Research On The Key Technologies Of The MC-CDMA Communication System

Orthogonal Frequency Division Multiplexing (OFDM) has become a very attracttive multicarrier transmission technique for wireless high speed data communications. OFDM offers robustness to multipath fading without having to provide powerful channel equalization. In order to support multiple users with high speed data communications, the Multi-Carrier Code Division Multiple Access (MC-CDMA) technique is used to address these challenges. MC-CDMA is a combination of OFDM and Code Division Multiple Access (CDMA) and has the benefits of both systems, has the advantages of excellent capacity to resist frequency selective shadow, high data rate and frequency efficiency and simple system structure.MC-CDMA uses the spread spectrum technology of CDMA, the performance of spreading code directly determines the performance of MC-CDMA system, and because MC-CDMA systems using OFDM technology, was to make MC-CDMA also inherits OFDM's shortcomings, namely the peak to average power ratio (PAPR) high, while the introduction of multi-carrier transmission system, it is compared to single carrier, MC-CDMA system timing synchronization and carrier synchronization requirements and more strict, while the MC-CDMA is very sensitive to the frequency offset, making synchronization a direct decision of the MC-CDMA system performance, therefore,although MC-CDMA in future mobile communications has good prospects, MC-CDMA must solve these key problems that will encouter from lab to practical applications,such as PAPR, timing and carrier synchronization.Introduced OFDM and CDMA technology, analyse the theoretical basis, main characteristics of OFDM and CDMA, which the advantage of the combination of the two. This thesis mainly the key technology of MC-CDMA, one of the three combination schemes of OFDM and CDMA. Discussed three aspects of the carrier interferometry, resistence of high PAPR and system synchronization of the MC-CDMA systems. The primary contributions included in this thesis can be summarized as follows: 1. Discussed the three combination schemes of OFDM and CDMA techniques in the way of their advantages and disadvantages, the MC-CDMA transmitter model and receiver model were given, and the influence of the number of subcarriers and different numbers of users on the performance of MC-CDMA systems were analyzed.2. Researched the carrier interferometry sequence (CI). Introduced the composition of CI codes, academic computing the difference on resisting the MAI between applying the WH codes and CI codes, improved the structure of the CI/MC-CDMA systems, improved the BER performance on the MC-CDMA systems. The thesis also improved the POCI codes that sustained further users.3. Investigated the techniques for PAPR reduction, introduced the adaptive peak suppression algorithm, and improved the adaptive peak suppriession algorithm. The thesis analyzed the performance of PAPR to apply the APS into the uplink and downlink of the MC-CDMA systems.The result of simulator showed that the APS algorithm possessed the better performace on PAPR.4. Researched the timing and carrier synchronization, and analyzed the impact about the timing synchronization offset and carrier synchronization offset, and analyzed the timing and carrier synchronization algorithm. The thesis advanced the theory based on MUSIC algorithm, the result of simulator showed that the algorithm could be capable of effectively estimating the frequency offset.