Question 1: Which of the following are power-saving features in NB-IoT? (Select ALL that apply)
NB-IoT includes several power-saving mechanisms:
PSM (A) - Device enters deep sleep (<5 µA) while remaining registered to network. Not reachable for mobile-terminated data. Battery life 10+ years. T3412 timer (TAU) configures sleep duration (minutes to days).
eDRX (B) - Device sleeps (~15 µA) but wakes periodically to check for paging. Reachable for downlink with seconds-to-minutes latency. eDRX cycle up to 10,485 seconds (2.91 hours) in NB-IoT. Balances power and reachability.
Coverage Extension (D) - Repetition coding extends coverage (+20 dB) but increases transmission time. Longer transmissions consume more energy. Trade-off: deeper coverage vs power consumption.
Half-duplex (E) - Transmit OR receive, not simultaneously. Single RF chain reduces module cost (~30%) and power consumption vs full-duplex. Acceptable for IoT’s asymmetric traffic.
CSMA/CA (C) is INCORRECT - NB-IoT uses scheduled access (grant-based), not CSMA/CA contention.
Always-on reception (F) is INCORRECT - This is highest power mode (15-20 mA), opposite of power saving.
Question 2: Mark each statement about NB-IoT as True (T) or False (F):
1. PSM (Power Saving Mode) allows devices to sleep deeply but they cannot receive downlink messages while in PSM
2. eDRX (Extended Discontinuous Reception) enables devices to remain reachable for mobile-terminated data while still saving power
3. NB-IoT supports full-duplex operation allowing simultaneous transmit and receive for lower latency
4. Coverage extension through repetitions improves link budget at the cost of increased latency and power consumption
1. ✓ True - In PSM, device enters deep sleep (<5 µA) and is NOT reachable by network. Device must wake and reconnect to send/receive data. Used for uplink-only applications (e.g., daily meter readings).
2. ✓ True - eDRX extends paging cycle (up to 2.91 hours) while maintaining reachability. Device wakes periodically to listen for paging. Sleep current ~15 µA. Enables mobile-terminated messaging with seconds-to-minutes latency.
3. ✗ False - NB-IoT uses half-duplex operation (transmit OR receive, never simultaneously). This reduces hardware complexity, module cost (~30% savings), and power consumption. Full-duplex not needed for IoT's asymmetric low-rate traffic.
4. ✓ True - Repetition coding transmits same message multiple times. Receiver combines copies to improve SNR (~3 dB per repetition). Up to 2048 repetitions possible. Extends coverage (+20 dB) but increases time-on-air (higher latency and energy consumption). Example: 100 repetitions × 50 ms = 5 seconds transmission time.
1143.4 Scenario-Based Questions
NoteQuestion 3: Deployment Modes
A mobile operator has an existing LTE network with 10 MHz carriers and wants to introduce NB-IoT services. They have 900 MHz spectrum previously used for GSM that is now idle. What deployment mode options do they have, and what are the trade-offs?
Only in-band mode within the LTE carriers
Only standalone mode using the 900 MHz spectrum
Both standalone (900 MHz) and in-band (LTE) are options, each with different trade-offs
Guard-band mode only
Click to reveal answer
Answer: C) Both standalone (900 MHz) and in-band (LTE) are options, each with different trade-offs
Explanation:
The operator has multiple deployment options:
Option 1: Standalone Mode (900 MHz GSM spectrum)
Advantages: - Full 180 kHz bandwidth dedicated to NB-IoT - No impact on existing LTE services - Excellent coverage (900 MHz low-frequency propagation) - Simple network planning
Disadvantages: - Requires refarm of GSM spectrum - May need hardware upgrades if GSM still active - Separate frequency planning
Advantages: - Rapid deployment (software upgrade) - No new spectrum allocation needed - Shared infrastructure with LTE
Disadvantages: - Reduces LTE capacity slightly (1-2 PRBs = 180-360 kHz) - More complex interference management - Potential impact on LTE user experience
Recommendation for this scenario:
Deploy standalone mode in 900 MHz because: 1. Excellent coverage (low frequency) 2. No LTE impact 3. GSM spectrum is idle (no migration complexity) 4. Best customer experience for both IoT and LTE users
Use in-band mode as secondary coverage in areas without 900 MHz deployment or for capacity expansion.
