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Advantages of Reconfigurable Intelligent Surface | Disadvantages of Reconfigurable Intelligent Surface

This page covers advantages and disadvantages of Reconfigurable Intelligent Surface (RIS) or metasurface used in wireless network. It mentions benefits or advantages of Reconfigurable Intelligent Surface and drawbacks or disadvantages of Reconfigurable Intelligent Surface.

What is Reconfigurable Intelligent Surface (RIS) ?

The surface which uses passive reflecting elements which are controlled by software is known as RIS or reconfigurable Intelligent Surface. It is also known as software controlled metasurface. The principle of working is as per variation to snell's law. The input to RIS is plane waves where as output is scattered waves whose phase shifts are controlled to meet desired reflection.

The metasurface is made of 'N' number of meta atoms with sub-λ size. These elements scatter incoming waves with controllable delay/phase and polarization. It changes wireless propagation channel environment by carefully tuning phase shifts of a large number of low cost passive reflecting elements.

Reconfigurable Intelligent Surface RIS in wireless network

Let us understand working of RIS.
• The EM (Electromagnetic) waves transmitted from BS are impinged on RIS which produces induction current in the RIS.
• RIS reflects these signals toward the users.
• During reflection, RIS changes response by controlling phase and amplitude. Phase shifts are controlled by PIN diodes used in RIS.

RIS element

RIS is ultra thin meta-surface which is composed of three layers viz. Outer layer, Middle layer and Inner layer.
Outer layer: It is a dielectric substrate with RIS elements. These elements directly interact with incident signals. RIS elements use several PIN diodes which helps in controlling the phase response of scattered wave by turning themselves ON and OFF as required. They support frequency from sub 6 GHz to THz range.
Middle layer: It is a copper plate which prevents signal energy leakage.
Inner layer: It consists of control circuit board. It is known as RIS controller.

Metasurfaces are used in various applications. It aids in various systems which include cell edge systems, mmwave systems (e.g. 6G wireless systems), IoT (Internet of Things), Indoor WiFi systems, UAV sensor based systems, Physical layer secure systems, SWIPT systems etc.

Benefits or advantages of Reconfigurable Intelligent Surface

Following are the benefits or advantages of Reconfigurable Intelligent Surface:
➨Wireless subscribers or mobile phones which are behind any blockage are not served by Base Station or eNB directly. RIS with N elements serves these blocked subscribers by varying the channel.
➨Metasurfaces outperform SISO (Single Input Single Output) system with same distance.
➨It offers better beamforming gain compare to massive MIMO. The received power is increased by factor 'N' in massive MIMO where as it is increased by factor 'N2' in RIS.
➨It enhances spectrum efficiency by providing extra spatial diversity gain.
➨It extends network coverage or BS (Base Station) coverage by serving cell edge users or subscribers.
➨It improves energy efficiency as RIS does not require energy hungry hardware. It offers low energy consumption which is better than relay, massive MIMO and backscatter technologies.
➨It uses low cost passive reflecting elements. It does not require ADC/DAC and amplifier devices as used in classical relay. Hence Reconfigurable Intelligent Surfaces are available at affordable cost.
➨It is hard to design and build conventional arrays for operation above 100 GHz. RIS can address this issue.
➨It is easy to implement, flexible to deploy and extend.
➨RIS integrates large number of antenna elements in compact space.

Drawbacks or disadvantages of Reconfigurable Intelligent Surface

Following are the drawbacks or disadvantages of Reconfigurable Intelligent Surface:
➨It does not outperform relay. To make performance similar to relay, requires metasurface with higher number of elements (~200).
➨RIS has worst SNR (Signal to Noise Ratio) than massive MIMO.
➨RIS elements do not support digital processing capability as it is designed based on concept of analog beamforming.



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