460 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
Extended GFDM Framework: OTFS and GFDM Comparison
Orthogonal time frequency space modulation (OTFS) has been recently proposed
to achieve time and frequency diversity, especially in linear time-variant
(LTV) channels with large Doppler frequencies. The idea is based on the
precoding of the data symbols using symplectic finite Fourier transform (SFFT)
then transmitting them by mean of orthogonal frequency division multiplexing
(OFDM) waveform. Consequently, the demodulator and channel equalization can be
coupled in one processing step. As a distinguished feature, the demodulated
data symbols have roughly equal gain independent of the channel selectivity. On
the other hand, generalized frequency division multiplexing (GFDM) modulation
also employs the spreading over the time and frequency domains using circular
filtering. Accordingly, the data symbols are implicitly precoded in a similar
way as applying SFFT in OTFS. In this paper, we present an extended
representation of GFDM which shows that OTFS can be processed as a GFDM signal
with simple permutation. Nevertheless, this permutation is the key factor
behind the outstanding performance of OTFS in LTV channels, as demonstrated in
this work. Furthermore, the representation of OTFS in the GFDM framework
provides an efficient implementation, that has been intensively investigated
for GFDM, and facilitates the understanding of the OTFS distinct features.Comment: Accepted in IEEE Global Communications Conference 9-13 December 2018
Abu Dhabi, UA
Low-Complexity Iterative Detection for Orthogonal Time Frequency Space Modulation
We elaborate on the recently proposed orthogonal time frequency space (OTFS)
modulation technique, which provides significant advantages over orthogonal
frequency division multiplexing (OFDM) in Doppler channels. We first derive the
input--output relation describing OTFS modulation and demodulation (mod/demod)
for delay--Doppler channels with arbitrary number of paths, with given delay
and Doppler values. We then propose a low-complexity message passing (MP)
detection algorithm, which is suitable for large-scale OTFS taking advantage of
the inherent channel sparsity. Since the fractional Doppler paths (i.e., not
exactly aligned with the Doppler taps) produce the inter Doppler interference
(IDI), we adapt the MP detection algorithm to compensate for the effect of IDI
in order to further improve performance. Simulations results illustrate the
superior performance gains of OTFS over OFDM under various channel conditions.Comment: 6 pages, 7 figure
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
Delay-Doppler Reversal for OTFS System in Doubly-selective Fading Channels
The recent proposed orthogonal time frequency space (OTFS) modulation shows
signifcant advantages than conventional orthogonal frequency division
multiplexing (OFDM) for high mobility wireless communications. However, a
challenging problem is the development of effcient receivers for practical OTFS
systems with low complexity. In this paper, we propose a novel delay-Doppler
reversal (DDR) technology for OTFS system with desired performance and low
complexity. We present the DDR technology from a perspective of two-dimensional
cascaded channel model, analyze its computational complexity and also analyze
its performance gain compared to the direct processing (DP) receiver without
DDR. Simulation results demonstrate that our proposed DDR receiver outperforms
traditional receivers in doubly-selective fading channels
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