OFDM(A) Transmission in 3D
See how Wi-Fi sends hundreds of subcarriers at once, one OFDM symbol after another, and how channel width, guard interval and modulation change the data rate.
How to use this tool controls and what to look for
Watch OFDM symbols travel through time and frequency in 3D, then change the channel and the echoes to see what the guard interval protects against.
Controls to change
- Standard: compare Wi-Fi 4/5 OFDM with Wi-Fi 6 OFDMA, which has four times as many subcarriers, each four times longer.
- Channel width: switch between 20 and 40 MHz to double the number of subcarriers.
- Guard interval: change the gap added to every symbol.
- Modulation: change how many bits each subcarrier carries.
- Echo delay: add an echo from a small room up to an outdoor path (No echo, 50 ns to 2 µs).
- Echo strength: make the echo weaker (−10 dB) or stronger (−3 dB).
- Top view: look straight down on the time-frequency grid. Reset view brings the 3D view back.
What to look for
- An echo shorter than the guard interval is absorbed. Longer than it, you get intersymbol interference and the constellation smears.
- A longer guard interval survives bigger rooms but lowers the data rate, because more of every symbol is gap.
- Pilot, DC and guard subcarriers carry no data. Zoom in on the edges and centre of the channel to find them.
About this tool
Wi-Fi doesn't send one fast signal: it splits the channel into hundreds of narrow subcarriers and sends them all at once, one OFDM symbol after another. This 3D view shows time, frequency and amplitude together, so you can see how channel width, guard interval and modulation shape a transmission, how echoes cause interference between symbols, and how OFDMA hands groups of subcarriers to different clients.
What you'll learn
- Why OFDM splits a channel into many narrow subcarriers
- What the guard interval does against echoes, and what it costs in airtime
- Where pilot, DC and guard subcarriers fit in
- How Wi-Fi 6 uses four times as many subcarriers, each four times longer
Common questions
How many subcarriers does a 20 MHz Wi-Fi channel have?
64 in 802.11a/g/n/ac, of which 52 (a/g) or 56 (n/ac) carry data and pilots, and 256 in Wi-Fi 6 and 7, of which 242 are used.
What is the guard interval?
A short copy of the end of each symbol sent in front of it, so echoes die away before the next symbol matters. It is 0.8 µs normally (0.4 µs short) in Wi-Fi 4 and 5, and 0.8, 1.6 or 3.2 µs in Wi-Fi 6.
What's the difference between OFDM and OFDMA?
With OFDM, all subcarriers of a transmission go to one client. OFDMA, new in Wi-Fi 6, splits them into resource units so several clients share one transmission.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.