Introduction

Radio spectrum is a limited natural resource shared by all users, so every country regulates who may transmit, on which frequency, with what power and for what service. Without regulation, systems would interfere with one another.

Regulatory bodies

• International: ITU (International Telecommunication Union), through ITU-R and the World Radiocommunication Conference (WRC), divides the spectrum among services (mobile, broadcasting, satellite, radar) for three ITU regions.
• National: each country has its own regulator, e.g. FCC (USA), Ofcom (UK), ETSI/CEPT (Europe, standards). In Nepal, the Radio Frequency Policy Determination Committee (under the Ministry of Communication and Information Technology) fixes frequency policy and the Nepal Telecommunications Authority (NTA) licenses operators under the Telecommunications Act, 2053.

Spectrum allocation issues

1. Allocation – deciding which band is used for which service (e.g. 900/1800 MHz for GSM, 2.1 GHz for 3G, 3.5 GHz for 5G).
2. Assignment – giving a specific block to a specific operator.
3. Harmonisation – using the same bands across countries so phones can roam and equipment is cheap.
4. Interference control – limits on transmit power, out-of-band emission, guard bands and border coordination.
5. Refarming – moving old services (e.g. 2G) to new technologies (4G/5G) in the same band.

Licensing issues

1. Licensed spectrum – exclusive use for a fixed period (e.g. 10–15 years), obtained by auction, beauty contest (comparative evaluation) or fixed fee. It guarantees quality but is costly.
2. Unlicensed spectrum – ISM bands (2.4 GHz, 5 GHz) used freely by Wi-Fi, Bluetooth under power limits; no protection from interference.
3. License conditions – coverage obligations, quality of service, number portability, security and lawful interception, payment of royalty and Rural Telecommunication Development Fund contribution.
4. Technology neutrality – whether the license allows any technology in the band.
5. Fair competition – spectrum caps to prevent one operator holding too much spectrum.

Good regulation balances efficient spectrum use, fair competition, affordable services and protection from interference.

Each generation of mobile communication brought a major change in technology: 1G was analog voice, 2G digital voice, 3G mobile data/multimedia, and 4G all-IP mobile broadband.

Key technology advancements

• 1G → 2G: digital modulation, speech coding, error control, encryption, SIM card, better spectrum efficiency, SMS.
• 2G → 3G: wideband CDMA with 5 MHz carriers, soft handoff, packet data, global roaming (IMT-2000), multimedia.
• 3G → 4G: OFDM to combat multipath, MIMO antennas, flat all-IP architecture (eNodeB connects to the EPC), low latency (~10 ms), carrier aggregation; voice carried as VoIP (VoLTE).

Mobile communication developed from early manual radio telephone systems to automatic cellular networks, and then through generations that added digital voice and finally mobile data.

Early development (pre-cellular)

• 1946: first public mobile telephone service in the USA (Mobile Telephone Service), single high-power transmitter, few channels, push-to-talk.
• 1960s: IMTS (Improved Mobile Telephone Service) – automatic dialling, full duplex, but still very limited capacity.
• 1970s: Bell Labs developed the cellular concept – small cells, low-power transmitters and frequency reuse – which solved the capacity problem.

First generation (1G) – analog cellular (1980s)

• Analog FM voice, FDMA, circuit switched.
• Systems: AMPS (USA, 1983), NMT (Nordic), TACS (UK), NTT (Japan).
• Problems: poor security (easy to eavesdrop), low capacity, no data, incompatible standards.

Second generation (2G) – digital (1990s)

• Digital modulation and speech coding, TDMA or CDMA, encryption, SMS.
• Systems: GSM (Europe, TDMA, 200 kHz), IS-136 (USA Digital AMPS), IS-95 cdmaOne (CDMA, 1.25 MHz), PDC (Japan).

2.5G – data on 2G networks

• HSCSD (circuit-switched multiple slots), GPRS (packet switched, up to ~171 kbps), EDGE (8-PSK, up to ~384 kbps), IS-95B.

Third generation (3G) – IMT-2000 (2000s)

• Wideband CDMA, 5 MHz carriers, up to 2 Mbps; video calls, internet, global roaming.
• Systems: UMTS/W-CDMA (3GPP), CDMA2000 (3GPP2), TD-SCDMA (China). Later HSPA (3.5G).

