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Tag: LoRa

Cayenne Low Power Payload

Overview

The Cayenne Low Power Payload (LPP) provides a convenient and easy way to send data over LPWAN networks such as LoRaWAN. The Cayenne LPP is compliant with the payload size restriction, which can be lowered down to 11 bytes, and allows the device to send multiple sensor data at one time.

Additionally, the Cayenne LPP allows the device to send different sensor data in different frames. In order to do that, each sensor data must be prefixed with two bytes:

  • Data Channel: Uniquely identifies each sensor in the device across frames, eg. “indoor sensor”
  • Data Type: Identifies the data type in the frame, eg. “temperature”.

Payload structure

1 Byte1 ByteN Bytes1 Byte1 ByteM Bytes
Data1 Ch.Data1 TypeData1Data2 Ch.Data2 TypeData2

Data Types

Data Types conform to the IPSO Alliance Smart Objects Guidelines, which identifies each data type with an “Object ID”. However, as shown below, a conversion is made to fit the Object ID into a single byte.

LPP_DATA_TYPE = IPSO_OBJECT_ID - 3200

Each data type can use 1 or more bytes to send the data according to the following table.

TypeIPSOLPPHexData SizeData Resolution per bit
Digital Input32000011
Digital Output32011111
Analog Input32022220.01 Signed
Analog Output32033320.01 Signed
Illuminance Sensor33011016521 Lux Unsigned MSB
Presence Sensor33021026611
Temperature Sensor33031036720.1 °C Signed MSB
Humidity Sensor33041046810.5 % Unsigned
Accelerometer33131137160.001 G Signed MSB per axis
Barometer33151157320.1 hPa Unsigned MSB
Gyrometer33341348660.01 °/s Signed MSB per axis
GPS Location3336136889Latitude : 0.0001 ° Signed MSB
Longitude : 0.0001 ° Signed MSB
Altitude : 0.01 meter Signed MSB

Examples

Device with 2 temperature sensors

Payload (Hex)03 67 01 10 05 67 00 FF
Data ChannelTypeValue
03 ⇒ 367 ⇒ Temperature0110 = 272 ⇒ 27.2°C
05 ⇒ 567 ⇒ Temperature00FF = 255 ⇒ 25.5°C

Device with temperature and acceleration sensors

Frame N

Payload (Hex)01 67 FF D7
Data ChannelTypeValue
01 ⇒ 167 ⇒ TemperatureFFD7 = -41 ⇒ -4.1°C

Frame N+1

Payload (Hex)06 71 04 D2 FB 2E 00 00
Data ChannelTypeValue
06 ⇒ 671 ⇒ AccelerometerX: 04D2 = +1234 ⇒ +1.234G
Y: FB2E = -1234 ⇒ -1.234G
Z: 0000 = 0 ⇒ 0G

Device with GPS

Payload (Hex)01 88 06 76 5f f2 96 0a 00 03 e8
Data ChannelTypeValue
01 ⇒ 188 ⇒ GPSLatitude: 06765f ⇒ 42.3519
Longitude: F2960a ⇒ -87.9094
Altitude: 0003E8 ⇒ 10 meters

Source : https://github.com/myDevicesIoT/cayenne-docs/blob/master/docs/LORA.md#lora-cayenne-low-power-payload-data-types

LoRaWAN End Devices

End Devices

The LoRaWAN specification defines three device types. All LoRaWAN devices must implement Class A, whereas Class B and Class C are extensions to the specification of Class A devices.

Class A devices support bi-directional communication between a device and a gateway. Uplink messages (from the device to the server) can be sent at any time (randomly). The device then opens two receive windows at specified times (1s and 2s) after an uplink transmission. If the server does not respond in either of these receive windows (situation 1 in the figure), the next opportunity will be after the next uplink transmission from the device. The server can respond either in the first receive window, or in the second receive window, but should not use both windows.

Class A Receive Windows

Class B devices extend Class A by adding scheduled receive windows for downlink messages from the server. Using time-synchronized beacons transmitted by the gateway, the devices periodically open receive windows.

Class C devices extend Class A by keeping the receive windows open unless they are transmitting, as shown in the figure below. This allows for low-latency communication but is many times more energy consuming than Class A devices.

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