Lesson 6: Cellular Networks (CRITICAL)

This is the money section — if you want to work for telecom operators (Orange, Ooredoo, Tunisie Telecom), vendors (Nokia, Huawei, Ericsson), or in 5G/6G R&D, most jobs live here.

Modern cellular combines:

RF and physical layer (Lessons 1–4)
Digital communications & modulation (Lesson 3)
IP networking (Lesson 5)
Mobility, QoS, massive scale, slicing, beamforming

Why Cellular Networks Are Critical

Main revenue source for mobile operators (voice, data, SMS, IoT)
Highest complexity: RF + IP + mobility + security + virtualization
Fastest evolution: 2G → 5G in ~25 years (6G research already active)
Typical job roles: Radio Network Optimization, Core Engineer, RAN Engineer, 5G Planner, Drive Test Engineer

1. Cellular Evolution – From Voice to Everything

Generation	Access Technology	Peak Speed (theoretical)	Latency	Core Network	Key Innovation
2G (GSM)	TDMA / FDMA	~384 kbps (EDGE)	~100 ms	Circuit + GPRS	Digital voice, SMS
3G (UMTS)	WCDMA	~42 Mbps (HSPA+)	~50 ms	Circuit + Packet	Mobile Internet
4G (LTE)	OFDMA / SC-FDMA	~1–3 Gbps	~20 ms	EPC (all-IP)	Flat architecture, high-speed mobile
5G (NR)	OFDMA + massive MIMO	10–20 Gbps	<1 ms (URLLC)	5GC (cloud-native)	Network slicing, beamforming, mmWave

5G service pillars:

eMBB – enhanced Mobile Broadband (very high throughput)
URLLC – Ultra-Reliable Low Latency Communications (mission-critical)
mMTC – massive Machine-Type Communications (massive IoT)

2. Architecture – RAN + Core

Radio Access Network (RAN)

4G: eNodeB (eNB) — single integrated base station
5G: gNodeB (gNB) — often split architecture:
- CU (Central Unit) – higher layers
- DU (Distributed Unit) – lower layers
- RU (Radio Unit) – RF front-end
  → Enables Cloud RAN, Open RAN, flexible deployment

4G Core – EPC (Evolved Packet Core)

Flat, all-IP architecture:

MME – Mobility Management Entity (control plane, authentication, mobility)
HSS – Home Subscriber Server (subscriber database)
SGW – Serving Gateway (user plane anchor)
PGW – PDN Gateway (IP allocation, policy, Internet breakout)
PCRF – Policy & Charging Rules Function

Typical 4G EPC: UE → eNB → MME/SGW/PGW → PDN (Internet)

5G Core – 5GC (Service-Based Architecture)

Cloud-native, microservices-based:

AMF – Access & Mobility Management Function
SMF – Session Management Function
UPF – User Plane Function
UDM – Unified Data Management
AUSF – Authentication Server Function
NRF – Network Repository Function (service discovery)
Others: PCF, NSSF, NEF, CHF, …

5G Core: HTTP/2 + REST APIs between Network Functions

IMS (IP Multimedia Subsystem) – SIP-based subsystem for VoLTE / VoNR (voice over LTE/5G)

3. Key Concepts

Handover

Seamless cell change while moving.

Measurement → Decision → Preparation → Execution → Path Switch
5G supports Xn handover (direct gNB–gNB) for lower latency

Roaming

Home network ↔ Visited network via GRX/IPX. Authentication stays with home operator.

QoS (Quality of Service)

5QI (5G QoS Identifier) defines priority, packet delay budget, error rate
Dedicated bearers/flows for voice, video, URLLC, best-effort

Network Slicing

One physical infrastructure → multiple virtual networks (slices)

Each slice: dedicated resources, isolation, SLA
Examples:
- eMBB slice → high throughput (video streaming)
- URLLC slice → ultra-low latency (autonomous driving)
- mMTC slice → massive connections (smart meters)

Massive MIMO & Beamforming

64T64R, 128T128R antenna arrays
Spatial multiplexing → many users at once
Beamforming directs energy → higher SNR, less interference

Next Steps – Hands-on Practice

Deploy private 4G/5G lab: Open5GS (5GC) + srsRAN (gNB + UE emulator)
Simulate handover, slicing, mobility in ns-3
Capture VoLTE calls → analyze SIP + GTP with Wireshark

Milestone Questions

Main differences between 4G EPC and 5G Core?
Why was network slicing introduced in 5G? Give three concrete use cases.
How does massive MIMO increase network capacity?
Describe the basic steps of a 5G Xn handover.
Why is the 5G Core designed as a Service-Based Architecture (SBA)?

Master this section → VoIP, security, satellite integration, and real projects become much easier to understand.

Continue to Lesson 7: Telephony & VoIP →