--- title: "Forward/reverse channel and 5G versus 4G" subject: "Wireless Communication" chapter: 1 key: "semester_7/wireless_communication:forward-reverse-5g-vs-4g" source: https://www.bctengineer.com/q/semester_7/wireless_communication/forward-reverse-5g-vs-4g site: BCT Engineering --- # Forward/reverse channel and 5G versus 4G Wireless Communication · Chapter 1: Introduction - Asked in: 2079 Bhadra, 2+2 marks; 2079 Chaitra, 2+2 marks (asked 2 times) - Video: [Uplink and Downlink communication – Forward and Reverse Channels](https://www.youtube.com/watch?v=r7196pdGpew) — Commsbrief Limited Official - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/wireless_communication/forward-reverse-5g-vs-4g - Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-1 ## Question Define forward and reverse channel. How 5G will be different from 4G mobile communication? ## Short answer Forward channel carries base station to mobile; reverse channel carries mobile to base station, for example GSM 935-960 MHz downlink and 890-915 MHz uplink. 5G differs from 4G in peak rate up to 20 Gbps, about 1 ms latency, mmWave, massive MIMO and beamforming, network slicing, and support for eMBB, URLLC and mMTC. ## Answer #### 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. Both directions contain voice (traffic) channels and control channels. The control channels (forward control channel and reverse control channel) carry call set-up, paging and access messages. #### How 5G differs from 4G | Feature | 4G (LTE-A) | 5G (NR) | |---|---|---| | Peak data rate | ~1 Gbps | up to 20 Gbps | | Latency | ~10 ms | ~1 ms | | Spectrum | below 6 GHz | sub-6 GHz + mmWave (24–100 GHz) | | Antennas | MIMO up to 8×8 | Massive MIMO (64+ elements), beamforming | | Device density | ~10⁵/km² | ~10⁶/km² | | Core | EPC, hardware based | Service-based, cloud-native, SDN/NFV, network slicing | | Use cases | Mobile broadband | eMBB, URLLC, mMTC (IoT) | 5G also uses flexible numerology (subcarrier spacing 15–240 kHz) and small cells to serve many more users with lower energy per bit. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the forward channel? A. The channel from the mobile to the base station B. The channel from the base station to the mobile (downlink) C. A channel used only for control signals D. A channel between two base stations Answer: B. Forward = downlink, base station to mobile; e.g. GSM-900 935-960 MHz. (Key point: Forward channel) 2. In GSM-900, which band is the reverse channel? A. 890-915 MHz B. 935-960 MHz C. 1710-1785 MHz D. 2.4 GHz Answer: A. Uplink (mobile to BS) is 890-915 MHz; downlink is 935-960 MHz. (Key point: Reverse channel example) 3. Compared with 4G, 5G offers: A. Similar 1 Gbps rate with 10 ms latency B. Up to 20 Gbps peak rate and about 1 ms latency C. Lower rate but bigger coverage D. Only sub-6 GHz bands Answer: B. 5G peak is up to 20 Gbps with ~1 ms latency versus ~1 Gbps and ~10 ms for 4G. (Key point: 5G latency and rate) 4. Which describes 5G antennas and core? A. Massive MIMO with beamforming; service-based cloud-native core with network slicing B. MIMO up to 8x8; hardware-based EPC C. Single antenna; circuit core D. Massive MIMO but circuit-switched core Answer: A. 5G uses 64+ element massive MIMO and an SDN/NFV, sliceable core. (Key point: 5G antennas and core) ## Related in Wireless Communication - [Forward/reverse channel and features of 5G](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aforward-reverse-5g-features) — Wireless Communication, chapter 1 - [3G versus 4G mobile communication](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3A3g-vs-4g) — Wireless Communication, chapter 1, asked 6× - [Forward and reverse channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aforward-reverse-channel) — Wireless Communication, chapter 1 - [Comparison of 1G to 4G mobile standards](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Agenerations-1g-to-4g-comparison) — Wireless Communication, chapter 1, asked 6× - [Benefits of wireless communication and 4G](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Awireless-benefits-4g) — Wireless Communication, chapter 1 - [Parameters of mobile multipath channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Amobile-multipath-channel-parameters) — Wireless Communication, chapter 3 ## Related in other subjects - [Forward vs reverse engineering merits and demerits](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Aforward-reverse-engineering-merits) — Object Oriented Analysis and Design, chapter 4, asked 3× - [Short note: Information in forward/reverse engineering](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Ashort-note-information-content-forward-reverse) — Object Oriented Analysis and Design, chapter 4 - [Forward and reverse biased pn junction](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Aforward-reverse-bias) — Electrical Engineering Material, chapter 6