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