Quasi-orthogonal sequences for code-division multiple-access systems
- 1 May 2000
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Information Theory
- Vol. 46 (3) , 982-993
- https://doi.org/10.1109/18.841175
Abstract
The notion of quasi-orthogonal sequence (QOS) as a means of increasing the number of channels in synchronous code-division multiple-access (CDMA) systems that employ Walsh sequences for spreading information signals and separating channels is introduced. It is shown that a QOS sequence may be regarded as a class of Bent (almost Bent) functions possessing, in addition, a certain window property. Such sequences while increasing the system capacity, minimize interference to the existing set of Walsh sequences. The window property gives the system the ability to handle variable data rates. A general procedure of constructing QOSs from well-known families of binary sequences with good correlation, including the Kasami and Gold (1967) sequence families, as well as from the binary Kerdock code is provided. Examples of QOSs are presented for small lengths. Some examples of quaternary QOSs drawn from Family A are also includedKeywords
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