1,721,017 research outputs found
Demonstration of 5G non-terrestrial network regenerative L1 processing
No full textThe regenerative architecture for 5G Non- Terrestrial Networks (NTNs) offers several advantages over the transparent architecture, including reduced latency, improved quality of service, lower feeder link bandwidth, support for inter-satellite links and the provision of edge compute services. However, it has the challenge of requiring computationally intensive 5G base stations to be placed into the Low-Earth Orbit (LEO) satellites, rather than into ground stations as is done in the transparent architecture. Based on AccelerComm's portfolio of flexible O-RAN L1 solutions, this paper describes a demonstration of a low-power radiation-tolerant 5G base station L1 implementation which addresses this challenge, making it suitable for LEO satellite deployment
A soft-input soft-output polar decoding algorithm for turbo-detection in MIMO-aided 5G new radio
No full textSoft-Input Soft-Output (SISO) polar decoding algorithms, such as Belief Propagation (BP) and Soft Cancellation (SCAN) polar decoding, offer iteration capability for facilitating turbo-style detection. However, at lower Signal-to-Noise Ratios (SNRs), the performance of the BP and SCAN decoders is about 1.5 dB and 0.5 dB worse than that of the state-of-the-art hard-decision Successive Cancellation List (SCL) decoding algorithm, respectively, despite iteratively exchanging information with a Multiple Input Multiple Output (MIMO) detector. Motivated by this gap, we conceive a novel G-SCAN polar decoder, which generates both soft-decision and hard-decision outputs. This is achieved by intrinsically amalgamating a list decoder with a novel SISO decoder. These soft-decision outputs may be used for turbo-detection, but they also support the hard-decision outputs of the SCL algorithm for achieving superior block error rate (BLER) performance. As a result of these benefits, the proposed G-SCAN algorithm using a list size of L = 2 offers around 1 dB BLER gain compared to the conventional hard-decision SCL decoder relying on L = 32. Furthermore, we have carried out its Extrinsic Information Transfer (EXIT) chart analysis, and characterized the performance vs. the complexity of the proposed G-SCAN algorithm, and compared it to various soft-and hard-decision output benchmarks for a wide variety of different rate-matching modes and block lengths. Furthermore, in order to reduce the complexity of the proposed algorithm, a novel Cyclic Redundancy Check (CRC)-aided G-SCAN algorithm is also proposed, which facilitates early termination and improves the BLER performance.</p
Multiple-Objective Packet Routing Optimization for Aeronautical ad-hoc Networks
Full text linkProviding Internet service above the clouds is of
ever-increasing interest and in this context aeronautical ad-hoc
networking (AANET) constitutes a promising solution. However,
the optimization of packet routing in large ad hoc networks is
quite challenging. In this paper, we develop a discrete ε multiobjective genetic algorithm (ε-DMOGA) for jointly optimizing
the end-to-end latency, the end-to-end spectral efficiency (SE),
and the path expiration time (PET) that specifies how long
the routing path can be relied on without re-optimizing the
path. More specifically, a distance-based adaptive coding and
modulation (ACM) scheme specifically designed for aeronautical communications is exploited for quantifying each link’s
achievable SE. Furthermore, the queueing delay at each node is
also incorporated into the multiple-objective optimization metric.
