What's the optimal distance for wifi

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mdf

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Topic # 193690 20-Mar-2016 17:32

Random query. I download reasonably large files to my phone over wifi (audiobooks, the usually clock in at 150-250MB). I can place my phone anywhere from (literally) on the wifi router to across the room, ~4-5 meters away. I was wondering if there was an "optimal" distance (for speed) to place the phone while downloading?

I don't think it will make a huge difference, as the server at the other end will always be the bottleneck, but thought I'd ask.

AC over 5GHz if it makes a difference. It's a Nighthawk router with 3 antennae.

MikeB4

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Reply # 1516525 20-Mar-2016 17:53

I maybe wrong but I have always found the 2.5 ghz has far better range than the 5ghz band. But the 5ghz has better through put close to the WiFi router.

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johnr

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Reply # 1516527 20-Mar-2016 17:55

Yes 2.4 will have a far better coverage footprint over 5

mdf

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Reply # 1516539 20-Mar-2016 18:01

Yep, agree 2.4 GHz has a better coverage footprint, but I've found 5GHz AC faster, albeit with a shorter range (and I don't think 2.4GHz AC exists). I'm not worried about what the maximum range is, rather what's the ideal range for speed. There will always be some attenuation over distance, but I also guess there may be some issue "focussing" (for want of a better word) at too short a distance?

Basically I want to solve for X, where X = distance from router for fastest download speeds.

sbiddle

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Reply # 1516543 20-Mar-2016 18:15

There is no ideal range. There is however an ideal SNR.

Sideface

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Reply # 1516544 20-Mar-2016 18:22

5GHz in the same room.

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Reply # 1516586 20-Mar-2016 19:02

Umm ... depending on your connection, the wifi is not the limiting factor. Eg VDSL 50Mbps down, wifi 1200Mbps connection, downloading server 20kbps ;p

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Reply # 1516587 20-Mar-2016 19:03

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Serious answer: AC wifi at 2m (not less than 1.5m)

mdf

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Reply # 1516599 20-Mar-2016 20:14

joker97:

Serious answer: AC wifi at 2m (not less than 1.5m)

Super, thanks.

sbiddle

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Reply # 1516608 20-Mar-2016 20:34

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It's not really something that is distance based so you can't really give that as an answer. At the end of the day for many devices being closer will deliver a worse connection, not a better one.

Signal strength and SNR are the two most important factors. Both will determine the modulation rate that the connection both transmits and receives at. Signal strength will vary depending on a huge number of variables. Many WiFi capable devices have poor front end design that makes them easily overloaded when you end up with a signal strength under -40dBm so ensuring you're at least 3-4m or so away from an AP if it's in the same room can minimise such issues.

If you want the best performance then your goal is to target an SNR of at last 20dBm and a signal strength of -70dBm or better. Distance does not really factor in as a calculation for determining the quality of a WiFi connection.

Crowdie

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Reply # 1516727 21-Mar-2016 09:47

You also have to take into consideration the radio(s) in the client device(s). For an iPad, for example, you don't want to have a transmit power higher than 15 dBm.

If you are running video and/or voice applications then aim for a RSSI of -65 dBm, which should give you a SNR of 25 dB or higher.

1101

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Reply # 1516755 21-Mar-2016 11:06

http://www.intech.co.nz/products/microscanscada/microscanwirelessdatalinks/Wireless-Antennas.pdf

I would think more about where the wifi router/AP is in the room than your distance to it.
Its never going to be so simple , fresnel zone (ha) , out of phase reflections, noise form other sources ,Signal being blocked by hands/body etc etc
Install wifi analyzer on the ph/tablet , wander around the room & see if you detect any difference or sweet spot.

Where are the HAM guys when you need them to chirp in :-)
Would the optimal distance be anything further than some fraction of the wavelength ?

mdf

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Reply # 1516819 21-Mar-2016 11:56

1101:

http://www.intech.co.nz/products/microscanscada/microscanwirelessdatalinks/Wireless-Antennas.pdf

I would think more about where the wifi router/AP is in the room than your distance to it.
Its never going to be so simple , fresnel zone (ha) , out of phase reflections, noise form other sources ,Signal being blocked by hands/body etc etc
Install wifi analyzer on the ph/tablet , wander around the room & see if you detect any difference or sweet spot.

Where are the HAM guys when you need them to chirp in :-)
Would the optimal distance be anything further than some fraction of the wavelength ?

Thanks - "Fresnel zone" is a new term for me but (I think) describes what I was groping towards with the initial query.

I think what I am taking away from the discussion is that there's a whole lot of "it depends" , but there is likely to be a (non-symmetrical) bell graph of signal quality. Too close and the quality goes down, too far away and the quality goes down. It's not a case of signal quality is best right beside/on top of the router and degrades in a straight line/geometric curve the further away you get.

Crowdie

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Reply # 1516853 21-Mar-2016 12:47

I wouldn't be worried about fresnel zones (there are more than one) with a residential deployment.

raytaylor

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Reply # 1518066 23-Mar-2016 00:58

Fresnel zones are irrelevant in this situation.

The ideal signal is -65 with a noise level lower than -90 which can now be hard to achieve in many urban areas.

If the signal is over -55 then you will have problems.

If the SNR is less than 20db you will have problems. Eg if the signal drops to -75 and the noise comes up to -90 then thats only 15db of margin and not enough for a good fast connection and the speed will be reduced accordingly.

You can download a wifi analyser app for your phone or laptop to test the signal level for the particular radio and antenna within the device, at various locations

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Crowdie

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Reply # 1518412 23-Mar-2016 13:07

If you are using smartphones and tablets the most then download an analyzer application to a smartphone/tablet and use that. If you are using a laptop the most then use the laptop to determine the signal strength. The two device types can give different results, commonly the smartphone/tablet can report signal strengths up to 10 dBm lower than a laptop, so you want to ensure your results reflect what your most commonly used wireless device will experience.