821  Cellular Network Architecture for IoT

821.1 Learning Objectives

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

  • Understand Cellular Architecture: Explain the components of LTE/5G networks and how IoT traffic flows
  • Select Cellular IoT Technologies: Choose between NB-IoT, LTE-M, and 5G profiles based on requirements
  • Analyze Mobility Requirements: Determine when handover support is critical for your application
  • Compare Core Network Functions: Understand the roles of MME, S-GW, P-GW, and HSS in IoT connectivity

821.2 Prerequisites

Required Chapters: - Mobile Wireless Technologies Basics - Core concepts - Cellular IoT Fundamentals - Cellular technologies - Networking Fundamentals - Basic networking

Technical Background: - Cellular generations (2G, 3G, 4G, 5G) - Frequency spectrum concepts - Handoff and roaming basics

Estimated Time: 30 minutes

What is cellular architecture? Cellular networks divide geographic areas into “cells” served by base stations. When your phone moves between cells, the network hands off the connection seamlessly.

Why does it matter for IoT? IoT devices using cellular connectivity (NB-IoT, LTE-M, 5G) rely on this architecture for coverage, but many IoT devices are stationary and don’t need full mobility support.

Key Terms: - UE (User Equipment): Your IoT device - eNodeB/gNB: The cell tower/base station - EPC (Evolved Packet Core): The “brain” of the cellular network - MME: Manages device connections and mobility

821.3 Cellular Network Architecture Overview

Time: ~15 min | Difficulty: Intermediate | Unit: P08.C15.U01

Understanding how mobile cellular networks route IoT traffic is essential for deployment planning.

821.3.1 LTE/4G Architecture for IoT

The LTE architecture consists of three main domains: the User Equipment (UE), the Radio Access Network (RAN), and the Evolved Packet Core (EPC). IoT devices connect through the radio interface to base stations (eNodeBs), which then connect to the core network for routing to the internet and cloud services.

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor':'#2C3E50','primaryTextColor':'#fff','primaryBorderColor':'#16A085','lineColor':'#16A085','secondaryColor':'#E67E22','tertiaryColor':'#ecf0f1','textColor':'#2C3E50','fontSize':'14px'}}}%%
graph TB
    subgraph "IoT Devices (UE)"
        DEV1["Smartphones"]
        DEV2["NB-IoT Sensors"]
        DEV3["LTE-M Trackers"]
    end

    subgraph "RAN (Radio Access Network)"
        BS["Base Station<br/>eNodeB (4G)<br/>gNB (5G)"]
    end

    subgraph "EPC (Evolved Packet Core)"
        MME["MME<br/>Mobility<br/>Management"]
        SGW["S-GW<br/>Serving<br/>Gateway"]
        PGW["P-GW<br/>PDN<br/>Gateway"]
        HSS["HSS<br/>Subscriber<br/>Database"]
    end

    INTERNET["Internet"]

    subgraph "IoT Cloud"
        CLOUD1["MQTT Broker"]
        CLOUD2["CoAP Server"]
        CLOUD3["HTTPS API"]
    end

    DEV1 & DEV2 & DEV3 -->|LTE/5G/NB-IoT Radio| BS
    BS --> MME
    BS --> SGW
    MME --> HSS
    MME --> SGW
    SGW --> PGW
    PGW --> INTERNET
    INTERNET --> CLOUD1 & CLOUD2 & CLOUD3

    style DEV1 fill:#E67E22,stroke:#2C3E50,color:#fff
    style DEV2 fill:#E67E22,stroke:#2C3E50,color:#fff
    style DEV3 fill:#E67E22,stroke:#2C3E50,color:#fff
    style BS fill:#16A085,stroke:#2C3E50,color:#fff
    style MME fill:#16A085,stroke:#2C3E50,color:#fff
    style SGW fill:#16A085,stroke:#2C3E50,color:#fff
    style PGW fill:#16A085,stroke:#2C3E50,color:#fff
    style HSS fill:#16A085,stroke:#2C3E50,color:#fff
    style INTERNET fill:#2C3E50,stroke:#16A085,color:#fff
    style CLOUD1 fill:#2C3E50,stroke:#16A085,color:#fff
    style CLOUD2 fill:#2C3E50,stroke:#16A085,color:#fff
    style CLOUD3 fill:#2C3E50,stroke:#16A085,color:#fff

