5 research outputs found
mmWave Beam Alignment using Hierarchical Codebooks and Successive Subtree Elimination
We propose a best arm identification multi-armed bandit algorithm in the
fixed-confidence setting for mmWave beam alignment initial access called
\ac{SSE}. The algorithm performance approaches that of state-of-the-art
Bayesian algorithms at a fraction of the complexity and without requiring
channel state information. The algorithm simultaneously exploits the benefits
of hierarchical codebooks and the approximate unimodality of rewards to achieve
fast beam steering, in a sense that we precisely define to provide fair
comparison with existing algorithms. We derive a closed-form sample complexity,
which enables tuning of design parameters. We also perform extensive
simulations over slow fading channels to demonstrate the appealing performance
versus complexity trade-off struck by the algorithm across a wide range of
channel condition
Beam Alignment in mmWave User-Centric Cell-Free Massive MIMO Systems
The problem of beam alignment (BA) in a cell-free massive multiple-input
multiple-output (CF-mMIMO) system operating at millimeter wave (mmWaves)
carrier frequencies is considered in this paper. Two estimation algorithms are
proposed, in association with a protocol that permits simultaneous estimation,
on a shared set of frequencies, for each user equipment (UE), of the direction
of arrival and departure of the radio waves associated to the strongest
propagation paths from each of the surrounding access points (APs), so that
UE-AP association can take place. The proposed procedure relies on the
existence of a reliable control channel at sub-6 GHz frequency, so as to enable
exchange of estimated values between the UEs and the network, and assumes that
APs can be identifies based on the prior knowledge of the orthogonal channels
and transmit beamforming codebook. A strategy for assigning codebook entries to
the several APs is also proposed, with the aim of minimizing the mutual
interference between APs that are assigned the same entry. Numerical results
show the effectiveness of the proposed detection strategy, thus enabling one
shot fast BA for CF-mMIMO systems.Comment: 6 pages, 3 figures, submitted to the 2021 IEEE Global Communications
Conference (GLOBECOM