Constructions Of Spreading Sequences And Their Assignments

In code division multiple access?CDMA?systems,the number of users and the anti-interference ability are two important conditions to judge the quality of systems.The design of spreading sequences and the theoretical bounds are two main issues in the theory of spreading sequences,and the design of spreading sequences is to construct a set of sequences satisfying the theoretical bounds.The main problem in the theory of spreading sequences is the design of spreading sequences.Spreading sequences affect the capacity and the anti-interference ability of a communication system.The number of sequences within a sequence set determines the number of users that the system can accommodate.The correlation function determines the self-interference,the multi-access interference within cells,and the adjacent cell interference.Therefore,it is one of an important aspects of the design of spreading sequences to construct spreading sequences to meet the needs of CDMA systems.CD-MA has been widely applied in digital cellular systems.In thses systems,the spreading sequences can be reused in different locations.A reasonable sequence assignment can also be used to reduce the adjacent cell interference.Therefore,both the construction of the spreading sequences and the sequence assignments are important research topics.In the dissertation,the constructions of orthogonal sequence sets in synchronous CDMA?S-CDMA?systems,the optimal zero correlation zone?ZCZ?sequence sets and the Z-periodic complementary sequence?ZPCS?sets in quasisynchronous CDMA?QS-CDMA?systems are proposed,and their assignments in hexagon networks are provided.A large set of low correlation sequence sets in asynchronous CDMA?A-CDMA?system is then constructed.The innovations of the dissertation can be listed as follows:?1?Two classes of orthogonal sequence sets are constructed based on ternary semi-bent functions and a complex Hadamard matrix.An efficient sequence assignment in regular hexagonal cellular networks is proposed by using the positions of zero spectral value of ternary semi-bent functions,which ensures that the sequences in the same cell and adjacent cells are orthogonal to each other and the sum of the number of orthogonal sequences assigned in any three adjacent cells equals to the length of sequences which implies our assignment is optimal in number.The new assignment improves the utilization of orthogonal sequences.The maximum reuse distance in the assignment is ?27?^1/2,and the maximum spectral value of the semi-bent function guarantees a low level cross-correlation between the non-orthogonal sequences.A class of optimal ZCZ sequence sets is obtained and an effective assignment of ZCZ sequences in cellular networks is proposed.A new method for the construction of optimal ZCZ sequence sets is proposed.?2?Based on a perfect sequence and three new generalized 2-ary semi-bent functions,four optimal ZPCS sets can be obtained.Then the optimal ZPCS sets can be divided into four ZPCS by utilizing the spectral distribution of the generalized 2-ary semi-bent functions.In order to eliminate the multi-path interference and multi-access interference,each ZPCS partition is assigned to a cell and the ZPCS partitions assigned to any three adjacent cells have a zero correlation zone.The low correlation between ZPCSs assigned to nonadjacent cells can ensure a low level of interference.Each ZPCS partition has a variable flock size,which is suitable for different application requirements.?3?The correlation properties between two decimated sequences of p-ary m sequences are analyzed,and a large sequence family with low correlation is constructed.The decimated factor by Kim et al is generalized to a more general form:wp^n/2+2-w.The number of decimated sequences in this form and the upper bound of the correlation values of any two decimated sequences are determined.By shift and add method,a small sequence families with low correlation is constructed.A sequence family with flexible parameters is con-structed by using these decimated sequences,which is suitable for different communication scenarios.The sequence family can achieve a tradeoff between the number of sequences and the maximum correlation value by choosing appropriate parameters.