Here is an illustration of the multiple access resources, as I told you, that you can have: space is one resource, frequency is another, and time is another. Now, if I use the space, then each user can be given a separate space segment for accessing the particular facility, in which case we call it space division multiple access. Alternatively, one can consider the given spectrum and the spectrum is sub-divided into small segments and each segment is allocated to a user giving the facility to a large number of users, leading to what we call frequency division multiple access. Similarly, if you have a time interval, then that time interval can be segmented into smaller slots and each slots is allocated to a user separately, thus we have what we call time division multiple access, and individual users without any interference could either use SDMA, FDMA or TDMA. But then we do not stop here, there could be a combination of these, or as we call it hybrid schemes. For example: if you combine the space here and the frequency, we get a space frequency division multiple access, that is both space and frequency are utilised; on other hand, if we combine space with time, we get a space time division multiple access, and, once again, we utilise space as well as time to increase the number of users, to give them multiple access facility. And, lastly, one could combine the frequency and the time domains, into the FT-matrix or FT-signalling, and we get what is known as the code division multiple access, and a spread spectrum multiple access.

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