【作者】 文红；

【导师】 靳蕃；

【作者基本信息】 西南交通大学 ， 交通信息工程及控制， 2004， 博士

【摘要】 本文研究了扩频通信系统中的编码问题。扩频码设计是扩频通信系统的核心课题之一，以扩频码的相关特性为主要研究指标，构造了奇周期互补扩频码集，讨论了具有优良相关性的扩频码的设计；差错控制编码是扩频通信系统另一项核心技术，研究了能以较低译码复杂度逼近信道容量的低密度校验(LDPC)码，提出了一类性能优良的代数构造LDPC码，研究了在中、短长度与LDPC码性能接近的复数旋转码的迭代译码。 定义了各码序列的奇周期自相关函数的和是一个冲击函数的奇周期互补码集；基于奇完备几乎二元扩频码构造了奇周期二元互补集。讨论了奇周期二元互补集的综合方法；指出了奇周期互补码集和周期互补码集的关系：若集中各码序列的长度Ⅳ是奇数，周期二元互补码集和奇周期二元互补码集可相互转换，由此得到新的周期互补码集。 提出了一种称为扩展d-型扩频码的新家族，用TN扩频码族构造了在Welch界意义下具有最优周期互相关性的二元扩展TN扩频码族。作为一个例子，由Mersenne素数周期的L扩频码构造了最优互相关性的二元扩展TN扩频码族。 基于光正交码构造了规则LDPC码，称为OOC-LDPC码，将矩阵的行、列分解技术、组合重叠技术用于新构造的OOC-LDPC码，得到各种不同码率和码长的扩展OOC-LDPC码，用BP迭代译码算法在AWGN信道下进行仿真，新构造码显示了良好的性能，新构造的规则OOC-LDPC码及扩展OOC-LDPC码具有准循环的结构，编码简单。 在规则OOC-LDPC码的基础上构造了不规则OOC-LDPC码，适当设计的不规则码可以有效地改进规则码的性能，同样不规则OOC-LDPC码具有准循环的结构，其编码复杂度与码长呈线性关系。 LDPC码和一步大数逻辑可译码都可以由每个码元的一个正交校验集来第11页西南交通大学博士研究生学位论文定义，本文研究了作为一步大数逻辑可译码一类的复数旋转码的BP迭代译码，并与一步大数逻辑可译码的差分循环(DSC)码和有限几何码进行了比较，它们有非常接近的译码效果，在中、短长度都略优于相近参数的随机LDPC码，且复数旋转码的参数选择比DSC码和有限几何码更灵活。 同时本文针对BP译码算法复杂度较高的缺点，根据复数旋转码的特点提出了两种低复杂度的迭代译码方法，与BP译码方法相比，这两种译码方法的译码复杂度极大地降低了。研究了高复杂度的BP迭代译码和快速简单的传统代数译码方法结合的译码性能。关键词:扩频通信系统;扩频码;置信传播迭代译码;LDPC码;复数旋转码更多还原

【Abstract】 The codes of the spreading-spectrum communication systems are investigated in this thesis. The spreading codes designs are one of the key points of the spreading-spectrum communication systems. Two spreading codes design topics related to the correlation properties of spreading codes are discussed, which are the construction of odd-periodic complementary spreading codes set and the design of spreading codes with the good correlation properties. Error control coding is an other key point of the spreading spectrum communication systems. The low density-parity check (LDPC) codes are researched, which can approach the Shannon bound with lower decoding complexity. The algebraic constructing LDPC codes from the optical orthogonal codes are presented. The researches of the iterative decoding of complex-rotary codes (CRC) whose performance is close to that of LDPC codes is given.Two or more code-sequences are called a set of odd-periodic complementary spreading codes (OPCS) if the sum of their respective odd-periodic autocorrelation function is a delta function. The definition of OPCS is given. The construction and synthesis methods of OPCS are discussed. The relation of the sets of odd-periodic complementary binary sequences with the sets of periodic complementary binary sequences is pointed out. Some new PCS are obtained.A construction method to generate binary extended d-form spreading codes is proposed. By using the TN spreading codes (a special case of d-form spreading codes), the optimal extended TN spreading codes set in the sense of Welch bounds are constructed. Finally, an example of the families of the extended TN spreading codes, which are constructed from Legendre spreading codes is given.Based on the optical orthogonal codes, a method for constructing regular LDPC codes was presented. The new codes are called OOC-LDPC codes. By using row and column decomposition, the extended OOC-LDPC with different rate and length is presented. OOC-LDPC codes and extended OOC-LDPC codes performwell with the iterative decoding based on belief propagation (BP) on an AWGN channel. The resulting codes are quasi-cyclic codes and can be encoded by using the shift registers. The encoding complexity is low.The new irregular OOC-LDOC codes are constructed on the base of the regular OOC-LDOC codes. The irregular codes are compared to the regular codes with similar parameters. Simulations demonstrate that the decoding performance of the new carefully constructed irregular codes achieves a modest gain over that of the new regular codes. The resulting codes are also quasi-cyclic codes. The encoding complexity is low.Both LDPC codes and one-step majority logic decodable codes can be defined by a set of orthogonal parity check sums for each bit. In this thesis, the iterative decoding of Complex Rotary Codes (CRC) that is one-step majority logic decodable codes is investigated. The decoding performance of CRC is as good as the finite geometry codes and the difference set cyclic (DSC) codes and a modest performance gain to be made over LDPC codes with similar parameters. But complex-rotary codes have more choice about code parameters than the finite geometry codes and the difference set cyclic codes.Two new low complexity algorithms for decoding complex-rotary codes are developed. The complexity of the new algorithms is remarkably low in comparison with BP algorithm. The belief-propagation iterative decoding algorithm with the most computational complexity is combined with algebraic decoding algorithm to form hybrid decoding.更多还原