Spatial tessellations: concepts and applications of Voronoi diagrams
Spatial tessellations: concepts and applications of Voronoi diagrams
On the use of some known methods for T-colorings of graphs
Annals of Operations Research - Special issue on Tabu search
Frequency assignment, multiple interference and binary constraints
Wireless Networks
Gold codes, Hadamard partitions and the security of CDMA systems
Designs, Codes and Cryptography
IEEE Transactions on Information Theory
Quasi-orthogonal sequences for code-division multiple-access systems
IEEE Transactions on Information Theory
Spreading codes for direct sequence CDMA and wideband CDMA cellular networks
IEEE Communications Magazine
Design of spreading codes for quasi-synchronous CDMA with intercell interference
IEEE Journal on Selected Areas in Communications
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Almost bent functions and Hadamard matrices can be used to construct spreading codes for code-division multiple-access (CDMA) systems. Four specific Hadamard matrices can be constructed and each one can be divided into eight octants in such a way that spreading codewords from certain pairs of octants have zero correlation. It is possible to assign these octants to a regular tessellation of hexagonal cells in such a way that there is zero correlation between adjacent cells, small correlation between non-adjacent cells and a large codeword re-use distance. If synchronous CDMA is used in a satellite system, interference is reduced in comparison with the use of a single Hadamard matrix. In this case the regular hexagonal tessellation is usually a good model of the areas covered by satellite spot beams. The same approach can be advantageous when the Hadamard matrices are used to construct loosely synchronized codes for a terrestrial system. The tessellation of cells is unlikely to be a regular hexagonal tessellation and the question arises of whether an assignment to an irregular tessellation with these properties can be found. In this paper a positive answer is given to this question, confirming that the approach is applicable to a terrestrial system.