How to diagnose weak Wi-Fi PC-->router signal?

Question

My friend's network consists of a Wi-Fi router/access point and about 10 wireless devices.

Wireless client devices show good strength signal but the router's internal diagnostics indicates very poor reception. Devices drop out of session sporadically and have to reconnect, internet also is reportedly slow unless close to the router.

Router indicates 2 to 4 (of 5) bars of reception for closeby devices; farther away ones behind a drywall get 0 to 2; 5 bars only if almost touching antennas. The devices themselves show 3 to 5 (of 5) bars - as normally is expected in this situation.

This network encompasses a medium-sized single-floor apartment within a 10-floor building in densely populated city, internal walls are drywalls. Router is an oldish middle-class one. Devices are mostly iPhones and iPads of varying generations, but also couple of PCs and a network printer.

Wi-Fi configuration is on its defaults, automatic channel, 2.4GHz. This router also supports a 5GHz network but brief tests show similar situation with this network. There are about 10 to 15 other neighbor networks visible throughout the apartment.

GSM and UMTS signal reception is Ok as normally expected. No obviously-EM-intensive appliances or microwave ovens are plugged in. There should be no devices transferring huge amounts of data all the time. Security is WPA2-PSK, WPS was allowed.

The following did not cause any visible improvement:

• Rebooting router
• Shutting down some devices
• Updating firmware (it had latest one installed)
• Virus and intruder checks on devices or router
• Moving router a tiny amount and rotating antennas somewhat
• Unscrewing and reattaching antennas
• Using a known-good client device (results are same as other devices)
• Searching the internet for potential problems with this exact router model\

What was NOT tried because I was not able to physically visit the place yet:

• Shutting down all client devices except one
• Changing wi-fi settings including selecting a radio channel
• Moving router to a different room (due to short cables) or mounting it high
• Precisely measuring (or mapping) reception strength in varying spots
• Trying to determine exact composition of drywalls with a drill or metal detector
• Trying to use another router / repeater / booster
• Installing enthusiast firmwares such as OpenWRT
• Creating wi-fi networks on smartphones and measuring strength
• Measuring signal strength changes throughout the day

(if any of above could help in diagnostics feel free to add to your answer)

I am not sure what could cause this exact situation apart from, obviously, a malfunctioning router.

What tools or techniques would you use to diagnose a similar problem?

I am mostly interested in what an average system administrator could accomplish within few hours with a smartphone and a known-good router but professional diagnostic tools may be worth mentioning too. Links to in-depth wireless troubleshooting guides would likewise be appreciated.

Answer 1

You've found most of the right things to do, given the limited budget, probable lack of drop ceilings, and likely aesthetic limitations.

Some things to consider :

Spectrum congestion. Sounds like there's lots of devices nearby. Use a smartphone app like Android Wifi Analyzer to determine the least-busy channels, and switch the network to use that channel. Don't forget the 5 GHz channels... if all of the user's devices can connect to them, then turn off the 2.4 GHz channels and only use the 5 GHz. Note that this is because 5 tends to be less congested, but is poorer at penetrating walls.

Draw a 2D map of the apartment, and try to guess at neighbor's walls. Confirm the placement of metal in the walls (power lines, pipes, etc) if you can. Put your map into a wifi survey smartphone app. Do a survey scientifically, and slowly walk the apartment to find the weakest spots. Save the heatmap if you have the option. Move the antennas and repeat the survey, saving the heatmap. Move the whole router to another location and repeat the survey, saving the heatmap. Find the best location to put the router... screwing it to the wall up and out of the way is a good idea.

Recent routers with multiple antennas perform beamforming to transmit more effectively, but the single-antenna end user devices can only send with one. This is important for TCP transmissions, which require constant ACKnowledgement of successful receipt of packets. This means that many aspects of using the network are dependent on the end user devices sending loudly back to the router.