Research On Code Construction And System Design For CC-CDMA

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.