Research On New Receiving Technology Of Vortex Wave

Communication service is getting continuously developed with the maturity of information technology. Thus, it brings high request to the communication rate and bandwidth, and the contradictory between the limited frequency spectrum resources and the growing communication requirements becomes more and more obviously. Especially for the service which needs high bandwidth, such as the communication between satellite and the earth, the super-speed cloud computing, and etc. Based on this background, vortex wave communication, a novel communication technology which can largely improve frequency spectrum efficiency and transmission speed emerges. Vortex wave carrying orbital angular momentum (OAM) is able to improve the spectrum efficiency and communication rate due to the orthogonality among different vortex states. Recently the communication based on OAM has attracted much more attention.It is said that vortex wave has a phase singular point in the beam center and a dark hollow structure radiation pattern. In the practical application, especially for the radio vortex wave, the radius of dark zone increase with the increasing transmission distance owing to the beam divergence. Theoretically the orthogonality among different OAM modes is based on the whole angular aperture receiving (WAAR). Once the whole aperture receiving can’t be guaranteed owing to beam divergence, the orthoganality of different vortex is break down. Hence, these facts increase the difficulty and cost of receiving end in the OAM communication system undoubtedly. In order to solve these problems, the paper focuses on a feasible and effective vortex wave receiving technology so that to realize a practical radio vortex communication system.For the vortex wave receiving technology, the devices which are made to realize the opposite phase distribution of the OAM waves, such as spiral phase plate, holographic plate, etc., are generally used to effectively receive the vortex wave. However, as the transmitting distance increases, there rarely exists large aperture receiving antenna due to the beam divergence even in the short distance communication. Therefore, sampling receiving technology of whole aperture will be adopted in the radio field. i.e., by uniformly sampling in the whole aperture, disperse small apertures constitute into a whole large aperture. In the practical case, the effects of some non-ideal receiver conditions, e.g. misalignment between transmitter & receiver and the placement of the sampling antennas, meanwhile the channel noise will have significant influence on vortex wave receiving. Hence in this paper, the research significance, research status review, and development trend are firstly introduced. Based on which, a conventional receiving method, whole aperture sampling receiving (WASR) radio OAM link is simulated considering channel factors and non-ideal receiver conditions in order to analyze the impact of each factor. Next, a new and practical receiving scheme named partial aperture sampling receiving (PASR) in consideration of the fact that beam divergence will restrict the whole aperture receiving is proposed. The relationship between angular size and orthogonal OAM mode selection, OAM multiplexing channels and the number of sampling antennas is studied in the theory. Meanwhile, the simulations are carried on in the case of channel factors and the effects of some non-ideal transmitter-receiver conditions by means of Matlab and Simulink models. In addition, the superiority that PASR compares with WASR and application conditions are discussed by the system performance comparisons. Finally, experimental platform used in OAM multiplexed communication link on basis of partial aperture sampling receiving is built to verify the feasibility of OAM radio communication base on PASR.The paper proposes a new receiving technology of PASR, which is a small aperture receiving method while guarantee the orthogonality of different OAM modes. This scheme can solve the receiving difficulties for the radio OAM communication, and put forward a practical way for the real radio vortex wave communications.