NoteQuestion 4: Power Saving Modes
An NB-IoT smart parking sensor needs to report occupancy changes immediately (event-driven) and send a daily heartbeat. It must respond to configuration commands from the platform within 1 minute. Which power-saving configuration is most appropriate?
PSM with T3412 = 24 hours (lowest power)
eDRX with 10-minute cycle (balance power and reachability)
Normal DRX (always listening, highest power)
eDRX with 1-hour cycle (longer battery, acceptable latency)
Click to reveal answer
Answer: B) eDRX with 10-minute cycle (balance power and reachability)
Explanation:
Let’s analyze the requirements:
Requirements: 1. Event-driven uplink: Report occupancy changes immediately (device-initiated) 2. Daily heartbeat: Once per 24 hours if no events 3. Downlink commands: Respond within 1 minute to configuration
Analysis of each option:
Option A: PSM with T3412 = 24 hours - Excellent battery life (< 5 µA sleep) - Can wake up immediately for events (uplink) - Cannot receive downlink while in PSM (network cannot reach device) - Config commands would wait up to 24 hours (unacceptable)
Option B: eDRX with 10-minute cycle - Good battery life (~15 µA sleep) - Can wake up immediately for events (uplink) - Reachable for downlink every 10 minutes - Config commands delivered within 10 min (< 1 min requirement on average) - Slightly higher power than PSM
Option C: Normal DRX - Always reachable (seconds latency) - Fast downlink delivery - High power consumption (1-5 mA continuous) - Battery life measured in months, not years
Option D: eDRX with 1-hour cycle - Better battery life than shorter eDRX - Can wake for events - Config commands wait up to 1 hour (exceeds 1 min requirement)
Why Option B is optimal:
Uplink (events): Device can wake anytime to report occupancy change
Downlink (config): With 10-minute eDRX cycle, device listens for paging every 10 minutes
Average latency for downlink: 5 minutes (half the cycle)
Maximum latency: 10 minutes (end of cycle)
Current consumption estimate for Option B: - Sleep (eDRX): 15 µA × 99% time - Paging window: 50 mA × 1% time - Average: ~0.5 mA → 5-10 year battery life with 5 Ah battery
Note: If strict < 1 minute downlink is required, eDRX cycle should be configured < 2 minutes.
NoteQuestion 5: Coverage Enhancement
An NB-IoT water meter is deployed in a basement with significant signal attenuation. The link budget shows 150 dB coupling loss. The eNodeB needs to communicate reliably. How does NB-IoT achieve this, and what are the trade-offs?
Use higher transmit power (> 23 dBm) to overcome path loss
Use message repetitions to improve SNR through processing gain
Switch to LTE-M which has better coverage
Deploy a local repeater/amplifier
Click to reveal answer
Answer: B) Use message repetitions to improve SNR through processing gain
Explanation:
NB-IoT is designed for 164 dB Maximum Coupling Loss (MCL), which is more than sufficient for this 150 dB scenario. The key technique is repetition coding.
How repetition coding works:
Transmit the same message multiple times on the physical layer
Receiver combines all copies (maximal ratio combining)
Each repetition improves SNR by ~3 dB
Link budget for 150 dB coupling loss: - Device TX power: +23 dBm - eNB RX sensitivity (normal): -141 dBm (after processing gain) - Maximum path loss supported: 23 - (-141) = 164 dB MCL - Link margin: 164 - 150 = 14 dB margin - comfortable!
Coverage classes: - Class 0: Normal coverage (no/minimal repetitions) - Latency: < 1 second - Class 1: Extended coverage (10-100 repetitions) - Latency: 1-10 seconds - Class 2: Extreme coverage (up to 2048 repetitions) - Latency: > 10 seconds
Trade-offs of repetition:
Advantages: - No additional hardware cost - Automatic in NB-IoT protocol - Effective coverage enhancement
Disadvantages: - Increased latency: Each repetition adds transmission time - Higher power consumption: More transmissions = more energy - Reduced capacity: More air time per device = fewer devices per cell
Why other options are incorrect:
Option A: Higher transmit power - NB-IoT devices are limited to 23 dBm (200 mW) by standard - Regulatory limits prevent higher power - Not a practical solution
Option C: Switch to LTE-M - LTE-M has 156 dB MCL vs NB-IoT’s 164 dB MCL - NB-IoT has BETTER coverage than LTE-M (by 8 dB) - LTE-M would perform worse in this scenario
Option D: Deploy repeater - Expensive additional hardware - Maintenance burden - Not necessary when NB-IoT coverage is already sufficient
1143.5 Technology Selection Quiz
Question 6: For a smart water meter deployment requiring 15-year battery life, deep basement coverage, and 100 bytes/day transmission, which technology is BEST?
