Sub-GHz Statutory Duty Cycle Limits in Industrial Telemetry
Statutory duty cycle limits capping airtime at 0.1 to 10 percent govern sub-GHz telemetry, requiring precise packet timing to avoid legal non-compliance.
Spreading Factor Airtime
Meaning
The duration that a radio transmission occupies a frequency channel is directly linked to the configuration of its chirp modulation parameters. This duration, known as spreading factor airtime, represents the time on air required to transmit a packet of a given size at a specific spreading factor. It dictates the maximum packet throughput and power consumption of a wireless node.
Physical Mechanics
In chirp spread spectrum modulation, the spreading factor determines the number of chirps used to represent a single piece of data. A higher setting increases the spreading factor airtime because the receiver needs more time to integrate the incoming signal and decode it against the noise floor. While this mechanism improves the receiver sensitivity and extends the communication range, it also locks the channel for a longer duration.
Consequently, the device spends more time in active transmission mode, drawing more current from the system power supply.
Network Planning
Network operators must manage the distribution of these settings across a fleet of devices to optimize channel utilization and prevent collisions. Since a higher spreading factor airtime reduces the overall capacity of the cell, the gateway must dynamically allocate the lowest viable spreading factor to each device. This allocation is managed through adaptive data rate algorithms that assess the signal-to-noise ratio of the incoming transmissions.
The resulting adjustments balance signal coverage against the available channel capacity.
System Efficiency
Hardware developers must minimize packet sizes when using high spreading factors to keep the transmission duration within acceptable limits. A lower spreading factor airtime reduces the collision probability in dense networks and saves battery energy by returning the transceiver to sleep mode sooner. Engineers document these duration calculations in the handover documentation to verify compliance with local duty cycle regulations.
This verification ensures that the hardware performs reliably without exceeding regional operational limits.