Theory of wireless data transmission

jsmoke

jsmoke

jsmoke

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Looking for some sort of an understanding. As far as I know, wired transmission is to do with electrons and frequency modulation, either a digital peak(1) or trough(0) is enough to build up a system of data.

I think wireless is is to do with Photons and the Photo-electric effect. Is wireless data still sent in packets, if so how, is there an equivalent to wired frequency modulation. If it is then there must also be a constant stream of packets being sent, for example if you were to capture someone's wifi using a packet sniffer then there must be multiple of the same packet sent as the both you and the router your sniffing packets to both receive the packet.

Can anybody shed any light on the process of wireless transmission, be as technical as you like. How to send Photons as either 1 or 0, is there a constant stream of packets sent and if so how, which physical route do photons take, i.e are they sent in a certain direction and just find a path from A to B through the atmosphere etc.
 
Wireless is electromagnetic waves at high frequencies and there are different types of modulation which incorporate the amplitude, frequency and phase of the wave being transmitted.

I'd suggest looking at constellation diagrams to see how data is transferred and how these properties of amplitude, frequency and phase correspond to different data values i.e. basic schemes like amplitude shift keying, phase shift keying, frequency shift keying, and then scheme which incorporate multiple wave properties, i.e. qam, apsk.

When a antenna sends modulated waveforms they essentially shoot them all over the place and most the time they are reflected, but sometimes absorbed. So having a "packet sniffer" receiving the signal won't specifically hide a signal from anyone else.
 
You dont use photons to transmit wireless signals. You modulate your information onto a carrier signal which is then transmitted across the air via an antenna.
 
Imagine dropping a series of pebbles into a pond - you'd create a series of ripples.

If you drop pebbles of various sizes into the pond, then you'd create a pattern - the height of each ripple based on the size of the pebble, and the distance between the ripples based on the time between dropping the pebbles.

If you have a device capable of detecting those ripples, then based on the height and distance between them you'd be able to work out the size of each pebble dropped and how long between each one.

If you used a certain size and frequency combination to denote each character*, then you could use this as a rudimentary communication system.

Now imagine this on a much smaller, faster scale, using radio waves rather than water ripples.

The analogy also goes some way to explain interference, and why you should try to use different channels to your neighbours:

If someone else is also dropping pebbles in the same pond as you, their ripples are going to distort yours and cause some issues with your detection equipment.

This is obviously a very simplified analogy though!



* e.g.:
1 x 5 gram pebble = "a"
1 x 10 gram pebble = "A"
2 x 5 gram pebble dropped 2 seconds apart = "b"
and so on
 
Haggisman said:
Imagine dropping a series of pebbles into a pond - you'd create a series of ripples.

If you drop pebbles of various sizes into the pond, then you'd create a pattern - the height of each ripple based on the size of the pebble, and the distance between the ripples based on the time between dropping the pebbles.

If you have a device capable of detecting those ripples, then based on the height and distance between them you'd be able to work out the size of each pebble dropped and how long between each one.

If you used a certain size and frequency combination to denote each character*, then you could use this as a rudimentary communication system.

Now imagine this on a much smaller, faster scale, using radio waves rather than water ripples.

The analogy also goes some way to explain interference, and why you should try to use different channels to your neighbours:

If someone else is also dropping pebbles in the same pond as you, their ripples are going to distort yours and cause some issues with your detection equipment.

This is obviously a very simplified analogy though!



* e.g.:
1 x 5 gram pebble = "a"
1 x 10 gram pebble = "A"
2 x 5 gram pebble dropped 2 seconds apart = "b"
and so on
Click to expand...

Great analogy.
 
kthula666 said:
Nope can't shed any light on the subject.
Click to expand...

most useful post of the year so far :confused:

Haggisman said:
Imagine dropping a series of pebbles into a pond - you'd create a series of ripples.

If you drop pebbles of various sizes into the pond, then you'd create a pattern - the height of each ripple based on the size of the pebble, and the distance between the ripples based on the time between dropping the pebbles.

If you have a device capable of detecting those ripples, then based on the height and distance between them you'd be able to work out the size of each pebble dropped and how long between each one.

If you used a certain size and frequency combination to denote each character*, then you could use this as a rudimentary communication system.

Now imagine this on a much smaller, faster scale, using radio waves rather than water ripples.

The analogy also goes some way to explain interference, and why you should try to use different channels to your neighbours:

If someone else is also dropping pebbles in the same pond as you, their ripples are going to distort yours and cause some issues with your detection equipment.

This is obviously a very simplified analogy though!



* e.g.:
1 x 5 gram pebble = "a"
1 x 10 gram pebble = "A"
2 x 5 gram pebble dropped 2 seconds apart = "b"
and so on
Click to expand...

excellent analogy
 
jsmoke said:
there must also be a constant stream of packets being sent, for example if you were to capture someone's wifi using a packet sniffer then there must be multiple of the same packet sent as the both you and the router your sniffing packets to both receive the packet.
Click to expand...

Wireless packets are transmitted once and will be received by any device receiving on that frequency.

Most devices will ignore packets that aren't for them. Packet sniffers just log everything. If you're connected to a site using HTTPS or though a VPN, those packets will just show the encrypted data. If you connect to a site just using HTTP, anything you send (eg username, password, etc) can be read in the packets.
 
john_s said:
Wireless packets are transmitted once and will be received by any device receiving on that frequency.

Most devices will ignore packets that aren't for them. Packet sniffers just log everything. If you're connected to a site using HTTPS or though a VPN, those packets will just show the encrypted data. If you connect to a site just using HTTP, anything you send (eg username, password, etc) can be read in the packets.
Click to expand...

Is that correct if you are using wpa2 for example, aren't only authenticated clients able to decrypt packets?
 
stewski said:
Is that correct if you are using wpa2 for example, aren't only authenticated clients able to decrypt packets?
Click to expand...

I think he was assuming you ignore wireless encryption for that example.

If your wifi is secured, e.g. using WPA, then you will need the key to decrypt any packets sent (except for the handshakes)

Cosimo said:
Zillions of them. :D
Click to expand...

Isn't it only millions?

I thought the speed notation for wifi (e.g. 300Mbps), stands for Million Bats Per Second?
 
Haggisman said:
I think he was assuming you ignore wireless encryption for that example.

If your wifi is secured, e.g. using WPA, then you will need the key to decrypt any packets sent (except for the handshakes)



Isn't it only millions?

I thought the speed notation for wifi (e.g. 300Mbps), stands for Million Bats Per Second?
Click to expand...

Millibats*
 
Bear said:
Eerr no, light is part of the electromagnetic spectrum but a radio wave isn't necessarily light and is dependant on frequency.
Click to expand...
Visible light is photons of a specific frequency - photons exist across the electromagnetic frequency spectrum, i.e. x-rays are high energy photons
 
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