Hybrid and Full-Digital Beamforming in mmWave Massive MIMO Systems: A Comparison Considering Low-Resolution ADCs

In a millimeter-wave(mmWave)Massive multiple-input multiple-output(MIMO)systems,full-digital beamforming(i.e.,connecting each antenna with a specific radio-frequency(RF)chain)becomes inefficient due to the hardware cost and power consumption.Therefore,hybrid analog and digital transceiver where the number of RF chains are much smaller than that of the antennas has drawn great research interest.In this work,we investigate the use of low-resolution analog-to-digital converters(ADCs)in the uplink of multi-user hybrid and full-digital mmWave Massive MIMO systems.To be specific,we compare the performance of full-digital minimum mean square error(MMSE)and hybrid MMSE beamforming in both sum rates and energy efficiency.Accurate approximations of sum rates and energy efficiency are provided for both schemes,which captures the dominant factors.The analytical results show that full-digital beamforming outperforms hybrid beamforming in terms of sum rates and requires only a small portion(γ)of antennas used by hybrid beamforming to achieve the same sum rates.We given sufficient condition for full-digital beamforming to outperform hybrid beamforming in terms of energy efficiency.Moreover,an algorithm is proposed to search for the optimal ADC resolution bits.Numerical results demonstrate the correctness of the analysis.

Propagation Characterization and Analysis for 5G mmWave Through Field Experiments

The 5G network has been intensively investigated to realize the ongoing early deployment stage as an effort to match the exponential growth of the number of connected users and their increasing demands for high throughput,bandwidth with Quality of Service(QoS),and low latency.Given that most of the spectrums below 6 GHz are nearly used up,it is not feasible to employ the traditional spectrum,which is currently in use.Therefore,a promising and highly feasible effort to satisfy this insufficient frequency spectrum is to acquire new frequency bands for next-generation mobile communications.Toward this end,the primary effort has been focused on utilizing the millimeter-wave(mmWave)as the most promising candidate for the frequency spectrum.However,though the mmWave frequency band can fulfill the desired bandwidth requirements,it has been demonstrated to endure several issues like scattering,atmospheric absorption,fading,and especially penetration losses compared to the existing sub-6 GHz frequency band.Then,it is fundamental to optimize the mmWave band propagation channel to facilitate the practical 5G implementation for the network operators.Therefore,this study intends to investigate the outdoor channel characteristics of 26,28,36,and 38 GHz frequency bands for the communication infrastructure at the building to the ground floor in both Line of Sight(LOS)and Non-Line of Sight(NLOS)environments.The experimental campaign has studied the propagation path loss models such as Floating-Intercept(FI)and Close-In(CI)for the building to ground floor environment in LOS and NLOS scenarios.The findings obtained from the field experiments clearly show that the CI propagation model delivers much better performance in comparison with the FI model,thanks to its simple setup,accuracy,and precise function.

柔性版印刷中瓦楞纸板的印刷均匀性--瓦楞纸板对网目调网点变形的影响

印刷不均匀性是柔性版印刷的一个常见问题。多数印刷的不均匀性都被认为是由瓦楞纸板的结构本身引起的。虽然其他印刷质量问题也可能与结构有关,但条杠是最明显的一种。本文致力于研究纸板变形导致印刷不均匀性的原因,以及网目调柔性版印刷中条杠产生的机理。本文用有限的因子模型,分析在一定印刷压力下,瓦楞纸板的变形对网目调网点变形的影响。结果表明,由湿压压力不均匀引起的纸板变形被认为是引起印刷不均匀的一个潜在原因。瓦楞结构中楞峰和楞谷处不同的网点增大值造成了网目调印刷品的条杠。

Building an Ecological Civilization in China： Towards a Practice Based Learning Approach

The adoption by the 18th Congress of the Communist Party of China in November 2012 of a policy on ecological civilization is a landmark event for the nation and the world community. China＇s vision for building an ecological civilization is comprehensive, multi-sectoral and systemic and is intended to direct and balance progress among ecological, economic, social, cultural and political dimensions of change. Some on-going efforts and potential future activities that meet China＇s vision of an ecological civilization are described. Establishment of dedicated ecological civilization areas for experimenting with legal, regulatory and administrative incentives that would facilitate the march towards the ideal is encouraged. Chinese biosphere reserves which are designated with the explicit aim of building harmony between humans and nature would be suitable candidates for designing and developing such dedicated ecological civilization areas.

Observation of intermolecular double-quantum coherence signal dips in nuclear magnetic resonance

The correlated spectroscopy revamped by asymmetric Z-gradient echo detection （CRAZED） sequence is modified to investigate intermolecular double-quantum coherence nuclear magnetic resonance signal dips in highly polarized spin systems. It is found that the occurrence of intermolecular double-quantum coherence signal dips is related to sample geometry, field inhomogeneity and dipolar correlation distance. If the field inhomogeneity is refocused, the signal dip occurs at a fixed position whenever the dipolar correlation distance approaches the sample dimension. However, the position is shifted when the field inhomogeneity exists. Experiments and simulations are performed to validate our theoretic analysis. These signal features may offer a unique way to investigate porous structures and may find applications in biomedicine and material science.