摘要
Wireless Communications with Reconfigurable Intelligent Surfaces With the commercialization of the fifth generation(5G)wireless networks in 2019,developing the next generation wireless standard has been put on the agenda.To cope with the 1000x capacity requirements,the 5G wireless networks has adopted massive MIMO as a key enabling physical layer technology to boost the spectral efficiency.In addition,higher frequency band such as millimeter wave band is exploited to address the spectrum shortage problem.Looking ahead,it has been envisioned that further scaling up the antenna number,such as ultra-massive MIMO and moving into even higher frequency band such as Terahertz(THz)band,are two promising directions.However,deploying thousands of antennas in the conventional approach is unsustainable due to the huge cost associated with the massive number of RF chains.Moreover,cost-effective and high-performance RF components working in the extremely high frequency band are currently not available.These challenges should be properly addressed before ultra-massive MIMO and THz technologies can be possibly implemented in practice.
