I find it hard to find on the internet a simplified explanation of the principle of operation of the CDMA system. Could you give me an example of how it works and how a receiver can correctly identify a user's message?
Precisely, as I understand it, each user sends a certain message, often called spreading code, which is composed of a series of pulses called chips.
For example, the spreading codes of two users may be:
User 1: 1, 1, -1, -1
User 2: -1, -1.1, -1
I read on the internet that each user has a personal code, which is chosen to ensure orthogonality to avoid interference. However it is not specified which sequences must be orthogonal: orthogonality between the spreading codes, orthogonality between the personal code of a user and those of the other users, orthogonality between the personal code of a user and the spreading codes of other users?