         GSM → GPRS → EDGE ─┐
 1G  →   IS-136 ────────────┼→ W-CDMA/UMTS → HSPA
(AMPS)   PDC ───────────────┘
         IS-95 → IS-95B ──────→ CDMA2000 1x → EV-DO
  1G        2G       2.5G           3G

Cellular systems have evolved roughly every ten years, each generation adding new services and better spectrum efficiency.

1G (1980s) – analog voice

• Analog FM, FDMA, 30 kHz channels, circuit switching.
• AMPS, NMT, TACS. Voice only, poor security, low capacity, no roaming between standards.

2G (1990s) – digital voice

• Digital modulation (GMSK, QPSK), speech coding, TDMA and CDMA, encryption, SIM.
• GSM, IS-136, IS-95. Services: voice, SMS, 9.6–14.4 kbps data.
• 2.5G: GPRS and EDGE add packet data (up to ~384 kbps), enabling WAP, MMS, e-mail.

3G (2000s) – mobile data and multimedia

• IMT-2000 family: UMTS/W-CDMA, CDMA2000, TD-SCDMA; 5 MHz carriers; up to 2 Mbps.
• Video calls, mobile internet, global roaming; soft handoff.
• 3.5G/3.75G: HSPA, HSPA+, EV-DO (up to tens of Mbps).

4G (2010s) – all-IP mobile broadband

• LTE-Advanced, WiMAX (IMT-Advanced): OFDMA, MIMO, carrier aggregation.
• Peak rates 100 Mbps (high mobility) to 1 Gbps (low mobility), latency ~10 ms, voice over IP (VoLTE), HD video streaming.

5G (2020s) – IMT-2020

• New Radio (NR), mmWave and sub-6 GHz bands, massive MIMO, beamforming, network slicing.
• Peak 20 Gbps, latency ~1 ms, up to 10⁶ devices/km².
• Use cases: eMBB, URLLC (self-driving, remote surgery), mMTC (IoT).

3G (IMT-2000) introduced mobile data and multimedia using wideband CDMA, while 4G (IMT-Advanced) provides high-speed all-IP broadband using OFDMA and MIMO.

Main technology advancements in 4G

1. OFDM splits the wide channel into many narrow orthogonal subcarriers, so each sees flat fading; a cyclic prefix removes ISI, avoiding complex equalisers.
2. MIMO gives spatial multiplexing (higher rate) and diversity (reliability).
3. Flat architecture – the eNodeB includes radio control functions previously done by the RNC, reducing latency.
4. Link adaptation and fast scheduling (adaptive modulation and coding, HARQ).
5. Carrier aggregation and support for both FDD and TDD.

Forward and reverse channel

• Forward channel (downlink): the radio channel used to carry information from the base station to the mobile user. Example: in GSM-900 the forward band is 935–960 MHz.
• Reverse channel (uplink): the radio channel used to carry information from the mobile user to the base station. Example: in GSM-900 the reverse band is 890–915 MHz.

Each channel type has voice (traffic) channels and control channels (forward control and reverse control channels used for call set-up, paging and access).

How 5G differs from 4G

5G also uses flexible numerology (subcarrier spacing 15–240 kHz) and small cells to serve many more users with lower energy per bit.

Significance of spectrum management

Spectrum management is the process of planning, allocating, assigning, licensing and monitoring the use of the radio frequency spectrum.

• The radio spectrum is limited and shared; without management, users would cause harmful interference.
• It ensures efficient use – frequency reuse, narrow guard bands, refarming old bands for new technology.
• It allows international harmonisation for roaming and cheap equipment.
• It protects critical services (aviation, defence, emergency, satellite).
• It supports fair competition between operators and earns revenue for the state (license and royalty fees).

Functions of the regulatory body

A telecom regulator (e.g. Nepal Telecommunications Authority, FCC in the USA, with ITU at international level) performs:

1. Spectrum planning and allocation – national frequency allocation table following ITU Radio Regulations; deciding bands for mobile, broadcast, Wi-Fi, etc.
2. Licensing – issuing service and frequency licenses through auction or fixed fees; setting license period and obligations.
3. Frequency assignment and coordination – giving specific channels to operators, coordinating at borders.
4. Monitoring and enforcement – checking that transmitters follow power and emission limits, detecting illegal transmitters, fining violators.
5. Type approval / standards – approving equipment and handsets to meet technical standards.
6. Tariff and quality of service regulation – setting QoS benchmarks, controlling unfair tariffs, consumer protection.
7. Interconnection – rules for interconnecting operators and sharing infrastructure.
8. Promoting universal access – managing funds (e.g. Rural Telecommunication Development Fund in Nepal) to extend service to rural areas.
9. Numbering – allocating number series and number portability.
10. Dispute resolution between operators and between operators and consumers.

