[KayEyeDoubleDee]

As I understand it, CD is at the physical layer, and MA is basically the concept of multiplex access protocol, so it can be considered to exist at the network layer, although CDMA apparently could be conceptually lumped together and considered as the physical layer for other link/network layers, such as TCP/IP, but the latency calls for clever work-arounds

I will have to pick nits and note that CDMA is a very specific physical layer solution to the problem of multiple access of the air interface.

Not to get too technical, but compared to TDMA and FDMA, it is a more efficient use of the observation that multiplication in the time domain equals convolution in the frequency domain. This latter fact is the single most important fact behind the old school analog stuff (FM,AM) and most of the modern digital stuff (which is helped out by them fast little chips that crunch the little bits)

[apochromat]

True, but I think you are somwhat confusingly using the term "physical layer" to lump together that which is actually a radio physical layer and a cellular network layer.

[KayEyeDoubleDee]

Sorry, the linked demo didn't do what I thought it would and I can't immediately find a good demo showing it.

[apochromat]

Right. Direct Sequence spread spectrum typically uses correlation filtering sets for each coded channel. Correlation is a variation of convolution.