| How to make the transmit signals with high reliability in extremely low signal-to-noise ratios and high dynamic complex environments is a hot issue in the future research of wireless.As the multiple access technology,Code Division Multiple Access(CDMA)technology has the advantages of large system capacity,anti-fading,and strong anti-interference ability;Orthogonal frequency division multiplexing(OFDM)as a multi-carrier modulation technique for efficient parallel data transmission,which has the advantages of high spectrum utilization and strong resistance to multi-path.Multiple Input Multiple Output(MIMO)technology can fully utilize space resources without increasing spectrum resources and antenna transmission power,it can double the system channel capacity.Therefore,it has important practical significance to study the MIMO-OFDM-CDMA system combining these three technologies and make the wireless communication system can obtain considerable system capacity,power efficiency,diversity gain,and transmission error rate performance.Firstly,several existing schemes of multi-carrier spread spectrum communication systems are introduced.By comparing their performances,the MIMO-MC-CDMA system with simple structure and good performance is selected as the system model of this paper.For the problem that the performance of MIMO-MC-CDMA system cannot meet the actual demand under the harsh channel environment,the system is further designed and optimized from the three aspects of spreading sequence design,subcarrier allocation and space-time coding technology..Secondly,the orthogonal spreading sequence with excellent correlation characteristics are selected as the user spreading sequences in MIMO-MC-CDMA system.The effects of orthogonal spreading sequences on the system power efficiency and the transmission error rate are discussed in this paper.Then,when the traditional selection mapping algorithm is applied to the space-time coding MIMO-MC-CDMA system,the algorithm complexity and the system performance are insufficient.This paper proposes an improved spread spectrum method based on the joint selection mapping method,By using the spreading sequence as the phase selection factor of the selective mapping method and combining space-time encoding orthogonal properties,which improves the system performance and reduces the computational complexity by half.Finally,this thesis deduces the receiver mathematical model of the space-time coded MIMO-MC-CDMA system in detail,and then introduces the existing user detection algorithm.Basedon the known weighting coefficients of single-antenna MC-CDMA system detection algorithms,the user detection algorithm weighting coefficients suitable for space-time coded MIMO-MC-CDMA systems are deduced theoretically.Aiming at the problem of insufficient performance of existing algorithms under bad channel environment,this paper proposes a user detection algorithm based on joint Partial Parallel Interference Cancellation.The algorithm is based on parallel interference elimination algorithm with excellent performance multiplied by partial elimination factor,and has excellent use.Utilize the existing user detection technology with excellent performance as an initial estimate estimator for partial parallel interference cancellation algorithms.The experimental results show that this method achieves good performance in harsh channel environments.At the same time,this paper uses the AD9361 software radio platform as a verification platform to verify the system's simulation platform. |
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