Difference between Reconfigurable Intelligent Surface and Relay | RIS vs Relay
This page compares Reconfigurable Intelligent Surface (RIS) Vs Relay and mentions difference between Reconfigurable Intelligent Surface and Relay.
Introduction: Wireless communication consists of transmitter (i.e. Base Station or eNB), receiver (UE or mobile subcriber) and channel. When there is blockage between transmitter and receiver, it will be difficult to serve subscribers behind this blockage. There are two main ways, these subscribers can be served viz. by using intelligent reflecting surfaces or metasurfaces or using classical relay.
Reconfigurable Intelligent Surface (RIS)
The RIS uses two dimensional passive reflecting elements. These surfaces are also known as metasurfaces. It works based on modified snell's law principle. RIS converts plane waves into scattered waves. The elements of RIS are controlled by RIS controller which helps in controlling delay/phase and polarization of scattered waves. The figure-1 depicts RIS used in one such wireless network scenario. Metasurfaces are mainly used to serve subscribers which are blocked by any obstacles.
Relay
The figure-2 depicts relay used in LTE network.
As shown it receives the signal from LTE Base Station i.e. eNB.
It processes the received signal and transmits back to the UE.
The common functional blocks which relay uses include following.
• RF Down conversion
• Demodulation and decoding
• Modulation and Encoding
• RF Up conversion
• Signal power amplification
Difference between RIS and Relay
The figure-3 and figure-4 depict wireless communication systems using IRS and Relay respectively. The spectral efficiencies of both the cases are mentioned below in the table taking into considering path losses, transmit power and 'N' elements in RIS.
Following table mentions difference between RIS and Relay.
| Parameters | RIS (Reconfigurable Intelligent Surface) | Relay |
|---|---|---|
| Definition | The reflecting surface which scatters incoming EM waves with controllable delay/phase and polarization is known as RIS. | The device which decodes incoming EM signal, amplifies and retransmit it back is known as relay. |
| Operating mechanism | Passive/active reflection | Active reception and transmission |
| Duplex | Full | Half/Full |
| Number of transmit RF chains required | Zero | N |
| ADC/DAC and amplifier | Not required | Required |
| Hardware cost | Low | High |
| Energy consumption | Low | High |
| Prelog Penalty | No | Yes ( ~ 1/2) |
| Sprectral efficiency formula |  |
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