5,755 research outputs found

    Beam Management for Millimeter Wave Beamspace MU-MIMO Systems

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    Millimeter wave (mmWave) communication has attracted increasing attention as a promising technology for 5G networks. One of the key architectural features of mmWave is the use of massive antenna arrays at both the transmitter and the receiver sides. Therefore, by employing directional beamforming (BF), both mmWave base stations (MBSs) and mmWave users (MUEs) are capable of supporting multi-beam simultaneous transmissions. However, most researches have only considered a single beam, which means that they do not make full potential of mmWave. In this context, in order to improve the performance of short-range indoor mmWave networks with multiple reflections, we investigate the challenges and potential solutions of downlink multi-user multi-beam transmission, which can be described as a high-dimensional (i.e., beamspace) multi-user multiple-input multiple-output (MU-MIMO) technique, including multi-user BF training, simultaneous users' grouping, and multi-user multibeam power allocation. Furthermore, we present the theoretical and numerical results to demonstrate that beamspace MU-MIMO compared with single beam transmission can largely improve the rate performance of mmWave systems.Comment: The sixth IEEE/CIC International Conference on Communications in China (ICCC2017

    B\"acklund-Darboux Transformations and Discretizations of Super KdV Equation

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    For a generalized super KdV equation, three Darboux transformations and the corresponding B\"acklund transformations are constructed. The compatibility of these Darboux transformations leads to three discrete systems and their Lax representations. The reduction of one of the B\"acklund-Darboux transformations and the corresponding discrete system are considered for Kupershmidt's super KdV equation. When all the odd variables vanish, a nonlinear superposition formula is obtained for Levi's B\"acklund transformation for the KdV equation

    A case study based inquiry into the adoption and adaptation of communicative language teaching in Chinese universities

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    The aim of this study is to investigate the extent to which Communicative Language Teaching (CLT) is adopted and/or adapted by Chinese tertiary teachers of English with the experience of teacher education overseas. It employs a case study approach in order to explore the extent to which CLT is compatible with the Chinese EFL context at tertiary level. Twenty-three informants in four institutions participated in this study (including two participating in the pilot study). Classroom observation and semi-structured interview were adopted as instruments for data collection. By looking into the teaching beliefs and actual practice of the target group, an attempt was made to reveal their general conceptions of CLT and their perceptions of good language teaching beyond CLT, as well as to identify the factors conceived as constraints on CLT implementation in the local context. In addition, through observation, an effort was made to explore the extent to which CLT was adopted and adapted in real teaching practice. Adjustments made by the participants to facilitate adoption of the approach were particularly focused on, as well as the extent to which intercultural experience contributed to effective teaching. The main findings suggest that the CLT is seen as important by nearly all the informants in terms of its effectiveness and contributions, potential usefulness and complexity. Although constraints on CLT implementation were both mentioned and observed, ‘communicative ideas’ were found to be widely reflected in the teaching practice of the majority of the participants. The findings show that great attention is paid to learners as they are nowadays greatly involved in different teaching phases (pre-teaching, while-teaching and after-teaching). There exists a tendency of eclecticism in the teaching practices of many informants and the phenomenon of what is termed a ‘seeming-communicative’ approach is reflected in some participants’ ways of teaching due to a recognition of the fundamental importance of the learning skills of recitation and memorization. The experience of teacher education overseas is generally considered as conducive to enhancing practitioners’ intercultural competence and critical thinking -- two factors identified as essential prerequisites for CLT implementation and seeking of appropriate methodology. The findings give rise to discussion of three major problems in relation to interpreting CLT as an appropriate approach in Chinese EFL teaching context. These problems are essentialism, overgeneralization and labeling. The prevalence of these problems confirms that there is a need to understand CLT and its appropriateness in different cultural contexts from an anti-essentialist perspective

    Morphology, diversity, taxonomy and phylogeny of Tylenchidae (Nematoda, Tylenchomorpha)

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    Utilizing the Updated Gamma-Ray Bursts and Type Ia Supernovae to Constrain the Cardassian Expansion Model and Dark Energy

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    We update gamma-ray burst (GRB) luminosity relations among certain spectral and light-curve features with 139 GRBs. The distance modulus of 82 GRBs at z>1.4z>1.4 can be calibrated with the sample at z1.4z\leq1.4 by using the cubic spline interpolation method from the Union2.1 Type Ia supernovae (SNe Ia) set. We investigate the joint constraints on the Cardassian expansion model and dark energy with 580 Union2.1 SNe Ia sample (z<1.4z<1.4) and 82 calibrated GRBs data (1.4<z8.21.4<z\leq8.2). In Λ\LambdaCDM, we find that adding 82 high-\emph{z} GRBs to 580 SNe Ia significantly improves the constrain on ΩmΩΛ\Omega_{m}-\Omega_{\Lambda} plane. In the Cardassian expansion model, the best fit is Ωm=0.240.15+0.15\Omega_{m}= 0.24_{-0.15}^{+0.15} and n=0.160.52+0.30n=0.16_{-0.52}^{+0.30} (1σ)(1\sigma), which is consistent with the Λ\LambdaCDM cosmology (n=0)(n=0) in the 1σ1\sigma confidence region. We also discuss two dark energy models in which the equation of state w(z)w(z) is parametrized as w(z)=w0w(z)=w_{0} and w(z)=w0+w1z/(1+z)w(z)=w_{0}+w_{1}z/(1+z), respectively. Based on our analysis, we see that our Universe at higher redshift up to z=8.2z=8.2 is consistent with the concordance model within 1σ1\sigma confidence level.Comment: 17 pages, 6 figures, 2 tables; accepted for publication in Advances in Astronomy, special issue on Gamma-Ray Burst in Swift and Fermi Era. arXiv admin note: text overlap with arXiv:0802.4262, arXiv:0706.0938 by other author
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