NB-IoT eDRX Extended Idle
Extended Discontinuous Reception with Paging Windows
NB-IoT eDRX: Extended Discontinuous Reception
This interactive animation demonstrates how NB-IoT devices use Extended Discontinuous Reception (eDRX) to achieve extreme power savings while maintaining periodic reachability for downlink messages.
This animation shows how eDRX extends traditional DRX cycles to save power:
- eDRX Cycle: Extended idle period (up to 2.91 hours for NB-IoT)
- Paging Time Window (PTW): Short window where device listens for pages
- Device States: Deep Sleep, Wake, Listen, Back to Sleep
- Power Profile: Visualize power consumption over the cycle
Compare regular DRX vs eDRX to understand the dramatic power savings.
- Select eDRX cycle duration using the slider (5.12s to 2.91 hours)
- Configure PTW duration to set how long the device listens
- Click “Start Timeline” to animate the eDRX cycle
- Observe the power consumption graph showing energy usage
- Compare with Regular DRX to see power savings
- Use the Power Calculator to estimate battery life
How eDRX Works in NB-IoT
Extended Discontinuous Reception (eDRX) is a power-saving mechanism that extends the traditional DRX cycle from seconds to hours:
Key eDRX Parameters
- eDRX Cycle (T_eDRX): Total time between paging opportunities
- Range: 5.12 seconds to 10,485.76 seconds (2.91 hours)
- NB-IoT supports longer cycles than LTE-M
- Configured by network and device negotiation
- Paging Time Window (PTW): Duration device listens for pages
- Range: 2.56 seconds to 40.96 seconds
- Contains multiple paging occasions
- Device must stay awake for entire PTW
- Paging Occasion (PO): Specific instants for paging messages
- Multiple POs within each PTW
- Network schedules downlinks at these times
- Device listens for its specific paging identity
eDRX Cycle Values
NB-IoT supports 16 eDRX cycle values, encoded in a 4-bit field:
| Code | eDRX Cycle | Best For |
|---|---|---|
| 0 | 5.12s | Frequent updates needed |
| 1 | 10.24s | Near real-time monitoring |
| 2 | 20.48s | Regular sensor polling |
| 5 | 81.92s | Hourly-ish updates |
| 10 | 5.46min | Periodic monitoring |
| 13 | 43.69min | Hourly reports |
| 14 | 1.46hr | Infrequent updates |
| 15 | 2.91hr | Maximum power savings |
PTW Duration Values
Paging Time Window determines how long the device listens:
| Code | PTW Duration | Power Impact |
|---|---|---|
| 0 | 2.56s | Minimum (best for battery) |
| 3 | 10.24s | Low (good balance) |
| 7 | 20.48s | Medium |
| 15 | 40.96s | Maximum (longest listening) |
The PTW cannot exceed the eDRX cycle duration. If a longer PTW is configured, it will be capped at the eDRX cycle length.
Power Consumption Analysis
Current Consumption Comparison
| State | Regular DRX | eDRX |
|---|---|---|
| Deep Sleep | N/A (always paging) | 3 uA |
| Light Sleep | ~1 mA average | N/A |
| Paging Listen | 50 mA (brief) | 50 mA (during PTW) |
| Active TX/RX | 200 mA | 200 mA |
Example: Water Meter with eDRX
Configuration:
- eDRX Cycle: 10,485.76s (2.91 hours)
- PTW: 5.12 seconds
- Reports: Once per day
Power Calculation:
- Deep Sleep: 3 uA x 10,480.64s = 31,442 uAs per cycle
- PTW Listen: 50,000 uA x 5.12s = 256,000 uAs per cycle
- Total per cycle: 287,442 uAs
Cycles per day: 24 hours / 2.91 hours = 8.25 cycles
Daily consumption: 287,442 x 8.25 = 2,371,397 uAs = 0.66 mAh/day
With 2000mAh battery:
Battery life = 2000 / 0.66 = 3,030 days = 8.3 yearseDRX vs PSM Comparison
| Feature | eDRX | PSM |
|---|---|---|
| Reachability | Periodic (at PTW) | Only at device wake |
| Max Sleep | 2.91 hours | 310 hours (12.9 days) |
| Use Case | Needs some downlinks | Pure uplink sensors |
| Latency | Predictable (eDRX cycle) | Unpredictable |
| Power | Higher than PSM | Lowest possible |
| Network Load | Higher (paging) | Lower |
For optimal power savings, NB-IoT devices can use both: 1. eDRX during active period: Device is reachable at PTW 2. PSM during extended idle: Deep sleep for hours/days 3. TAU wakes from PSM: Resume eDRX cycle
This provides balanced reachability and maximum battery life.
Network Paging in eDRX
When the network needs to send a downlink:
Configuring eDRX
AT Command Example
// Request eDRX with cycle value 5 (81.92s) and PTW 3 (10.24s)
AT+CEDRXS=2,5,"0101","0011"
// Query current eDRX settings
AT+CEDRXRDP
// Response: +CEDRXRDP: 5,"0101","0011","0101"
// AcT-type, Requested, Network-provided, Paging_time_windowParameter Encoding
- eDRX value: 4-bit binary (0000 to 1111)
- PTW value: 4-bit binary (0000 to 1111)
- AcT-type: 5 = NB-IoT
Real-World Deployment Considerations
When to Use eDRX
- Device needs periodic downlink capability
- Latency tolerance: Can wait up to eDRX cycle for commands
- Battery life: Need 5+ years on single charge
- Examples: Smart meters, asset trackers, environmental sensors
When to Use PSM Instead
- No downlinks needed between reports
- Maximum battery life is critical (10+ years)
- Device-initiated only: Sensors that just upload data
- Examples: Parking sensors, soil moisture, water leak detectors
Network Support
Not all carriers support all eDRX values. Check with your network operator for: - Supported eDRX cycle range - Supported PTW values - Any restrictions on combinations
Technical Implementation Notes
This animation demonstrates key NB-IoT eDRX specifications from 3GPP Release 13+:
- eDRX cycles: 16 values from 5.12s to 10,485.76s
- PTW durations: 16 values from 2.56s to 40.96s
- Paging occasions: Multiple per PTW for network flexibility
- Power states: Deep sleep (3 uA) to paging listen (50 mA)
- Navy (#2C3E50): Deep sleep state and primary elements
- Teal (#16A085): Paging Time Window and active states
- Orange (#E67E22): Wake transitions
- Gray (#7F8C8D): Neutral elements and comparisons
What’s Next
- NB-IoT Labs - Hands-on implementation
- Cellular IoT Applications - Real-world use cases
- LPWAN Comparison - NB-IoT vs LoRaWAN vs Sigfox
Selection Guidelines: Use PSM-only for pure uplink sensors (parking, soil moisture), eDRX for devices needing periodic commands (smart meters, trackers), and combined PSM+eDRX when you need both extended battery life AND occasional reachability windows.