Describe mobile communication systems (3G, 4G, 5G)

Communications Technology – Mobile Communication Systems

Learning Objective

Describe the structure of a cellular network, the key characteristics and enabling technologies of 3G, 4G and 5G, the role of satellite links, and the wireless technologies and protocols that support modern mobile devices (Cambridge AS & A‑Level IT 9626 – 14.6 – 14.8).

1. Overview of Mobile Generations

Mobile communication has evolved through successive generations, each delivering higher data rates, lower latency and new services.

• 1G – Analogue voice only.
• 2G – Digital voice, SMS, limited data (GPRS/EDGE).
• 3G – Broadband data, video calls, mobile internet.
• 4G – High‑speed IP‑based broadband, HD video, VoIP.
• 5G – Ultra‑high speed, ultra‑low latency, massive device connectivity.

2. End‑to‑End Cellular Network Architecture

The mobile network is conventionally divided into three logical layers. The diagram below (Figure 1) shows the main elements and the flow of traffic from a User Equipment (UE) to the Internet.

2.1 Logical Layers

1. User Equipment (UE) – Smartphones, tablets, wearables, IoT modules.
2. Radio Access Network (RAN)
   • Base‑station types: Node B (3G), eNodeB (4G), gNodeB (5G).
   • Radio technologies:
     • 3G – WCDMA, CDMA2000.
     • 4G – OFDMA (downlink), SC‑FDMA (uplink).
     • 5G – OFDM with flexible numerology, massive MIMO, beamforming.
   • Back‑haul: microwave, fibre, millimetre‑wave (mmWave) links to the core.
   • Key RAN functions: hand‑over (intra‑ and inter‑cell), radio‑resource control, QoS enforcement.
3. Core Network
   • 3G – Circuit‑Switched (CS) voice + Packet‑Switched (PS) data (GPRS/EDGE).
   • 4G – Evolved Packet Core (EPC) – fully IP‑based.
   • 5G – 5G Core (5GC) – Service‑Based Architecture (SBA) with network slicing.

2.2 Core‑Network Elements by Generation

2.3 Satellite‑Based Mobile Services

Satellites complement terrestrial cells in remote, maritime or disaster‑affected areas.

• Frequency bands – L‑band (1–2 GHz) for low‑rate services; Ka‑band (26–40 GHz) for high‑throughput broadband.
• Hybrid architectures – Ground‑based RAN connects to a satellite gateway; the satellite can act as a back‑haul or as a direct “space‑cell” (e.g., 5G‑NR on Non‑Terrestrial Networks – NTN).
• Typical use‑cases – Rural broadband, disaster recovery, aeronautical and maritime communications.

3. Third Generation (3G)

• Key standards: UMTS (WCDMA), CDMA2000.
• Typical downlink data rate: 384 kbps (mobile) – 2 Mbps (stationary).
• Frequency bands: 850 MHz, 900 MHz, 1900 MHz, 2100 MHz.
• Core network: MSC/VLR + SGSN/GGSN (CS + PS).
• Modulation & coding: QPSK, 16‑QAM; convolutional or Turbo coding.
• Key enabling technologies: WCDMA, soft hand‑over, packet‑switched data (GPRS/EDGE).

4. Fourth Generation (4G)

• Key standards: LTE (Long Term Evolution), LTE‑Advanced.
• Typical downlink data rate: 100 Mbps (mobile) – 1 Gbps (stationary).
• Frequency bands: 700 MHz – 2600 MHz (region‑dependent).
• Core network: EPC – MME, SGW, PGW, HSS (all‑IP).
• Modulation & coding: OFDMA (downlink), SC‑FDMA (uplink), up to 256‑QAM, adaptive modulation.
• Latency: 30–50 ms (typical).
• Key enabling technologies: MIMO (2×2, 4×4), carrier aggregation, VoLTE (IP‑based voice), LTE‑Advanced features (e.g., higher order MIMO, LTE‑Pro).

