Replies to post #59333 on Calypso Wireless (fka CLYW)

[HighRider]

Just curious, what's the formula for determining signal strength?

[woops]

Lurker,


from the patent:

"In order to accomplish this identification parameter, [the distance at which the wireless communication device 10 communicates with the computer (access point) 20] must be within [maximum distance between wireless communication device 10 and the computer (access point) 20], which of course may vary, as described above."

- words in brackets are judges interpretations


Signal strength and quality alone are not good enough. As the amorphous zone (where wireless phone and access point can communicate) may all be within the access point "up to" distance, by constructive interference or other beneficial factors the amorphous zone may also extend outside the access point "up to" distance. This outside distance is not the place to do a handoff even though the signal strength and quality are good because the affects which may extend the manufacturer's "up to distance" will not necessarily be more reliable outside the manufacturer's recommendation. Even within the access point distance, it cannot be guaranteed that your phone will stay in the amorphous zone, but chances are much higher with good signal strength and quality that the handoff will be more successful than if the handoff occurred outside the "up to" distance.

Lurker, do you disagree with these arguments? You are saying that WHENEVER signal strength and quality are good enough then the handoff should occur. Do you really believe that will always be the most reliable time to handoff?

[woops]

Lurker,

You have already indicated that some access points have far greater range than others. The point is not to be within 200 feet of ALL access points, the point is to be within theoretical maximum distance of EACH access point which may vary greatly.

How can that be done? Would that distance be broadcast?

[sirhaggus]

You are totally missing the point Lurker.

I agree with you that signal strength is important, but signal strength is just another way of saying distance plus something else.

The point is that you cannot compute signal strength without distance being part of the calculation which is why T-mobile has a major problem. A wavelength is called a wave length because it is a measurement of the distance between two identical points on the waveform.

Read this intro article to frequency and wavelength here:

http://www.lucketts.net/tutorial.html

Then Read this article on Free Space path loss:

http://en.wikipedia.org/wiki/Free-space_path_loss

And Finally read this article on Link Budgeting:

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

I also copied this from stack overflow for you as well:

Free Space Path Loss depends on two parameters: First is the frequency of radio signals;Second is the wireless transmission distance. The following formula can reflect the relationship between them.

FSPL (dB) = 20log10(d) + 20log10(f) + K

d = distance
f = frequency
K= constant that depends on the units used for d and f
If d is measured in kilometers, f in MHz, the formula is:

FSPL (dB) = 20log10(d)+ 20log10(f) + 32.44

From the Fade Margin equation, Free Space Path Loss can be computed with the following equation.

Free Space Path Loss=Tx Power-Tx Cable Loss+Tx Antenna Gain+Rx Antenna Gain - Rx Cable Loss - Rx Sensitivity - Fade Margin

With the above two Free Space Path Loss equations, we can find out the Distance in km.

Distance (km) = 10(Free Space Path Loss – 32.44 – 20log10(f))/20

The Fresnel Zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. You want a clear line of sight to maintain strength, especially for 2.4GHz wireless systems. This is because 2.4GHz waves are absorbed by water, like the water found in trees. The rule of thumb is that 60% of Fresnel Zone must be clear of obstacles. Typically, 20% Fresnel Zone blockage introduces little signal loss to the link. Beyond 40% blockage the signal loss will become significant.

FSPLr=17.32*v(d/4f)

d = distance [km]
f = frequency [GHz]
r = radius [m]