Generic CDMA Principles and Techniques

Generic CDMA Principles and Techniques pdf

Code Division Multiple Access (CDMA)
In this case, a radio channel supports a number of simultaneous users who are
separated only by digital coding of their signals, such that the coding of each user’s
signal is as different as possible to every other user’s code. Careful decoding at the
receiver can then separate users. An analogy can be drawn by considering a crowded
restaurant. If many diners are speaking simultaneously, the human ear can “tune” into
one voice by using the unique audio characteristics (“coding”) of the voice. This is
possible if no diner is speaking very loudly or softly, i.e. all are speaking with similar
volume. The listener’s decoding task is made even easier if the speaker of interest
uses a language (e.g. French) different from all others (e.g. English). This is equivalent
in CDMA to a user being given a code very different from all others. CDMA appear to
offer better spectral efficiency than FDM/TDMA – perhaps 4 or 5 times better. Other
benefits will discussed later.