64 research outputs found
Information-Theoretic Study of Time-Domain Energy-Saving Techniques in Radio Access
Reduction of wireless network energy consumption is becoming increasingly
important to reduce environmental footprint and operational costs. A key
concept to achieve it is the use of lean transmission techniques that
dynamically (de)activate hardware resources as a function of the load. In this
paper, we propose a pioneering information-theoretic study of time-domain
energy-saving techniques, relying on a practical hardware power consumption
model of sleep and active modes. By minimizing the power consumption under a
quality of service constraint (rate, latency), we propose simple yet powerful
techniques to allocate power and choose which resources to activate or to put
in sleep mode. Power consumption scaling regimes are identified. We show that a
``rush-to-sleep" approach (maximal power in fewest symbols followed by sleep)
is only optimal in a high noise regime. It is shown how consumption can be made
linear with the load and achieve massive energy reduction (factor of 10) at
low-to-medium load. The trade-off between energy efficiency (EE) and spectral
efficiency (SE) is also characterized, followed by a multi-user study based on
time division multiple access (TDMA)
Impact of Realistic Propagation Conditions on Reciprocity-Based Secret-Key Capacity
Secret-key generation exploiting the channel reciprocity between two
legitimate parties is an interesting alternative solution to cryptographic
primitives for key distribution in wireless systems as it does not rely on an
access infrastructure and provides information-theoretic security. The large
majority of works in the literature generally assumes that the eavesdropper
gets no side information about the key from her observations provided that (i)
it is spaced more than a wavelength away from a legitimate party and (ii) the
channel is rich enough in scattering. In this paper, we show that this
condition is not always verified in practice and we analyze the secret-key
capacity under realistic propagation conditions
Deep Unfolding for Fast Linear Massive MIMO Precoders under a PA Consumption Model
Massive multiple-input multiple-output (MIMO) precoders are typically
designed by minimizing the transmit power subject to a quality-of-service (QoS)
constraint. However, current sustainability goals incentivize more
energy-efficient solutions and thus it is of paramount importance to minimize
the consumed power directly. Minimizing the consumed power of the power
amplifier (PA), one of the most consuming components, gives rise to a convex,
non-differentiable optimization problem, which has been solved in the past
using conventional convex solvers. Additionally, this problem can be solved
using a proximal gradient descent (PGD) algorithm, which suffers from slow
convergence. In this work, to overcome the slow convergence, a deep unfolded
version of the algorithm is proposed, which can achieve close-to-optimal
solutions in only 20 iterations compared to the 3500 plus iterations needed by
the PGD algorithm. Results indicate that the deep unfolding algorithm is three
orders of magnitude faster than a conventional convex solver and four orders of
magnitude faster than the PGD.Comment: This paper is presented at VTC2023-Spring. T. Feys, X. Mestre, E.
Peschiera, and F. Rottenberg, "Deep Unfolding for Fast Linear Massive MIMO
Precoders under a PA Consumption Model," in 2023 IEEE 97th Vehicular
Technology Conference (VTC2023-Spring), Florence, Italy, June 202
CSI-based versus RSS-based Secret-Key Generation under Correlated Eavesdropping
Physical-layer security (PLS) has the potential to strongly enhance the
overall system security as an alternative to or in combination with
conventional cryptographic primitives usually implemented at higher network
layers. Secret-key generation relying on wireless channel reciprocity is an
interesting solution as it can be efficiently implemented at the physical layer
of emerging wireless communication networks, while providing
information-theoretic security guarantees. In this paper, we investigate and
compare the secret-key capacity based on the sampling of the entire complex
channel state information (CSI) or only its envelope, the received signal
strength (RSS). Moreover, as opposed to previous works, we take into account
the fact that the eavesdropper's observations might be correlated and we
consider the high signal-to-noise ratio (SNR) regime where we can find simple
analytical expressions for the secret-key capacity. As already found in
previous works, we find that RSS-based secret-key generation is heavily
penalized as compared to CSI-based systems. At high SNR, we are able to
precisely and simply quantify this penalty: a halved pre-log factor and a
constant penalty of about 0.69 bit, which disappears as Eve's channel gets
highly correlated
Robust Non-Coherent Beamforming for FDD Downlink Massive MIMO
Designing beamforming techniques for the downlink (DL) of frequency division
duplex (FDD) massive MIMO is known to be a challenging problem due to the
difficulty of obtaining channel state information (CSI). Indeed, since the
uplink-downlink bands are disjoint, the system cannot rely on channel
reciprocity to estimate the channel from uplink (UL) pilots as in time division
duplexing (TDD) system. Still, in this paper, we propose original designs for
robust beamformers that do not require any feedback from the users and only
rely on the transmission of UL pilots. The price to pay is that the beamformer
is non-coherent in the sense that it does not leverage full knowledge of the
phase of each multipath component. A large variety of novel designs are
proposed under different criterion and partial phase knowledge
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