| Reconfigurable intelligent surface(RIS)is a new type of artificial electromagnetic surface that can reconfigure the electromagnetic environment with high accuracy by flexibly regulating the reflection coefficient of its surface cells,promising new design freedom for future mobile communication architectures and becoming an essential solution for increasing communication rates,enhancing communication coverage,and reducing system energy consumption.Based on the above background,this thesis conducts research on the design of RIS and its phase optimization in communication systems,starting from the regulatory mechanism of RIS.1.a 1-bit RIS with low control overhead is designed to address the difficulty of balancing the control flexibility and low hardware control costs of RIS.On the basis of the principle of RIS regulation,a row-controlled and column-controlled scheme based on the phase addition rule is proposed,which only requires row + column number of ports to achieve beam deflection coding for row * column cells.This thesis introduces the structure and control logic of the designed RIS from three aspects: unit design,stability design,and circuit design.It is verified through simulations that the RIS unit can achieve a phase difference of π by means of a specific feed pattern.Furthermore,by encoding and simulating the target adjustment angle of RIS,it is shown that the designed RIS achieves directional adjustment of the corresponding angle of the beam.2.for the phase optimization problem of RIS deployed in communication systems,this thesis designs the corresponding encoding schemes based on the known channel state information(CSI)and unknown CSI of the base station.First,for the RIS phase coding when the statistical CSI is known,this thesis takes maximizing the uplink traversal channel capacity as an indicator,and derives the optimal phase closed-form expression based on the angle of arrival(Ao A)and angle of departure(Ao D)in the beam space.Simulation shows that RIS significantly improves the uplink traversal channel capacity of the system under the optimal phase setting.Besides,the influence of the 1-bit discrete phase shift on the uplink traversal channel capacity of the system is analyzed through theoretical derivation and Monte Carlo simulation.Secondly,a code-book based beamforming training protocol is proposed for RIS phase encoding with unknown CSI.In terms of codebook design,this thesis proposes a codebook generation scheme based on the discrete Fourier transform(DFT)matrix from the perspective of beamforming;In terms of codebook search methods,this thesis designs a hierarchical search scheme for block codebooks based on the principle of minimum chord distance.Numerical simulation results show that,compared with the traditional row and column codebook search method,the beam shaping training protocol can reduce the beam training overhead to 30% of the former while ensuring that the system uplink traversal channel capacity performance falls back less than 0.3%.3.this thesis presents a practical measurement and verification of the designed RIS.Firstly,the reflection phase of the RIS is tested using a lens platform under the four designed bias modes.The test results show that the reflection phase can be quantified as two groups of 0 and π based on the number of diodes.This proves that the designed RIS achieves the correspondence between the feed mode and the phase addition rule.Subsequently,this thesis verifies the effectiveness of the RIS beam modulation and the feasibility of the codebook search scheme in the darkroom.The test results show that the maximum beam angle of the far-field directional map obtained by the coding method in section 2.2 and the coding method based on the codebook basically coincide with the simulation results,which well verifies the function of the designed RIS for the directional control of electromagnetic waves,thus providing practical support for the introduction of RIS in future wireless communications. |
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