Joint-Detection using Fast Fourier Transforms in TD-CDMA based Mobile Radio Systems

Third generation mobile radio systems will employ TD-CDMA in their TDD mode. In a TD-CDMA mobile radio system, jointdetection is equivalent to solving a least squares problem with a block-Toeplitz system matrix. By extending this matrix to a block-circulant matrix, it is possible to blockdiagonalize the matrix with Fast Fourier Transforms. For the typical system scenario of a TD-CDMA system, the circularization requires only a slight modification of the system matrix. In addition, overlap-save techniques can be employed to reduce the computational complexity even further. The resulting joint detection algorithm is able to produce better bit error ratios than the conventional algorithm that is based on an approximate Cholesky decomposition while requiring even less computational effort.