【作者】 李国栋；

【导师】 孟维晓；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2016， 博士

【摘要】 在无线通信系统中,多址技术决定了用户如何共享系统的频谱资源。得益于其优异的特性,码分多址在第二代和第三代移动通信系统中获得广泛应用。在码分多址无线通信系统中,扩频码的相关特性至关重要,拥有理想相关特性的扩频码可以大大简化系统的复杂度,并且可获得完全频谱利用效率。然而,具有一维结构的传统扩频码无法实现理想的相关特性,使得传统码分多址无线通信系统必须依赖复杂的辅助子系统,如开环／闭环功率控制、Rake接收机、速率匹配、上行链路同步控制等。不同于传统扩频码,具有二维结构的互补码可以实现理想的相关特性,于是提出用于构建下一代码分多址无线通信系统。互补码的理想相关特性使得基于互补码的下一代码分多址技术不再受多径和多址干扰影响,从而摆脱传统码分多址无线通信系统中的各种复杂的辅助子系统,因此,是未来蜂窝移动通信系统中富有竞争力的技术之一。另外,在国防和航天等特殊领域,互补码的理想相关特性也使得基于互补码的码分多址技术具有极大的应用价值。尽管研究人员已验证在高斯白噪声信道和平坦慢衰落信道环境下基于互补码的码分多址(CC-CDMA)无线通信系统不受多用户干扰影响,但由于互补码的二维结构,频率选择性慢衰落信道使得CC-CDMA无线通信系统面临着巨大的挑战。另一方面,互补码的集大小决定了CC-CDMA无线通信系统可支持的最大用户个数,然而具有理想相关特性的互补码的集大小较小,会限制CC-CDMA无线通信系统的实际应用。因此,本文主要围绕这两个方面展开研究,重点研究了频率选择性慢衰落信道下的检测算法、抗信道频率选择衰落的互补码的构造方法及传输系统、以及可以支持更多用户的互补码的构造方法及传输系统,研究结果对于CC-CDMA无线通信系统的实际应用具有重要价值。具体研究内容和成果如下：针对采用理想相关互补码和传统相关检测接收机的CC-CDMA无线通信系统进行研究。首先描述了两种具有理想相关特性的互补码——完全互补码和超级互补码的产生方法。接下来,基于子信道平坦衰落的信道模型和收发机模型,建立了接收机相关检测前子信道输出信号的向量表达形式。然后,基于各子信道输出的接收向量,分析了平坦慢衰落信道、频率选择性慢衰落信道、平坦快衰落信道、以及码片不同步情况下采用理想相关互补码和传统相关检测接收机的CC-CDMA无线通信系统的性能。分析和仿真结果表明,信道的频率选择性衰落和时间选择性衰落会破坏用户间的正交性,引入多用户干扰。针对频率选择性慢衰落信道下CC-CDMA无线通信系统中的检测算法进行研究,分别为下行通信和上行通信提出了基于最小均方误差准则的单用户检测算法和多用户检测算法。对于下行通信,基于单用户检测接收机结构,提出了子载波级MMSE和用户级MMSE单用户检测算法,相比于正交恢复合并和最大比合并检测算法,它们既不是噪声受限的,也不是干扰受限的。对于上行通信,基于多用户检测接收机结构,提出了子载波联合MMSE-MUD和子载波独立MMSE-MUD多用户检测算法。仿真结果验证了基于最小均方误差的单用户检测接收机和多用户检测接收机具有优异的误码率性能。针对频率选择性慢衰落信道下互补码的构造进行研究,提出了抗频选互补码及其传输系统。首先讨论了不受信道频率选择性衰落影响的互补码的特征,提出了借助Golay互补对构造抗频选互补码的方法,并分析了它的相关特性。其次,针对下行通信,提出了基于抗频选互补码的发射机和接收机结构,分析和仿真结果验证了基于抗频选互补码的CDMA下行通信系统中无多用户干扰。针对上行通信,提出了基于抗频选互补码的发射机和接收机结构,分析和仿真结果同样表明基于抗频选互补码的CDMA上行通信系统中无多用户干扰。针对如何提高互补码的最大可支持用户个数进行研究,提出了偶位移互补码及其传输方案。相比于具有理想相关特性的互补码,偶位移互补码的最大可支持用户个数扩大一倍。首先阐明偶位移互补码的思想来源,并给出偶位移互补码的概念和相关特性。接下来,提出了偶位移互补码的传输方案,并证明了结合该传输方案,偶位移互补码等价为具有理想相关特性的互补码。最后,提出了一种偶位移互补码——I/Q列式互补码的构造方法,并分别分析了基于I/Q列式互补码的CDMA下行通信系统和上行通信系统的抗多用户干扰性能。仿真结果表明基于I/Q列式互补码的CDMA无线通信系统的误码率性能并不差于基于理想相关互补码的CDMA无线通信系统。更多还原

