This document discusses using reconfigurable intelligent surfaces (RIS) for wireless communications. It introduces RIS and how they can function as programmable metasurfaces to manipulate electromagnetic waves. This allows RIS to potentially serve as an RF chain-free transmitter or enable space-down conversion receivers. Experimental results demonstrating 5 MHz down conversion using an RIS receiver are presented. The document argues that RIS may shift wireless transceiver design by simplifying hardware complexity and reducing costs for technologies like ultra-massive MIMO and THz communications. However, challenges remain to realize the full potential of RIS for 6G and beyond.

1. Wireless Communications
Through
Reconfigurable Intelligent
Surfaces

2. 1.
Introduction
• UM-MIMO and THz suffer from high
cost and hardware complexity.
• Two prospective paradigms:
1. RF chain-free Transmitter.
2. Down-conversion Receiver.
• We will introduce the basic concept of
programmable Metasurfaces
• Wireless communication enabled by
programmable Metasurfaces to
address the above issues.
• Experimental results and advantages of
these new paradigms and their
challenges toward 6G with low hardware
complexity, low cost, and high energy
efficiency.

3. Metal
plate
Ideal
Metasurface
Practical
Metasurface
2. What is a Reconfigurable Intelligent Surface (RIS)?
Altering surface
impedance to
phase-shift
reflection
Constant
surface
impedance
Approximation
with discrete
elements
𝜃₁ 𝜃₂
e.g.
λ
5
x
λ
5
(Snell’s law) (Generalized Snell’s
law)
(Discretization)

4. Evolution of the concept
1. Fixed reflect array
3. Software controlled Metasurface
4. Real-time software controlled
Metasurfaces
2. Reconfigurable reflect array/
Metasurface

5. Intelligent Propagation Environments
We conventionally control
1) Transmitter
2) Receiver
Now we can control the
channel!

6. Comparison of conventional wireless transmitter and metasurface
transmitter.
02. Programmable
Metasurface Reduce the
hardware complexity targeting
UM-MIMO and THz
communications. When the
programmable metasurface is
01. Conventional Wireless
Transmitter
Hardware cost and power
consumption when applied in
UM-MIMO & suffers from low
transmission rate due to the slow

7. 1
The incident EM wave
is converted into the
reflected EM wave, with
its amplitude and
phase adjusted by the
external control signals
Reflection Type
2
Programmable
Metasurface, the
incident EM wave is
mainly converted into
the transmitted wave.
Transmission
Type.
Types of Programmable Metasurfaces
50%
22%
28%

8. 3. Space down conversion using Reconfigurable Intelligent Surface
Captured by the Antenna
array
It works such as Filters, LNAs, Mixers and
local Oscillators

9. The test-bed setup of the Integrated Transceiver Design
EM Down
Converted
by RIS
2 x 2 MIMO
256 unit cells
Receiving antennas
16-QAM
transmission
with 20 Mb/s
data rate is
achieved

10. 5 MHz space-down-conversion
 This result verifies the feasibility of the metasurface-based space-
down-conversion receiver paradigm.

11. The test-bed setup of the metasurface-based transceiver Advantages :
1. Simplify the architecture hardware, cost of future wireless
transceivers.
2. Open the door toward ultra-massive 6G communications with low
hardware complexity, low cost, and high energy efficiency.
3. If each unit cell can be controlled independently by (DAC), the RF
chain-free transmitter can generate multi-channel RF signals
simultaneously, which consequently enables advanced signal
processing methods such as space-time modulation and beam
steering for MIMO and the future UM-MIMO technologies.
At the moment, only 5 MHz frequency down conversion is realized, as
the sampling rate of the DAC modules used in the experiment is only
can reach 5 MHz .
the programmable metasurface is fast enough in GHz and even THz
level space-down-conversion can be potentially implemented in the
future,
which will greatly reduce the hardware complexity and the cost of the
UM-MIMO or THz receiver in the 6G era.

12. INTERESTED
4.CONCLUSION
In this presentation we have introduced
1. Overview about Metasurface and Reconfigurable
Intelligent Surfaces & its types.
2. Comparison of programmable Metasurface &
conventional communication system
3. Two paradigms to utilize the programmable
Metasurfaces as RF chain-free transmitter and space-
down-conversion receiver.
4. advantages of these novel paradigms are presented.
It is demonstrated that programmable Metasurfaces
may bring a paradigm shift in wireless transceiver
design, due to their superior capability of manipulating
the EM waves
5. Future Research directions.

13. Received power increases as 𝑁.
Is it better than Massive MIMO
where it grows as 𝑁 !
Reality: An IRS always has worse
SNR.
The gap reduces but remains as 𝑁
→ ∞
A Large Surface is Needed to Beat Relays
Additional Slides :-
200 Elements needed to beat relay
But can be fitted in 1x1.5 m²
80 m
10 m 𝒅𝟏
Source Destination

14. Additional Slides :-
IRS is Not a Mirror But a Lens!

15. 5.REFERENCES
2. E. Björnson, Ö. Özdogan and E. G. Larsson, "Intelligent Reflecting Surface Versus
Decode-and-Forward: How Large Surfaces are Needed to Beat Relaying?," in IEEE
Wireless Communications Letters, vol. 9, no. 2, pp. 244-248, Feb. 2020, doi:
10.1109/LWC.2019.2950624.
3. Björnson, E., Sanguinetti, L., Wymeersch, H., Hoydis, J., & Marzetta, T. L. (2019).
Massive MIMO is a reality—What is next? Digital Signal Processing.
doi:10.1016/j.dsp.2019.06.007
1. W. Tang et al., "Wireless Communications with Programmable Metasurface: New
Paradigms, Opportunities, and Challenges on Transceiver Design," in IEEE Wireless
Communications, vol. 27, no. 2, pp. 180-187, April 2020, doi:
10.1109/MWC.001.1900308.

16. THANKS