--- title: "Uses of microwaves in communication and protocols" subject: "RF and Microwave Engineering" chapter: 1 key: "semester_7/rf_and_microwave_engineering:microwave-communication-uses-protocols" source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/microwave-communication-uses-protocols site: BCT Engineering --- # Uses of microwaves in communication and protocols RF and Microwave Engineering · Chapter 1: Introduction - Asked in: 2081 Baisakh, 2+6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/microwave-communication-uses-protocols - Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-1 ## Question List out the uses of microwaves in communication systems and [?] communication protocols of any three of them. ## Short answer Microwaves are used in terrestrial backhaul, satellite, cellular, Wi-Fi, Bluetooth, radar, GPS, and telemetry. Three protocols: Wi-Fi (2.4/5 GHz, OFDM, CSMA/CA), cellular (GSM 900/1800 MHz with GMSK/TDMA, LTE OFDMA, 5G NR), and satellite (C/Ku/Ka bands, FDMA/TDMA/CDMA, QPSK/DVB-S2). ## Answer #### Uses of microwaves in communication systems 1. Terrestrial point-to-point microwave links (backhaul for mobile networks and TV relay). 2. Satellite communication (telephony, DTH TV, VSAT, Internet). 3. Cellular mobile communication (GSM, CDMA, LTE, 5G). 4. Wireless LAN (Wi-Fi) and WiMAX. 5. Personal area networks (Bluetooth, ZigBee). 6. Navigation (GPS, radar beacons, aircraft landing systems). 7. Radar (it conveys target information through reflected signals). 8. Deep-space and telemetry links. #### Communication protocols of three of them **1. Wi-Fi (IEEE 802.11 WLAN)** - Bands: 2.4 GHz ISM (2.400–2.4835 GHz), 5 GHz (5.15–5.85 GHz), and 6 GHz for Wi-Fi 6E. - Channels: 20/40/80/160 MHz wide. At 2.4 GHz there are 13 channels 5 MHz apart, and only 1, 6 and 11 do not overlap. - Modulation: OFDM with BPSK up to 1024-QAM (802.11ax). 802.11b used DSSS/CCK. - Access: CSMA/CA with optional RTS/CTS. Duplexing is TDD. - Rates: 11 Mbps (b), 54 Mbps (a/g), 600 Mbps (n, MIMO), about 9.6 Gbps (ax). - Security: WPA2/WPA3 (AES). **2. Cellular mobile (GSM / LTE / 5G NR)** - GSM: 900/1800 MHz, 200 kHz carriers, GMSK modulation, TDMA with 8 time slots per carrier, FDD (uplink 890–915 MHz, downlink 935–960 MHz). - LTE (4G): 700 MHz–2.6 GHz, 1.4–20 MHz bandwidth, OFDMA downlink and SC-FDMA uplink, up to 64-QAM, MIMO, FDD or TDD. - 5G NR: FR1 below 6 GHz and FR2 at 24–52 GHz (mm-wave), up to 400 MHz bandwidth, flexible numerology, massive MIMO and beamforming. - Architecture: mobile station, base station (BTS/eNodeB/gNB), core network. Frequency reuse in hexagonal cells, with handover between cells. **3. Satellite communication** - Geostationary orbit at 35,786 km. The ground-to-satellite delay is about 120 ms, so one hop (up and down) takes about 240 ms. - Bands: C band (uplink 5.925–6.425 GHz, downlink 3.7–4.2 GHz, written 6/4 GHz), Ku band (14/12 GHz), Ka band (30/20 GHz). - A transponder receives the uplink, translates the frequency down, amplifies with a TWTA or SSPA, and retransmits. Typical transponder bandwidth is 36 MHz. - Access: FDMA, TDMA, CDMA. Example: VSAT networks with QPSK/8PSK and DVB-S2. - Uplink is at the higher frequency because the ground station can afford more power to overcome the greater loss. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is NOT listed as a microwave use in communication systems? A. Satellite communication B. Wireless LAN C. Submarine sonar communication D. Terrestrial point-to-point links Answer: C. Sonar is acoustic; microwaves are absorbed in water. (Key point: Uses) 2. Which multiple access schemes does LTE (4G) use? A. TDMA on both links B. CSMA/CA on both links C. OFDMA on the downlink and SC-FDMA on the uplink D. SC-FDMA on the downlink and OFDMA on the uplink Answer: C. LTE downlink uses OFDMA; uplink uses SC-FDMA because its lower peak-to-average power ratio suits handsets. (Key point: LTE) 3. Which medium access method does Wi-Fi (802.11) use? A. TDMA with fixed slots B. CSMA/CA with optional RTS/CTS C. FDMA with fixed channels per user D. Token passing Answer: B. Wi-Fi stations listen before sending and avoid collisions with CSMA/CA, optionally using RTS/CTS. 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