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If UE is put in IDLE state and can save battery then why we need DRX for the same..

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If UE is put in IDLE state and can save battery then why we need DRX for the same..

posted Apr 15, 2016 by Chotu Vats

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1 Answer

+2 votes

In Idle state no RRC connection exists between the device and the network. However, the device should be able to listen to paging messages (for incoming connections), system information changes or public warning system (PWS) notifications.

Theoretically, there is a paging radio network temporary identifier (P-RNTI) on the physical downlink control channel (PDCCH) every 1 ms. Having to monitor the channel constantly would heavily impact a device’s battery life. Therefore, LTE includes a mode for discontinuous monitoring of the PDCCH for paging messages. This is commonly known as the DRX in idle mode. In this mode, the device only monitors certain subframes in a specific radio frame for its paging message. The reminder of the time, the UE enters sleep mode to conserve battery power.

Now I hope this would clear your doubt.

answer Apr 15, 2016 by Salil Agrawal
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+2 votes
When UE is in the Connected State, How UE could use DRX configuration which is intended to use in IDLE state?

During my study about the measurement and ANR, I have the question. Please help to let me get the proper answer.
[ Condition]
1. UE is in the connected state.
2. UE measures one PCI and reports it to eNB but it does not belong to NRT(Neighbor Relation Table) in eNB.
3. eNB sends rrcConnectionReconfigurationMessage to read CGI for that PCI.
4. UE should read MIB/SIB1 to report CGI info to eNB.

In Step 4), In some materials on the web, UE should use IDLE periods to get SIB1, which is configured as DRX config in rrcConectionReconfigurationMesage. Because Measurement Gap is too short to read MIB/SIB1 and it's only for the measurement purpose.

[Question]
When UE is in the Connected State, How UE could use DRX configuration which is intended to use in IDLE state?

As my basic understanding, DRX configuration is to improve the battery life in idle mode.

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