1140  NB-IoT Deployment Modes

1140.1 Learning Objectives

By the end of this chapter, you will be able to:

  • Compare Deployment Modes: Evaluate in-band, guard band, and standalone NB-IoT configurations
  • Calculate Resource Allocation: Compute PRB capacity impact for NB-IoT within LTE carriers
  • Select Optimal Mode: Choose the best deployment option based on infrastructure and requirements
  • Plan Spectrum Strategy: Leverage existing 4G/LTE infrastructure for NB-IoT rollout

1140.2 Prerequisites

Required Chapters:

Technical Background:

  • LTE network basics
  • Frequency bands and spectrum allocation
  • Physical Resource Block (PRB) concepts

Estimated Time: 20 minutes

1140.3 NB-IoT Deployment Modes Overview

NB-IoT supports three flexible deployment options leveraging existing cellular infrastructure. Each mode offers different trade-offs between deployment speed, spectrum efficiency, and LTE impact.

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graph TB
    subgraph "In-Band (Most Common)"
        IB["Within LTE Carrier<br/>Uses 1 PRB = 180 kHz"]
        IB_PRO["• Software upgrade only<br/>• Fast deployment<br/>• Reuses LTE spectrum"]
        IB_CON["• 2% LTE capacity loss<br/>• 10 MHz LTE → 1 PRB for NB-IoT"]
    end

    subgraph "Guard-Band"
        GB["LTE Guard Band<br/>200 kHz carrier"]
        GB_PRO["• No LTE impact<br/>• Uses unused spectrum<br/>• Good urban coverage"]
        GB_CON["• Limited availability<br/>• Depends on LTE config<br/>• Guard bands not always wide enough"]
    end

    subgraph "Standalone"
        SA["Dedicated Spectrum<br/>Repurposed GSM (200 kHz)"]
        SA_PRO["• Zero LTE impact<br/>• Low frequencies (900 MHz)<br/>• Excellent rural coverage"]
        SA_CON["• Requires GSM shutdown<br/>• Spectrum refarming needed<br/>• Regulatory approval"]
    end

    IB --> IB_PRO
    IB --> IB_CON
    GB --> GB_PRO
    GB --> GB_CON
    SA --> SA_PRO
    SA --> SA_CON

    style IB fill:#27AE60,color:#fff
    style GB fill:#F39C12,color:#fff
    style SA fill:#3498DB,color:#fff

Figure 1140.1: NB-IoT Deployment Modes: In-Band, Guard-Band, and Standalone

1140.4 Deployment Mode Selection

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flowchart TD
    START(["Choose Deployment Mode"]) --> Q1{"Have LTE<br/>infrastructure?"}

    Q1 -->|Yes| Q2{"Can afford 2%<br/>LTE capacity?"}
    Q1 -->|No| SA["Standalone<br/>Repurpose GSM"]

    Q2 -->|Yes| IB["In-Band<br/>Software upgrade only"]
    Q2 -->|No| Q3{"Guard band<br/>available?"}

    Q3 -->|Yes| GB["Guard-Band<br/>Zero LTE impact"]
    Q3 -->|No| IB

    style IB fill:#16A085,stroke:#2C3E50,color:#fff
    style GB fill:#E67E22,stroke:#2C3E50,color:#fff
    style SA fill:#2C3E50,stroke:#16A085,color:#fff

This flowchart guides deployment mode selection based on existing infrastructure and capacity constraints.

1140.5 Detailed Deployment Modes

1140.5.1 Mode Comparison Table

Mode Spectrum Usage Pros Cons
1. In-Band Uses PRB from LTE carrier (e.g., PRB 25 from 10 MHz/50 PRB carrier) Rapid deployment, Software upgrade only 2% LTE capacity loss
2. Guard-Band Uses unused guard band between LTE carriers (200 kHz) No LTE impact, Efficient spectrum use Limited scalability
3. Standalone Repurposed GSM carrier (200 kHz @ 900 MHz) No LTE impact, Excellent coverage Spectrum refarming needed

1140.5.2 In-Band Deployment Example

For a 10 MHz LTE Carrier:

PRB Range Usage Bandwidth
PRB 1-24 LTE Data 4.32 MHz
PRB 25 NB-IoT 180 kHz
PRB 26-50 LTE Data 4.5 MHz

What is a PRB (Physical Resource Block)?

