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Technology Stocks : Winstar Comm. (WCII) -- Ignore unavailable to you. Want to Upgrade?

To: SteveG who wrote (10118)	1/21/1999 9:49:00 PM
From: Bernard Levy	Read Replies (2) \| Respond to of 12468

Hi Steve: 2 points, one on your wireless question, the other one on xDSL. a) First, when you go from 28 to 38GHz, you need to overcome 2 effects: greater frequency attenuation, and greater rain fade. As I indicated earlier, if you use antennas of the same size at 28Ghz and 38Ghz, the increased frequency attenuation is more than made up by the increased transmitter and antenna gains. However, the increased rain fade effect can be quite severe and is not quite made up by the combined effect of the increased antenna gains. You are asking for a very precise quantification for a computation I have never liked. As WW pointed out, the rain fade effect is computed based either on 99.9% or 99.99% service availability. This means that in every area, you are trying to find the most intense rain storms and you are trying to design a system which can handle the rain fade under these worst case conditions. But then you are trying to draw BW conclusions which hold on average. To give you an example, where I live we don't see rain typically from May to October, but 2 years ago, we had a set of unbelievably intense rain storms which created massive floods for the Sacramento river and all its tributaries. I am almost certain that a rain fade computation would use these storms as benchmark, and based on the attenuation figures used by rain fade models, would conclude that the information carrying capacity of 100MHz at 38Ghz is much less than 100Mhz at 28Ghz. However, this is a computation based on may be 2 or 3 days out of several years. Most of the time, the information carrying capacity of 100MHz at 38Ghz is at least equal to 100MHz at 28Ghz. You are using worst-case conditions to draw some conclusions which hold on an average basis. I am sure WW may have a slightly different opinion, but except for system design purposes (such as sizing of cells), I have never been comfortable with drawing very general conclusions out of a rain fade analysis. Note that even for system design purposes there are all sorts of contingencies that can be used for handling large rain storms (increase in power, fallback in modulation scheme from higher order QAM to QPSK, etc...) b) I know you tend to be somewhat pessimistic about xDSL, but in the residential market, I fail completely to see what advantage an HFC cable structure would have over FTTC+VDSL for the last 100 feet. The architectures are similar (they make a similar use of fiber), but VDSL will not only carry more information than cable, it is dedicated to each user. In the long run, I really fail to see how cable will dominate over xDSL in residential markets (for business markets, like most posters on this thread, I must plead guilty to a wireless bias). Best regards, Bernard Levy