| Along with the rapid development of the further combination of mobile communication and internet technology and the application of multi-media information, multicarrier communication has been the focus of attention due to its natural advantages in improving spectral efficiency, resisting multipath fading and supporting different services. Multicarrier communication represented by OFDM has been one of the core technologies for 4th generation mobile communication. Furthermore, CDMA is a practical communication scheme for 3G. Meanwhile, MC-CDMA, combined with OFDM and CDMA, is a potential communication system scheme because of its advantage in both OFDM and CDMA.Considering that MC-CDMA is an interference-limited system, multiple-access interference(MAI) is the main interference which affects system performance and reduces system capacity with large number of users in communication. Multi-user detection thus is a key technology to affect MC-CDMA system performance.The principles of OFDM and three multicarrier CDMA communication schemes are introduced in this thesis. Detail analysis and comparation in each scheme are presented. MC-CDMA scheme is mainly discussed and the mathematical model on uplink/downlink is also given. Then five equalization and combining schemes for downlink MC-CDMA are described. Simulations as well as analysis are shown.Multi-user detection (MUD) methods, including optimum multiuser detection and suboptimal multiuser detection methods, for uplink MC-CDMA are introduced. Detail analysis and simulations for each algorithm are presented. Based on the theory of the ant colony algorithm (ACO), an MC-CDMA system model in which ACO is applied is proposed with the feature of multi-user detection for uplink MC-CDMA systems. Simulations show that the performance of proposed algorithm is approached to optimum multiuser detection via selecting ACO parameters properly and there is a large saving in computational complexity, compared to optimum multiuser detection. |
PDF Full Text Request