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If a Wi Fi setup uses a high gain directional quarter wave antenna say 15dbi gain at a height and it got a range of 1 kilometers. If a client laptop or a smartphone placed 900 meters away from the antenna is connected to the hotspot, will the client be able to get an internet connection.

Since the antenna in the client phone is very smaller say(lambda/8) ,it must have lesser range(max 50 meters).

So will the data from the mobile phone be unable to travel back to the main antenna, thus resulting in a one way connection(not possible for internet).

It seems so impossible based on antenna theory but in practice it appears to be not so.

The Mobile Hotspot case. Make a WiFi hotspot on your Android phone and connect with any other Android phone. You can find that the maximum range you can get is a couple of meters(It's the max range of the inbuilt wifi antenna in the phone).

Now connect your phone to a router in the house, the range increases to ten or twenty meters or more. But consider the fact that the range of the antenna inside the phone is just a couple of meters(from the hotspot experiment) and the signal from the phone will be unable to reach back at the antenna of the router.

But this scenario is totally possible.

Could anybody please clarify on the matter, advanced answers are welcome too.

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It is (obviously) invalid to draw conclusions about the phone's antenna from comparing WiFi ad-hoc mode against WiFi infrastructure mode.

Even if it were valid, the antenna itself is not the only limiting factor.

  • Modern 802.11 infrastructure modes (such as 802.11ac) deploy beamforming to extend ranges (some vendors support it already with 802.11n, but interoperability was poor).
  • Modern 802.11 infrastructure modes deploy radio power management techniques to adjust for the desired range.

As opposed to that, WiFI Direct/ad-hoc may well require a fallback to older 802.11 transmission standards, not only limiting bandwidth, but also power management and beamforming abilities (in general or with specific hardware). Additionally, radio power management in ad-hoc networks is nontrivial, so even if it were implemented, that doesn't mean it would work well. With huge WiFi problmes in metropolitan areas already, the cheapest and safest approach is to not bother at all and reduce radio power to the minimum in ad-hoc scenarios.

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  • Does mobile phones usually have antennas of lambda/8 or something like that while high gain antennas are lambda/2 or lambda/4 which obviously has more range and gain than the latter.
    – Amal
    Commented Oct 8, 2015 at 10:29

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