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To: Bernard Levy who wrote (13085)	7/29/1998 3:11:00 AM
From: Clarksterh	Read Replies (1) \| Respond to of 152472

Bernard - Like all fixed assignment schemes (which include also TDMA), it [CDMA] does not allocate bandwidth dynamically to users as a function of their needs. In contrast, contention based protocols allocate bandwidth to users as a function of their needs at a given time. ??? Multiple transmit CDMA inherently acts like a stat mux (i.e. acts like it dynamically assigns bandwidth). As with any stat mux it is possible to swamp the system. For a TDMA systems this results in bits dropped from the buffer, while for CDMA it results in bits dropped from the ether, but there is no inherent disadvantage to CDMA per se. Having said that, I agree that if you have a point to point transmission with stat muxes on either end then CDMA loses much of its advantage since a second stat mux isn't needed. But if you have a many to one system CDMA provides to only way to dynamically assign bandwidth without significant coordination and complexity. Another reason is that the robustness to noise and interference of CDMA, as well as the number of users that can be supported, are proportional to the spreading gain. If you want to offer about 50Mb/sec to users with a spreading gain of 100, and assuming about 2bits/Hz/sec, you would need a bandwidth of 2.5GHz. But what if the 50Mb/sec were actually 10 different TV signals? These could then each be spread 10 times and all neatly fit in 25Mhz. This might be worthwhile if the assigned frequencies had lots of narrowband noise spikes, although in general I would admit that it is probably more trouble than it is worth in a point to point system (compared to an interleaved TDMA system). The big advantage of CDMA in this context is stat muxing over spacially separate senders. All JMO Clark