LoRaWAN Dwell Time Specification & its application

Dwell Time : It refers to maximum amount of time wireless device is allowed to transmit at specific frequency channel continuously. It is measured in units of milliseconds or seconds. It is defined by regulatory bodies such as FCC or ETSI.

LoRaWAN uses unlicensed ISM bands and hence the channel is shared among many devices or users. To prevent congestion of channel and to avoid spectrum misuse, it is very essential to limit how long the device can occupy the channel.

Dwell Time in LoRaWAN

• For US region (US915/AU915 Band), it is typically about 400 ms per transmission for channels 0-63.
• For EU region (EU868 band), there is no limit on dwell time; it is defined with respect to its duty cycle counterpart. Duty cycle of 1% is specified and it comes out to be only 36 seconds of transmission per hour per channel.
• Other regions : For Asia (AS923 band), it is about 400 ms. For china, there is no dwell time limit but regional variations exist.

Example : For SF10, 51 byte payload fits within about 400 ms dwell time. Larger payload would exceed this limit and hence are not allowed in this SF10.

• Dwell time limits affect maximum payload size, data rate and duty cycle.
• Firmwware of the end device must be designed to take care of dwell time specification to remain compliant.
• LoRaWAN networks may adapt spreading factor (SF) and payload size to stay within dwell time limits.

Conclusion : As mentioned it defines transmit duration per channel. It is enforced by regulations. It ensures fair use of spectrum and determines payload limits in LoRaWAN system.