3 ms·
They are still technical. The spreading doesn’t buy you anything in terms of channel capacity, just processing gain over narrow band interference, and the down
by madengr 7y ago
They are still technical. The spreading doesn’t buy you anything in terms of channel capacity, just processing gain over narrow band interference, and the downside is now you need precise power control to keep all those codes at the same noise level.
4G & 5G uses OFDM, essentially distributing the data over slow, narrow band channels to get around the multi-path issues with trying to use even wider band CDMA. Then MIMO to actually increase the capacity, which only works when you have multi path.
This gives a good summary, specifically page 32, but CDMA is essentially dead soon.
http://www.pitt.edu/~dtipper/2720/2720_Slides9.pdf http://www.pitt.edu/~dtipper/2720/2720_Slides9.pdf
- CamperBob2 7y agoDude, your entire post history calls to mind the question, "What am I doing on a site called 'Hacker News'?" Channel capacity is not the problem. Do you own a radio capable of VHF/UHF reception? Turn it on. Tune it to a randomly-chosen frequency between, say, 600 and 1000 MHz. What do you hear? Now, repeat this exercise 5,000 times, and let me know how many of those iterations yield anything but white noise from your receiver's own front end and IF strip. There's your "channel capacity." This problem is purely regulatory. Everything should be frequency-agile at this point in time, but it's not. Never mind CDMA or TDMA, we haven't even picked the lowest of the low-hanging FDMA fruit yet.