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To: Bernard Levy who wrote (1223)	4/11/1999 9:18:00 PM
From: Clarksterh	Respond to of 5853

Bernard - If UWB radio employs truly a very large BW (say of the order of a GHz), its interference effect on narrowband channels, such as TV channels, will be minimal, even with many users. Depends on the number of users. Lets assume 1 GHz of spectrum. CDMAOne can get about 10 users per 1.25 MHz, so lets assume the same for TD, but lets cut it by 10 to minimize the interference. So that is 800 users per cell. Lets also assume that the cell is the same size as a current cell, say 5 miles radius. For users at the outer edge of the cell to get adequate S/N the basestation will probably need to transmit about 0.3W per user or 240W total or 0.24W/MHz. A television station on the other hand is perhaps 1000 W over 6MHz but is 20 miles away. Out to about 3/4 of a mile out from the basestation a TV will actually be receiving more signal in the television band from the basestation than from the television broadcaster. Thus houses are screwed out to about 1 mile or a little more. Of course it is true that the handsets themselves will cause interference only when within 70 or 80 feet of the TV. (That r^2 term is a bitch.<g>) The point here is that in a traditional cell system this does not provide all of the benefits touted, but you make a good point below. It is true that theoretically, impulse radio with time hopping multiple access leads to the same processing gains as standard CDMA over a channel with the same BW. However, QCOM would find it impossible to make its CDMA work with a BW of one or more Ghz, while impulse radio has already been demonstrated to work (admittedly not commercially) in such situations. True, you are right that my point was a theoretical one to get the point across. But I also pointed out that most of the benefit to spreading in terms of multipath and fading comes in the first 100 times spreading, and that additional spreading only provides incremental improvement. Impulse radio has a very good chance of being successful for indoor local area networks, i.e. for short ranges. I agree that the problem given in the first part of this post becomes much less severe in a microcell which has two advantages - lowering the transmitter power of the basestation since it has to transmit less far, and lowering the number of users per cell since you can fit fewer users in the smaller area. If you assume a microcell of 500 ft instead of 5 miles and the number of users drops correspondingly to 3 or 4 then the TV interference problem drops to on the order of 5 to 10 feet from the basestation. The point in total is that this technology's chief benefits are equipment simplicity, somewhat lesser need for frequency planning and jam resistance. But the number of users per MHz does not go up, nor does the power draw and interference do not drop to nothing without shrinking the cell (in which case the power draw would drop to nothing for regular CDMA or TDMA anyway.). And the benefits from UWB in terms of multipath and fading are probably not that much greater than just ordinary DSSS. Good discussion. Clark