Blockage and imperfect beam alignment are two principal difficulties in high-frequency bands directional transmissions.In this paper,the coverage performance of downlink directional transmissions in ultra-dense networ...Blockage and imperfect beam alignment are two principal difficulties in high-frequency bands directional transmissions.In this paper,the coverage performance of downlink directional transmissions in ultra-dense networks is analyzed,with the consideration of beam alignment error and link blockage through stochastic geometry.Numerical experiments demonstrate that narrower beam leads to higher coverage probability with perfect beam alignment,but it is not the case with imperfect beam alignment.Therefore,the optimal beamwidth that maximize the coverage probability is characterized and a closed-form approximation of the optimal beamwidth is derived under imperfect beam alignment,accordingly.Furthermore,the optimal beamwidth is a monotonically increasing function of the standard deviation of the beam alignment error,and a monotonically decreasing function of the beamwidth of correspondent communication end,indicating that the beamwidth of the communication pairs ought to be jointly designed.展开更多
In this paper, we propose directdetection optical orthogonal frequency division multiplexing superchannel （DDOOFDMS） and optical multiband receiving method （OMBR） to support a greater than 200 Gb/s data rate and l...In this paper, we propose directdetection optical orthogonal frequency division multiplexing superchannel （DDOOFDMS） and optical multiband receiving method （OMBR） to support a greater than 200 Gb/s data rate and longer distance for direct-detection systems. For the new OMBR, we discuss the optimum carriertosideband power ratio （CSPR） in the cases of backtoback and post transmission. We derive the analytical form for CSPR and theoretically verify it. A low overhead training method for estimating I/Q imbalance is also introduced in order to improve performance and maintain high system throughput. The experiment results show that these proposals enable an unprecedented data rate of 214 Gb/s （190 Gb/s without overhead） per wavelength over an unprecedented distance of 720 km SSMF in greater than 100 Gb/s DDOFDM systems.展开更多
The demands for massive renewable energy integration, passive network power supply, and global energy interconnection have all gradually increased, posing new challenges for high voltage direct current(HVDC) power tra...The demands for massive renewable energy integration, passive network power supply, and global energy interconnection have all gradually increased, posing new challenges for high voltage direct current(HVDC) power transmission systems, including more complex topology and increased diversity of bipolar HVDC transmission. This study proposes that these two factors have led to new requirements for HVDC control strategies. Moreover, due to the diverse applications of HVDC transmission technology, each station in the system has different requirements. Furthermore, the topology of the AC-DC converter is being continuously developed, revealing a trend towards hybrid converter stations.展开更多
Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, ...Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, direct digital frequency synthesis(DDS) technology to modulate the phase front of the laser and measure the TM. By judiciously modulating the phase front of a He–Ne laser beam, we experimentally generate a high quality focus at any targeted location through a 2 mm thick 120 grit ground glass diffuser, which is commercially used in laser display and laser holographic display for improving brightness uniformity and reducing speckle. The signal to noise ratio(SNR) of the clear round focus is 50 and the size is about 44 μm. Our study will open up new avenues for enhancing light energy delivery to the optical engine in laser TV to lower the power consumption, phase compensation to reduce the speckle noise, and controlling the lasing threshold in random lasers.展开更多
针对异步分区后电力系统调频资源不足、频率响应恶化等问题,提出了一种基于电网换相换流器型高压直流输电(line commutated converter high voltage direct current,LCC-HVDC)的异步互联系统双向主动频率控制策略。该策略通过灵活地调...针对异步分区后电力系统调频资源不足、频率响应恶化等问题,提出了一种基于电网换相换流器型高压直流输电(line commutated converter high voltage direct current,LCC-HVDC)的异步互联系统双向主动频率控制策略。该策略通过灵活地调整直流电流和直流电压,在实现双侧频率调节的同时,保持逆变侧消耗的无功功率不变,最小化交流电压的波动。此外,为避免调节过程中,控制指令不当导致的换相失败问题,所提策略在设计过程中兼顾了最小熄弧角约束,保证了直流系统在频率调节过程中的稳定运行。在利用LCC-HVDC互联的四机两区域(four machines two areas,4G2A)系统进行仿真验证,证明了所提方法的有效性。本研究为异步互联系统的频率控制提供了一种新的解决方案,具有广阔的应用前景。展开更多
基金This work is sponsored in part by the National Key R&D Program of China No.2020YFB1806605by the Nature Science Foundation of China(No.62022049,No.61871254,No.62111530197)by Open Research Fund Program of Beijing National Research Center for Information Science and Technology,and Hitachi Ltd.
