Blind detection of multirate asynchronous CDMA signals in multipath channels

Blind detection of a desired user´s signal in a multirate direct sequence code division multiple access (DS-CDMA) system (using either variable sequence length, VSL, or multicode, MC, access) is considered. In multirate CDMA systems, a high-rate user signal may be treated as the superposition of several virtual basic-rate signals. A code-constrained inverse filter criterion (IFC)-based (also CMA-based) blind detector for equal-rate CDMA signals to detect a desired user´s signal was recently presented by J.K. Tugnait and Tongtong Li (see IEEE Trans. Sig. Proc., vol.SP-49, p.1300-09, 2001; IEEE Journal on Selected Areas in Communications, vol.SAC-19, p.1520-30, 2001; Li and Tugnait, Proc. IEEE 2001 ICASSP, 2001). Novel approaches combining the code-constrained IFC and a penalty function are developed to extract simultaneously all virtual users associated with a given high-rate user in VSL and MC multirate access methods. Global minima of the proposed cost functions are analyzed. An illustrative simulation example is provided.