WiFi speed decreased when laptop connected to monitor

Question

I"m using my Dell XPS 15 9520 laptop (Win11) with my home WiFi network which provides both 5 and 2.4 GHz coverage with 100Mbps provider uplink. The room corner where I'm sitting has not so good WiFi coverage - only 2.4Ghz wifi is available here, however both my laptop and my phone show about 10...30Mbps (measured with Speedtest web).

I'd like to connect my Dell laptop to my Dell P2720 monitor through USB-C cable. The problem is once I connect my laptop to the monitor, WiFi receiving speed on the laptop is decreased to 1 Mbps or even less. The speed is restored if I disconnect the monitor from the laptop.

I also used "netsh wlan show interfaces" command to see WiFi properties.

With the monitor disconnected it shows:

Receive rate (Mbps)    : 15
Transmit rate (Mbps)   : 39

When connected:

Receive rate (Mbps)    : 2
Transmit rate (Mbps)   : 39

Dell Utility says all the drivers are up to date. The problem occurs regardless I connect the laptop to the power adapter or not. The problem occurs regardless I connect the laptop to the monitor with USB-C_USB-C cable, or USB-C_HDMI. The problem seems don't occur in the good coverage area neither with 5GHz nor 2.4GHz.

I'd appreciate any help.

Answer 1

You might try a utility such as Nirsoft's WiFi Info View or an alternative, such as wavemon for Linux OS. These assess the WiFi connection 88in real time**, updating reading many times per second.

These tools enable you to check the signal as you move the laptop to try to improve the connection.

WiFi Info View also enables you to select a specific connection. For example, in the image below, note that the laptop is connected on Channel 52 in the 5 GHz band, which has a signal quality of 68%. Though the 2.4 GHz has a theoretical slower maximum speed, by switching to Channel 1 on that router, where signal quality is 99.9% (because the lower frequency has better penetration), the actual I/O throughput might increase. To switch, right-click on the line and select Connect Selected Access Point. If that improves the connection, make a desktop shortcut to it, so there's no need to start WiFi Info View to pick that connection.

Another option is to buy a USB WiFi adapter, such as one of these. One with an external antenna might get better signal pickup. You can put the adapter at the end of a short extension cable, allowing it to be placed for maximum reception while the laptop remains in a convenient position.

Answer 2

TLDR

Using WiFi extender, with a different SSID, installed right beside my table solves the problem.

Explanation

As I described in my question, there is no good WiFi coverage in my corner, so the signal strength is poor. However, all devices tested here are able to produce ~20Mbps, including WiFi extender.

Since the only device which meets the problem is the laptop with a monitor connected, there is possibly interference from monitor/cable/whatever, which becomes critical only when the signal strength is poor. The problem doesn't occur in the good coverage area neither with 5GHz nor 2.4GHz. If so, I need to have another access point with a good signal strength.

I tested the laptop connection speed through a mobile phone working as a WiFi access point - it was good, no problem. The signal strength was OK, because the smartphone was close to the laptop.

Finally, I've turned a WiFi extender with a different SSID on next to the table. It has stable connection speed (~20Mbps) into my main WiFi network, and has good signal strength as an access point. So now my laptop automatically connects to the WiFi extender's SSID (because this network has better signal strength), and has good connection speed ~20Mbps through the WiFi extender.

Answer 3

Same issue here... Asus laptop, Samsung C27F398 monitor. After connecting the monitor via a HDMI-HDMI cable WiFi speed drops from 69/30 (D/U, Mbps) to 16.5/21.5

I replaced the generic cable with a fancier Philips HDMI-HDMI cable (gold plated etc.) and the speed increased to 31/25 Mbps. So, using a good quality cable is also helpful.