US Patent 7643584 Efficient joint detection

Data signals are received over a shared spectrum in a code division multiple access communication format as a combined signal. The combined signal is sampled as a plurality of received vector versions. A plurality of system matrices and an associated covariance matrix using codes and estimated impulse responses of the data signals is produced. Each system matrix corresponds to a received vector version. The system and covariance matrices are extended and approximated as block circulant matrices. A diagonal matrix of each of the extended and approximated system and covariance matrices are determined by prime factor algorithm-fast Fourier transform (PFA-FFT)without division of the matrix. The received vector versions are extended. A product of the diagonal matrices and the extended received vector versions is taken. An inverse block discrete Fourier transform is performed by a PFA-FFT a on a result of the product to produce the estimated data.