Doubly spread DS-CDMA for efficient interference cancellation

In this paper, a new spreading scheme, which consists of two stages of spreading, is considered for DS-CDMA systems. The data of a user is spread first with a long signature sequence and then with a short signature sequence. The scheme combines the advantages of the two types of spreading techniques and allows us to suppress multiple access interference (MAI) by performing both beamforming and multiuser detection efficiently. A joint receiver with blind multiuser detection and blind beamforming is proposed for the new spreading scheme. Simulations show that the joint receiver performs better than either beamforming or multiuser detection alone. To speed up convergence, an iterative version of the joint receiver is also considered.