Adaptive variable step-size Griffiths' algorithm for blind demodulation ofDS/CDMA signals

The minimum mean-squared error (MMSE) linear detector [1], [2] has been pro posed to successfully suppress the multiple access interference and mitigat e the near-far problem in direct-sequence code-division multiple access com munication systems. In the presence of unknown or time-varying channel para meters, the MMSE linear detector can be implemented by the blind Griffiths' algorithm [3], which uses the desired signal vector instead of a training sequence of symbols for initial adaptation. In this paper, a variable step- size (VSS) Griffiths' algorithm is proposed for accelerating the convergenc e speed, especially in the presence of strong interference. Numerical resul ts show that the convergence properties of the VSS Griffiths' algorithm are robust against the wide eigenvalue-spread problem of the correlation matri x associated with the received signal vector compared to the Griffiths' alg orithm using a fixed step-size.