A method and arrangement for use in a single user detector in a CDMA multi-path system, comprising providing a finite impulse response (FIR) filter; and configuring the FIR filter to derive at least a first, then a second, then a third, then a fourth of the following parameters for single user detection: R (auto-correlation) function; L (Cholesky decomposition) value; X value representative of the complex conjugate of a channel impulse response multiplied and summed with time shifted versions of a received signal; back substitution value Y (function of R, X and L); and back substitution value S (function of R, X, Y and L).