When to Use 20mhz vs 40mhz vs 80mhz
When to Use 20mhz vs 40mhz vs 80mhz
| certifications | cisco - David Zomaya

When to Use 20mhz vs 40mhz vs 80mhz

Improving and managing Wi-Fi performance is important to everyone, from home users to large enterprises. Channel width plays a big role in Wi-Fi performance. Selecting the right width can have a huge impact. Getting it right isn’t always straightforward, though. With multiple standards and a variety of tradeoffs, it can be hard to keep up with best practices.

Every wireless environment is different and you need to tailor your equipment to the conditions. With 5 GHz, increasing channel width can improve performance, but there are some tradeoffs. With 5 GHz, if you don’t have to worry about interference and all your client devices support it, go with the highest width available.

In fact, CBT Nuggets trainer Keith Barker uses NetSpot and SweetSpots to examine channels for potential interference, map his coverage, and improve his home wireless network in this video.

However, there are plenty of “gotchas” and the rules of thumb above won’t always be best for you. Like most things in tech, the right answer to this question depends on context. Let’s explore the “why” behind these generalizations to help you gain a better understanding of the topic.

Understanding Wi-Fi Bands

Understanding Wi-Fi bands is vital to understanding when to use 20 MHz versus 40 MHz versus 80 MHz channel widths. The two main Wi-Fi bands are 2.4 GHz and 5 GHz. These Wi-Fi bands are then split into channels for wireless devices to communicate on.

2.4 GHz Wi-Fi Band

The 2.4 GHz band covers a 100 MHz range of 2400 MHz to 2500 MHz (equivalent to 2.4 GHz to 2.5 GHz). The 2.4 GHz band is split into 14 discrete channels that are 20 MHz each (more on other channel sizes in a bit).

The 14 channels in the 2.4 GHz band. Note that channels 1, 6, 11, and 14 do not overlap.

If you do the math, you’ll quickly see that 14 bands of 20 MHz equals 180 Mhz. This is greater than the 100 MHz size of the 2.4 GHz band, which means that channels overlap. This is important to understand because overlapping Wi-Fi channels can interfere with one another. With 2.4 GHz Wi-Fi, there are four non-overlapping 20 MHz channels: 1, 6, 11, and 14. Note that due to varying regulations, not all channels are available for use in all locations. For example, only 11 channels are available in the United States.

5 GHz Wi-Fi Band

The 5 GHz Wi-Fi band covers a 150 MHz range from 5.725 MHz to 5.875 MHz. However, an additional range of Unlicensed National Information Infrastructure (UNII) bands widens that range to 750 MHz. Using 20 MHz, there are 24 non-overlapping channels available within the 5 GHz band. Note that this is a generalization and available channels vary depending on location and channel size.

2.4 GHz vs 5 GHz: Popularity, interference, throughput, and range

2.4 GHz is more popular than 5 GHz at the moment, but both are widely used. 2.4 GHz is cheaper to implement than its 5 GHz counterpart, so manufacturers leverage it to save costs. 2.4 GHz has also been widely used for a longer period of time, so more 2.4 GHz devices have been deployed.

This popularity does have a downside, though. The prevalence of 2.4 GHz devices and limited number of non-overlapping channels with 2.4 GHz can exacerbate network congestion issues.

Many consumer devices, such as cordless phones and microwaves, use 2.4 GHz frequency bands. As a result, 2.4 GHz bands are more likely to experience interference. The relative abundance of non-overlapping channels on 5 GHz Wi-Fi makes it less susceptible to interference.

Higher frequencies offer faster uploads and downloads. This means that 5 GHz Wi-Fi generally provides more throughput than 2.4 GHz Wi-Fi. However, there is a tradeoff between increased performance and range of coverage. Namely, 2.4 GHz is better at passing through solid objects and can cover a wider range than 5 GHz. Here’s a breakdown of different 2.4 GHz vs 5 GHz speeds and ranges.

Understanding IEEE 802.11 Standards

If you are exploring router specs, studying for a Network+, or trying to determine Wi-Fi compatibility, 802.11 has likely come up. IEEE develops the 802.11 Wi-Fi standards, and these standards dictate what speeds and frequencies are supported.

Here is a quick rundown on the well-known IEEE 802.11 standards:

  • 802.11a was an early 5 GHz 54 Mbps Wi-Fi standard.
  • 802.11b was a popular early 2.4 GHz 11 Mbps version of Wi-Fi.
  • 802.11g increased 2.4 GHz Wi-Fi speeds up to 54 Mbps.
  • 802.11n a.k.a. “Wi-Fi 4”supports both 2.4 GHz and 5 GHz Wi-Fi at speeds up to 450 Mbps.
  • 802.11ac a.k.a. “Wi-Fi 5” supports 5 GHz only and speeds of up to 1300 Mbps.
  • 802.11ax a.k.a “Wi-Fi 6” should be ratified later in 2019, but vendors have already released some 802.11ax products based on earlier drafts. 802.11ax supports both 2.4 GHz and 5 GHz and has a maximum speed of up to 10 Gbps.

