1,720,978 research outputs found
Resource allocation in millimeter-wave multicarrier-division duplex systems with hybrid beamforming
No full textIn-band full-duplex (IBFD) systems require promising resource allocation (RA) strategies to fully exploit the available time-frequency resources. Furthermore, the acquisition of channel state information and signal reception in IBFD systems are significantly impacted by insufficient self-interference cancellation (SIC), impeding the applications of IBFD in practical wireless systems. Multicarrier-division duplex (MDD), which benefits low-budget SI mitigation in digital domain and flexible subcarrier assignment, is expected to be a promising transitional technique from half-duplex (HD) to IBFD. To demonstrate the advantages of MDD over HD, this paper first compares the upper-bound performance of MDD and HD by applying unfair greedy RA. Then, considering the millimeter-wave (mmWave) with hybrid beamforming, we propose the RA optimization with the quality-of-service constraints on both downlink (DL) and uplink (UL) mobile-stations (MSs). To solve this non-convex RA problem, we divide it into a suboptimal subcarrier allocation problem solved by the proposed improved fair greedy (IFG) algorithm, and a convex power allocation problem. Furthermore, we design two general hybrid precoder based on matrix factorization and direct approach, and a combiner having high SIC capability. Our results show that the proposed RA algorithm can achieve the performance near the upper-bound achieved by the unfair greedy algorithm, while guaranteeing the proportional fairness among all DL/UL MSs. The performance of the two precoding schemes is depended on the number of radio frequency chains supported. Finally, the proposed SIC algorithm is able to provide sufficient SI mitigation, which can be implemented without impacting the RA operation.</p
Self-interference cancellation and channel estimation in multicarrier-division duplex systems with hybrid beamforming
No full textDesign of full-duplex (FD) wireless systems faces many challenges, including self-interference cancellation (SIC), capability to provide high capacity, high flexibility for operation, best usage of resources, etc. In this paper, we propose and investigate a multicarrier-division duplex (MDD) based hybrid beamforming system operated in FD mode, which is endowed with the advantages of both time-division duplex and frequency-division duplex. It also shares some merits of FD and allows to be free of self-interference (SI) in digital domain, but faces the same challenge of SI as the FD in analog domain. Hence in this paper, we first propose an adaptive beamforming assisted SI cancellation scheme with taking into account the practical requirement of analog-to-digital conversion (ADC). It can be shown that the proposed approach is capable of jointly coping with the desired signals’ transmission and SI suppression. Then, channel estimation (CEst) in MDD/MU-MIMO system is proposed by exploiting the reciprocity between the uplink and downlink subcarrier channels that is provided by MDD. Correspondingly, the orthogonality-achieving pilot symbols are designed, and the least-square (LS) CEst as well as linear minimum mean-square error (LMMSE) CEst are derived. Finally, the performance of MDD/MU-MIMO systems employing the proposed SIC method is investigated, with respect to the SI cancellation capability, sum-rate potential, CEst performance, and the effect of CEst on the achievable performance. Our studies show that MDD/MU-MIMO provides an effective option for design of future wireless transceivers
Spectral-efficiency of cell-free massive MIMO with multicarrier-division duplex
No full textA multicarrier-division duplex (MDD)-based cell-free (CF) scheme, namely MDD-CF, is proposed, which enables downlink (DL) data and uplink (UL) data or pilots to be concurrently transmitted on mutually orthogonal subcarriers in distributed CF massive MIMO (mMIMO) systems. To demonstrate the advantages of MDD-CF, we firstly study the spectral-efficiency (SE) performance in terms of one coherence time (CT) interval associated with access point (AP)-selection, power- and subcarrier-allocation. Since the formulated SE optimization is a mixed-integer non-convex problem that is NP-hard to solve, we leverage the inherent association between involved variables to transform it into a continuous-integer convex-concave problem. Then, a quadratic transform (QT)-assisted iterative algorithm is proposed to achieve SE maximization. Next, we extend our study to the case of one radio frame consisting of several CT intervals. In this regard, a novel two-phase CT interval (TPCT) scheme is designed to not only improve the SE in radio frame but also provide consistent data transmissions over fast time-varying channels. Correspondingly, to facilitate the optimization, we propose a two-step iterative algorithm by building the connections between two phases in TPCT through an iteration factor. Simulation results show that, MDD-CF can significantly outperform in-band full duplex (IBFD)-CF due to the efficient interference management. Furthermore, compared with time-division duplex (TDD)-CF, MDD-CF is more robust to high-mobility scenarios and achieves better SE performance
Multicarrier-Division Duplex: A Duplexing Technique for the Shift to 6G Wireless Communications
No full textIn band full duplex (IBFD) has the potential to not only double spectral efficiency (SE) but also greatly reduce transmission latency. However, the immaturity of existing self-interference cancellation (SIC) techniques renders IBFD impractical for near-future wireless applications. To inherit the merits of FD but with practical SIC requirements, multicarrier-division duplex (MDD) was recently proposed and studied. In this article, we demonstrate the advantages of MDD over the IBFD mode and the conventional half-duplex (HD) modes of frequency-division duplex (FDD) and time-division duplex (TDD) from several essential aspects, including SIC capability, resource integration, and the support for high-mobility communications. Several numerical results are included to show that MDD outperforms IBFD in terms of energy efficiency (EE) and SIC. Compared with the HD modes, MDD is capable of efficiently integrating DL/UL resources to achieve higher SE and significantly outperforms TDD when communicating over fast time-varying channels. Finally, some implementation challenges of MDD systems are discussed.</p
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Heterogeneous graph neural network for power allocation in multicarrier-division duplex cell-free massive MIMO systems
No full textIn-band full duplex-based cell-free (IBFD-CF) systems suffer from severe
interference problem including self-interference (SI) and cross-link
interference (CLI), especially when cell-free (CF) systems are operated in a
distributed way. To this end, we propose multicarrier-division duplex (MDD) as
an enabler for full-duplex (FD)-style operation in distributed CF massive MIMO
systems, where DL and UL transmissions take place simultaneously at the same
frequency band but mutually orthogonal subcarrier sets. In order to maximize
the spectral efficiency (SE) in the proposed systems, we present heterogeneous
graph neural network specific for CF systems (CF-HGNN), which consists of an
adaptive node embedding layer, meta-path based message passing, meta-path based
attention and downstream power allocation learning. In particular, the adaptive
node embedding layer can handle the varying number of access points (APs),
mobile stations (MSs) and subcarriers, and the involved attention mechanism
enables each AP/MS node in CF-HGNN to aggregate the information from
interfering path and communication path with different priorities. Numerical
results show that CF-HGNN is capable of using times less operation time
to achieve the 99% performance of the SE of quadratic transform and successive
convex approximation (QT-SCA). Additionally, CF-HGNN also significantly
outperforms unfair greedy method in terms of SE performance. Furthermore,
CF-HGNN exhibits good adaptivity to varying number of nodes and subcarriers,
and also generalization ability to different sizes of CF network
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