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Wrong maximum speed for 802.11n standard. What can I do?

Super User Asked on November 9, 2021

I just upgraded my internet connection to 120Mbps. My notebook wireless networking card supports 802.11n, which theoretically would give me a max speed of 300-450Mbps if I did a correct research. However, I’m getting speeds around 60-70Mbps.

This is what command prompt shows me:

Show image

I have an iPhone 6s Plus which is recieving 120Mbps, which means the internet company is delivering the correct speed.

How can I achieve the maximum speed in my notebook? Networking card driver is up to date.

Any thoughts would be appreciated!

One Answer

Short answer: Make sure your AP (wireless router) is set to use 40MHz-wide channels, and perhaps try some other 5GHz channels instead of 132, in case your client is choking on 132 and accidentally treating it like a 20MHz-wide channel.

Long Answer:
The 802.11n standard allowed for a wide range of hardware with different capabilities. The main options were how many "spatial streams" your hardware would support, and how wide of channels your hardware would support. 802.11n allowed for 1, 2, 3, or 4 spatial streams (this is closely related to the "MIMO" numbers like 1x1, 2x2, etc.). Four spatial streams is 4x the speed of a single spatial stream. 802.11n also allowed for 20MHz- and 40MHz-wide channels, 40MHz-wide channels are slightly more than twice as fast as 20MHz-wide channels.

According to your screenshot, your notebook's wireless networking card uses the Qualcomm/Atheros QCA9377 chipset, which only supports a single spatial stream, but is capable of a 433Mbps "PHY rate" when talking to an AC-capable AP using 80MHz-wide channels. (The PHY rate is the basic signaling rate before subtracting protocol overhead of typically ~30%.)

If your AP is not capable of AC (802.11ac), but is only capable of N (802.11n) and earlier, then your QCA9377's maximum PHY rate will be 150Mbps if your N-capable AP is capable of 40MHz-wide channels, and 72.2Mbps if your N-capable AP is only capable of 20MHz-wide channels. This is because your QCA9377 chipset only supports a single spatial stream, so it doesn't get the speed-multiplying effect of additional spatial streams.

Your screenshot shows that your AP is using channel 132. It also shows that your Transmit and Receive PHY rates are both 72.2Mbps. This suggests to me that your AP is set to use 20MHz-wide channels. However, if your AP really was only using 20MHz-wide channels, your measured throughput in a speed test would probably max out around 50Mbps, and would never even quite hit a full 60Mbps, much less 70Mbps. So those two data points seem to contradict each other a little bit; it's unclear if you're limited to 20MHz-wide channels or not.

You most likely need to look at your AP's settings. Make sure it's set for 40MHz (or wider) channels, and just in case your client device is for some reason choking on channel 132, try using a different 5GHz channel.

Please note that even under perfect radio signal/noise conditions, your QCA9377 will never quite be able to get a full 120Mbps of throughput when talking to an 802.11n AP. You may be able to hit 105Mbps, but not 120. So if you want to get full 120Mbps wireless speeds to your laptop, you'll either need to upgrade your AP to AC, or upgrade your laptop's wireless networking card to support a faster flavor of 802.11n. Note that if your laptop only has a single internal antenna, you won't be able to just replace the internal wireless card to support two spatial streams. You would probably need to switch to an external USB Wi-Fi adapter instead.

Answered by Spiff on November 9, 2021

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