LoraWan
Low Range communication
Low power

=====components=====
  * end devices
  * Gateways
  * lorawan network server
  * applications
  
  
lora is the physical layer ultra low power consumption
long range -  small bandwidth
lorawan mac media access control

{{:lorawan:screenshot_from_2023-04-17_23-15-54.png?400|}}

devicese usually are asleep

only enable wifi when it needs to send a lot of information

frequency  on a free spectrum 
for example:
  eu 863 to 870 mhz, 433 to 434 mhz
  china 779 to 787
  us 902 to 928
  australia 915 to 928
  + many others
  
modulation: chirp spectrum modulation
{{:lorawan:screenshot_from_2023-04-17_23-28-25.png?400|}}

super robust on interference because ti change modulation, differently from narrowband

{{:lorawan:screenshot_from_2023-04-17_23-30-48.png?400|}}

differences between end devices and a gateway is that the gateway can listen on multiple frequency at the same time


uplink from device to gateway

downlink from gateway to device


====spreading factor====
number of databit per second: the symbols that are modulated per time units  
the higher is the spreading factor, the slower is the communication


lower SF -> Shorter range -> less time on air -> lower energy consumption -> higher data rate

{{:lorawan:screenshot_from_2023-04-17_23-39-08.png?400|}}


=====Adaptive Data Rate mechanism=====
minute 13:00 2 lorawan fundamentals


=====what is lorawan=====lora
lorawan is a protocol based on 

example of frequency plan
in usa

US915 is from 902 to 928 Mhz

fixed number of channels; 
for uplink on perspective of end device
  * 64 channels of 125khz BW
  * 8 channels of 500khz BW
for downlink
  * 8 channles of 500khz BW (to end devices)

=====class devices=====
Class A: 
  * implemented by all end devices
  * end devices start transmissions 
  * for example: every devices at any time can send an hearthbeat like : hey i'm here and my battery life is...

class B:
  * transmission initiated by the end deice or o- n fixed interval - by network
  beaconing - segnalazione - sent by network at fixed interval through the gateway
  for example my end device wake up every 2 minutes to check if network want to start a downlink or not. 

class C:
  * transmission initiated by the network at any time
  continuos downlink: end devices continue to check if network wants to send a message to the end device
  it can be an end devices connected to electrical source, like street light


{{:lorawan:screenshot_from_2023-04-19_22-29-19.png?400|}}

handlinkg downlink based on different class:

{{:lorawan:screenshot_from_2023-04-19_22-40-30.png?400|}}


=====limitations=====
  * limited payload 51-241 bytes depending on data rate (they send json)
  * low data rates - max 5.5kbps on 125khz
  * region specific rules 
    - EU duty cycle restrictions
    - US dwell time restrictions 
  * asynchronous communications - more uplink then downlink capacity


=====security in lorawan=====
physical layer doesn't provide security mechanisms
it only has an optional crc field that helps detecting transmission errors

lorawan provides security with the 3 pillars of security:
  * Authenticity - every device are authenticate 
  * Integrity - no intermediate can modify the message
  * Confidentiality - on the application layer we can encrypt the data so nobody can understand the payload
 

two layer security with aes encryption algorithm

  * 128-bit network session key - authentication, integrity
  * 128-bit for application session key - confidentiality
{{:lorawan:screenshot_from_2023-04-19_22-54-38.png?400|}}


=====sessions=====
network sessions:
  * device address devaddr
  * network session key nwkskey
  * frame counters fcntup fcntdown
  * mac state - channels, data rate, etc

application session - between end device and application server
  * application session key appskey
  * frame counters fcntup fcntdown

during a lorawan session:
  * session keys remain the same
  * frame counters are incremented and never reused

a session can be 
  * dynamically established joining a network OTAA over the air activation
  * hardcoded (apb activation by personalization)

  devaddr and security keys are hardcoded into device