Think of an LTE carrier like a highway with multiple lanes. Each lane (PRB) is exactly 180 kHz wide:

  • A 10 MHz LTE carrier has 50 PRBs (50 lanes)
  • NB-IoT uses just 1 PRB (1 lane)
  • This leaves 49 PRBs for regular LTE traffic

The 2% Calculation: - 1 PRB out of 50 PRBs = 1/50 = 2% - This small sacrifice enables thousands of IoT devices

Real-World Analogy: It’s like reserving one lane on a 50-lane highway exclusively for bicycles. You lose 2% of car capacity, but gain dedicated infrastructure for a different type of traffic.

1140.6 Capacity Impact Analysis

1140.6.1 In-Band Capacity Calculation

Calculation:

  • Total LTE carrier: 10 MHz = 50 PRBs (each PRB = 180 kHz)
  • NB-IoT allocation: 1 PRB = 180 kHz
  • Remaining for LTE: 49 PRBs = 8.82 MHz
  • Capacity loss: (1 PRB / 50 PRBs) x 100% = 2%

1140.6.2 Practical Considerations

  • Most carriers accept 2% loss for IoT revenue
  • Can allocate more PRBs during off-peak hours
  • LTE spectral efficiency is ~3 bps/Hz, so 180 kHz = ~540 kbps lost
  • That 540 kbps supports thousands of NB-IoT devices (each using only 25-160 kbps occasionally)

1140.6.3 Cost-Benefit Analysis

  • Lost LTE capacity: ~540 kbps continuous
  • Gained IoT capacity: 50,000+ devices per cell
  • Revenue from IoT subscriptions often exceeds lost LTE revenue

This makes in-band mode the most popular initial deployment strategy.

1140.7 Standalone Mode Deep Dive

Standalone mode uses dedicated spectrum, typically repurposed from legacy 2G/GSM networks:

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 required

Best For:

  • Rural deployments needing maximum coverage
  • Operators with idle GSM spectrum
  • New market entrants without LTE

1140.8 Guard-Band Mode Considerations

Guard-band deployment places NB-IoT in the unused spectrum at LTE carrier edges:

Requirements:

  • Guard band width >= 200 kHz
  • Careful interference management at band edges
  • May vary by LTE carrier configuration

Advantages:

  • Zero impact on LTE data capacity
  • Uses otherwise wasted spectrum
  • No spectrum refarming needed

Limitations:

  • Not all LTE configurations have suitable guard bands
  • Limited scalability (can’t add more NB-IoT capacity easily)
  • More complex RF planning

1140.9 Knowledge Check

Question 1: 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?

In-band deployment allocates specific PRBs from the LTE carrier to NB-IoT. With 1 PRB allocated from 50 total PRBs, the capacity loss is (1/50) x 100% = 2%.

Question 2: Which of the following are valid NB-IoT deployment modes? (Select ALL that apply)

NB-IoT supports three deployment modes standardized by 3GPP: In-band (A), Guard-band (B), Standalone (C), and operators can deploy all three simultaneously (D) across different cells based on spectrum availability. Options E and F are incorrect - NB-IoT never shares PRBs with LTE simultaneously, and always uses licensed spectrum.

1140.10 Summary

  • Three deployment modes provide flexibility: in-band (fastest), guard-band (zero LTE impact), standalone (best coverage)
  • In-band mode is most popular due to software-only deployment, with acceptable 2% LTE capacity trade-off
  • PRB allocation of 180 kHz supports 50,000+ IoT devices per cell while minimizing LTE impact
  • Standalone mode offers excellent coverage at low frequencies (900 MHz) when GSM spectrum is available
  • Guard-band mode efficiently uses otherwise wasted spectrum but has limited scalability
  • Mode selection depends on existing infrastructure, spectrum assets, and coverage requirements

1140.11 What’s Next

Continue exploring NB-IoT architecture and components: