---
title: "Forward/reverse channel and features of 5G"
subject: "Wireless Communication"
chapter: 1
key: "semester_7/wireless_communication:forward-reverse-5g-features"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/forward-reverse-5g-features
site: BCT Engineering
---

# Forward/reverse channel and features of 5G

Wireless Communication · Chapter 1: Introduction

- Asked in: 2080 Chaitra, 2+2 marks
- Video: [Chapter-5 Forward and Reverse channel of W-CDMA and CDMA 2000](https://www.youtube.com/watch?v=9XKskoZvlkk) — Jagadeesh Hallur
- 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-features
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-1

## Question

Define forward and reverse channel. List out the features of 5G.

## Short answer

Forward channel (downlink) is from base station to mobile; reverse channel (uplink) is from mobile to base station. 5G features include up to 20 Gbps data rate, ~1 ms latency, massive MIMO with mmWave bands, network slicing, and support for 10^6 devices/km² for IoT.

## 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.

#### 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The reverse channel carries information:
   A. From mobile to base station
   B. From base station to mobile
   C. Only paging
   D. Only SMS
   Answer: A. Reverse = uplink, mobile to BS. (Key point: Reverse channel)

2. Which 5G target suits self-driving cars and remote surgery?
   A. About 1 ms latency (URLLC)
   B. 20 Gbps peak rate only
   C. 10^6 devices per km2 only
   D. Mobility 5 km/h
   Answer: A. Ultra-reliable low-latency communication needs ~1 ms latency. (Key point: 5G URLLC)

3. What device density does 5G mMTC target?
   A. About 10^3 per km2
   B. About 10^6 per km2
   C. About 10^2 per km2
   D. About 10^4 per km2
   Answer: B. 5G supports roughly a million IoT devices per km2. (Key point: Massive connectivity)

4. Which technologies does 5G use?
   A. Only sub-6 GHz with single antennas
   B. Analog FM and FDMA
   C. mmWave, massive MIMO, beamforming, network slicing and service-based core
   D. A circuit-switched RNC-based core
   Answer: C. These are listed 5G features. (Key point: 5G radio and core)

## Related in Wireless Communication

- [Forward/reverse channel and 5G versus 4G](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aforward-reverse-5g-vs-4g) — Wireless Communication, chapter 1, asked 2×
- [Forward and reverse channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aforward-reverse-channel) — Wireless Communication, chapter 1
- [Features introduced from 2G to 5G](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afeatures-2g-to-5g) — Wireless Communication, chapter 1
- [Forward CDMA (IS-95) channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aforward-cdma-is95-channel) — Wireless Communication, chapter 8, asked 4×
- [Reverse CDMA (IS-95) channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Areverse-cdma-is95-channel) — Wireless Communication, chapter 8

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- [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
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