Why Does CDMA Utilize Entire Bandwidth for Multiple Users?

[netizen]

Hi!

I've been reading up on FDMA and CDMA and wondering why is it that in CDMA, each message is spread over the entire bandwidth allotted instead of using a single range of frequencies (say, alloted to one user in FDMA), for several users (by assigning a unique code to each of them)?

Why is it that the entire bandwidth is utilised by all users instead of many ranges accomodating several users each? Is the restriction imposed by capacity?

This probably sounds very childish but I'm a greenhorn and would really appreciate some clarification. Thanks in advance...

 

[mgb_phys]

Why is it that the entire bandwidth is utilised by all users instead of many ranges accomodating several users each?

Because then you would have to implement all the hardware for both systems FDMA and CMDA.

Really they aren't all that different if you think of them in Fourier terms - but that gets a bit mathematically complex

 

[netizen]

Yeah I get that you would then have to implement hardware for both technologies. But won't it be compensated by the fact that the number of users can now be increased manifold?

 

[mgb_phys]

CDMA let's you use the entire bandwidth (all frequenices) by mixing the signals from all the users with a code and then decoding them, FDMA let's you use the entire bandwidth by giving each user a different frequency.
They both fill the available bandwidth, so other than signal-noise and practical engineering considerations they are equivalent.