Why does Wi-Fi use collision avoidance instead of collision detection like wired Ethernet?

A wireless transmitter generally cannot listen for collisions while sending, because its own signal overwhelms any incoming one, and a station may not even hear another that is colliding at the receiver (the hidden-terminal problem). So Wi-Fi avoids collisions in advance using carrier sensing, random backoff, and acknowledgments rather than detecting them mid-transmission.

What is the difference between a wireless network and a mobile network?

Wireless refers to the use of a radio link instead of a wire for a single hop, while mobility refers to a device changing its point of attachment to the network over time. A device can be wireless but stationary, or mobile across wired docking points; mobile networking specifically addresses keeping connectivity and addressing intact as the attachment point changes.

Wireless and Mobile Networking

Wireless and mobile networking covers communication over shared radio links and the support needed when end systems change their point of attachment, spanning Wi-Fi, cellular networks, and the protocols that keep a moving device connected.

Definition

Wireless and mobile networking is the subfield of computer networks concerned with data communication over wireless (radio) links and with the network mechanisms that maintain connectivity, addressing, and sessions for mobile, location-changing end systems.

Scope

This area covers the distinctive challenges of wireless links — attenuation, interference, multipath, and a hidden-terminal problem absent from wired media — and the technologies that address them: IEEE 802.11 wireless LANs with their CSMA/CA medium access, cellular networks from earlier generations through 4G/5G architecture, and mobility management, which lets a device retain connectivity and addressing as it moves between networks. It treats wireless as a link and access technology with implications up the stack, and excludes detailed radio-frequency physical-layer engineering.

Sub-topics

Core questions

How do wireless links differ from wired links, and how do those differences affect protocols?
How does the hidden-terminal problem arise, and how does CSMA/CA mitigate collisions in Wi-Fi?
How is a cellular network organized into cells, base stations, and a core, and how has it evolved across generations?
How is a host's address and routing maintained when it moves between networks (mobility management)?
What is the difference between handling mobility and merely handling wireless links?

Key concepts

wireless link impairments (attenuation, interference, multipath)
hidden-terminal problem
CSMA/CA
IEEE 802.11 (Wi-Fi)
access points and association
cellular cells and base stations
frequency reuse
handoff (handover)
Mobile IP and care-of addresses
4G/5G core networks

Key theories

Wireless link impairments and CSMA/CA: Radio links suffer from signal attenuation, interference, and multipath, and collision detection is impractical, so Wi-Fi uses carrier-sense multiple access with collision avoidance plus optional RTS/CTS handshakes to address the hidden-terminal problem.
Cellular architecture and frequency reuse: Cellular networks divide a region into cells served by base stations and reuse frequencies across non-adjacent cells to maximize spectral efficiency, with a core network handling authentication, session management, and connection to the wider Internet.
Mobility management and indirection: Keeping a moving device reachable requires tracking its location and routing traffic to its current network, classically via a home agent and care-of address (Mobile IP) or, in cellular systems, via the core network's mobility-management entities.

Clinical relevance

Wireless and mobile networking is how most people now reach the Internet: Wi-Fi connects homes, offices, and public spaces, while cellular networks deliver mobile broadband to billions of devices. Mobility management makes seamless handoff possible as users move, and 5G's architecture targets low-latency and massive-device use cases such as industrial automation and the Internet of Things. Capacity planning, spectrum use, and roaming all depend on these concepts.

History

Packet radio research in the 1970s, including the ALOHA system, established random access over wireless channels. The IEEE 802.11 standard (1997 onward) made wireless LANs ubiquitous, while cellular networks evolved from analog 1G through digital GSM and on to packet-based 4G LTE and 5G. Mobility support for IP hosts was standardized as Mobile IP, and modern cellular cores integrate mobility, security, and IP connectivity.

Key figures

Charles Perkins
Norman Abramson
Andrew S. Tanenbaum

Seminal works

kurose2021
ieee80211-2020
tanenbaum2010

Frequently asked questions

Why does Wi-Fi use collision avoidance instead of collision detection like wired Ethernet?: A wireless transmitter generally cannot listen for collisions while sending, because its own signal overwhelms any incoming one, and a station may not even hear another that is colliding at the receiver (the hidden-terminal problem). So Wi-Fi avoids collisions in advance using carrier sensing, random backoff, and acknowledgments rather than detecting them mid-transmission.
What is the difference between a wireless network and a mobile network?: Wireless refers to the use of a radio link instead of a wire for a single hop, while mobility refers to a device changing its point of attachment to the network over time. A device can be wireless but stationary, or mobile across wired docking points; mobile networking specifically addresses keeping connectivity and addressing intact as the attachment point changes.