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One of my friends (that knows very well Wireless world) told me following:

Consider we have high speed AP. If one user stays out of the range of AP WiFi (lets say 51 meter away) - he will have low throughput and therefore all users that connected to the same AP will suffer from low traffic.

Is it true?

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3 Answers 3

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Does distance of one user from WiFi AP have negative impact on other connected users?

Yes, this is true at least in the traditional 802.11 network.

Why? By the nature of 802.11 wireless, a channel (i.e. frequency range) is a shared medium. Only one device can be using the channel at a single moment in time. So a device connecting at a lower data rate will potentially consume more of the "airtime" available for communication; using more airtime to send/receive the same amount of data.

There are a couple of features in many modern 802.11 networks that mitigate or reduce this impact. Some wireless systems provide for client "airtime fairness" mechanisms. By manipulating the traffic in some fashion, each client is given an equal amount of time to use the channel, passing as much data as it can during it's allotted time.

Second, starting with 802.11ac, multi-user MIMO (aka MU-MIMO) was introduced. Combined with beam forming, this allows an 802.11ac access point to allocate radio resources to communicate with more than one downstream client at the same time. 802.11ax (still in the draft process) provides an improvement to allow MU-MIMO in both downstream and upstream directions.

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An individual station will receive traffic at whatever speed it can, independent of any other stations. In infrastructure mode (with an AP), stations communicate with the AP, not each other, so the ability for each station to hear and understand each other is (a) not necessary, and (b) often not even possible (see also: hidden node problem.)

What will be slow is broadcast (and thus multicast) traffic as that has to be sent at a rate ALL stations can hear. That's one frame that will only be sent once with no acknowledgement. (that's call basic-rate, and is substantially less than any main-rate.)

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Well it depends... See, wireless interference is unfortunately inevitable, because wireless LAN communications are based on radio frequency signals that require a clear and unobstructed transmission path.

Quickly,

WAP's cant detect "collisions", since these "signals" are in the air. So their mechanism WAPs have to deal with collisions is "carrier sense multiple access/collision avoidance" (CSMA/CA). Basically what that is, is a threshold/window in which a single devices can transmit data. Therefore the more people attached to a WAP the slower they transmit because their time slot they're allowed to transmit through becomes smaller and smaller and smaller...

Now, I believe what might be happening is that its taking a long time for the WAP to relay to the device/determine when what device has this "right of way" to transmit its data. And that since wireless is typically slower then wired speeds so is the network broadcasts, as a result they too are slower when relaying to the WAP.

I hope that makes sense. And it could be possible however, I don't believe that his throughput would drop significantly enough for him to notice it.

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    That's not exactly how it works (i.e. TDM), and isn't the question he asked. If you are connected at 400mbps, and I connect at 100mbps, my association doesn't drag the whole network down to 100mbps. Yes, my traffic will take 4x as long to transmit, but it otherwise has no effect on anyone elses transfer speed.
    – Ricky
    Jan 14, 2019 at 19:55
  • ahhh I see makes sence
    – Boschko
    Jan 14, 2019 at 21:02

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