What is eDRX?

eDRX stands for Extended Discontinuous Reception. It is an extension of the DRX feature that is used by IoT devices to reduce power consumption. DRX is a mechanism in which a device goes into sleep mode for a certain period and then wakes up after a fixed interval to receive signals. The basic principle for eDRX is to extend DRX cycles to allow a device to remain in a power-saving state for a longer period of time. eDRX can be used with or without power save mode (PSM) to obtain additional power savings. Power Save Mode (PSM) is a feature of a cellular modem that turns off the device radio and puts the device to sleep without the need of reconnecting itself to the network when it next wakes up. It only reconnects to the network when required. Re-connecting to a network increases energy consumptions and PSM helps in reducing that. eDRX was developed by mobile network standardization body 3GPP and introduced in 3GPP Rel.13.

Extended Discontinuous Reception is a mode that improves power efficiency for cellular devices by reducing the chattiness between the device and the network. With eDRX, the device can listen for pending data indications without having to establish a full network connection. By just listening for a pending data indication, eDRX uses less power than if it made a full network connection. The time needed for this listening process is also much shorter than the time it takes to make a full network connection.

For example, a normal LTE device is required to be active for a paging cycle every 1.28 seconds. Paging in the LTE network is used to inform and notify the device about various events. An LTE device that leverages eDRX is only required to be active for a paging cycle every 10.24 seconds. This means a device that is connected to the network and communicating or idle is required to be in an active, power-consuming state for about 10x less time, compared to devices that don't support this mode. eDRX also allows the device to tell the network that it would like to skip some pre-determined number of these 10.24 s cycles, extending paging intervals to 40 minutes or more. Hence eDRX facilitates reduced power consumption for devices that are awake and connected/idle with the network.

Earlier the time duration that a device would sleep before waking up was dictated by the network. With eDRX the device, rather than the network, chooses the duration it will sleep, a period referred to as the eDRX cycle. Since a device is not reachable when it is sleeping, the time to reach a device depends on how long the application developer sets the eDRX cycle. This ability to set the length of the eDRX cycle provides IoT application developers with a lot more flexibility when it comes to balancing a device’s reachability versus its battery consumption. For example, if the application chooses an eDRX cycle of 82 seconds when a cloud service sends the device a command (e.g. report user’s location), it could take up to 82 seconds for the device to get that command before it would report its location. This delay is often referred to as mobile terminated latency.