Chat: Electromagnetic Signal and Information
Theory for Communications
Why future wireless systems
need advances in Electromagnetic Signal and Information Theory? Some
answers in the interview with the Guest Editors of the upcoming
special issue in IEEE JSAC.
IEEE JSAC Guest Editorial Team: Rodrigo C. de Lamare (RCdL), Kumar
Vijay Mishra (KVM), Michalis Matthaiou (MM), and Gerhard Kramer
(GK). The responses are very insightful and stimulating for further
exploration of the research problems in this area.
JSAC: Information theory is quite a general mathematical
framework. For instance, in information theory it is known that
"channel is a part of the system we are unwilling or unable to
change", but once the channel is defined, we can use Shannon theory
to analyze its capacity and error probability. Why, then, do we need
information theory tailored to the electromagnetic features of the
signals?
RCdL: Taking into account the electromagnetic features of the
signals has the potential to bring more accurate information
theoretic results and eventually improve the design of communication
systems.
KVM: One of the major drivers behind the recent interest in
electromagnetic signal and information theory (ESIT) is the ongoing
active research in metasurfaces. These devices comprise an array of
spatially-varying sub-wavelength scattering elements that can
control and manipulate electromagnetic waves through modified
surface boundary conditions. Hence, it becomes pertinent to study
the information theory of metasurface-based wireless communications
through the lens of electromagnetics. These ESIT insights then
naturally extend to several other applications where the system
performance is directly linked with electromagnetics of the devices
or channel, such as near-field architectures, terahertz
electromagnetics, and even radio wave interaction with biological
systems.
MM: While information theory is undoubtedly a versatile
mathematical tool, it is based on mathematical logic. This
theoretical framework now needs to be extended and reshaped to
incorporate the main feature of future communication systems, namely
their capability of sensing the system’s response to the radio
waves, and thereby informing its modification.
GK: The statement suggests that information theory is limited
to “channels”, “capacity”, and “error probability” but this is a
narrow perspective. Information theory addresses the design of the
entire communications chain from the application layer (video
coding, speech coding, bit coding, security coding) to the physical
layer (FEC, feedback, multi-carrier signaling, power control) for
all block lengths. Moreover, multi-user information theory provides
the right framework for multi-user systems (multi-access, random
access, spatial multiplexing). For instance, the optimality of
separating source and channel coding for point-to-point links
suggested a layered approach to communications that continues to be
important today to ensure flexibility. And the refined statement
that one cannot separate source and channel coding for multi-user
systems motivates cross-layer improvements. Inevitably, we must
combine information theory with channel modeling. This happened for
telephone channels (1980s-2000s), wireless channels (1990s-2010s),
and fiber channels (2000s-2020s). The further development of this
fascinating synergy is one goals of this issue.
JSAC: Can you give an example of a research question in
Electromagnetic Signal and Information theory that you see as
particularly challenging or interesting?
RCdL: An interesting challenge of Electromagnetic Signal and
Information theory is to come up with sufficiently simple models
that accurately capture impairments and practical effects related to
Electromagnetics, which would then allow the development of
cost-effective signal processing solutions and yet facilitate the
use of information theory to provide better insights on system
design than those we currently have.
KVM: Yes. A particularly interesting research problem could
be to include the electromagnetic parameters such as the operating
frequency, polarization, dielectric properties, and permeability of
the metasurfaces directly into the information-theoretic analysis of
metasurface-aided wireless communications.
MM: As the number of antenna elements in future arrays
increases (e.g XL MIMO, THz arrays), their near-field zone will
continue to expand. To date, near-field communication has been a
black box for information theorists. In order to understand the
impact of near-field propagation (e.g. non-stanionarities, spherical
wavefronts), we need to go back to our information theoretic models
and recalibrate them using these unique electromagnetic
characteristics.
GK: A simple and obvious answer is: all practical channels,
including copper, optical fiber, wireless, magnetic, free-space
optical, etc. Combining channel modeling and information theory is
particularly challenging because both theories are sophisticated on
their own.
JSAC: During the past 25 years we have seen a continuous
evolution in the area of multi-antenna communication and witnessed
the direct impact of those techniques to practical systems and
standards. Do you see a potential in Electromagnetic Signal and
Information theory, over a longer run, to trace an evolution path
that will lead to new waveforms, new types of devices or new types
of network elements? Can you elaborate upon that?
RCdL: There is tremendous potential in Electromagnetic Signal
and Information (ESIT) theory to better inform designers about how
to obtain performance benefits by using more realistic modeling of
multiple-antenna systems and networks. In particular, when a
designer employs ESIT theory on a particular network element such as
an access point or an intelligent reflective surface it could
potentially provide more clear directions on how to obtain
performance benefits.
KVM: Yes. ESIT has the potential to enable more accurate and
reliable characterization of communications systems. At present, the
multi-antenna multi-functional metasurface-aided systems are already
being evaluated by start-ups and even some large telecommunications
organizations. Future wireless communications are likely to employ a
suite of metasurface-aided techniques (e.g., near-field, THz, OAM,
and holographic systems) that must also have an
electromagnetically-compliant design.
MM: Multiple-antenna communications have indeed witnessed an
unprecedented evolution over the past 25 years. The emerging
multiple-antenna technologies, such as THz communications, RIS and
OAM, create new challenges in their modeling, transceiver
design/optimisation and waveform design. In this context, injecting
electromagnetic knowledge into the conventional Gaussian-type
information theoretic models becomes a timely and extremely
interesting exercise.
GK: Yes, only foundational theories can support sustainable
progress in communications. History has taught us that
electromagnetic theory and information theory are two of those
theories, and that they complement each other.
Chat with the Guest Editors: Special
Issue on Electromagnetic Signal and Information Theory for
Communications | IEEE Communications Society (comsoc.org) - By Petar
Popovski, Editor in Chief of IEEE JSAC and part of the Guest
Editorial Team
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TACS is a leading top consultancy in the field of information, communication
and energy technologies (ICET).
The heart of our consulting spectrum comprises strategic,
organizational, and technology-intensive tasks that arise from the use of new
information, communication and energy technologies. The major emphasis in our work is found in innovative consulting and
implementation solutions which result from the use of modern information,
communication and energy technologies.
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