Meaning
Reference timestamps for synchronized broadcast transmissions define the starting boundary from which a low power wide area network endpoint schedules its downlink reception windows. By aligning with the lorawan class b epoch, the endpoint can open periodic receive slots.
Broadcast Synchronization
The gateway transmits a synchronization frame at regular intervals to maintain time synchronization across all Class B devices. Each synchronization frame contains a timestamp that aligns the local clock of the endpoint with the lorawan class b epoch. If the device misses several broadcast signals, its internal clock drifts, causing it to miss the scheduled downlink slots because of timing misalignment.
This misalignment requires a fresh search sequence.
Slot Calculation
Reception windows are calculated as offsets from the synchronization interval. The formula uses the device address and frame number to randomize slot positions. This calculation depends entirely on a shared understanding of the lorawan class b epoch by both parties.
Power Management
Reducing the time spent listening for broadcast signals is the primary method of extending battery life in Class B endpoints. When the device is synchronized, the receiver is active for only a few milliseconds per slot. If synchronization to the lorawan class b epoch is lost, the device must enter a high power continuous receive state to capture the next synchronization frame, which significantly increases the average current draw.
