Mobile and Wireless Communication Technologies
What this domain covers
Cellular and wireless technology: how a radio network reuses spectrum across cells, how the generations differ, and how many users share one carrier.
Core rules
- Cellular principle: many low-power cells instead of one high-power transmitter; the same frequencies are reused in cells far enough apart (cluster of N cells, reuse distance D = R√(3N)).
- Handover keeps a call alive while the mobile moves between cells; roaming gives service on another operator's network.
- GSM (2G): 900/1800 MHz, TDMA, 200 kHz carriers, 8 time slots, 124 carriers in GSM900, SMS, about 13 kbps speech. GPRS/EDGE add packet data.
- 3G: UMTS/WCDMA, 5 MHz carriers, 2100 MHz in India. 4G: LTE, all-IP, OFDMA downlink and SC-FDMA uplink, VoLTE. 5G NR: sub-6 GHz and mmWave, with eMBB, URLLC and mMTC use cases.
- Multiple access: FDMA splits frequency, TDMA splits time, CDMA splits by code, OFDMA splits into many orthogonal subcarriers.
- Duplexing: FDD uses paired uplink/downlink bands; TDD uses one band split in time.
- Registers: HLR holds permanent subscriber data, VLR the visiting copy, AUC authentication keys, EIR equipment identity.
Worked example
An operator holds 84 duplex channels and uses a 7-cell cluster. Channels per cell = 84 ÷ 7 = 12. Reasoning: every cell in a cluster must use a different channel set, so the total is divided equally; the cluster then repeats, so capacity grows with coverage.
Traps
- Saying 1G was digital - it was analogue.
- Confusing CDMA (code) with FDMA (frequency).
- Treating handover and roaming as the same thing.
- Assuming mmWave 5G gives wide coverage - it gives short range and needs dense small cells.