Beyond 3G, wireless systems moved from voice-centred circuit networks to data-centred, all-IP broadband networks.

Key technological trends

1. OFDM/OFDMA instead of CDMA – wide channels split into many narrow subcarriers; robust to multipath and easy to scale bandwidth (LTE, WiMAX, Wi-Fi).
2. MIMO and smart antennas – multiple antennas for spatial multiplexing and beamforming, growing to massive MIMO in 5G.
3. All-IP flat architecture – no separate circuit-switched core; voice as VoIP (VoLTE); fewer network nodes, lower latency.
4. Higher-order adaptive modulation and coding – 64/256-QAM, turbo/LDPC codes, HARQ.
5. Wider bandwidth and carrier aggregation, use of new bands including mmWave.
6. Small cells and HetNets – macro, micro, pico and femto cells, Wi-Fi offloading for capacity.
7. Software-defined networking and virtualisation (SDN/NFV), cloud RAN, network slicing.
8. Convergence – fixed, mobile and broadcast services, and machine-type communication (IoT, M2M).
9. Cognitive radio and dynamic spectrum sharing to use spectrum more efficiently.

Result: data rates rose from ~2 Mbps (3G) to 1 Gbps (4G) and 20 Gbps (5G), with latency falling to a few ms.

Major benefits of wireless communication

• Mobility – users communicate while moving.
• No cabling – faster and cheaper deployment, especially in hilly or remote areas such as rural Nepal.
• Wide coverage and accessibility – voice, internet and banking reach places without wired infrastructure.
• Flexibility and scalability – easy to add users and relocate equipment.
• Rapid disaster recovery – temporary networks can be set up quickly.
• Supports new services – IoT, location services, mobile payments.

4G wireless communication system

4G is the fourth generation of cellular systems defined by ITU as IMT-Advanced; the main standard is LTE-Advanced (3GPP), with WiMAX 2 as another candidate.

Requirements / features

• Peak data rates of about 100 Mbps for high mobility and 1 Gbps for low mobility.
• All-IP packet-switched network; voice carried as VoIP (VoLTE).
• Latency about 10 ms; seamless handover with other networks.
• Scalable bandwidth 1.4–20 MHz, aggregated up to 100 MHz.

Key technologies

• OFDMA in downlink and SC-FDMA in uplink (lower PAPR saves mobile battery).
• MIMO (up to 8×8) for spatial multiplexing and diversity.
• Adaptive modulation (QPSK–64/256 QAM), turbo coding, HARQ.
• FDD and TDD modes.

Architecture (LTE / EPS)

 UE ── eNodeB ── S1 ── EPC
        |  X2          ├─ MME  (control, mobility)
      eNodeB           ├─ S-GW (user data)
                       └─ P-GW ── Internet

Only eNodeBs in the radio network (no RNC), giving a flat, low-latency design.

Applications: HD video streaming, online gaming, video conferencing, mobile broadband (e.g. Nepal Telecom and Ncell 4G LTE).

Duplexing is the technique that allows a communication link to send and receive at the same time (two-way communication), separating the forward (base to mobile) and reverse (mobile to base) channels either in frequency or in time.

A simplex system is one-way (paging), half duplex allows two-way but one direction at a time (walkie-talkie), and full duplex allows both directions at once (telephone). Duplexing methods give full or near full duplex operation.

1. Frequency Division Duplexing (FDD)

• Two separate frequency bands are used: one for the forward channel and one for the reverse channel, separated by a fixed duplex spacing.
• A duplexer filter in the handset and base station lets one antenna transmit and receive together.
• Example: GSM-900 uplink 890–915 MHz, downlink 935–960 MHz, spacing 45 MHz.

 Freq ↑  Downlink (forward) ███████████
       |      45 MHz spacing
       |  Uplink (reverse)   ███████████
       +------------------------------ time

• Advantages: true simultaneous transmission, no timing guard needed, suited to symmetric voice traffic.
• Disadvantages: needs paired spectrum and a duplexer; fixed split cannot adapt to asymmetric data.

