Hadamard codewords as orthogonal spreading sequences in synchronous DS CDMA systems for mobile radio channels

This paper addresses the question if orthogonal spreading sequences, especially Hadamard codewords, can improve the performance of synchronous direct-sequence code-division multiple-access systems applied in a mobile radio environment. For this purpose, the correlation properties of Hadamard codewords are determined and performance simulations are carried out. The results show, that Hadamard codewords have rather poor autocorrelation properties and very inhomogeous crosscorrelation properties ranging from excellent up to very poor depending on which codeword is considered. The performance simulations reveal a behaviour similar to the crosscorrelation properties. Using additional scrambling the autocorrelation properties are improved and the crosscorrelation properties are made more homogenous yielding performance results similar to those obtained for conventional spreading using Gold-codes or preferentially phased Gold-codes