5. Fifth Generation (5G)

• Key standards: 3GPP Release 15/16 – NR (New Radio).
• Typical downlink data rate: 1–10 Gbps (mobile) – up to 20 Gbps (fixed).
• Frequency bands: Sub‑6 GHz (e.g., 3.5 GHz) and mmWave (24 GHz – 100 GHz).
• Core network: 5GC – Service‑Based Architecture, network slicing, edge computing.
• Modulation & coding: OFDM with flexible numerology, up to 1024‑QAM; LDPC for data, Polar codes for control.
• Latency: 1 ms (URLLC) – 10 ms (eMBB).
• Key enabling technologies:
  • Massive MIMO (64‑antenna+ arrays)
  • Beamforming & beam‑tracking
  • Carrier aggregation across sub‑6 GHz and mmWave
  • Network slicing (eMBB, URLLC, mMTC)
  • Multi‑Access Edge Computing (MEC)
• Use‑case categories: Enhanced Mobile Broadband (eMBB), Ultra‑Reliable Low‑Latency Communications (URLLC), Massive Machine‑Type Communications (mMTC).

6. Comparison of 3G, 4G and 5G

7. Wireless Technologies Supporting Mobile Devices

Modern smartphones combine the cellular link with several short‑range wireless standards.

• Wi‑Fi – IEEE 802.11ac (5 GHz, up to 3.5 Gbps) and 802.11ax (Wi‑Fi 6, up to 9.6 Gbps). Used for indoor broadband, hotspot tethering and data off‑load.
• Bluetooth 5 – Low‑Energy mode, up to 2 Mbps, range ≈240 m (outdoor). Enables wearables, audio streaming, file transfer.
• NFC (Near‑Field Communication) – 13.56 MHz, ≤424 kbps, ≤10 cm. Used for contactless payments and quick device pairing.
• Infra‑red (IR) – Simple line‑of‑sight remote control; rarely used for data.
• Microwave / point‑to‑point radio – Forms part of the cellular back‑haul and private‑network links.

7.1 Security Issues & Mitigation

• Wi‑Fi: WPA3 encryption, 802.11w management‑frame protection, rogue‑AP detection.
• Bluetooth: Secure Simple Pairing (SSP), LE Secure Connections, regular firmware updates.
• NFC: Very short range limits eavesdropping; secure element & tokenisation for payments.
• Cellular: Mutual authentication via SIM/USIM, integrity protection (EPS integrity), encryption (AES‑128, SNOW‑3G for 4G; 128‑bit SNOW‑3G / 128‑bit AES for 5G).

8. Network Protocols in Mobile Systems (Syllabus 14.6)

Mobile devices use the same IP‑based protocol suite as wired networks, with additional layers for radio‑specific control.

• IP (Internet Protocol) – IPv4/IPv6; 5G mandates IPv6 for massive device counts.
• TCP (Transmission Control Protocol) – Reliable, connection‑oriented transport (web, file transfer).
• UDP (User Datagram Protocol) – Connectionless, low‑overhead; preferred for real‑time services (VoIP, video, gaming).
• SCTP (Stream Control Transmission Protocol) – Supports multi‑homing and ordered delivery; used in LTE signalling (e.g., S1‑AP).
• RRC (Radio Resource Control) & NAS (Non‑Access Stratum) – Control signalling between UE and the core (attach, authentication, session management).
• QoS handling – DSCP (Differentiated Services Code Point) in IP headers; 5G QoS Identifier (5QI) maps traffic to appropriate radio resources.

9. Theoretical Capacity – Shannon‑Hartley Law

The maximum achievable data rate for a communication channel is given by:

$$C = B \log_2\!\bigl(1 + \text{SNR}\bigr)$$

where C is capacity (bits s⁻¹), B is bandwidth (Hz) and SNR is the signal‑to‑noise ratio. 5G’s use of very wide bandwidths (up to 400 MHz in mmWave) together with high SNR achieved through massive MIMO and beamforming dramatically increases C compared with 3G and 4G.

10. Future Directions (Syllabus 14.8)

• Integration of satellite and terrestrial 5G (Non‑Terrestrial Networks – NTN) for truly global coverage.
• Emerging 6G research: terahertz (THz) frequencies, AI‑driven network orchestration, holographic‑type communications, tactile internet.
• Continued expansion of the Internet of Things via massive Machine‑Type Communications (mMTC) and ultra‑dense small‑cell deployments.

11. Suggested Diagrams for Teaching

• Evolution of mobile generations (1G‑5G) showing frequency bands, typical data rates, latency, and key enabling technologies.
• Simplified cellular architecture (UE → RAN → Core → Internet) with hand‑over points and a satellite back‑haul link.
• Core‑network element map for each generation (MSC/VLR, MME/SGW/PGW, AMF/SMF/UPF).