Our ε-DMOGA assisted multiple-objective routing optimization
is validated by real historical flight data collected over the
Australian airspace on two selected representative dates
Multicarrier-Division Duplex for Solving the Channel Aging Problem in Massive MIMO Systems
No full textThe separation of training and data transmission as well as the frequent
uplink/downlink (UL/DL) switching make time-division duplex (TDD)-based massive
multiple-input multiple-output (mMIMO) systems less competent in fast
time-varying scenarios due to the resulted severe channel aging. To this end, a
multicarrier-division duplex (MDD) mMIMO scheme associated with two types of
well-designed frame structures are introduced for combating channel aging when
communicating over fast time-varying channels. To compare with TDD, the
corresponding frame structures related to 3GPP standards and their variant
forms are presented. The MDD-specific general Wiener predictor and
decision-directed Wiener predictor are introduced to predict the channel state
information, respectively, in the time domain based on UL pilots and in the
frequency domain based on the detected UL data, considering the impact of
residual self-interference (SI). Moreover, by applying the zero-forcing
precoding and maximum ratio combining, the closed-form approximations for the
lower bounded rate achieved by TDD and MDD systems over time-varying channels
are derived. Our main conclusion from this study is that the MDD, endowed with
the capability of full-duplex but less demand on SI cancellation than in-band
full-duplex (IBFD), outperforms both the conventional TDD and IBFD in combating
channel aging
Universal decoding of quantum stabilizer codes via classical guesswork
No full textA universal decoding scheme is conceived for quantum stabilizer codes (QSCs) by appropriately adaptingthe ‘guessing random additive noise decoding’ (GRAND) philosophy of classical domain codes. We demonstrate that the generalized quantum decoder conceived is eminently suitable for different QSC decoding paradigms, namely for both stabilizer-measurement-based as well as the inverse-encoder-based decoding. We then harness the resultant decoder for both quantum Bose-Chaudhuri-Hocquenghem (BCH) codes and quantum polar codes and quantify both their quantum block error rate (QBLER), and QBLER per logical qubits as well as their decoding complexity. Furthermore, we provide a parametric study of the associated design trade-offs and offer design guideline for the implementation of GRAND-based QSC decoders
Channel estimation for reconfigurable intelligent surface assisted high-mobility wireless systems
No full textNext-generation communication systems aim for providing pervasive services, including the high-mobility scenarios routinely encountered in mission-critical applications. Hence we harness the recently-developed reconfigurable intelligent surfaces (RIS) to assist the high-mobility cell-edge users. More explicitly, the passive elements of RISs generate beneficial phase rotations for the reflected signals, so that the signal power received by the high-mobility users is enhanced. However, in the face of high Doppler frequencies, the existing RIS channel estimation techniques that assume block fading generally result in irreducible error floors. In order to mitigate this problem, we propose a new RIS channel estimation technique, which is the first one that performs minimum mean square error (MMSE) based interpolation for the sake of taking into account the time-varying nature of fading even within the coherence time. The RIS modelling invokes only passive elements without relying on RF chains, where both the direct link and RIS-reflected links as well as both the line-of-sight (LoS) and non-LoS (NLoS) paths are taken into account. As a result, the cascaded base station (BS)-RIS-user links involve the multiplicative concatenation of the channel coefficients in the LoS and NLoS paths across the two segments of the BS-RIS and RIS-user links. Against this background, we model the multiplicative RIS fading correlation functions for the first time in the literature, which facilitates MMSE interpolation for estimating the high-dimensional and high-Doppler RIS-reflected fading channels. Our simulation results demonstrate that for a vehicle travelling at a speed as high as 90 mph, employing a low-complexity RIS at the cell-edge using as few as 16 RIS elements is sufficient for achieving substantial power-effieincy gains, where the Doppler-induced error floor is mitigated by the proposed channel estimation technique
OTFS-aided RIS-assisted SAGIN systems outperform their OFDM counterparts in doubly-selective high-doppler scenarios
No full textThe recently-developed reconfigurable intelligent surfaces (RISs) are capable of improving the coverage of space-air-ground integrated networks (SAGINs), where the signals can be reflected in the desired direction without relying on power-thirsty radio-frequency (RF) chains. However, in the face of the substantially increased Doppler frequency, the classic orthogonal frequency-division multiplexing (OFDM) becomes inadequate in supporting RIS for the following reasons. Firstly, the detrimental doubly-selective fading leads to inter-symbol interference (ISI) and inter-carrier interference (ICI), which result in error floors for OFDM operating in the time-frequency (TF) domain. Secondly, it is far from trivial to configure RIS based on the time-varying fading channels. Thirdly, the interpolation-based TF-domain channel estimation methods become impractical for the high-Doppler and high-dimensional RIS systems. Against this background, in this paper, we propose the powerful two-dimensional orthogonal time frequency space (OTFS) modulation for RIS-aided SAGINs, which transforms the time-varying fading encountered in the TF-domain to the time-invariant fading in the delay-Doppler (DD) domain. More explicitly, first of all, for the first time in the literature, we devise the DD-domain channel model of RIS assisted SAGINs in the face of doubly-selective fading. Secondly, in order to facilitate the RIS configuration in the DD-domain, we propose to create “virtual” Doppler frequencies that guide the phase changes at the RIS, even though the RIS phase rotations do not suffer from Doppler effects. Thirdly, we conceive an attractive DD-domain RIS channel estimation method that can support both OFDM and OTFS, where the TF-domain interpolation is eliminated. Our simulation results demonstrate that the proposed DD-domain RIS configuration and channel estimation methods for both OFDM and OTFS are capable of mitigating the error floors encountered in the TF-domain. Furthermore, our simulation results confirm that OTFS-based RIS-assisted SAGIN systems are capable of outperforming their OFDM counterparts and exhibit excellent performance across a wide range of SAGIN channel parameters including the Ricean K factor, Doppler frequency, delay spread, coverage distance and carrier frequency
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