Synchronous CDMA systems with group-orthogonal signature waveforms

Synchronous Gaussian code-division multiple access (CDMA) systems employing group-orthogonal signature waveforms are proposed and analyzed. All users in the system are divided into groups of users. The signature waveforms are constructed such that all the signature waveforms in one group are orthogonal to all the signature waveforms used in any other groups. This construction of signature waveforms ensures that there is no inter-group interference, but at the expense of having intra-group interference. However, by choosing a small size for each group, the intra-group interference can be effectively handled by a low-complexity, optimal (or suboptimal) multiuser detector. It is shown that the proposed technique can accommodate a large number of users relative to the processing gain, N, with an excellent error performance. The proposed technique is also very effective for coded CDMA systems when iterative soft interference cancellation and decoding is applied to further cancel the multiple access interference.