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TR 38.869
Study on low-power Wake-up Signal and Receiver for NR

V18.0.0 (Wzip)  2023/12  261 p.
Mr. Pan, Xueming
vivo Mobile Communication Co.,

full Table of Contents for  TR 38.869  Word version:  18.0.0

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1  Scopep. 10

The present document is intended to capture the output of study item for " Study on low-power wake up signal and receiver for NR" [2].
The study includes investigations to
  • the impact of low-power wake-up signal and receiver , including power saving benefit, coverage, system overhead impact, network energy impact and other related aspects.
  • the receiver architecture for low-power wake-up receiver and provide analysis for power consumption, noise figure and etc.
  • L1 designs and procedures changes needed to support the wake-up signal and evaluations for the link performances.
  • higher layer protocol changes needed to support the wake-up signals
  • related RAN4 impacts

2  Referencesp. 10

3  Definitions of terms, symbols and abbreviationsp. 12

3.1  Termsp. 12

3.2  Symbolsp. 13

3.3  Abbreviationsp. 13

4  Introductionp. 14

5G systems are designed and developed targeting for both mobile telephony and vertical use cases. Besides latency, reliability, and availability, UE energy efficiency is also critical to 5G. Currently, 5G devices may have to be recharged per week or day, depending on individual's usage time. In general, 5G devices consume tens of milliwatts in RRC idle/inactive state and hundreds of milliwatts in RRC connected state. Designs to prolong battery life is a necessity for improving energy efficiency as well as for better user experience.
Energy efficiency is even more critical for UEs without a continuous energy source, e.g., UEs using small rechargeable and single coin cell batteries. Among vertical use cases, sensors and actuators are deployed extensively for monitoring, measuring, charging, etc. Generally, their batteries are not rechargeable and expected to last at least few years as described in TR 38.875. Wearables include smart watches, rings, eHealth related devices, and medical monitoring devices. With typical battery capacity, it is challenging to sustain up to 1-2 weeks as required.
The power consumption depends on the configured length of wake-up periods, e.g., paging cycle. To meet the battery life requirements above, eDRX cycle with large value is expected to be used, resulting in high latency, which is not suitable for such services with requirements of both long battery life and low latency. For example, in fire detection and extinguishment use case, fire shutters shall be closed and fire sprinklers shall be turned on by the actuators within 1 to 2 seconds from the time the fire is detected by sensors, long eDRX cycle cannot meet the delay requirements. eDRX is apparently not suitable for latency-critical use cases. Thus, the intention is to study ultra-low power mechanism that can support low latency in Rel-18, e.g. lower than eDRX latency.
Currently, UEs need to periodically wake up once per DRX cycle, which dominates the power consumption in periods with no signalling or data traffic. If UEs are able to wake up only when they are triggered, e.g., paging, power consumption could be dramatically reduced. This can be achieved by using a wake-up signal to trigger the main radio and a separate receiver which has the ability to monitor wake-up signal with ultra-low power consumption. Main radio works for data transmission and reception, which can be turned off or set to deep sleep unless it is turned on.
The power consumption for monitoring wake-up signal depends on the wake-up signal design and the hardware module of the wake-up receiver used for signal detecting and processing.
The study should primarily target low-power WUS/WUR for power-sensitive, small form-factor devices including IoT use cases (such as industrial sensors, controllers) and wearables. Other use cases are not precluded, e.g.XR/smart glasses, smart phones.
As opposed to the work on UE power savings in previous releases, this study will not require existing signals to be used as WUS. All WUS solutions identified shall be able to operate in a cell supporting legacy UEs. Solutions should target substantial gains compared to the existing Rel-15/16/17 UE power saving mechanisms. Other aspects such as detection performance, coverage, UE complexity, should be covered by the evaluation.
The study item includes the following objectives:
  • Identify evaluation methodology (including the use cases) & KPIs [RAN1]
    • Primarily target low-power WUS/WUR for power-sensitive, small form-factor devices including IoT use cases (such as industrial sensors, controllers) and wearables
      • Other use cases are not precluded
  • Study and evaluate low-power wake-up receiver architectures [RAN1, RAN4]
  • Study and evaluate wake-up signal designs to support wake-up receivers [RAN1, RAN4]
  • Study and evaluate L1 procedures and higher layer protocol changes needed to support the wake-up signals [RAN2, RAN1]
  • Study potential UE power saving gains compared to the existing Rel-15/16/17 UE power saving mechanisms, the coverage availability, as well as latency impact of low-power WUR/WUS. System impact, such as network power consumption, coexistence with non-low-power-WUR UEs, network coverage/capacity/resource overhead should be included in the study [RAN1]
Use the following terminology for future discussion,
  • Main radio (MR): the Tx/Rx module operating for NR signals/channels apart from signals/channel related to low-power wake-up
  • LP-WUR (LR): The Rx module operating for receiving/processing signals/channel related to low-power wake-up.

5  Use cases & KPIp. 15

6  Evaluation methodologyp. 16

7  LP-WUR and LP-WUS designp. 25

7.1  LP-WUS receiver architecturesp. 25

7.2  LP-WUS design and L1 procedurep. 67

7.3  Higher-layer aspectsp. 77

7.4  RAN4 RRM studyp. 86

8  Evaluation resultsp. 87

8.1  Power and latency evaluationp. 87

8.1.1  RRC IDLE/INACTIVE modep. 87

8.1.2  RRC CONNECTED modep. 122

8.2  Coveragep. 138

8.2.1  Comparison between LP-WUS and NR reference channelp. 138

8.2.2  Results for urbanp. 145

8.2.3  Results for ruralp. 170

8.3  LLS results observationsp. 190

8.4  Network power consumptionp. 216

8.5  System overheadp. 218

9  Conclusionsp. 237

A  -p. 243

$  Change historyp. 261

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