The Optimization And Application Research In Multicarrier System Of SSD

With the rapid development of cellular mobile communications,mobile Internet and multimedia services,the capacity requirements for wireless communications are growing,that posing a new challenge to the use of very limited wireless spectrum resources.On the other hand,fading is the one of the main reason for the decline of communication quslity in the process of transmitting.Signal space diversity(SSD)has attracted much attention as a diversity method that can effectively eliminate the influence of channel fading and doesn't need to occupy extra time and band resource.However,despite the advantages of SSD technology has been confirmed,the flexible and simple design of structural and simple and effective demodulation algorithm in receiver-side is still a huge challenge.The thesis studied from corresponding angle,the specific content is as follows:1.The introduction of SSD makes the QAM constellation no longer a regular pattern.The simple and effective demodulation scheme in square QAM is no longer applicable whether soft demodulation or hard decision.The SSD increases the demodulation complexity exponentially with the increase of modulation order.Therefore,the thesis presents a new low complexity constellation pattern segmentation(CPS)soft demodulation algorithm.The algorithm adds a preprocessing module to the traditional Max-Log-MAP algorithm.The equivalent reference constellation is considered as the sub-constellation of two different grid structures using the mapping property.Selecting constellation points on every constellation grid line by comparing the distance between the projection point on the constellation grid line and all the constellation points on corresponding grid line,a subset will be divided from original constellation pattern.CPS algorithm reduces the demodulation complexity to a certain extent,and it is very effective in the high-order modulation.Theoretical analysis and simulation results show that the demodulation accuracy of the optimization algorithm is not affected compared with the traditional Max-Log-MAP algorithm with full search.2.The multicarrier time division multiple access(MC-TDMA)proposed in our team introduces the advantages of single carrier modulation system on the basis of traditional filter group multicarrier modulation system,and thus has very low peak average power ratio(PAPR)and a stong ability of anti-multipath fading and carrier non-synchronous.The thesis design more flexible and efficient modified signal space diversity(MSSD)using the special modified discrete Fourier transform(MDFT)filter group in MC-TDMA.MSSD can not only play the dual roles of MDFT filter group and SSD technology,but also easy to implement.Based on the self-structure of MC-TDMA system,the thesis establishes MSSD-MC-TDMA system and studies its rapid implementation.The simulation of PAPR shows that adding MSSD has no effect on the advantages of the original system.In order to verify the validity of the MSSD,the MSSD-MC-TDMA system is simulated in the frequency selective fading channel,the flat fading channel and erasure channel respectively,the relative gain of MC-TDMA with different modulation order and turbo rate are obtained.