Figure 821.1

821.3.2 Core Network Components

MME (Mobility Management Entity): The MME is the control plane component that handles device attachment, authentication, and mobility. For IoT devices, the MME manages:

  • Device registration and deregistration
  • Security procedures (authentication, encryption)
  • Paging for incoming data when device is in sleep mode
  • Handover control between cells (for mobile devices)

S-GW (Serving Gateway): The S-GW is the user plane anchor that routes data packets between the device and the internet. It:

  • Buffers data during handover
  • Collects charging information
  • Routes packets to the correct P-GW

P-GW (PDN Gateway): The P-GW connects the cellular network to external IP networks (the internet). It:

  • Assigns IP addresses to devices
  • Performs policy enforcement
  • Handles QoS for different traffic types

HSS (Home Subscriber Server): The HSS stores subscriber information including:

  • Device identity (IMSI)
  • Service subscriptions
  • Authentication credentials (for SIM-based authentication)

821.3.3 IoT-Specific Optimizations

Cellular IoT technologies (NB-IoT and LTE-M) include optimizations for low-power, infrequent transmissions:

Power Saving Mode (PSM): Devices can enter deep sleep for extended periods (hours to days) while maintaining network registration. The network doesn’t page the device during PSM, dramatically reducing power consumption.

Extended Discontinuous Reception (eDRX): Devices negotiate longer sleep cycles between paging opportunities. Instead of waking every few seconds, devices can sleep for minutes, saving battery while remaining reachable.

Control Plane CIoT EPS Optimization: Small data payloads (up to ~1500 bytes) can be sent through the control plane (signaling channel) without establishing a full data bearer. This reduces latency and power for small, infrequent transmissions.

821.4 Cellular IoT Technology Selection

Choosing the right cellular IoT technology depends on mobility, coverage, data rate, and latency requirements.

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#16A085', 'secondaryColor': '#E67E22', 'tertiaryColor': '#7F8C8D'}}}%%
flowchart TD
    START([Cellular IoT<br/>Selection]) --> Q1{Device<br/>mobile?}

    Q1 -->|Yes - Moves| Q2{Need<br/>voice?}
    Q1 -->|No - Fixed| Q3{Deep indoor<br/>coverage?}

    Q2 -->|Yes| LTEM[LTE-M<br/>Asset tracking<br/>Wearables, Voice]
    Q2 -->|No| Q4{Data rate<br/>needed?}

    Q3 -->|Yes| NBIOT[NB-IoT<br/>Basements, meters<br/>10+ year battery]
    Q3 -->|No| Q4

    Q4 -->|<100 kbps| NBIOT
    Q4 -->|100 kbps - 1 Mbps| LTEM
    Q4 -->|>1 Mbps| Q5{Latency<br/>critical?}

    Q5 -->|Yes <10ms| URLLC[5G URLLC<br/>Industrial control<br/>V2X, Robotics]
    Q5 -->|No| EMBB[5G eMBB<br/>Video streaming<br/>AR/VR]

    style START fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style LTEM fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style NBIOT fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style URLLC fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff
    style EMBB fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff

Figure 821.2: Cellular IoT technology selection based on mobility, coverage, data rate, and latency requirements. NB-IoT for static deep-indoor sensors, LTE-M for mobile tracking with voice, 5G for high-bandwidth or ultra-low-latency applications.

821.4.1 NB-IoT (Narrowband IoT)

Best For: Stationary sensors with small, infrequent payloads requiring deep indoor penetration.

