45 research outputs found
OTFS-NOMA: An Efficient Approach for Exploiting Heterogenous User Mobility Profiles
This paper considers a challenging communication scenario, in which users
have heterogenous mobility profiles, e.g., some users are moving at high speeds
and some users are static. A new non-orthogonal multiple-access (NOMA)
transmission protocol that incorporates orthogonal time frequency space (OTFS)
modulation is proposed. Thereby, users with different mobility profiles are
grouped together for the implementation of NOMA. The proposed OTFS-NOMA
protocol is shown to be applicable to both uplink and downlink transmission,
where sophisticated transmit and receive strategies are developed to remove
inter-symbol interference and harvest both multi-path and multi-user diversity.
Analytical results demonstrate that both the high-mobility and low-mobility
users benefit from the application of OTFS-NOMA. In particular, the use of NOMA
allows the spreading of the high-mobility users' signals over a large amount of
time-frequency resources, which enhances the OTFS resolution and improves the
detection reliability. In addition, OTFS-NOMA ensures that low-mobility users
have access to bandwidth resources which in conventional OTFS-orthogonal
multiple access (OTFS-NOMA) would be solely occupied by the high-mobility
users. Thus, OTFS-NOMA improves the spectral efficiency and reduces latency
A Proof of Concept for OTFS Resilience in Doubly-Selective Channels by GPU-Enabled Real-Time SDR
Orthogonal time frequency space (OTFS) is a modulation technique which is
robust against the disruptive effects of doubly-selective channels. In this
paper, we perform an experimental study of OTFS by a real-time software defined
radio (SDR) setup. Our SDR consists of a Graphical Processing Unit (GPU) for
signal processing programmed using Sionna and TensorFlow, and Universal
Software Radio Peripheral (USRP) devices for air interface. We implement a
low-latency transceiver structure for OTFS and investigate its performance
under various Doppler values. By comparing the performance of OTFS with
Orthogonal Frequency Division Multiplexing (OFDM), we demonstrate that OTFS is
highly robust against the disruptive effects of doubly-selective channels in a
real-time experimental setup.Comment: ACCEPTED for 2023 IEEE Global Communications Conference: Wireless
Communication
Application-Based Coexistence of Different Waveforms on Non-orthogonal Multiple Access
The coexistence of different wireless communication systems such as LTE and
Wi-Fi by sharing the unlicensed band is well studied in the literature. In
these studies, various methods are proposed to support the coexistence of
systems, including listen-before-talk mechanism, joint user association and
resource allocation. However, in this study, the coexistence of different
waveform structures in the same resource elements are studied under the theory
of non-orthogonal multiple access. This study introduces a paradigm-shift on
NOMA towards the application-centric waveform coexistence. Throughout the
paper, the coexistence of different waveforms is explained with two specific
use cases, which are power-balanced NOMA and joint radar-sensing and
communication with NOMA. In addition, some of the previous works in the
literature regarding non-orthogonal waveform coexistence are reviewed. However,
the concept is not limited to these use cases. With the rapid development of
wireless technology, next-generation wireless systems are proposed to be
flexible and hybrid, having different kinds of capabilities such as sensing,
security, intelligence, control, and computing. Therefore, the concept of
different waveforms' coexistence to meet these concerns are becoming impressive
for researchers.Comment: Submitted to IEEE for possible publication. arXiv admin note: text
overlap with arXiv:2007.05753, arXiv:2003.0554
Sparsity in the Delay-Doppler Domain for Measured 60 GHz Vehicle-to-Infrastructure Communication Channels
We report results from millimeter wave vehicle-to-infrastructure (V2I)
channel measurements conducted on Sept. 25, 2018 in an urban street
environment, down-town Vienna, Austria. Measurements of a frequency-division
multiplexed multiple-input single-output channel have been acquired with a
time-domain channel sounder at 60 GHz with a bandwidth of 100 MHz and a
frequency resolution of 5 MHz. Two horn antennas were used on a moving
transmitter vehicle: one horn emitted a beam towards the horizon and the second
horn emitted an elevated beam at 15-degrees up-tilt. This configuration was
chosen to assess the impact of beam elevation on V2I communication channel
characteristics: propagation loss and sparsity of the local scattering function
in the delay-Doppler domain. The measurement results within urban speed limits
show high sparsity in the delay-Doppler domain.Comment: submitted to IEEE International Conference on Communication