Research On The CDMA System Based On A Novel Asymmetric Frequency Division Duplex Technology

With the development of mobile communications, the combination of mobile communications network and internet has become more and more close. The kinds of mobile communications services are richer. Because of the characters of internet, the service requirement of downlink is much greater than that of uplink both in the total amount of transmission and in the kinds of service. Meanwhile, the effects of electromagnetic radiation on the surrounding environment has caught people's attention. Under the restriction of electromagnetic radiation, the largest transmission capabilities, namely the largest capacities, of uplink and downlink of mobile communications system are asymmetric. With the users' increasing requirements of servises, the limited spectrum resources are more scarce. How to design an efficient transmission system according to the asymmetry of uplink and downlink has become a key issue in future mobile communications systems. In NSFC project "Research on a novel Asymmetric Frequency Division Duplex technique", a novel Asymmetric Frequency Division Duplex scheme—AFDD has been proposed. It has advantages of both TDD and FDD. Like TDD, it can assign the uplink and downlink resources flexibly adapted to asymmetric service demands. Meanwhile it has strong robustness and large coverage inheriting from FDD.Based on AFDD, this article has a deeply research on asymmmetric transmission, duplex scheme and the characteristics of uplink and downlink of mobile communications system and expands the content of AFDD. Besides the asymmetric characteristics, this article also discusses that AFDD could assign frequency resources dynamicaly according to the services status.This atcicle also designs AFDD\CDMA system combining AFDD and CDMA and proves that compared with FDD\CDMA system AFDD\CDMA can not only adapt well to asymmetry but also improve the capacity and coverage of system in theory. Meanwhile, this article also puts forward a bandwidth determining method, the frequency allocation strategy and access control strategy and analyse the performance through simulation.