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MTN Ghana saves your battery with cDRX technology


In 4G LTE, cDRX lets the phone fall asleep, even while connected. 

cDRX stands for connected mode discontinuous reception. A device remains connected until there is inactivity for 5 seconds.

cDRX only works while connected. In the idle (disconnected) state, only a few features are available (refer to 3GPP TS 36.304). These features include: Taking measurements of the signal; receiving system information; notifying the network after moving into a different area; notifying the network of availability every 54 minutes; and connecting when there is something to do (call, text, or data). Every 0.32 seconds, a phone wakes up to listen for one of the towers in the area possibly requesting it to connect.

While the phone is asleep due to cDRX or otherwise, latency (lag) may occur. This isn't the only reason why it occurs.

What are the conditions required before a phone can fall asleep while connected (cDRX)?

Conditions vary. For example, here are results gathered during a test:

89.79% LTE_cDRX - short_drx_cycle:40, long_drx_cycle:320, on_duration_timer:10, inactivity_timer:200

5.37% LTE_cDRX - No config

1.70% LTE_cDRX - short_drx_cycle:80, long_drx_cycle:320, on_duration_timer:10, inactivity_timer:100

1.18% LTE_cDRX - short_drx_cycle:0, long_drx_cycle:40, on_duration_timer:2, inactivity_timer:30

0.79% LTE_cDRX - short_drx_cycle:40, long_drx_cycle:320, on_duration_timer:5, inactivity_timer:20

0.52% LTE_cDRX - short_drx_cycle:40, long_drx_cycle:40, on_duration_timer:2, inactivity_timer:30

0.39% LTE_cDRX - short_drx_cycle:40, long_drx_cycle:160, on_duration_timer:10, inactivity_timer:100

0.26% LTE_cDRX - short_drx_cycle:40, long_drx_cycle:320, on_duration_timer:200, inactivity_timer:200


What do these mean?

Here is a simplified and context-dependent explanation that does not replace correct explanations (including 3GPP TS 36.321, 3GPP TS 36.300, and 3GPP TS 36.331).

short_drx_cycle: Length of cycle initially used after inactivity, in milliseconds. There may be multiple short drx cycles before long drx cycles are used instead.

long_drx_cycle: Length of long cycle in milliseconds.

on_duration_timer: At the beginning of the cycle, stay awake for __ milliseconds.

inactivity_timer: After receiving instructions (data will be transferred), stay awake for __ more milliseconds.



What about the rest of the cDRX settings?

Those weren't gathered for the statistics above. Here are some of those:

onDurationTimer: psf10 (7)

drx-InactivityTimer: psf200 (15)

drx-RetransmissionTimer: psf2 (1)

longDRX-CycleStartOffset: sf320 (9)

  sf320: ...

shortDRX

  shortDRX-Cycle: sf40 (7)

  drxShortCycleTimer: 4 shortDRX-Cycles


onDurationTimer: psf10 (7)

drx-InactivityTimer: psf100 (14)

drx-RetransmissionTimer: psf8 (4)

longDRX-CycleStartOffset: sf320 (9)

  sf320: ...

shortDRX

  shortDRX-Cycle: sf80 (9)

  drxShortCycleTimer: 1 shortDRX-Cycle


onDurationTimer: psf2 (1)

drx-InactivityTimer: psf30 (9)

drx-RetransmissionTimer: psf2 (1)

longDRX-CycleStartOffset: sf40 (3)

  sf40: ..


And here are the other referenced settings that are not part of cDRX:

defaultPagingCycle: rf32 (0)

nB: oneT (2)


RRC/UE Inactivity Timer: 5 sec, estimated

T3412: 54 min


Some phones and modems may support long cDRX only, some phones and modems may not support cDRX at all.


All settings in this page are subject to change and/or may differ.

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