2. Time Division Duplexing (TDD)

• A single frequency is used; time is divided into slots for forward and reverse transmission, switched fast enough that the user sees it as full duplex.
• Guard time is needed between transmit and receive.
• Example: DECT cordless phones, TD-SCDMA, LTE-TDD, WiMAX, 5G NR TDD bands.

 Freq ↑  [DL][UL][DL][UL][DL][UL]...  one carrier
       +------------------------------ time

• Advantages: unpaired spectrum, flexible DL/UL ratio for asymmetric data traffic, same channel in both directions helps beamforming.
• Disadvantages: needs strict time synchronisation, guard time reduces efficiency, limited range due to propagation delay.

• Forward channel (downlink): the radio channel used to carry information from the base station to the mobile user. Example: in GSM-900 the forward band is 935–960 MHz.
• Reverse channel (uplink): the radio channel used to carry information from the mobile user to the base station. Example: in GSM-900 the reverse band is 890–915 MHz.

Each channel type has voice (traffic) channels and control channels (forward control and reverse control channels used for call set-up, paging and access).

Forward and reverse channel

• Forward channel (downlink): the radio channel used to carry information from the base station to the mobile user. Example: in GSM-900 the forward band is 935–960 MHz.
• Reverse channel (uplink): the radio channel used to carry information from the mobile user to the base station. Example: in GSM-900 the reverse band is 890–915 MHz.

Each channel type has voice (traffic) channels and control channels (forward control and reverse control channels used for call set-up, paging and access).

Features of 5G

• Peak data rate up to 20 Gbps (eMBB) and user-experienced rate ~100 Mbps.
• Very low latency, about 1 ms (URLLC) for self-driving cars, remote surgery, industrial control.
• Massive connectivity: about 10⁶ devices/km² for IoT (mMTC).
• Uses sub-6 GHz and mmWave bands with massive MIMO and beamforming.
• Network slicing, SDN/NFV and cloud-native service-based core.
• Flexible numerology, small cells, better energy efficiency, mobility up to 500 km/h.

2G

First digital systems (GSM, IS-95, IS-136). Digital speech coding and error control gave clearer voice and higher capacity than analog 1G; authentication and encryption added security; SIM cards and SMS were introduced; international roaming in GSM.

3G

IMT-2000 systems (UMTS/W-CDMA, CDMA2000). Wideband CDMA and packet core brought mobile internet, video telephony and multimedia; HSPA later raised speeds greatly.

4G

IMT-Advanced (LTE-A). Flat all-IP architecture, OFDMA and MIMO for high spectral efficiency; voice as VoIP; scalable bandwidth; HD video and broadband on the move.

5G

IMT-2020 (NR). Three service types: eMBB (very high data rates), URLLC (ultra-reliable, low latency), mMTC (massive IoT). Uses mmWave, massive MIMO, edge computing and network slicing.

2G vs 3G

Prioritized handoff

Dropping an ongoing call is more annoying than blocking a new call, so systems give priority to handoff requests over new call requests:

• Guard channel concept: a fraction of channels in each cell is reserved only for handoffs.
• Queuing of handoff requests: a handoff request is queued during the time the signal falls from the handoff threshold to the minimum usable level, increasing the chance of getting a free channel.

Cell dragging

Cell dragging happens when a slow-moving user with a strong line-of-sight path (e.g. a pedestrian near the base station) travels far into a neighbouring cell while the received signal from the old base station stays above the handoff threshold. No handoff is triggered, so the user is "dragged" outside the planned cell boundary, causing interference and traffic management problems. It is reduced by careful setting of handoff thresholds and by using umbrella/microcell planning.

The TDMA path of cellular evolution started from analog FDMA systems and led to GSM and IS-136, which were then upgraded for packet data.

1G (analog FDMA)

• AMPS (USA), TACS (UK), NMT; analog FM voice on 30/25 kHz channels, one user per channel, circuit switched, no security, voice only.

2G (digital TDMA)

• GSM (Europe): 200 kHz carriers, each divided into 8 time slots (8 users per carrier), GMSK modulation, 9.6 kbps data, SMS, SIM, encryption.
• IS-136 (USDC/D-AMPS) (USA): keeps 30 kHz AMPS channels but puts 3 users per channel using π/4-DQPSK; backward compatible with AMPS.
• PDC (Japan): TDMA, 25 kHz.

