How 5G Can Improve the Battery Life of User Equipment

5G enables more timely data scheduling and larger bandwidths than its predecessors, bringing lower latency and faster data rates. However, users will find that when they opt to use 5G, it consumes more power in user equipment (UEs) than other legacy radio access technologies (RATs). So, the battery life of UEs needs to be improved so that users can enjoy 5G’s benefits without worrying about power consumption. But this cannot be done just by improving UEs. In this article, I will talk about how 5G networks have improved power saving for UEs.

RRC_INACTIVE State

A UE can access network services only if it establishes a radio resource control (RRC) connection with the base station. In legacy RATs, a UE is either in the RRC_CONNECTED state (it has an RRC connection) or the RRC_IDLE state (it does not have an RRC connection). However, transitioning from the RRC_IDLE state to the RRC_CONNECTED state takes a long time, so it cannot meet the low latency requirement of some 5G services. But a UE cannot just stay in the RRC_CONNECTED state because this will consume much more UE power.

To solve this problem, 5G introduces the RRC_INACTIVE state, where the RRC connection is released but the UE context is retained (called RRC Release with Suspend), so an RRC connection can be quickly resumed when needed. This way, a UE in the RRC_INACTIVE state can access low-latency services whenever needed but consume the same amount of power as it does in the RRC_IDLE state.

DRX + WUS

Discontinuous reception (DRX) enables a UE in the RRC_CONNECTED state to periodically, instead of constantly, monitor the physical downlink control channel (PDCCH) to save power. To meet the requirements of different UE services, both short and long DRX cycles can be configured for a UE. However, when to wake up is determined by the predefined cycle, so the UE might wake up unnecessarily when there is no data scheduled.

Is there a way for a UE to wake up only when it needs to? Wake-up Signal (WUS) proposed in Release 16 is the answer. This signal can be sent before the next On Duration period (during which the UE monitors the PDCCH) so that the UE wakes up only when it receives this signal from the network. Because the length of a WUS is shorter than the On Duration Timer, using WUS to wake up a UE saves more power than using only DRX.

BWP Adaptation

In theory, working on a larger bandwidth consumes more UE power. 5G provides large bandwidths, but it is unnecessary for a UE to always work on large bandwidth. For example, if you play online mobile games on a UE, only 10 MHz of bandwidth is needed for 87% of the data transmission time. As such, Bandwidth Part (BWP) is proposed in 5G to enable UEs to work on narrower bandwidths without sacrificing user experience.

BWP adaptation enables the base station to dynamically switch between BWPs based on the UE’s traffic volume. When the traffic volume is large, a UE can work on a wide BWP, and when the traffic volume is small, the UE can work on a narrow one. BWP switching can be performed based on the downlink control information (DCI) and RRC reconfiguration messages. This ensures that a UE always works on a bandwidth that supports the traffic volume but does not consume too much power.

Maximum MIMO Layers Reduction

According to 3GPP specifications, the number of receive and transmit antennas used by a UE cannot be fewer than the maximum number of MIMO layers in the downlink and uplink, respectively. For example, when a maximum of four downlink MIMO layers are configured for a UE, the UE must enable at least four receive antennas to receive data. Therefore, if the maximum number of MIMO layers can be reduced, the UE does not have to activate as many antennas, reducing power consumption.

This can be achieved in 5G because the number of MIMO layers can be re-configured based on assistance information from UEs. After receiving a request to reduce the number of MIMO layers from a UE, the base station configures fewer MIMO layers for the UE through an RRC reconfiguration message. In this way, the UE can deactivate some antennas to save power.

Summary

On the 5G RAN side, specific network configurations as well as technologies in time, frequency, and space domains can be used to enable a UE to save more power. The introduction of RRC_INACTIVE state, WUS, and BWP in 5G not only enables UEs to quickly respond to scheduling and access various services, but also reduces the UE’s power consumption. In addition, RRC reconfiguration based on UE assistance information enables the 5G network to adjust to UEs’ power saving requests.

But this is not all that 5G networks have done to make the world greener. We are excited to see what new technologies will emerge as 5G develops.

Read more about Huawei’s 5G carrier solutions.

Disclaimer: Any views and/or opinions expressed in this post by individual authors or contributors are their personal views and/or opinions and do not necessarily reflect the views and/or opinions of Huawei Technologies.