Sensing Assisted Power Saving
Introduction
Power saving is a critical concern for both UE battery life and network energy consumption. In 5G NR, UE power saving mechanisms include DRX (Discontinuous Reception), BWP (Bandwidth Part) adaptation, PDCCH monitoring reduction, and cross-slot scheduling. On the network side, cell DTX, antenna muting, and carrier shutdown reduce gNB energy consumption during low-traffic periods.
Sensing-assisted power saving leverages environmental and situational awareness from sensing to make smarter decisions about when to activate or deactivate communication components, reducing energy waste without sacrificing performance when it matters.
Sensing-Assisted Power Saving: Conceptual Flow
┌──────────────────────────────────────────────────────────────────────┐
│ │
│ ┌──────────────┐ ┌──────────────────┐ ┌──────────────────┐ │
│ │ Sensing │ │ Activity │ │ Power Saving │ │
│ │ Subsystem │───▶│ Assessment │───▶│ Decisions │ │
│ │ │ │ │ │ │ │
│ └──────────────┘ │ ● UE detected? │ │ ● Activate DRX │ │
│ │ ● UE moving? │ │ ● Mute antennas│ │
│ │ ● UE approaching?│ │ ● Reduce BW │ │
│ │ ● Area empty? │ │ ● Wake-up │ │
│ └──────────────────┘ └──────────────────┘ │
│ │
└──────────────────────────────────────────────────────────────────────┘
Key Concepts
Sensing-Aware DRX Adaptation
DRX (Discontinuous Reception) allows the UE to sleep during periods of inactivity. Conventionally, DRX parameters (on-duration timer, inactivity timer, cycle length) are semi-statically configured. Sensing can dynamically adapt DRX by detecting UE activity:
DRX Adaptation Based on Sensing
┌──────────────────────────────────────────────────────────────────┐
│ │
│ Scenario 1: Sensing detects UE is stationary │
│ → Extend DRX cycle (longer sleep, save power) │
│ │
│ ┌───┐ ┌───┐ ┌───┐ │
│ │ ON│ │OFF│ ........long sleep.... │ ON│ │
│ └───┘ └───┘ └───┘ │
│ │
│ Scenario 2: Sensing detects UE is moving fast │
│ → Shorten DRX cycle (frequent wake-ups for HO prep) │
│ │
│ ┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐┌───┐ │
│ │ ON││OFF││ ON││OFF││ ON││OFF││ ON││OFF│ │
│ └───┘└───┘└───┘└───┘└───┘└───┘└───┘└───┘ │
│ │
│ Scenario 3: Sensing detects no UEs in area │
│ → gNB enters cell DTX / deep sleep │
│ │
│ ┌──────────────────────────────────────────┐ │
│ │ gNB DEEP SLEEP │ │
│ └──────────────────────────────────────────┘ │
│ │
└──────────────────────────────────────────────────────────────────┘
Network Energy Saving via Sensing
On the gNB side, sensing enables aggressive energy saving by detecting the absence of UEs or traffic:
Antenna muting: When sensing detects no targets in a particular angular sector, the corresponding antenna elements or panels can be powered down.
Carrier shutdown: If sensing confirms no active UEs in the cell, secondary carriers can be deactivated.
Lean carrier operation: Sensing-triggered lean operation reduces reference signal transmission (SSB, CSI-RS) when no UEs are detected, saving transmit power.
Sensing-triggered wake-up: When sensing detects an approaching UE or vehicle, the gNB proactively wakes up from sleep mode before the UE initiates RACH, reducing access latency.
Network Energy Saving State Machine
┌──────────────────────────────────────────────────────────────────┐
│ │
│ ┌──────────────────┐ │
│ Sensing: │ │ Sensing: │
│ No UE ─────────▶│ Deep Sleep │◀── all UEs left │
│ detected │ (minimal TX) │ │
│ │ │ │
│ └────────┬─────────┘ │
│ │ │
│ Sensing: │ UE approaching │
│ ▼ │
│ ┌──────────────────┐ │
│ │ │ │
│ │ Light Sleep │ │
│ │ (SSB only) │ │
│ │ │ │
│ └────────┬─────────┘ │
│ │ │
│ UE enters │ coverage │
│ ▼ │
│ ┌──────────────────┐ │
│ │ │ │
│ │ Active │ │
│ │ (Full operation)│ │
│ │ │ │
│ └──────────────────┘ │
│ │
└──────────────────────────────────────────────────────────────────┘
UE Wake-Up Signal Enhancement
3GPP Rel-16 introduced wake-up signals (WUS) for paging occasion optimization. Sensing can enhance WUS triggering by:
Proximity-based WUS: Sensing detects that a target (potential UE) is approaching the cell, triggering WUS transmission only when the UE is likely within range.
Directional WUS: WUS is transmitted only in the beam direction where sensing detects activity, saving power on idle beams.
Eliminating unnecessary WUS: If sensing confirms no targets are present, WUS can be skipped entirely for that paging occasion.
PDCCH Monitoring Reduction
Sensing can inform whether the UE needs to actively monitor PDCCH:
Stationary UE: If sensing confirms the UE is stationary with stable channel conditions, PDCCH monitoring can be reduced (fewer PDCCH monitoring occasions per DRX cycle).
Predictable mobility: If the UE is on a predictable trajectory (e.g., highway), PDCCH monitoring can be scheduled to coincide with expected beam switches rather than being continuous.
Benefits
Benefit |
Description |
|---|---|
Extended UE battery life |
Sensing-optimized DRX and PDCCH monitoring reduce UE power consumption. |
Reduced network energy |
Sensing-triggered sleep and antenna muting cut gNB energy usage during idle periods. |
Faster wake-up |
Proactive wake-up from sensing avoids cold-start delays when UEs arrive. |
Green network operation |
Intelligent sleep aligns with sustainability goals for 6G networks. |
Challenges
Sensing power consumption: The sensing subsystem itself consumes power. The net energy saving must account for the sensing overhead; sensing should be “lighter” than continuous communication monitoring.
False alarm rate: False sensing detections (ghost targets) could unnecessarily wake up the gNB, negating power savings. Low false-alarm sensing algorithms are needed.
Missed detection risk: If sensing fails to detect an approaching UE, the gNB may remain asleep, causing access delay or failure.
Standardization gap: No current 3GPP mechanism links sensing measurements to DRX/DTX configuration. New RRC/MAC signaling would be needed to enable sensing-driven power saving.