文摘Blockage and imperfect beam alignment are two principal difficulties in high-frequency bands directional transmissions.In this paper,the coverage performance of downlink directional transmissions in ultra-dense networks is analyzed,with the consideration of beam alignment error and link blockage through stochastic geometry.Numerical experiments demonstrate that narrower beam leads to higher coverage probability with perfect beam alignment,but it is not the case with imperfect beam alignment.Therefore,the optimal beamwidth that maximize the coverage probability is characterized and a closed-form approximation of the optimal beamwidth is derived under imperfect beam alignment,accordingly.Furthermore,the optimal beamwidth is a monotonically increasing function of the standard deviation of the beam alignment error,and a monotonically decreasing function of the beamwidth of correspondent communication end,indicating that the beamwidth of the communication pairs ought to be jointly designed.
文摘In this paper, we propose directdetection optical orthogonal frequency division multiplexing superchannel （DDOOFDMS） and optical multiband receiving method （OMBR） to support a greater than 200 Gb/s data rate and longer distance for direct-detection systems. For the new OMBR, we discuss the optimum carriertosideband power ratio （CSPR） in the cases of backtoback and post transmission. We derive the analytical form for CSPR and theoretically verify it. A low overhead training method for estimating I/Q imbalance is also introduced in order to improve performance and maintain high system throughput. The experiment results show that these proposals enable an unprecedented data rate of 214 Gb/s （190 Gb/s without overhead） per wavelength over an unprecedented distance of 720 km SSMF in greater than 100 Gb/s DDOFDM systems.
基金supported by the State Grid Science & Technology Project (GEIGC-E-[2018]026)
文摘The demands for massive renewable energy integration, passive network power supply, and global energy interconnection have all gradually increased, posing new challenges for high voltage direct current(HVDC) power transmission systems, including more complex topology and increased diversity of bipolar HVDC transmission. This study proposes that these two factors have led to new requirements for HVDC control strategies. Moreover, due to the diverse applications of HVDC transmission technology, each station in the system has different requirements. Furthermore, the topology of the AC-DC converter is being continuously developed, revealing a trend towards hybrid converter stations.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFB0401902 and 2016YFB0402001)Key-Area Research and Development Program of Guang Dong Province,China(Grant No.2019B010926001)。
文摘Phase modulation is a crucial step when the frequency-based wavefront optimization technique is exploited to measure the optical transmission matrix(TM) of a scattering medium. We report a simple but powerful method, direct digital frequency synthesis(DDS) technology to modulate the phase front of the laser and measure the TM. By judiciously modulating the phase front of a He–Ne laser beam, we experimentally generate a high quality focus at any targeted location through a 2 mm thick 120 grit ground glass diffuser, which is commercially used in laser display and laser holographic display for improving brightness uniformity and reducing speckle. The signal to noise ratio(SNR) of the clear round focus is 50 and the size is about 44 μm. Our study will open up new avenues for enhancing light energy delivery to the optical engine in laser TV to lower the power consumption, phase compensation to reduce the speckle noise, and controlling the lasing threshold in random lasers.
文摘针对异步分区后电力系统调频资源不足、频率响应恶化等问题,提出了一种基于电网换相换流器型高压直流输电(line commutated converter high voltage direct current,LCC-HVDC)的异步互联系统双向主动频率控制策略。该策略通过灵活地调整直流电流和直流电压,在实现双侧频率调节的同时,保持逆变侧消耗的无功功率不变,最小化交流电压的波动。此外,为避免调节过程中,控制指令不当导致的换相失败问题,所提策略在设计过程中兼顾了最小熄弧角约束,保证了直流系统在频率调节过程中的稳定运行。在利用LCC-HVDC互联的四机两区域(four machines two areas,4G2A)系统进行仿真验证,证明了所提方法的有效性。本研究为异步互联系统的频率控制提供了一种新的解决方案,具有广阔的应用前景。