2.5G (data upgrades on TDMA)

• HSCSD (High Speed Circuit Switched Data): one user gets up to 4 consecutive time slots; up to 57.6 kbps; circuit switched.
• GPRS (General Packet Radio Service): packet-switched, users share slots, up to 8 slots per user, up to ~171.2 kbps; adds SGSN and GGSN to the core; always-on internet.
• EDGE (Enhanced Data rates for GSM Evolution): 8-PSK modulation and adaptive coding on GSM carriers; up to ~384 kbps; also used by IS-136 operators to join the GSM path.

AMPS ──→ IS-136 ───────┐
                       ├──→ EDGE ──→ 3G W-CDMA
TACS/NMT → GSM → HSCSD → GPRS ─┘
  1G        2G       2.5G

Second generation (2G) improvements over 1G

• Digital modulation (GMSK, π/4-DQPSK) and digital speech coding – better voice quality and noise immunity.
• TDMA and CDMA – 3 to 8 or more users per carrier, higher spectral efficiency.
• Encryption and authentication, SIM card – secure, fraud-resistant.
• SMS and circuit-switched data (9.6–14.4 kbps).
• Mobile-assisted handoff (MAHO), international roaming (GSM).
• 2.5G: GPRS and EDGE packet data up to ~384 kbps.

Third generation (3G) improvements

• Wideband CDMA with 5 MHz carriers (UMTS, CDMA2000), up to 2 Mbps.
• Packet-switched core alongside circuit core – mobile internet, e-mail, streaming.
• Multimedia services – video calling, MMS.
• Soft handoff, fast power control, variable spreading factor for different data rates.
• Global standard (IMT-2000) and roaming.
• 3.5G HSPA: adaptive modulation (16-QAM), HARQ, fast scheduling, up to 14–42 Mbps.

Beyond 3G (4G and 5G)

• OFDMA/SC-FDMA replacing CDMA; scalable bandwidth, carrier aggregation.
• MIMO and later massive MIMO with beamforming.
• All-IP flat network, VoLTE, latency ~10 ms (4G) and ~1 ms (5G).
• Peak rates 1 Gbps (4G) and 20 Gbps (5G).
• Higher order QAM, turbo/LDPC/polar codes.
• Small cells, HetNets, SDN/NFV, network slicing, massive IoT support.

Wireless communication has grown from a few hundred radio-telephone users to billions of mobile subscribers in about 50 years, driven by the cellular concept and cheaper digital technology.

Technology evolution

1. Early radio (1897–1940s) – Marconi's radio transmission; police and military mobile radios.
2. Pre-cellular mobile telephone (1946–1970s) – MTS and IMTS in USA; one high-power transmitter covering a city, very few channels, long waiting lists.
3. Cellular concept (1970s) – Bell Labs: small cells, frequency reuse and handoff, giving large capacity.
4. 1G (1980s) – analog AMPS, NMT, TACS; bulky, expensive phones.
5. 2G (1990s) – digital GSM, IS-95, IS-136; small cheap handsets, SMS; worldwide adoption.
6. 3G (2000s) – UMTS, CDMA2000; mobile internet; smartphones appear.
7. 4G (2010s) – LTE; mobile broadband, apps, video streaming.
8. 5G (2020s) – very high rate, low latency, IoT. Alongside: cordless phones, paging, Wi-Fi (WLAN), Bluetooth (WPAN), satellite phones.

Worldwide market penetration

• Early growth was slow: in the 1980s cellular phones were luxury items; penetration was under 1 % even in rich countries.
• After 2G digital standards (1990s), costs fell and subscribers grew at about 40–50 % per year; mobile subscribers passed fixed lines worldwide around 2002.
• Global mobile subscriptions passed 1 billion in 2002, about 5 billion by 2010 and more than 8 billion subscriptions (over 100 % penetration) in the 2020s.
• Growth after 2010 came mainly from developing countries in Asia and Africa, where mobile leap-frogged fixed lines. In Nepal, mobile penetration is now above 100 % of population (NTA reports), while fixed lines are a few percent.
• Market focus shifted from voice to data: smartphone and mobile broadband subscriptions are now the main growth area.

Subscribers
 (billion)                         ___ 8+
                              ____/
                         ___/
                    ___/
 ______________,--'
 1985    1995    2005    2015    2025

Reasons for rapid penetration: falling handset and tariff prices, prepaid service, digital standards with economies of scale, and mobile data applications.