is measured in dBM

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# LoRa allows trading bit-rate for range

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# Relationship between bit rate and range

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# There is no free lunch !

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# LoRa is based on a clever modulation strategy

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# LoRa Physical Layer

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# Spreading factor vs Duration

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# LoRaWAN

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# LoRaWAN Architecture

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# WaziUP

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# WaziUP Platform

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# Summary

* Acknowledgements -- Slide Material drawn from:
   - "Wireless standards for IoT" by Ermanno Pietrosemoli: http://wireless.ictp.it/school_2019/slides/WirelessstandardsforIoT.pdf
   - "An Introduction to Bluetooth low energy" by Robin Heydon: https://datatracker.ietf.org/meeting/interim-2016-t2trg-02/materials/slides-interim-2016-t2trg-2-7
   - "Low-power, long-range radio technologies for Internet-of-Things" by IRD/UMMISCO–Yaoundé: http://cpham.perso.univ-pau.fr/LORA/WAZIUP/UMMISCO-LPWAN-review.pdf
   - Cover image "https://www.led-professional.com/technology/standardization/zigbee-alliance-and-thread-group-join-force#&gid=1&pid=1"
   - "WAZIUP: A low-cost infrastructure for deploying IoT in developing countries", Congduc Pham, AbdurRahim, Philippe Cousin.  AFRICOMM16

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181U Spring 2020

Low Energy Wireless Communications (BLE and Lora)

Agenda

Bluetooth Low Energy (BLE)

BLE Relationship to Bluetooth

Basic Concepts

Stack Architecture

Physical Layer

40 Physical Channels

Phy Summary

Link Layer

Link Layer State Machine

Link Layer Channels

Link Layer Channels

Scanning

Connections

Topology

Connections

Connection Events

Maximum Data Rate

Link Layer Encryption

Attribute Protocol

Attribute Protocol (ATT)

Servers Expose Data Using Attributes

Attributes are Addressable

Attributes are Typed

Attributes are Typed (Example)

Attribute Permissions

Protocol Methods

Generic Attribute Protocol (GATT)

Generic Access Profile

Building Applications – Two Approaches

The Energy-Range Tradeoff

LoRa and SigFox Offer an alternative

Link Budget is measured in dBM

LoRa allows trading bit-rate for range

Relationship between bit rate and range

There is no free lunch !

LoRa is based on a clever modulation strategy

LoRa Physical Layer

Spreading factor vs Duration

LoRaWAN

LoRaWAN Architecture

WaziUP

WaziUP Platform

Summary

Agenda

Help