RFRIS vs. Relay: Key Differences in Wireless Communication
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This article compares Reconfigurable Intelligent Surface (RIS) and Relay technologies, highlighting their key differences in the context of wireless communication.
Introduction
In wireless communication, the signal travels from a transmitter (like a Base Station or eNB) to a receiver (UE or mobile subscriber) through a channel. Obstacles in this channel can significantly impede signal propagation, making it difficult to serve subscribers located behind these blockages. Two primary solutions address this challenge: employing intelligent reflecting surfaces (or metasurfaces) and utilizing classical relays.
Reconfigurable Intelligent Surface (RIS)
RIS utilizes two-dimensional passive reflecting elements, often referred to as metasurfaces. It operates based on a modified Snell’s law principle, converting plane waves into scattered waves. A RIS controller manages the elements, enabling control over the delay, phase, and polarization of the scattered waves. Figure 1 illustrates RIS deployment in a wireless network scenario. Metasurfaces are particularly useful for serving subscribers blocked by obstacles.
Relay
Figure 2 depicts a relay used in an LTE network. As shown, it receives the signal from the LTE Base Station (eNB), processes it, and transmits it to the UE. Common functional blocks within a relay include:
- RF Down conversion
- Demodulation and decoding
- Modulation and Encoding
- RF Up conversion
- Signal power amplification
RIS vs. Relay: A Detailed Comparison
Figures 3 and 4 illustrate wireless communication systems employing IRS and Relay, respectively. The table below details the key differences between these technologies.
| Parameters | RIS (Reconfigurable Intelligent Surface) | Relay |
|---|---|---|
| Definition | The reflecting surface which scatters incoming EM waves with controllable delay/phase and polarization. | The device which decodes incoming EM signal, amplifies and retransmits it back. |
| Operating mechanism | Passive/active reflection | Active reception and transmission |
| Duplex | Full | Half/Full |
| Number of transmit RF chains | Zero | N ADC/DAC and amplifier |
| Hardware cost | Low | High |
| Energy consumption | Low | High |
| Prelog Penalty | No | Yes ( ~ 1/2) |
| Spectral efficiency formula |  |  |
