I would like to ask a question about how WIFI connection works. I couldn't find an answer on the internet. If both devices are within WIFI range of each other, there, of course, would be a connection. Would there be any connection in the below two scenarios (circles are wifi range)?
2 Answers
Laymen's terms like "transmission range" or especially "reception range" are oversimplifications that actually make things less clear / less understandable.
To understand if two devices can make a radio link, you have to calculate the "link budget", which includes things like:
- The transmission power of the transmitter.
- Any "cable loss" in the antenna cables of the transmitter, or losses due to the antenna not being a perfect radiator of the power.
- The "directional gain" of the transmitter's antenna (how well it focuses the transmitted power in the direction of the receiver).
- The distance between the transmitter and receiver, free space loss, absorption by the environment, absorption/scattering by obstructions, multi-path interference.
- The "directional gain" of the receiver's antenna.
- "Cable loss" in the receiver's antenna cable.
- The receiver's sensitivity and noise floor (how low of a signal it can get and still make use of).
Since Wi-Fi is a bi-directional communications medium, you have to calculate that link budget in both directions, taking into account that the two devices probably have different transmit power, antenna systems, and receive sensitivity. It doesn't matter if you're "only downloading" or "only uploading"; Wi-Fi packets have to be Acknowledged, so even if you spend most of your time sending data in one direction, the link has to be good in the other direction to, or the Acks will never get through, so the data packets will just keep getting retransmitted or timed out, instead of moving on to the next data packets.
That said, there are ways to improve the link budget just by upgrading one end of the link and not the other. Let's say you have a smartphone that, like all smartphones, has a small antenna (to save room) and a fairly low-power transmitter (to save battery). But you want it to get better range. Well, if you upgrade your Wi-Fi AP to one that has a high-power transmit amplifier (called a "high power PA"; PA == Power Amplifier), you can make the signals from the AP to the smartphone reach farther. But you can't add a high-power PA to the smartphone, so how can you make it so the smartphone's signals reach the AP better even from farther away? One approach, if you're an AP designer, is to add a high quality "Low-Noise Amplifier" (LNA) to the receiver circuitry on the AP. It's like giving your AP a super hearing-aid. And of course, adding great antennas to your AP design will help with both transmit and receive. So by upgrading to an AP that has "a loud voice and great hearing", you can increase the usable range of your smartphone.
Top-of-the-line APs come with high-power PAs, great LNAs, and great antennas. That's what they have to do to win the range/performance competitions. That's part of the reason why they cost up to US$299 instead of $99. The good PAs and LNAs are some of the first things they cut to reduce cost when you step down from top-of-the-line to mid-range devices.
Provided the router and device are able to pick up each others signal then the radius is largely irrelevant from the POV of picking up a signal.
That said, the diagram and your question do not discuss what range is being referred to. If its the transmission range, and if it is assumed that the reception range is the same as the transmission range (which is not a safe assumption), then in case - where the signal of the device overlaps/touches the center of the router signal (and assuming the router is located in the center of the circle) things should work. In case 2 where the router is outside the circle of the device then things will not work as neither device will be able to hear the other.
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1Blue is transmission range centered at router. Red is reception range centered at device. I am assuming the reception range is not equal to transmission range! Would scenario 1 work?– RamiDec 1, 2014 at 18:52
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1Yes. (I'm assuming here the red line touches or overlaps the router - its not exactly clear) - of-course, "its not exactly clear" also implies a marginal signal, so not great reception.– davidgoDec 1, 2014 at 19:07
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1So if you buy for example a router that has a 0.5 mile WIFI range. Your device which let's assume is an iphone 5. If you place the two devices in open space 0.4 miles apart. Would they connect to each other? Would you be able to both send and receive data?– RamiDec 1, 2014 at 19:29
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1I don't have an IPHONE 5, so I can't comment definitively, but I'd be very surprised if it could connect at 0.4 miles - however this is more a function of the crappy internal aerial in the iphone then anything else. If you were in the middle of nowhere (ie no other noise), and you were high up enough on both points, you might get a very, very bad signal - but in reality 0.5 miles is a very long distance for an omnidirectional AP - particularly one without an external aerial. In order to get 0.5 miles reliably in most cases you will need decent aerials.– davidgoDec 1, 2014 at 22:44
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1Relatedly (even though you didn't ask), if you have 1 device with a directional antenna connecting to a device with an omni or internal antenna, you can get further distances - and in fact this is how most cellphone towers work.– davidgoDec 1, 2014 at 22:45