Basics: AP and Client connectivity

Unanswered Question
Oct 14th, 2009

Hello,

This may be a very basic question for all of you but Iam confused.

Suppose we have an AP which has a range of say 500m. So i assume 500m around the AP will be the coverage area.

I understand that throughput will decrease as we move further from the AP.

Now suppose we have a client having a range of say 100 m only (genrally clients r not as powerful as AP rite) and this client is situated at the 400m range from the AP.

Will the AP and the client get connected?

Is it that the AP packets will travel and be received by the client since the client lies within the AP range but the client packets will not reach the AP? so there wont be a connection? Iam confused!!

I have also added a diagram to explan my query. please throw some light.

I have this problem too.
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Leo Laohoo Thu, 10/15/2009 - 00:59

Without any obstruction? Hypothetically? A client can connect/send-and-receive from a distance of "400" metres and "100" metres distance.

However, don't expect the same speed as the "100".

Consider the AP as a hi-fi boom-box or stereo. You are situated 100 metres away from it while a friend is situated 10 metres away from it. Who do you think will be able to hear the music better if the volume is cranked to a specific level?

Queen245_goa Thu, 10/15/2009 - 01:31

yes I do understand that speed/thoughput will reduce as the client moves away from the AP.

But i was considering the scenario just like the above,

AP as a hi-fi boom-box or stereo. Iam situated 400 metres away from it while a friend is situated 100 metres away from it.

My frd will definetely hear much better than I do.

Now if I or my frd turn our speakers on max which are much lesser volume that the AP. Say volume of both our speaks reaches 100 m. Since my frd is situated at 100 m to the AP, the AP can hear my Frd.

What abt me? will be AP be able to hear my speakers?

Or

Is it that if I can hear the AP situated at 400 m(even though its not very loud than my 100m frd) then the AP surely has the capacity/sensitivity to hear me?

meaning that if AP radio signals can travel 500 m, it can also receive client information of 500 m?

Iam confused abt this?

Peter Nugent Fri, 10/16/2009 - 15:07

I think what you are refering to is near far problems where it is quite possible for a client to be out of range of an ap to send to but still here the ap, generally this is the reason why you would match ap and client signal powers roughly the same. if the client doesnt have the power to send to the ap but can hear the ap its all one way trafic. Often seen with one way voice where the client receives voice but cant send effectively

Robert.N.Barrett_2 Sun, 10/18/2009 - 13:03

The best answer is "it depends". Whether or not an AP can hear a distant client is related to a number of factors. One of those factors, that many people forget about, is that the antenna gain on the AP also impacts its ability to RECEIVE transmissions from other radios (clients). The AP may be able to hear the distant client due to the gain of the AP's antenna.

When creating long-distance wireless links, a "Link Budget" is calculated that factors in power, antenna gain, etc. for the transmit and receive stations. If you think about it, the Link Budget logic applies when an AP communicates with a client (and vice versa). Check out this article:

http://en.wikipedia.org/wiki/Link_budget

The link budget, however, is only one factor in an AP's ability to hear a distant client. The "near/far" problem is another. It does start with your scenario of having one client closer to the AP than the other client. However, the near/far problem is seen when both clients transmit at the same time. The transmission from the near client is so much stronger that it makes the far client's transmission sound like noise.

There are a fair number of other issues to consider, but most of these get addressed by performing a site survey (ideally using the weak client), designing your network based on data from the site survey (factoring in the weak client), and then TESTING the network with all kinds of clients, weak and strong.

Queen245_goa Sun, 10/18/2009 - 23:25

Thanks for the informative posts.

I wnet through the link budget,

Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) - Losses (dB)

Now to calculate, whether or not the AP will receive the client packets situated within the range of the AP(400m) where AP range is 500m, i would have to use this formular.

That would mean that the receive power of the AP depends on the transmit power and antenna gain of the client. Now a days we get small USB plugin clients with inbuilt antennas, their range/transmit power would be small.

so u mean that they would have to be in close proximity to the AP to have connectivty even if the AP has a high power along with a high gain antenna?

I always thought that client power need not be that powerful as long as the AP is powerful.

That means when we buy a wifi enabled phone, we should see the power of its radio?

Queen245_goa Wed, 11/11/2009 - 01:43

Hi,

Considering the above scenario of the HI-FI stereo box. Both Person-A at 400m (from stereo) distance and Person-B at 100m distance(from stereo) can hear the music of the HI-FI stereo cranked up to a certain level, definately Person-B will hear much better and louder than Person-A.

Now what if Person-C stands near the Hi-FI stereo set and Person-A and Person-B play music from their respective locations(400m & 100m) at the same level/volume.

Person-C standing near the HI-FI stereo set can hear Person-B music clearly. What will determine whether Person-C can/will be able to hear Person-A(400m) music?

Will it be Person-A volume or will it be Person-C hearing capacity?

Iam still confused whether its the client's transmit power has to be strong enough(almost equal to) the AP power or whether its the AP's sensitivity that will determine whether a far away client can communicate with the AP?

I always thought that client power need not be that powerful as long as the AP is powerful and to increase AP range we use repeaters.. will thsi be correct??

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