| Summary: | Efficient spectrum utilization is always the fundamental challenge of mobile communication technology toward 6G. Instead of conventional spectral efficiency in bps/Hz, geographical region shall be brought into consideration in bps/Hz/unit-area, which suggests spatial domain technology as a generalization of conventional MIMO to elevate next generation mobile communication technology. Therefore, this paper introduces the formation of smart radio environment considering efficient utilization of radio spectrum in any given geographical area, which can be also viewed as a generalization of cognitive radio technology. By smart management of reconfigurable intelligent surface (RIS) and ambient backscatter communication (ABC) technologies, smart radio environment can be formed in any given area to achieve spectral-spatial efficiency. In this paper, the control of electromagnetic spatial radiation over a region is explored by utilizing repositionable dynamic RIS and harmony of multiple ABC nodes assisted with machine learning (ML) based control mechanism to form spectrum map. Such smart and reconfigurable radio technology demonstrates the superiority of mutual usage of RIS and ABC in terms of shaping the electromagnetic energy in coexisting radio systems. First, the use of multiple RISs is studied to enhance the capacity of secondary use inside the specific area by shaping the electromagnetic energy in the spatial domain. Secondly, a new degree of freedom with repositionable dynamic RIS is introduced. Controlling the time varied shadowing effects by re-positioning the RIS, it is shown that 15% more capacity can be achieved. Finally, the use of multiple coordinated ABCs to protect the region of primary use against the radiation due the secondary uses is investigated. Having coordinated network with repositionable dynamic RIS and multiple ABCs allow us to shape the electromagnetic wave in spatial domain by creating radiation rejection and coverage extension zones. A centralized or distributed mechanism to construct the spectrum map based on ABC sensor is also introduced to instruct existing repositionable dynamic RISs for better coverage. Merging these promising technologies will pave the way for the smart radio environment creating high spectral efficient wireless systems. © 2020 IEEE.
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