Construction Of Interference-Resistant Sequences For Multi-Carrier CDMA Communication Systems

Sequence design is a crucial technique of multi-carrier CDMA communication systems and can provide multiple access and multiplexing methods for the systems. The correlation properties of sequences have an important effect on multiple access interference and multi-path interference, and hence affect the bit error rate (BER) and data transfer rate of systems to a large extent. The set size of a sequence set usually limits the number of the users accommodated by systems. In order to support more users, a large set size is required. As a result, the design of sequence sets with good correlation properties and large set size is very significant.This thesis mainly researches the sequences suitable for multi-carrier CDMA communication systems, such as the Z-complementary sequences with two-width and multi-width zero cross-correlation zone (ZCCZ), the grouped complementary (GC) sequences and the unitary sequences with alternate periodic correlation values equal to zero. The set sizes of the constructed sequence sets are discussed, and their periodic and aperiodic correlation properties are analyzed. In addition, the conditions leading to optimal performance of these generated sequence sets are obtained on the basis of the theoretical bounds of sequence design.The innovation of this thesis can be listed as follows:(1) Based on orthogonal matrix expansion, a construction method of Z-complementary sequences with two-width ZCCZ is presented. The proposed method uses an unitary sequence set as a basic kernel. By the means of Kronecker product between the basic kernel and an orthogonal matrix, two different ZCCZ widths can be obtained, namely intra-group ZCCZ and inter-group ZCCZ. The constructed sequence set can achieve the theoretical bound on Z-complementary sequence design. Compared with the other design methods on the basis of orthogonal matrices, the presented method in this thesis can provide a more flexible choice of set size and flock size while the same correlation properties can be obtained.(2) Based on interleaving iteration, another design method of Z-complementary sequences with two-width ZCCZ is proposed. The zero auto-correlation zone (ZACZ) and intra-group ZCCZ of the generated sequence set can be widened by increasing the number of iteration while its inter-group cross-correlation properties are ideal. When a basic kernel is optimal, the presented sequence set can achieve the theoretical bound on Z-complementary sequence design.(3) The concept of Multi-width ZCCZ is defined, and a class of multi-width ZCCZ complementary (MWZC) sequence set is constructed. The designed set can include the sequences sets with single width or two-width ZCCZ as its combination sets composed of its specific subsets. As a result, MWZC sequence sets can provide a more flexible choice of ZCCZ widths and set sizes, and can satisfy more various application requirements. For these ZCCZ with different widths, one can always find the corresponding MWZC set or the corresponding combination sets of its specific subsets which achieve the theoretical bound. Hence the maximum set size can be obtained when correlation properties and sequence length are fixed. As a specific case, each sequence group in the MWZC set with ideal intra-group correlation properties becomes a complete complementary sequence set. Both the MWZC set with ideal intra-group correlation properties and its combination sets of specific subsets can achieve the theoretical bound as long as a complete complementary sequence set with subsequence length 1 is used a basic kernel.(4) A construction method of GC sequence set is presented. The constructed set has a huge set size. For the same processing gain, the set size of GC sequence set is much larger than that of traditional complementary sets and Z-complementary sets. The GC set possesses good correlation properties, and satisfies the periodic and aperiodic correlation properties within each sequence group are ideal. The inter-group correlation properties are almost ideal, and only inter-group cross-correlation function (CCF) values between specific sequences are nonzero at zero shift. The nonzero CCF values can be limited within a low scope when a suitable perfect sequence set is chosen. When multi-carrier CDMA systems use GC sequences, the problem of both the number of users and the interference between users can be efficiently solved. The simulation results show that the requirements of larger number of users can be satisfied and the good performance of BER can be obtained if the number of sequence groups is properly increased.(5) By employing the periodic correlation properties of DFT matrix sequences, this thesis designs a class of sequences with alternate periodic correlation values equal to zero. Three quarters or a half of periodic auto-correlation function (ACF) values and intra-group periodic CCF values of the constructed sequences are equal to zero, while the inter-group periodic cross-correlation properties are ideal just like DFT matrix sequences. (6) Based on perfect sequence set, another class of sequences with alternate periodic correlation values equal to zero is proposed, namely periodic odd/even shift orthogonal (POESO) sequences. The constructed POESO sequence set can be divided into multiple subsets. The periodic ACFs and intra-group periodic CCFs in the same subset satisfy odd shift orthogonality while inter-group periodic CCFs in the same subset satisfy even shift orthogonality. The inter-subset correlation properties are close to intra-subset properties, and only inter-subset CCF values between specific sequences are nonzero at zero shift. The nonzero CCF values can be limited within a low scope when a suitable perfect sequence set is chosen. By constructing multiple sequence subsets, the POESO set possesses a huge set size.