: Only Long DRX Cycle is configured and a PDCCH is received during a cycle (You will notice the real 'ON time' May get extended depending on DRX Inactivity Timer and when the PDCCH is recieved as shown in thick Blue line). : Only Long DRX Cycle is configured and No PDCCH is received during the cycle.
The consecutive number of subframes the UE shall follow the short DRX cycle after the DRX Inactivity Timer has expired(See the figure for below)īefore we go into further detail, let me give you a couple of figures that would help your understanding. Specifies the maximum number of consecutive PDCCH subframes the UE should remain active to wait an incoming retransmission after the first available retransmission timeĭRX cycle which can be implemented within the 'OFF' period of a long DRX Cycle.(See the figure for below) When this timer is on UE remains in 'ON state' which may extend UE ON period into the period which is 'OFF' period otherwise. Specify how long UE should remain 'ON' after the reception of a PDCCH. The duration of 'ON time' within one DRX cycle This is calculated by the subframe time and longdrx-CycleStartOffset)
(This value does not explicitely specified in RRC messages. The duration of one 'ON time' + one 'OFF time'. TimeAlignmentTimerDedicated: infinity (7)įollowing table shows the meaning of each DRX parameters. In reality, Network informs UE of this timing using RRC ConnectionReconfiguration or RRC Connection Setup as follows (Following is the example configuration from RRC ConnectionReconfiguration, but you can do the samething in RRC Connection Setup as well).ĭedicatedInfoNAS: 27bd5ad9de05620ec101050403696d730902000000000000. One solution would be that Network decide when to let UE sleepĪnd when towake it up and inform the timing to the UE using a RRC message. If these two timing does not match, there can be a worst case where UE is awake but Network does not transmit anything or Network transmit something for the UE but UE is in sleep mode. How can we synchronize UE-wakeup timing with Network transmission timing for the UE. DRX is a mechanism in which UE gets into sleep mode for a certain period of time and wake up for another period of time. There may be several ways, but one of the most common way is to use DRX. Then what would be the solution to save the energy on UE side. To it from the network, it would be wasting the energy. If UE is always up even when there is no data being transmitted Logically there is no problem with this, but there would be a practical problem. In normal operation, UE has to be awake all the time and monitor PDCCH for every subframe meaning that it has to be awake all the time since it doesn't know exactly when the network will transmit the data for it. RRC Connection Reconfiguration for DRX Setting
Now let's look into a little bit detailed aspect of CDRX (Connected Mode DRX) operation. This agreement is defined in 3GPP TS36.321 Section 5.7 for connected mode, and TS36.304 To prevent this kind of worst case scenario, UE and Network has a wellĭefined agreement about when UE has to be in sleep mode and when UE has to wake up. In worst case, Network tries to send some data while UE is in sleep mode and UE tries to wake up when there is no data to be recieved. but in reality implemting DRX may not be as simple as you may expected because there should be well designed synchronization between UE and Network. This kind of periodic repeatition of "sleep mode and wake up mode" is called DRX (Discontinous Reception".ĭoes it sound simple ? It may. One of the solution for this is let UE get into sleeping mode for a certain period of time and wake up again checking if there is any data coming from the network and getting into sleeping mode again if there is no data and wake up again. Then what would be the ideal solution for this ? what is the ideal solution to save battery consumption and still does not lose chance of receiving the data that Network sent to UE ? Sounds good, but what if Network tries to send some data to UE while the UE is in the sleep mode ? You may ask "Then why don't UE shut down (getting into a sleep mode) when there is no traffic ?". But being ON all the time would drain the battery. It means UE has to be "ON" all the time even when there is no traffic. At least it should be ready to decode PDCCH. LTE Quick Reference Go Back To Index Home : DRX (Discontinuous Reception) - CDRX (Connected Mode DRX)Įven while there is no traffic between the network and UE, UE has to keep listening to Network.
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