Energy-Saving MAC (Extended DRX / Wake-Up Radio)

MAC Overview DRX SPS & CG Sidelink NTN MAC AI Scheduling IAB MAC ISAC Scheduling Cell-Free MAC

1. DRX & Extended DRX (eDRX)

Standard NR DRX cycles up to 10.24 sec. eDRX extends to 43.69 minutes with Paging Time Windows (PTW). UE sleeps deeply between PTWs and uses normal DRX within each PTW.

DRX Cycle Comparison — Standard vs eDRX vs WuR

Compare wake patterns. See how eDRX and WuR dramatically reduce active time.

Mode:

Mode	Cycle Length	Wake Pattern	Power Saving
Standard DRX	10ms - 10.24s	Every cycle (mandatory)	60-80%
eDRX	Up to 43.69 min	Only during PTW	90-99%
WuR (6G)	Event-driven	Only when WUS detected	95-99.9%

2. Wake-Up Signal (WUS) & Wake-Up Receiver

A secondary ultra-low-power receiver (WuR) listens for WUS while the main radio sleeps. If WUS detected, main RX powers on. If no WUS, UE skips on-duration — saving 80-95% idle energy.

WUS Flow — Intelligent Wake vs Blind Wake

Compare: without WUS (blind wake every cycle) vs with WUS (wake only when data arrives).

Data arrival rate: 30%

WuR power: <1 uW (vs 100s of mW for main RX). WuR uses simple envelope detection, not full 5G demodulation. 6G target: <100 nW.

3. UE Power State Machine

UE transitions through multiple power states: Deep Sleep (WuR only) to WUS Listen to Active (full RX) to Micro-Sleep (between slots) and back. Each transition has a cost.

Power State Machine — Sleep, Listen, Active, Micro-Sleep

Watch UE transition through power states. See energy consumption per state.

Deep Sleep (~0 uW)

Main RX off. Only WuR or timer active. Lowest power state.

WUS Listen (~1 uW)

WuR checks for WUS. If detected -> transition to Active.

Active (100-500 mW)

Full PDCCH/PDSCH reception. Highest power. Minimize time here.

Micro-Sleep (~10 mW)

Brief sleep between scheduled slots. Cross-slot scheduling enables this.

4. Network Energy Saving

gNB-side mechanisms: Cell DTX (gNB stops TX when idle), SSB muting, carrier shutdown, and symbol-level power gating. Combined savings: 40-80% at the base station.

Mechanism	Savings	Latency Impact	Activation
Cell DTX	40-70%	UE must re-acquire	AI-predicted idle
SSB Muting	10-30%	Fewer beam options	Low-traffic period
Carrier Shutdown	30-50%	~3-8 ms reactivation	MAC CE deactivation
Symbol Power Gate	5-20%	None	Per empty symbol

AI-optimized sleep: AI predicts traffic per cell -> pre-schedules cell DTX during idle periods -> coordinates neighbor cells so one covers while other sleeps -> 50-80% network energy saving without QoS impact.

5. Practical Field Considerations

Scenario	Config	Rationale
IoT sensor (indoor)	eDRX 10 min + WUS	Max battery, tolerant latency
Smart meter (outdoor)	eDRX 43 min	Once-per-hour reading, extreme battery
Smartphone	C-DRX + PDCCH skip + SSSG	Reduce active power, keep responsive
Wearable (tiny battery)	WUS + eDRX 5 min	WuR saves 90%+ on idle
Network (night)	Cell DTX + carrier shutdown	gNB sleeps 60-80% off-hours

LTE vs 5G NR Energy Saving

Aspect	LTE	5G NR
eDRX	Cat-M1/NB-IoT only	All UE types
WUS	No	DCI 2_6 (Rel-16)
PDCCH skipping	No	Yes (Rel-16)
Cell DTX	No	Yes (Rel-17/18)
WuR hardware	No	Study (Rel-18/19)

6. 6G Evolution — Zero-Energy & AI-Optimized

Zero-Energy Devices

No battery. Harvest ambient RF + solar + vibration. MAC handles intermittent operation.

AI-Optimized Sleep

AI learns each UE's pattern. Personalized DRX/eDRX. Near-zero wasted on-durations.

WuR Standard

WuR becomes standard, not optional. <100 nW. Event-driven wake. 99.9% idle savings.

Energy Saving Evolution — 4G to 6G

Compare energy-saving capabilities across generations.

Generation:

Dimension	4G (LTE)	5G NR	6G (Target)
Max DRX	2.56s	43.69 min (eDRX)	Hours (AI-scheduled)
WuR	None	WUS (DCI)	<100 nW WuR
Network sleep	None	Cell DTX	AI-orchestrated
Zero-energy	No	Study	Standard
Energy efficiency	Baseline	10x vs 4G	100x vs 4G

Energy-Saving MAC — Extended DRX & Wake-Up Radio