【Abstract】 Multiple access techniques determine how to share spectrum resources among users in wireless communication systems. Due to the excellent characters of code division mul-tiple access, it is widely used in the second and third generation mobile communication systems. The correlation properties of spreading code are most important to a code di-vision multiple access wireless communication system, the complexity of which will be dramatically simplified and the full spectrum efficiency can be achieved if the spread code has perfect correlation properties. However, it is impossible for the traditional spreading codes with one-dimension structure to have ideal correlation properties, resulting in that the traditional code division multiple access wireless communication systems must de-pend on complex assistant subsystems, such as open-loop or close-loop power control, Rake receiver, rate matching, synchronization control in the uplink, and so on. Different from traditional spreading codes, complementary codes with two-dimension structure can achieve perfect correlation. So complementary codes were proposed to construct the next generation code division multiple access wireless communication system, which, without multipath and multiple access interferences, can extricate itself from various complex as-sistant subsystems used in the traditional code division multiple access wireless communi-cation systems with the help of the perfect correlation properties of complementary codes. Thus, the next generation code division multiple access based on complementary codes is one of the competitive techniques in the future cellular mobile communication systems. Besides, it has great application value in the area of national defense and aerospace due to ideal correlation properties of complementary codes.Though researchers have verified that complementary codes based code division multiple access (CC-CDMA) wireless communication systems are free of multiuser in-terference over additive white Gaussian noise channels and flat slowly fading channels, frequency-selective slowly fading channel is an enormous challenge to CC-CDMA wire-less communication systems due to the two-dimension structure of complementary code. In addition, the set size of complementary code determines the maximum supportable user number. However, the complementary codes with ideal correlation properties have smal-1 set size, which limits the practical application of CC-CDMA wireless communication systems. Thus, focusing on the above two aspects, the thesis mainly studies detection al- gorithms over frequency-selective slowly fading channels, construction method and trans-mission system of frequency-selective fading resistent complementary code, and construc-tion method and transmission system of complementary code supplying more users. The research results have important value for the practical application of CC-CDMA wireless communication system. Specific research contents and achievements are as follows.CC-CDMA wireless communication systems with perfect correlation complemen-tary codes and traditional correlation detection receivers are studied. The generation meth-ods of two kinds of complementary codes, i.e., complete complementary codes and super complementary codes, with ideal correlation properties are described. Next, based on the channel model with flat fading over each sub-channel and the transceiver model, we propose a vector expression of the output signal of each sub-channel before correlation detection in the receiver. And then, according to the output vectors of all sub-channels, the performances of a CC-CDMA wireless communication system with perfect correla-tion complementary codes and traditional correlation detection receiver are analyzed in the cases of flat slow fading channels, flat slowly fading channels, frequency-selective slowly fading channels, flat fast fading channels and chip asynchronization. The analysis and simulation results show that the frequency-selective fading and time-selective fading of the channel can destroy the orthogonality among the users, and introduce multiuser interference.The detection algorithms of the CC-CDMA wireless communication system are stud-ied over frequency selective slowly fading channels. The single user detection algorithms and multiuser detection algorithms based on minimum mean square error criterion are pro-posed for the downlink communication and uplink communication, respectively. Accord-ing to the structures of single user detection receiver, a subcarrier level MMSE detection algorithm and a user level MMSE detection algorithm are proposed for the downlink com-munication. Compared to orthogonal restoring combining and maximal ratio combining detection algorithms, they are neither noise-limited nor interference-limited. Then, in the light of the structure of multiuser detection receiver, a subcarrier-joint MMSE-MUD and a subcarrier-independent MMSE-MUD detection algorithms are proposed for the uplink communication. The simulation results verify that the single user detection receiver and multiuser detection receiver based on minimum mean square error criterion have excellent bit error rate performance.The construction of complementary codes over frequency-selective slowly fading channels is studied, and frequency-selective-fading-resistent complementary code and it-s transmission system is proposed. Firstly, the characteristics of complementary codes free of frequency-selective fading of the channel are discussed. A method of constructing frequency-selective-fading-resistent complementary code is proposed by means of Golay complementary pairs, and its correlation properties are analyzed. Secondly, the transmit-ter and receiver structures utilizing frequency-selective-fading-resistent complementary codes are proposed for the downlink communication, and the analysis and simulation results verify that there is not multiuser interference in the frequency-selective-fading-resistent complementary codes based CDMA downlink communication system. And the transmitter and receiver structures utilizing frequency-selective-fading-resistent comple-mentary codes are proposed for the uplink communication, and the analysis and simula-tion results show that the frequency-selective-fading-resistent complementary codes based CDMA uplink communication system has no multiuser interference too.How to improve the maximal supportable user number of complementary code is studied, and even shift complementary code and its transmission scheme are proposed. In comparison to complementary codes with ideal correlation properties, the maximal sup-portable user number of even shift complementary code is doubled. Firstly, the origin of idea of even shift complementary code is clarified, and its concepts and correlation properties are given. After that, the transmission scheme of even shift complementary code is proposed. Combined with the transmission scheme, even shift complementary code is proved to be equivalent to the complementary codes with ideal correlation prop-erties. Finally, we propose a method to construct a kind of even shift complementary code of I/Q column-wise complementary code and analyze the anti multiuser interference performances of I/Q column-wise complementary codes based CDMA downlink commu-nication system and uplink communication system, respectively. Simulation results show that the bit error rate performance of the I/Q column-wise complementary codes based CDMA wireless communication system is not worse than that of the CDMA wireless communication systems using ideal correlation complementary codes.更多还原