Effective implementation of the OFDM/CDMA base station transmitter using joint FHT and IFFT

In the paper, a multicarrier CDMA (OFDM/CDMA) technique for application in mobile radio communication systems is considered. In the base station (BS) transmitter, the orthogonal modulation of Walsh sequences can effectively be realized by fast Hadamard transform (FHT), while the orthogonal multicarrier modulation is implemented by inverse fast Fourier transform (IFFT). In the paper, the possibility of joining FHT and IFFT is shown. The fast algorithm for this new joint transform is presented. It is based on junction of the "butterfly" operations performed by FHT and IFFT, which is equivalent to a pair of simple multiplications. This algorithm is low computationally complex, and simplifies implementation of the BS transmitter. The computational complexity as the number of arithmetic operations is calculated for the presented method.