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To: JMD who wrote (6427)	12/14/1997 1:30:00 PM
From: dougjn	Respond to of 152472

Mike, will you forget wave forms for a while, and get you eyes back on the ball that matters?? Assuming money matters. Your thoughts re: exchange2000.com Doug

To: JMD who wrote (6427)	12/14/1997 1:47:00 PM
From: dougjn	Respond to of 152472

Mike, re wave forms and RF etc. I have no university physics/engineering training (some biology). However, I did take a course in a hoity toity HS called, for honest reasons, Harvard Freshman Physics. And I was an electronics geek in grade school, built my own ham radio, (as well as assorted rockets, radio controlled bombs, etc.) Cell phones, all of them, communicate by sending and receiving radio frequencies, rather high frequency radio frequencies that have basically only line of sight range. The basic carrier frequencies is varied in small way (modulated) by different techniques. Think of it as little micro ripples on the basic ocean wave. Its the little micro ripples that are coded (send), and decoded (receive), and that carry the information. The basic wave is what transports it, and what the cell phone tunes/listens to for info to decode. TDMA and CDMA are schemes to pack as much info as possible w/in the variation possibilities of the RF waveform. They are ways around having to dedicate a whole discrete frequency (RF waveform) for each conversation w/in a cell (radius of communication from a cell mini tower). TDMA does it by time chopping the waveform (since talking uses up considerably less than all of the info that the form can carry in a particular unit time, you flash switch many times a second between 3 or whatever number of conversations, A,B,C, in that set order, occupying a single frequency.) CDMA mixes all the frequencies of the tower and by some algorithm assignes a code to each conversation which then gets chopped up into tiny little bits, all with the same id code, and squirted out micro bit by micro bit onto the next available frequency / micro time segment. And at the receiving end the DSP looks for the assigned code, and plucks out the associated data and then strings all the data together back into a conversation, lickedy split. Like the TCP/IP of the internet, where nobody figures out ahead of time the wire route data will take from point A to B, it just sorta goes the route of least resistance/traffic, CDMA doesn't figure out in advance what frequency (among the group available) or what time part of the frequency your bit of coded data is gonna go. And it may/will take a lot of different frequencies /time segments in getting to you. Thats why its sometimes called spread spectrum communications. You can also see why the military likes CDMA for data encription. If you donna got the code, good luck in figuring out communications which is spread over a range of spectrum in a random manner, and looks like noise on the scope. Doug