Key Technologies Of Reconfigurable Intelligent Surface Aided High-Capacity Integrated Optical And Wireless Communications

With the explosion of multi-service user traffic,communications networks are placing greater demands on their access network architecture.Cloud-radio access network(C-RAN)for its cost and performance advantages and fiber-optic communication for its bandwidth and rate advantages have received a lot of attention.For radio access technologies,the combination of millimeter-wave(mmWave)and multipleinput multiple-output(MIMO)provides a technical approach to achieving Gbps and even 10 Gbps user rates and tens of Gbps maximum rates.However,the design of optical true time delay beamforming that can be seamlessly introduced into C-RAN and the introduction of emerging devices,such as reconfigurable intelligent surfaces(RISs)with the low-complexity active and passive beamforming optimization are the key research elements in realizing high-capacity optical and wireless networks.On this basis,considering the implementation cost after the introduction of RISs,it is necessary to study how to achieve low-overhead channel state information(CSI)acquisition and lowcomplexity RIS control techniques.For the broadband signal reception of high-capacity optical and wireless networks,the study of their high-performance channelized receivers is also an important research element.Therefore,this dissertation focuses on the key issues and investigates transmission and reception technologies in high-capacity optical and wireless networks.Specifically,this dissertation aims to investigate optically centralized-control beamforming,joint active and passive beamforming in RIS-aided optical and wireless networks,low overhead beam training and low complexity RIS control in multi-RIS-aided networks,and microwave photonic channelization,etc.The main contributions and innovations of this dissertation are summarized as follows.1.To address the problems caused by the separation of beamforming control and beamforming physical implementation in existing mmWave C-RAN systems,an optical true time delay pool(OTTDP)based centralized-control beamforming scheme has been proposed.By decoupling the beamforming weight control units of the different active antenna units(AAUs)and using only passive optical multiplexers at the AAUs instead of a set of expensive tunable optical filters,the structure at the AAUs is simplified,which can be seamlessly introduced into mmWave C-RAN systems.Based on the centralized implementation of the proposed OTTDP-based beamforming,about half of beamforming implementation resources can be saved.Moreover,the evolution of the proposed OTTDPbased beamforming scheme to single-user and multi-user hybrid beamforming has been presented.A design example of the proposed OTTDP is given,and the feasibility of the proposed single-user and multi-user hybrid beamforming is verified.2.Based on the proposed OTTDP-based single-user and multi-user hybrid beamforming,the scheme to the introduction of emerging RISs was designed and verified to further improve its performance.Moreover,low-overhead and low-complexity joint active and passive beamforming has been proposed for both single-RIS/single-user and multi-RIS/multi-user scenarios,respectively,with respect to the capacity limitations imposed by fronthaul of the mmWave C-RAN and the limited computing resources at the AAUs.For single-RIS-aided single-user systems,a non-iterative active and passive beamforming algorithm is developed by using codebooks to quantify passive beamforming at RIS and active beamforming at AAU.Considering more practical multiRIS-aided multi-user systems,sub-connected hybrid beamforming(SC-HBF)based on the proposed OTTDP is investigated.Compared with the conventional SC-HBF,the proposed OTTDP-based SC-HBF requires only about half of the physical resources.3.To address the problem of RIS control and channel estimation in multi-RIS-aided mmWave communication caused by the passive nature of RIS,a two-timescale based beam training method is proposed to reduce the beam training overhead by exploiting the two-timescale property of the RIS-assisted channel,and it is demonstrated that the proposed beam training method can achieve the maximum beamforming gain.Furthermore,it has been demonstrated that the scheme can achieve the maximum passive and analog beamform gain.For the performance loss due to lack of interference management in codebook-based schemes,a generalized Benders decomposition based joint active and passive beamforming algorithm has been proposed,which significantly improves the system performance by adding certain CSI acquisition overheads,while having the low-complexity control advantage of codebook-based passive beamforming.The proposed GBD-based active and passive beamforming provides near-optimal performance(≥ 99.9%)and saves 50% of the transmit power compared to the conventional codebook-based schemes.4.With the increasing bandwidth and frequency of transmit signals in high-capacity optical and wireless networks,the bandwidth limitation of electrical analog-to-digital converter/digital-to-analog converter(ADC/DAC)in high-frequency wideband signal processing becomes an increasingly serious problem.For this reason,research has been conducted on wideband signal reception techniques in optical and wireless convergence systems.To this end,research has been conducted on wideband signal reception in optical and wireless networks.In order to realize the reception of wideband signals,a microwave photonic channelization reception method based on tunable optical combs is proposed to realize reconfigurable microwave photonic coherent channelization reception.The relationship between the number of 1-d B comb lines and the gain of the voltage control module for the output of the proposed tunable comb generator is discussed.To verify the reconfigurability of the scheme,a wideband signal channelized with a center frequency of 20 GHz and a bandwidth of 4 GHz was channelized into four narrowband subsignals of 1 GHz,while a wideband signal channelized with a frequency of 18-28 GHz and a bandwidth of 10 GHz was channelized into five narrowband subsignals of 2 GHz.The results show that the proposed scheme effectively improves the efficiency of coherent channelized reception,and achieves low-latency channelized reception of dynamic wideband signals based on spectral analysis.