Research On Key Techniques In Unified Spread Spectrum TT & C System

With the rapid development in the space telemetry tracking and control (TT&C) field, the popular unified microwave TT&C system (UMTTCS) can not meet the requirements of the space industry in our country. Hence, a novel TT&C system, unified spread spectrum TT&C system (USSTTCS) has developed from the UMTTCS, and it can overcome the shortcomings of the UMTTCS effectively. However, some kinds of interferences exist in USSTTCS, such as multi-access interference, multipath interference, near-far effect, mutual interference between code division multiple access (CDMA) system and other narrow-band communication system and so on, because it applies CDMA or multicarrier CDMA (MC-CDMA) communication systems. These interferences affect the performance and system capacity of USSTTCS greatly, and the advantages of the USSTTCS will be made full use of only when the interferences are eliminated effectively. Therefore, several key techniques for eliminating the interferences in USSTTCS, such as multiuser detection, power control, and multi-symbol detection, have been studied in this dissertation to further improve the performance of the system and meet the requirements of the space TT&C industry in our country.Firstly, ant colony optimization (ACO) algorithm is used as the key technique to solve the multiuser detection problem in USSTTCS based on either CDMA of MC-CDMA system, hence the ACO algorithms are researched thoroughly in the dissertation. After introducing several traditional ACO algorithms, the population declining ACO algorithm and mutated ACO algorithm are proposed, and then a novel population declining mutated ant colony optimization (PDMACO) algorithm is proposed by combining these two algorithms together. The performance of PDMACO algorithm is evaluated through simulation using traveling salesman problem as simulation example, and it lays the foundation of the research in PDMACO multiuser detector in the following chapters.Secondly, the multiuser detection in the USSTTCS based on CDMA is researched. The CDMA system can be classified as synchronous CDMA system and asynchronous CDMA system, and they are used in the uplink and downlink of the USSTTCS respectively. Hence, the multiuser detection in CDMA system can also be classified as synchronous multiuser detection and asynchronous multiuser detection. The optimal multiuser detector and several linear suboptimal multiuser detectors are introduced, and then the PDMACO synchronous and asynchronous multiuser detectors are proposed. Especially in the asynchronous multiuser detector, the multipath interference can be seen as the signal of an asynchronous user to eliminate. The performance of the PDMACO synchronous and asynchronous multiuser detectors is simulated, and the results show that the PDMACO multiuser detector can achieve superior performance and it is suitable to be applied in the uplink and downlink of the USSTTCS respectively, and it can greatly improve the performance of the system.Thirdly, the multiuser detection in the USSTTCS based on MC-CDMA is researched. MC-CDMA system was proposed by combined orthogonal frequency division multiplexing (OFDM) and CDMA techniques, so it possesses the merits of these two systems and it also inherits the drawbacks of these two systems, which include multi-access interference and near-far effect. After introducing the optimal multiuser detector and several linear suboptimal multiuser detectors, the PDMACO multiuser detector for MC-CDMA is proposed in this dissertation. The simulation results show that the performance of the proposed detector is excellent and close to that of the optimal multiuser detector, and it can eliminate the multi-access interference and near-far effect effectively and improve the detection performance of the USSTTCS based on MC-CDMA greatly.Fourthly, CDMA system is a self-interfered system and it is very sensitive to the near-far effect, hence the power control technique in the USSTTCS based on CDMA is researched. The system model is introduced and the theory of estimator is given. Then the user-centric and network-centric control objectives are analyzed and the distributed multi-objective robust power control algorithm based onestimator is proposed in this dissertation. Plenty of simulations are taken about the speed of convergence, robust performance to the channel fading and multi-objective control analyzing. The simulation results show that the algorithm based on H_∞estimator is robust and it can adapt to different control objectives in several situations. The proposed algorithm can resist the near-far effect in the USSTTCS based on CDMA effectively.Lastly, the multi-symbol detection technique in PCM/FM system is researched. The power spectral density of CDMA and MC-CDMA signal is relatively low, hence other communication systems can exist in the same frequency band simultaneously, for example, the popular PCM/FM system in telemetry fields. Although the signal of CDMA or MC-CDMA system can be seen as background noise by PCM/FM system, the interference can decrease the performance of the PCM/FM detection. Therefore, a novel easily implemented baseband quadrature complex rotation multi-symbol detection (BQCR-MSD) algorithm is proposed and implemented on FPGA. Plenty of simulations are taken and it is also validated on the hardware platform, and the results show that the proposed algorithm can be accurately bit-synchronized when Eb/N0 is larger than 5dB, the detection performance of the conventional non-coherent frequency discriminator is improved 3dB by the proposed algorithm, and it can solve the mutual interference problem in the case of different systems and same channel in the USSTTCS effectively.