Study On Spreading Sequence Design For Spread-Spectrum Communication Systems

The spreading sequence designs are one of the key points of the spreading-spectrum communication systems. In this thesis, five sequence design topics related to the theory of spreading sequence are investigated, which are the lower bounds on the correlation functions of the spreading sequence set, the traditional spreading sequence design with interleaved structure, frequency-hopping spreading sequence design with optimal Hamming correlation functions, quadriphase sequences design with purely imaginary correlation value, and the spreading sequence design with low or zero correlation zone.The problem of finding bounds on the correlation functions of the multiple-phase spreading sequences is generally transformed to that of minimization of a quadratic form. Therefore, the general lower bounds on the correlation functions including the aperiodic correlation function, periodic correlation function and odd-periodic correlation function are obtained. The research shows that the obtained bounds include some famous bounds as special cases, and are tighter than that of some known sequence set, such as the bound of low or zero correlation zone sequences.Two new classes of spreading interleaved sequences with favorable correlation functions are obtained. One is the optimal generalized Kasami sequence set with respect to Welch bounds; the other is the almost low correlation zone sequence set with large size.The constructive method of new spreading sequence with ideal two-level autocorrelation function is obtained from the ideas of the d-form sequence and extended sequences. By employing the interleaved constructive method, new spreading sequences with ideal two-level autocorrelation functions are generated based on the existed ideal two-level autocorrelation property sequences. Therefore,the optimal Hamming correlation property frequency-hopping sequences can be constructed.The quadriphase sequences with purely imaginary correlation functions, which include aperiodic correlation function, periodic correlation function and odd-periodic correlation function, are constructed. Based on the odd-perfect almost binary sequences, the new odd-periodic correlation complementary sequence set is obtained.The interleaved method results in the general construction of low correlation zone spreading sequences, that is, by appropriately choosing of the base sequence set and using the shift sequence determined by the m-sequence, the interleaved method leads to approximately optimal multiple-phase sequence set (including binary sequence set) with larger size. The obtained sequence set has the property that, there exists low correlation zone where the out-of-phase autocorrelation and cross-correlation values are all equal to -1. Moreover, by employing the product technique, based on the generalized Chirp-like sequence set, two new classes of approximately optimal polyphase sequences with zero correlation zone can be easily generated.