Characteristic Value
Data Rate Up to 250 kbps (typical: 20-60 kbps)
Latency 1.5-10 seconds (depending on PSM/eDRX)
Coverage +20 dB link budget gain (basement, underground)
Battery Life 10+ years on AA batteries (with PSM)
Mobility Stationary or very low mobility
Voice Not supported

Use Cases: - Smart meters (electricity, gas, water) - Underground parking sensors - Basement environmental monitors - Agricultural soil sensors

821.4.2 LTE-M (Cat-M1)

Best For: Mobile devices requiring higher data rates, voice support, and full handover.

Characteristic Value
Data Rate Up to 1 Mbps
Latency 10-15 ms (connected mode)
Coverage +15 dB link budget gain
Battery Life 5-10 years (with PSM/eDRX)
Mobility Full handover support
Voice VoLTE supported

Use Cases: - Asset tracking (vehicles, containers) - Wearables with emergency calling - Point-of-sale terminals - Connected health devices

821.4.3 5G IoT Profiles

5G introduces multiple service categories with different IoT applicability:

eMBB (Enhanced Mobile Broadband): High bandwidth for video streaming, AR/VR. Typically not battery-constrained.

URLLC (Ultra-Reliable Low-Latency Communication): Sub-10ms latency for industrial control, V2X, robotics. Requires power for continuous connectivity.

mMTC (Massive Machine-Type Communication): Evolved from NB-IoT/LTE-M concepts. High device density, low power.

821.5 Mobile Technology Evolution

Understanding the evolution of cellular technology helps contextualize IoT options.

Generation Technology Data Rate IoT Relevance
2G GSM, GPRS tens of kbps (GPRS) Legacy M2M (sunsetting)
3G UMTS, HSPA Mbps peak (HSPA) Early IoT (sunsetting)
4G LTE, LTE-A 10s-100s Mbps peak Current IoT (LTE-M/NB-IoT)
5G NR 100s Mbps-Gbps peak Emerging IoT (profile-dependent)
WarningNetwork Sunset Considerations

2G and 3G networks are being decommissioned globally. New IoT deployments should use:

  • NB-IoT for stationary, low-data applications
  • LTE-M for mobile applications or higher data rates
  • 5G only if specific features (URLLC, slicing) are required

Check carrier timelines in your deployment region before selecting technology.

821.6 Cellular vs. LPWAN Comparison

When planning IoT deployments, compare cellular options with unlicensed LPWAN alternatives.

Factor Cellular (NB-IoT/LTE-M) LoRaWAN/Sigfox
Spectrum Licensed (operator-managed) Unlicensed ISM bands
Coverage Carrier-dependent Self-deployed gateways
QoS Managed, with SLAs possible Best-effort, shared spectrum
Recurring Cost Per-device subscription Gateway infrastructure
Battery Life 5-10+ years 5-10+ years
Mobility Full handover (LTE-M) Limited
Data Rate Higher (250 kbps - 1 Mbps) Lower (0.3-50 kbps)

Sammy Sensor: “Think of cellular networks like a pizza delivery system!”

Lila the Light Sensor: “The cell tower is like the pizza shop - it covers a neighborhood. When you order (send data), they deliver to your house (the cloud)!”

Max the Motion Detector: “And if you’re driving while ordering, the system transfers your order to the next pizza shop along your route - that’s handover!”

Bella the Button: “NB-IoT devices are like ordering just garlic bread - small order, but they’ll deliver to your basement! LTE-M is like ordering a whole feast - bigger delivery, and they’ll follow your car!”

821.7 Summary

This chapter covered the fundamental architecture of cellular networks for IoT:

Key Concepts: - Cellular architecture includes UE (devices), RAN (base stations), and EPC (core network) - The MME handles mobility and control, while S-GW and P-GW route data - IoT-specific optimizations (PSM, eDRX) enable multi-year battery life

Technology Selection: - NB-IoT: Deep indoor, stationary, low data rate, 10+ year battery - LTE-M: Mobile, higher data rate, voice support, full handover - 5G: High bandwidth (eMBB) or ultra-low latency (URLLC)

Design Considerations: - Licensed spectrum provides managed QoS but requires subscriptions - Check carrier coverage and network sunset timelines - Match technology to mobility, data rate, and coverage requirements

821.8 What’s Next

Continue your mobile wireless review with: