Large Sets of Orthogonal Sequences Suitable for Applications in CDMA Systems

摘要

In this paper, we employ the so-called semi-bent functions to achievesignificant improvements over currently known methods regarding the number oforthogonal sequences per cell that can be assigned to a regular tessellation ofhexagonal cells, typical for certain code-division multiple-access (CDMA)systems. Our initial design method generates a large family of orthogonal setsof sequences derived from vectorial semi-bent functions. A modification of theoriginal approach is proposed to avoid a hard combinatorial problem ofallocating several such orthogonal sets to a single cell of a regular hexagonalnetwork, while preserving the orthogonality to adjacent cells. Thismodification increases the number of users per cell by starting from shortercodewords and then extending the length of these codewords to the desiredlength. The specification and assignment of these orthogonal sets to a regulartessellation of hexagonal cells have been solved regardless of the parity andsize of $m$ (where $2^m$ is the length of the codewords). In particular, whenthe re-use distance is $D=4$ the number of users per cell is $2^{m-2}$ foralmost all $m$, which is twice as many as can be obtained by the best knownmethods.