The Precoding Research On Joint Processing And Coordinated Beamforming In C-RAN System

With the popularity of wireless communications, our daily lives have been closely related to wireless communication services. Saving energy and resources, as well as protecting the environment will become the research direction of the new generation of wireless technology. In response to the increasingly competitive market of communication services, China Mobile proposed the construction of real-time cloud infrastructures radio access network(C-RAN), which can promote the development of green information and communication technology at the same time. As a prospective green radio access network, C-RAN consists of the remote radio frequency unit and the centralized baseband pool. In this context, precoding technology in C-RAN cooperative wireless networks has been researched in this paper, and a reference solution for coordinated multi-point transmission technology is also be provided.In LTE-A network, two types of downlink CoMP transmission schemes have been identified, that is, joint processing(JP) and coordinated scheduling/coordinated beamforming(CS/CB).This thesis focuses on the precoding techniques in those two kinds of coordinated multipoint transmissions. To sum up, the main innovations of this thesis include the following two aspects:Firstly, cooperative multi-point signals are affected by symbol timing offset and carrier frequency offset in joint transmission. In order to reduce the sensitivity to asynchronous signal in joint transmission system, the orthogonal precoding synchronization algorithm is proposed. As Walsh code is orthogonal to each other, synchronization offset in cooperative multi-point system is suppressed. On this basis, two orthogonal precoding algorithms combined with different traditional estimation are proposed. Theory analyses and simulation results demonstrate that the problem of synchronization offset is effectively solved and the performance in collaborative transmission system is improved by this method.Secondly, in order to meet the requirements of green communication, the beamforming precoding is designed from the perspective of power consumption. For the beamforming precoding based on energy efficiency guidelines, we establish the power consumption model of cellular network, and propose a signal transmission scheme which combines collaboration beamforming with transmit antenna selection when the transmitting antenna is uncertain. Compared with the beamforming based on energy efficiency, not only the energy consumption is reduced, but also the inter-user interference be restrained through the algorithm. Simulation results show that the energy efficiency parameters of the communication system is effectively improved by using thep proposed method, furthermore, the performance of the method is better than the conventional beamforming precoding.