Technology
Bandwidth
Latency
Mobility
Battery Life
Coverage (MCL)
Select
NB-IoT
250 kbps
1.6-10 sec
Limited
10+ years
164 dB
LTE-M
1 Mbps
10-15 ms
Full handover
5-10 years
156 dB
EC-GSM-IoT
70-240 kbps
700-1400 ms
Full
5-10 years
164 dB
4G LTE
100 Mbps
20-50 ms
Full
Months
142 dB
💡 Explanation: NB-IoT is optimal for this smart metering application:
Coverage: 164 dB Maximum Coupling Loss matches deep basement requirements (+20 dB vs GPRS, +8 dB vs LTE-M).
Battery Life: 10+ years with PSM mode (5 µA sleep current), perfect for 15-year target.
Bandwidth: 250 kbps easily handles 100 bytes/day (0.008 kbps average).
Cost: Lowest module cost ($8-12) and data plans.
Stationary: No mobility needed for fixed meters.
LTE-M offers unnecessary mobility features at higher power. EC-GSM-IoT is being phased out with 2G sunset. 4G LTE consumes too much power for battery operation.
1143.6 Comprehensive Review Quiz
NoteQuiz: Comprehensive NB-IoT Review
Question 7: An NB-IoT deployment uses in-band mode within a 10 MHz LTE carrier. If each Physical Resource Block (PRB) is 180 kHz and the carrier has 50 PRBs total, how much LTE capacity is lost when allocating 1 PRB for NB-IoT?
This makes in-band mode the most popular initial deployment strategy because: - Most carriers accept 2% loss for IoT revenue - That 540 kbps supports thousands of NB-IoT devices - Revenue from IoT subscriptions often exceeds lost LTE revenue
Question 8: Compare NB-IoT’s data rates (25-160 kbps) with LoRaWAN (0.3-50 kbps) and LTE Cat-M1 (1 Mbps). For which IoT application is NB-IoT’s data rate MOST appropriate?
NB-IoT’s data rate is optimized for infrequent sensor data and occasional larger transfers:
Smart metering requirements: - Daily readings: 100 bytes per day → 0.001 kbps average (NB-IoT: 25-160 kbps ✓) - Firmware updates: 100 KB → 32 seconds at 25 kbps ✓
Why other options don’t work: - Video (2-4 Mbps): NB-IoT provides 250 kbps max - 12-160× too slow - Voice (64 kbps): NB-IoT has 1-10 second latency - unusable for real-time voice - Industrial control (1 ms): NB-IoT has 1,000-10,000× higher latency
Question 9: A logistics company needs to track refrigerated containers transporting vaccines. Each container reports temperature every 5 minutes, GPS location every 15 minutes, and must support emergency alerts with <1 minute latency. Containers move by truck/ship at varying speeds. Battery must last 30 days on 10 Ah battery. Which cellular IoT technology should you choose?
LTE-M is the only viable option for this mobile cold chain application:
Mobility Support: - LTE-M: Full handover at speeds up to 160 km/h - NB-IoT: Limited/no handover support (stationary devices only)
Latency: - LTE-M: 10-15 ms typical, supports <1 minute emergency alerts - NB-IoT: 1.6-10 seconds typical (marginal for emergency alerts)
Battery Life: - LTE-M with PSM: 30 days achievable with 10 Ah battery ✓
Why not alternatives: - NB-IoT (A): Fails mobility requirement - EC-GSM-IoT (C): Being phased out with 2G sunset - Wi-Fi (D): No coverage over ocean
1143.7 Cross-Hub Connections
NoteExplore NB-IoT Across Learning Resources
Explore NB-IoT across learning resources:
Videos Hub: Watch cellular IoT deployment tutorials, NB-IoT vs LTE-M comparisons, and real-world smart metering implementations
Quizzes Hub: Test your NB-IoT knowledge with interactive assessments on deployment modes, power-saving modes, and coverage enhancement techniques
Simulations Hub: Experiment with NB-IoT link budget calculators, PSM/eDRX power consumption simulators, and deployment mode decision tools
Knowledge Gaps Hub: Address common misconceptions about NB-IoT mobility support, latency characteristics, and comparison with LoRaWAN