RTT-aware scheduling of downlink transmissions to energy-constrained devices on low-power wide-area networks

A method, comprising:

• determining, at a backend server, one or more radio frequency (RF) gateways that are candidates for communicating with an end device over a RF link in a low-power wide-area network (LPWAN), the end device being energy-constrained and configured to listen for downlink communications only during pre-specified time slots after uplink transmission by the end device;
• obtaining, at the backend server, for each of the one or more RF gateways, a round trip time (RTT) of communications between the backend server and the RF gateway over a backhaul link;
• determining, at the backend server, whether at least one of the one or more RTTs exceeds a threshold value that is less than or equal to a configured time interval for the end device, the configured time interval corresponding to a time between transmission of an uplink message by the end device and a downlink receive time slot in which the end device is configured to listen for a downlink message, scheduled by the backend server, that is transmitted by the one or more RF gateways;
• and
• in response to determining that at least one of the one or more RTTs exceeds the threshold value, increasing, at the backend server, the configured time interval.

A backend server, comprising:

• one or more processors;
• and
• one or more non-transitory computer-readable storage medium storing instructions that, when executed by the one or more processors, cause the backend server to perform operations comprising:
• determining a first plurality of radio frequency (RF) gateways that forwarded to the backend server an uplink message transmitted by an end device over a RF link in a low-power wide-area network (LPWAN), the end device being energy-constrained and configured to listen for downlink communications only during pre-specified time slots after uplink transmission by the end device;
• determining one or more RF gateways of the plurality of RF gateways that are eligible to send a downlink message to the end device over the RF link;
• obtaining, for each of the one or more RF gateways, a round trip time (RTT) of communications between the backend server and the RF gateway over a backhaul link;
• determining whether any of the one or more RTTs exceeds a threshold value that is less than or equal to a configured time interval, the configured time interval corresponding to a time between transmission of the uplink message by the end device and a first downlink receive time slot of one or more downlink receive time slots in which the end device is configured to listen for a downlink message;
• in response to determining that none of the RTTs exceeds the threshold value, scheduling, based at least on the one or more RTTs, the one or more downlink receive time slots of the end device for a first RF gateway of the one or more RF gateways to transmit a downlink message to the end device;
• and
• transmitting the downlink message from the backend server to the first RF gateway to send to the end device during the one or more downlink receive time slots.