Increasing the capacity of CDMA using hybrid spreading sequences and iterative multistage detection

We introduce a code-division multiple access (CDMA) concept which allows one to accommodate a higher number of users than the spreading factor N. The idea is to assign orthogonal spreading sequences to the first N users and pseudo-noise (PN) spreading sequences to all additional users. The proposed technique can thus accommodate N users without any mutual interference and some additional at the expense of some signal-to-noise ratio (SNR) penalty. This represents a significant capacity increase with respect to presently available multiple access techniques. When the number of users is larger than N, detection is performed in two separate steps, one for the set of users with orthogonal spreading sequences and one for the set of users with PN sequences. Furthermore, the process is iterated two or more times to obtain more reliable receiver decisions