Wifi Technology Terms Explained – Channel Width, Frequency Band, Spatial Streams

There are a lot of technical terms and specifications around wifi technology that affect the performance of your wifi device. You would encounter these commonly on the specs of a wifi router, laptop wifi specs, and smartphone wifi specs.

Most of the time people only look at the broad branding terms like Wifi4 or Wifi5 or Wifi6 and assume that newer generation guarantees better performance in terms of speed.

However under the hood there are actually a lots of technical factors that affect the wifi speed on a local network. Often times people complain of not getting full speed on 5Ghz band and think something is wrong with their setup.

The goal of this article is to take a dive into this technical jargon and explain different bits of the technology that determine the wifi performance. The article is going to be a bit technical but we promise to make it as easy to read and understand.

Wifi Terms

We shall be discussing a lot of core specifications that control and affect the wireless radio communication between your wifi router and wifi devices like smartphones, tablets, laptops.

• Channel
• Channel Width
• Frequency Bands (2.4/5/6 Ghz)
• Spatial Streams (MIMO / MU-MIMO)
• Router Naming Convention
• MCS Index - Modulation and Coding Scheme Index

1. What is a Channel

Remember that most modern radio communication uses FM or Frequency Modulation wherein a sine wave's frequency is modulated or "changed" to represent "information" or data. This change of frequency happens around a base frequency (or middle frequency) often denoted as F0.

This range of frequency constitutes a "channel" which is needed to carry 1 "stream" of data.

For example the F0 = 2412 and range is 2401-2423 which makes a channel. Note that F0 is usually in the middle of the range.

2. Channel Width

Based on the above definition of the channel we can see that for each channel the frequency ranges from a minimum to a maximum level, and the difference is called width.

For example in 802.11a/b/g wifi protocols the channel width was always 20 Mhz.

The width affects how much data can be encoded in each cycle of the radiowave. Depending on the encoding method used higher channel width usually results into higher data throughput.

For example a 100Mhz carrier wave allowed to modulate between 98-102 Mhz will be able to carry less data compared to a 100 Mhz carrier that is allowed to modulate between 90-100 Mhz.

To learn more about the standard Wifi Channels check out the wikipedia page here.

Most wifi routers have configuration options that allow users to choose different channel width settings. Common settings are 20 Mhz, 40 Mhz and 20/40/80 Auto.

If you set the channel width to Auto, the wifi router will automatically select the best channel width depending on the operating conditions.

Here is an excellent pdf from Texas Instruments that explains the process and challenges of Channel Bonding

Highest speeds

Maximum Speeds of various wifi generations

So if you have a 2x2 MIMO router that supports Wifi 4 and Wifi 5, you would get speeds of 300 mbps on wifi 4 (2.4Ghz) and 867 mbps on Wifi 5 (5Ghz)

Routers that carry the name AC1200 derive refer to 802.11ac with 300+866.7 = 1166.7 mbps of total max throughput speed.

Similarly routers named AC3000 usually have 5Ghz 1733 + 5Ghz 867 + 2.4 Ghz

The number of antennas that you see on a router are related to number of spatial streams the router uses for implementing MIMO technology.

3. Frequency Bands

The frequency band refers to the region of frequency spectrum where the carrier wave is selected. The common bands used with Wifi are 2.4Ghz, 5Ghz and 6Ghz.

For example the 2.4Ghz band has carrier channels like 2412 / 2417 / 2422 Mhz and so on. The 5 Ghz band has carrier frequencies like 5200 / 5210 / 5220 Mhz and so on.

A complete list of all the carrier frequencies in each band can be found on the wikipedia page on wlan channels.

Most modern routers support multiple bands simultaneously. For example a router can connect on 2.4 Ghz with some devices band and on 5 Ghz band with other devices at the same time.

Though it will use different wifi generations on different bands. 2.4ghz band will be used only on wifi4 and 6. Whereas 5ghz band will be used with wifi5/6.

2.4Ghz vs 5Ghz

There are differences in performance of different bands as well. The 2.4 Ghz band has longer coverage, means it can reach farther, whereas the 5 Ghz band has shorter coverage, means the signal strength drops faster.

However the 5ghz band can deliver higher throughput due to using wifi 5/6 compared to 2.4

The shorter range of 5 Ghz band results in less interference and allows it to use higher channel widths like 80 Mhz which results in better throughput compared to 2.4 Ghz.

On the other hand The 2.4 Ghz band has more interference, forcing it to operate at lower channel widths (mostly at 20 Mhz) which has lower bandwidth.

Overall it is recommended that you use the 5ghz band whenever possible for least interference and highest throughput. However even with the 5 Ghz band the highest speed will often be determined by the wifi capabilities of the client device (smartphone/laptop/tablet) which are usually slower than the router. We have covered this in a previous article here.

4. MIMO - Multiple Input Multiple Output (Spatial Streams)

MIMO technology uses space division multiplexing to create multiple streams of communication using the same frequency channel. Since these streams use space division multiple-access, they are also called "spatial streams". They have been marked in the MCS chart shown above.

A router might mention how many streams it supports, for example 1, 2 or 3. Using more streams means more signal processing load on the router's cpu. Hence routers with powerful MIMO features need more processing power and more expensive.

MU-MIMO takes this technology a step further, allowing the router to talk to multiple client-devices (like your laptops, smartphones) using multiple spatials streams on same baseband frequency.

With more spatial streams a router (access point) can support more devices without drop in transfer speed. This is why a lot of wifi routers mention the stream count along with an estimate of how many devices it can support simultaneously. For example a 6 stream wifi router can support 25+ devices easily, whereas a 12 stream router is needed to support 50+ devices.

5. Naming Convention (Routers, usb-wifi adapters etc)

Routers from brands like Linksys, TP-Link, Netgear are often named in such a way that the name indicates the wifi technologies and speeds. Here is a table that summarises the same.

The 2.4 GHz band speeds are cited for a 40 MHz channel. Because 802.11n (wifi4) can have channel width of upto 40 Mhz only.

The 5 GHz speeds are cited for either an 80 MHz channel for 802.11ac (Wifi 5) or a 160 MHz channel for 802.11ax (Wifi 6). However note that Wifi5 can also work on 160 Mhz channel width, though it is not commonly seen.

6. How is maximum speed calculated - MCS Index

The mcs Index specifies the operating parameters that are used in a wifi connection. It specifies the modulation and coding scheme, the guard interval and few other things. It is important to note that a wifi connection will dynamically switch between different mcs index depending on the operating environment and the signal strength. If the signal strength is good, it will switch to an index with higher speed and vice-versa.

According to mcs data and specs Wifi 5 can reach its maximum limit of 6933 mbps (6.9 gbps) when using 160mhz wide channels and 8 MIMO streams. However such a configuration does not exist in any commercial products like wifi routers.

For instance, most consumer laptops use only 2x2 MIMO (2 spatial streams only) and 80 Mhz wide channels on 5Ghz frequency band, which results in a maximum throughput of 866.7 mbps using MCS-Index-9. This is a reason why you cannot hit speeds of 1 gbps when using 5Ghz wifi5 even when transferring files across devices over lan.

Links and resources

https://mcsindex.com/
https://mcsindex.net/
https://www.duckware.com/tech/wifi-in-the-us.html