802.11n and 802.11ac tend to be the most popular standards available today. You can expect 802.11ax to grown in popularity over the next few years. It is important to note that maximum theoretical speeds are NOT the same as real-world speeds. You can expect slower see significantly slower speeds in practice with a given iteration of Wi-Fi.

What’s Dual Band?

Dual band refers to Wi-Fi routers that support both 2.4 GHz and 5 GHz bands. Using a dual band router allows you to get the “best of both worlds”. Higher speeds and lower interference for 5 GHz devices, and wider range for 2.4 GHz devices. It is very common for modern Wi-Fi routers to support dual band functionality.

Wi-Fi Channels Other Than 20 MHz

So far, we have only discussed 20 MHz channels. 20 MHz was the norm and only option with 802.11a and 802.11g. 802.11n introduced channel bonding, which enabled 40 MHz widths. 802.11ac further extended bonding to allow for 80 MHz and 160 MHz channels.

Bonding channels increases throughput, which can improve performance. However, it also reduces the number of non-overlapping channels. This increases the probability for interference. Additionally, not all Wi-Fi client devices support channels other than 20 MHz so compatibility can be a concern.

A note on marketing lingo and tech talk: 20 MHz Wi-Fi channels are generally referred to as “narrow channels” or “narrow widths”. 40, 80, and 160 MHz Wi-Fi channels are labeled “wide channels” or “wide widths”.

When to Use 20mhz vs 40mhz vs 80mhz?

With an understanding of Wi-Fi frequencies and channel bonding, we can now dive into the decision making process.

When to Use 20 MHz

You should use 20 MHz on 2.4 GHz Wi-Fi bands. In the majority of cases, using wide widths on 2.4 GHz isn’t worthwhile. The performance tradeoffs from interference on overlapping channels will likely outweigh the throughput benefits. One possible exception to this rule is remote areas where there are not many other Wi-Fi networks or devices.

Broadest range of client device support. If you need to support legacy devices and Wi-Fi standards like 802.11b or 802.11g, you’ll need 2.4 GHz and 20 MHz.

Maximizing the amount of non-overlapping channels. Regardless of using 2.4 GHz or 5 GHz, 20 MHz leaves you with the largest amount of non-overlapping channels. This makes sense for high-density deployments and areas where interference is a major problem.

When to Use 40 MHz

Striking a balance between interference and throughput, 40 MHz offers more throughput than 20 MHz. It still leaves room for a dozen or so non-overlapping channels. This enables you to improve performance relative to 20 MHz, and without risking the interference associated with 80 MHz.

When to Use 80 MHz

If all your devices support it, and overlapping channels is not an issue, 80 MHz channels leave you with four or five non-overlapping channels. This increases the likelihood for interference. Additionally, clients often need to be very close (> 15 feet) to the Wi-Fi radio to get the most out of 80 MHz.

There are two common use cases for 80 MHz: mesh backhaul and bridging. However, any application where distances are minimal and there isn’t too much congestion can make sense for 80 MHz.

Conceptually, the takeaway here is that you must strike a balance among compatibility, throughput, and interference. While it seems intuitive that the right answer is always “up the width if you can”, it just isn’t that simple. Interference from overlapping channels can wreak havoc on network speeds, so you must account for it. This is particularly important in cities, industrial areas, and large businesses where high levels of wireless traffic are common.

When to Use 160 MHz

At this point, the use cases for 160 MHz are limited. However, as 802.11ax (Wi-Fi 6) grows in popularity, we can expect to see use of 160 MHz widths grow as well. With 160 MHz, there is only one available non-overlapping channel, so there will be interference tradeoffs to consider with 160 MHz.

Are there features that automate Wi-Fi channel and width selection? Yes.

For example, some Wi-Fi routers enable automatic detection and use of a channel size based on network conditions. This is usually achieved by selecting “Auto 20/40” or similar option as your channel width. Similarly, with most routers and devices, channel selection can be negotiated automatically. If you’re not experiencing issues, and aren’t looking to optimize performance, sticking with these settings makes sense.

How Can I Check for Wi-Fi Interference?

If you are looking to optimize performance, a Wi-Fi network analyzer may help. Wireless network analyzers can help you identify interference on different channels and select the least noisy option. Alternatively, manually switching between channels and observing performance is a less scientific alternative.

Selecting the Right Channel

When it comes to selecting the right Wi-Fi channel width, every situation is different. By understanding the fundamentals, you can more effectively select a configuration that works best for you. While there is no one-size-fits all answer to the “20MHz, 40MHz, or 80MHz?” question. However, understanding 2.4 GHz vs 5 GHz frequencies and the tradeoffs between non-overlapping channel and speed goes a long way.



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