DRX (Discontinuous Reception) is a power-saving feature used in LTE (Long-Term Evolution) networks to reduce power consumption in mobile devices by periodically turning off the radio when there is no data to be transmitted or received.

With DRX, a mobile device can inform the network that it is going to sleep for a certain period of time, during which the network will buffer any incoming data until the device wakes up. This reduces the need for the device to continuously monitor the network, which can lead to significant power savings.

In LTE, there are several types of DRX modes, including DRX for idle mode and DRX for connected mode. In idle mode DRX, the device periodically wakes up to check for paging messages from the network, while in connected mode DRX, the device enters a sleep mode while waiting for data to be transmitted from the network.

DRX can significantly extend the battery life of mobile devices, especially in applications where the data traffic is intermittent, such as voice calls or messaging applications. However, it can also introduce delays in data transmission, as the network has to buffer data until the device wakes up, which may not be suitable for applications that require real-time data transmission, such as video streaming or online gaming.

To extend UE’s battery lifetime, a RRC connected UE may be configured with a Discontinuous Reception (DRX) cycle.

DRX configuration in LTE involves setting the parameters that determine when and how long a mobile device will enter sleep mode. These parameters are typically configured by the network operator and can vary depending on the specific network deployment and device characteristics.

The main DRX parameters that need to be configured include (3GPP TS 36.321 version 13.3.0 Release 13):

DRX cycle: This parameter defines the period of time during which the device will stay awake before entering sleep mode. The DRX cycle can range from a few milliseconds to several seconds, depending on the network configuration.

DRX on duration: This parameter determines how long the device will stay awake before entering sleep mode. The on duration can vary from a few milliseconds to several seconds, depending on the network configuration.

DRX inactivity timer: This parameter sets the time period during which the device will remain in sleep mode before waking up to check for incoming data. The inactivity timer can range from a few seconds to several minutes, depending on the network configuration.

DRX guard timer: This parameter defines the period of time during which the device will remain in sleep mode after detecting an incoming data transmission. The guard timer is used to ensure that the device remains in sleep mode long enough to conserve power, while still allowing sufficient time for the network to send the buffered data to the device.

The DRX retransmission Timer: The DRX retransmission timer is a parameter used in LTE networks to ensure reliable transmission of data between the mobile device and the network. This timer determines the time period during which the network will attempt to retransmit data that has been lost or corrupted during transmission. It indicates the maximum number of subframes for which UE should be monitoring PDCCH when a retransmission from the eNodeB is expected by the UE.

Short DRX (Discontinuous Reception) cycle: Short DRX (Discontinuous Reception) cycle is a mechanism used in LTE networks to reduce the latency of data transmission and conserve power in mobile devices. Short DRX cycle is a shorter version of the regular DRX cycle, which is used when the mobile device has data to transmit or receive and needs to stay active for a shorter duration. In a regular DRX cycle, the mobile device periodically wakes up to check for incoming data, which can lead to higher latency and power consumption. However, in a short DRX cycle, the device wakes up more frequently, but for a shorter duration, to check for incoming data. This helps to reduce the latency of data transmission and conserve power, as the device spends less time in the active state.

RRC Connection Reconfiguration for DRX Setting

dedicatedInfoNASList: 1 item
Item 0
DedicatedInfoNASList: 27b**********************9020000****00000…
mac-MeasConfig: explicitValue (0)
explicitValue

ul-SCH-Config
…
drx-Config: setup (1)
setup
onDurationTimer: psf6 (5)
drx-InactivityTimer: psf1920 (20)
drx-RetransmissionTimer: psf16 (5)
longDRX-CycleStartOffset: sf1280 (13)
sf1280: 0
shortDRX
shortDRX-Cycle: sf10 (3)
drxShortCycleTimer: 10 shortDRX-Cycles 

figure reference :  www.sharetechnote.com

DRX Supportability in UE Capability Information

DRX Command MAC Control Element

eNodeB’s MAC can also control UE’s DRX behaviour by transmitting a command called DRX Command as a MAC Control Element apart from UE timers which has been configured in RRC reconfiguration,

When there is no data transmission from eNodeB side ,eNodeB transmit DRX Command MAC CE to the UE.

Once DRX Command MAC CE received, the UE enters short DRX cycle if configured, otherwise, the UE enters long DRX cycle.

In below table we can see the LCID mapped to DRX Command MAC Control Element

CDRX (Connected Mode DRX)

CDRX (Connected Mode DRX) is a mechanism used in LTE networks to reduce the power consumption of mobile devices while maintaining connectivity to the network. CDRX is used when a mobile device is in a connected state with the network, and is actively sending or receiving data.

In CDRX, the mobile device periodically enters a low-power sleep mode, known as DRX mode, while still maintaining the connection to the network. During DRX mode, the device does not receive any data, but periodically wakes up to check for incoming data. This helps to reduce power consumption in the device, while still maintaining connectivity to the network.

Fig reference : http://www.simpletechpost.com/

CDRX is an extension of the DRX mechanism used in LTE networks to reduce power consumption in mobile devices. CDRX is used when the mobile device is in a connected state and actively transmitting or receiving data.

The device then periodically enters DRX mode during periods of inactivity, while still maintaining the connection to the network.