Post by Progenitor A on Feb 18, 2011 17:33:28 GMT 1
Interesting guy Lord Rayleigh
Physicist
Nobel Prize winner
The one who made the sky look blue
Did a lot of work on statistical probability distributions.
Came up with something called the Rayleigh distribution
This was found to be useful in predicting interference in light waves and radio waves
Here it is
See that bumpy roller-caoster, well that is a Rayleigh distribution
Now Mobile Phones
Have you ever held your mobile phone in your hand and dialled the number with a strong radio signal, then when you put the phone to your ear, the signal disappears?
Well Raykleigh predicted that!
Look again at the bumpy roller-coaster graph above.
Note that the length of each bump is about (lamda/2) where lamda is the wavelength of your mobile phone (GSM) radio signal, about 1.5cm
Now if you make a call at the peak of one of those bumps, then when you move the phone to your ear it can easily slip into one of those big dips spaced at 1.5cm
As the difference between the peak of one of those little hills and theedip of one of those little hills can be 30dB, that means that your mobile phone signal can drop in level by a factor of 1000!
No wonder you sometimes lose the signal that way!
What causes those peaks and dips?
They only happen in urban areas where there are lots of reflections of the radio waves from skyscrapers and other buildinga
Big problem in cities
But not if you are in a car, because then you go zoomong through that roller-coaster pattern and your mobile gets a high average signal
The problem only happens for pedestrians
But Vodafone and Orange etc have solved the problem
Can you see how they solved it?
Physicist
Nobel Prize winner
The one who made the sky look blue
Did a lot of work on statistical probability distributions.
Came up with something called the Rayleigh distribution
This was found to be useful in predicting interference in light waves and radio waves
Here it is
See that bumpy roller-caoster, well that is a Rayleigh distribution
Now Mobile Phones
Have you ever held your mobile phone in your hand and dialled the number with a strong radio signal, then when you put the phone to your ear, the signal disappears?
Well Raykleigh predicted that!
Look again at the bumpy roller-coaster graph above.
Note that the length of each bump is about (lamda/2) where lamda is the wavelength of your mobile phone (GSM) radio signal, about 1.5cm
Now if you make a call at the peak of one of those bumps, then when you move the phone to your ear it can easily slip into one of those big dips spaced at 1.5cm
As the difference between the peak of one of those little hills and theedip of one of those little hills can be 30dB, that means that your mobile phone signal can drop in level by a factor of 1000!
No wonder you sometimes lose the signal that way!
What causes those peaks and dips?
They only happen in urban areas where there are lots of reflections of the radio waves from skyscrapers and other buildinga
Big problem in cities
But not if you are in a car, because then you go zoomong through that roller-coaster pattern and your mobile gets a high average signal
The problem only happens for pedestrians
But Vodafone and Orange etc have solved the problem
Can you see how they solved it?