Want to save power on your 5G phone? Wake it up first!

With the development of 5G networks, everyone has felt the convenience of 5G networks, but the high power consumption of terminals under 5G networks has always been a topic that cannot be avoided. In order to improve the energy efficiency of terminals, 5G has introduced many new features.

Earlier, we introduced the UAI (UE Assistance Information) energy-saving technology. You can learn more about this technology through "5G mobile phones consume more power? Don't panic, UAI will help!"

This time, I will introduce another energy-saving technology, WUS (Wake Up Signal). WUS adds a wake-up signal based on C-DRX (Connected Discontinuous reception) to indicate whether the terminal should wake up in the next cycle to monitor the scheduling.

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First, let us introduce the working mechanism of C-DRX.

C-DRX refers to the DRX (Discontinuous reception) function of the terminal in the connected state. C-DRX allows the terminal to periodically enter the sleep state at certain times and not monitor the PDCCH (Physical Downlink Control Channel).

The figure above is an example of a typical DRX cycle.

• On Duration: Active state, the terminal will remain awake and receive PDCCH.
• Opportunity for DRX: Sleep state, the terminal is asleep and does not receive PDCCH. The extent to which the terminal can save power depends on the length of this period of time.

This mechanism allows the terminal to wake up and sleep periodically, but in actual application scenarios, the terminal will not continuously send or receive data, that is, in most of the wake-up phases, the terminal will not receive PDCCH. For example, when we are reading a cached web page on a mobile phone, there is no need to interact with the network.

If the terminal still wakes up periodically, it will cause additional power consumption. Therefore, based on the original C-DRX mechanism, in order to further optimize the power consumption of the terminal, the WUS function was proposed in 3GPP 5G R16.

The base station sends DCI 2-6 to inform the terminal in advance whether it needs to wake up and monitor PDCCH during the C-DRX On Duration. If it does not need to wake up, the PDCCH monitoring time can be further reduced to improve power saving performance.

So what is WUS?

WUS is the wake-up signal. This "signal" is a special PDCCH, which is scrambled by Ps-Rnti. WUS is sent by the base station side before the DRX On Duration to indicate whether the terminal should wake up at the next DRX On Duration. As mentioned above, in C-DRX, the terminal will wake up periodically to monitor whether there is PDCCH. WUS is based on C-DRX, adding such a signal to indicate whether the terminal should wake up in the next period to monitor PDCCH.

As shown in the figure, after supporting the WUS function, the base station can send WUS before the DRX On Duration. The base station sends WUS to the terminal through DCI 2-6, and determines whether the terminal wakes up in the next DRX On Duration by detecting the value of Wake Indication in DCI 2-6.

If Wake Indicator Not Allow = 1 is detected, the terminal should be woken up and monitor the PDCCH situation, such as traditional C-DRX.

If WakeIndicatinotallow=0 is detected, the terminal may skip the entire C-DRX cycle and does not detect any PDCCH.

In the traditional C-DRX cycle, the terminal is always active during the On Duration period and needs to wake up to monitor the PDCCH even if there is no data.

After the WUS function is introduced, the base station side will inform the terminal whether it needs to wake up during the On Duration period through DCI 2-6 before the On Duration is activated. If it does not need to wake up, the terminal will not wake up during the On Duration period of the DRX cycle, that is, the terminal will no longer monitor the PDCCH during the entire DRX cycle, which is more power-saving than traditional C-DRX.

This is the end of the introduction to WUS functions. If you want to know more about other technologies, you can leave a comment and I will continue to introduce them to you.