Constructions For Low-Correlation-Zone Sequence Sets As The Spreading Codes In QS-CDMA Communication Systems

This thesis deals with a type of sequence sets called Low-Correlation-Zone sequence sets used (as the spreading codes) in Quasi-Synchronous Code Division Multiple Access communication systems. The contents included are as follows.1. A survey of Low-Correlation-Zone sequence sets, which will enable the readers to get to know problem under discussion.2. A now proof of a construction under development through pair-interleaving technique, which has greatly reduced the original proof as well as brought out the structure of the construction, and moreover, an assertion that no optimal Low-Correlation-Zone sequence set over F₂ can be attained through this construction in the light of the pair-interleaving structure.3. A construction for optimal Low-Correlation-Zone sequence sets over Z₄ with parameters not known before by applying the pair-interleaving technique to sequences over Z₄, utilizing the Gray map from sequences over F₂ to sequences over Z₄ to construct optimal Low-Correlation-Zone sequence sets over Z₄ from a sequence with ideal autocorrelation property over F₂.