Duty cycle is the ratio of on-time to total time, and it appears in three places. In PWM, it sets how much power reaches a load. In low-power design, it describes how a device alternates between deep sleep and brief activity; a lower duty cycle means longer battery life but less frequent data. In radio regulation, it caps how much of the time a transmitter may occupy a shared band.
The regulatory sense has real consequences for network design. In parts of the ISM band used by LoRaWAN in Europe, devices and gateways are limited to transmitting for a small percentage of each hour. That limits how often a node can send and how many downlink messages a gateway can serve, which is why LoRaWAN applications are designed to be uplink-heavy and send commands sparingly.
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