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To: Scott Zion who wrote (1643)	9/17/1999 9:04:00 PM
From: Clarksterh	Respond to of 13582

Scott - Pretty good, but just some corrections: Shannon proved that a channel has a fixed capacity For a given spectral bandwidth and signal power to noise power ratio! To the extent you can boost your power without boosting the noise, you can fit infinite amounts of data into any spectral bandwidth you want. In theory for a constant noise power I could put one million bits/sec into one hertz - although the modulator would be fabulously expensive to build, if not impossible in practice and it might require its own power plant. The rub in cell system communications is that my signal is your noise and vise versa. Thus when I boost my power to increase my data rate it forces you to do the same thing and neither of us have gained anything. CDMA is good in a cell system is good for a variety of reasons, but one is that it acts as a noise averager. In an ordinary cell system you have to assume that someone might start shouting in your ear at any second, but with CDMA you average everyone's power and this decreases your uncertainty. Thus you have decreased your 'designed for' noise floor, and the bits/sec goes up. As for other technologies being able to do the same thing, there are other technologies that, to my knowledge, have the potential to decrease the observed noise floor by removing those pesky other users signal. OFDM is the chief among these, but I have yet to see any compelling evidence that it actually works well in a mobile cell system. I am not worrying about it for the next several years anyway. Clark