Minimizing Age in Gateway Based Update Systems
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We consider a network of status updating sensors whose updates are collected and sent to a monitor by a gateway. The monitor desires as fresh as possible updates from the network of sensors. The gateway may either poll a sensor for its status update or it may transmit collected sensor updates to the monitor. We derive the average age at the monitor for such a setting. We observe that increasing the frequency of transmissions to the monitor has the upside of resetting sensor age at the monitor to smaller values. However, it has the downside of increasing the length of time that elapses before a sensor is polled again. This motivates our investigation of policies that fix the number of sensors they poll before transmitting to the monitor. For such policies, we show that when sensor transmission times to the monitor are independent and identically distributed (iid), for independent but possibly non-identical transmission times to the monitor, it is optimal to poll a sensor with the maximum age at the gateway first. For non-identical sensor transmission times, we consider a slight variant that polls a sensor such that the resulting average change in age is minimized. We compare our proposals with other policies that pick the frequency of transmission to the monitor and choose sensors to poll differently.
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