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To: bananawind who wrote (18225)	11/11/1998 1:49:00 PM
From: Clarksterh	Read Replies (2) \| Respond to of 152472

JF Two questions for our technical pros - 1)Is it true that this is an advantage of cdma over tdma? 2)would a cdma device chew up at least some capacity if it were connected to, say, the net, just from the signals telling the base station "I'm on and I'm in xyz sector", or is this not part of the 1.25 Mhz channel that we would refer to as capacity? Currently CDMA multiple access systems do indeed have this advantage over TDMA systems (they don't take up much spectral space when they have nothing to say). However, there is no reason that TDMA can't do some of the same, albeit with a lot more coordination between mobile and basestation and perhaps a little less efficiently. In fact I would suspect that the 3g TDMA standards do some of this (Mobile - 'I need a bigger timeslot, please give me one Mr basestation', Basestation - 'Ok, wait till we shuffle another user out of the way', ...) As for whether a connected device will chew up some bandwidth even when it is connected but idle - yes, at least with the current IS-95 system. Even when no speaker is talking, the mobile still transmits some data that it would not transmit if it were disconnected entirely. I imagine that this will continue to be true even with the next gen systems, but the dynamic range will be significantly greater than with the current system (the current system uses 1/8 the 'bandwidth' idle as it does full transmit, but with 3g I would expect the idle vs full transmit ratio is more like 1/1000 although it would remain 1/8 for voice.) Clark PS There is no reason that TDMA can't, in theory, get many of the same advantages as CDMA in terms of spectral efficiency, but in practice it takes lots of coordination between mobiles and basestations and between basestations and other basestations. In practice this coordination in-and-of-itself chews up bandwidth, and in some cases may turn out to be computationally intractible or be impossible due the speed of light.