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- 저자 : ( Guomei Zhang ) (검색결과 4 건)
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( Guomei Zhang ),( Bing Wang ),( Guobing Li ),( Fei Xiang ),( Gangming Lv ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.8
In order to accommodate huge number of antennas in a limited antenna size, a large scale antenna array is expected to have a three dimensional (3D) array structure. By using the Active Antenna Systems (AAS), the weights of the antenna elements arranged vertically could be configured adaptively. Then, a degree of freedom (DOF) in the vertical plane is provided for system design. So the three-dimension MIMO (3D MIMO) could be realized to solve the actual implementation problem of the massive MIMO. However, in 3D massive MIMO systems, the pilot contamination problem studied in 2D massive MIMO systems and the inter-cell interference as well as inter-vertical sector interference in 3D MIMO systems with vertical sectorization exist simultaneously, when the number of antenna is not large enough. This paper investigates the interference management towards the above challenges in 3D massive MIMO systems. Here, vertical sectorization based on vertical beamforming is included in the concerned systems. Firstly, a cooperative joint vertical beams adjustment and pilot assignment scheme is developed to improve the channel estimation precision of the uplink with pilots being reused across the vertical sectors. Secondly, a downlink interference coordination scheme by jointly controlling weight vectors and power of vertical beams is proposed, where the estimated channel state information is used in the optimization modelling, and the performance loss induced by pilot contamination could be compensated in some degree. Simulation results show that the proposed joint optimization algorithm with controllable vertical beams` weight vectors outperforms the method combining downtilts adjustment and power allocation.
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Comment Letters and Reporting Quality: Evidence from Financial Restatements
Zhang Qiuyue,Tang Guomei,Qin Xiuting 한국증권학회 2023 Asia-Pacific Journal of Financial Studies Vol.52 No.6
This study investigates the impact of comment letter reviews on reporting quality in terms of financial restatements, using comment letters from the Chinese market between 2013 and 2020. The baseline results indicate that although receiving a comment letter increases the next year's (year t + 1) restatements, it reduces later years' (year t + 2 onwards) restatements. Moreover, this effect is more pronounced among firms with lower external auditor quality, poorer information transparency, and those located in less marketized provinces. The mechanism analyses show that comment letter reviews improve financial reporting quality because of deterrent effects in the form of increased litigation risk.
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( Zongyi Liu ),( Guomei Zhang ),( Wei Meng ),( Xiaohui Ma ),( Guobing Li ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.3
Cognitive radio (CR) is regarded as an effective approach to avoid the inefficient use of spectrum. However, CRNs have more special security problems compared with the traditional wireless communication systems due to its open and dynamic characteristics. Primary user emulation attack (PUEA) is a common method which can hinder secondary users (SUs) from accessing the spectrum by transmitting signals who has the similar characteristics of the primary users’ (PUs) signals, and then the SUs’ quality of service (QoS) cannot be guaranteed. To handle this issue, we first design a multiple-phase energy detection scheme based on the cooperation of multiple SUs to detect the PUEA more precisely. Second, a joint SUs scheduling and power allocation scheme is proposed to maximize the weighted effective capacity of multiple SUs with a constraint of the average interference to the PU. The simulation results show that the proposed method can effectively improve the effective capacity of the secondary users compared with the traditional overlay scheme which cannot be aware of the existence of PUEA. Also the good delay QoS guarantee for the secondary users is provided.
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A New Dynamic Transmission-Mode Selection Scheme for AMC/HARQ-Based Wireless Networks
( Xiaohui Ma ),( Guobing Li ),( Guomei Zhang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.11
In this paper, we study the cross-layer design for the AMC/HARQ-based wireless networks, and propose a new dynamic transmission-mode selection scheme to improve system spectrum efficiency. In the proposed scheme, dynamic thresholds for transmission-mode selection in each packet transmission and retransmission are jointly designed under the constraint of the overall packet error rate. Comparing with the existing schemes, the proposed scheme is inclined to apply higher modulation order at the first several (re)transmissions, which corresponds to higher-rate transmission modes thus higher average system spectrum efficiency. We also extend the cross-layer design to MIMO (Multi-input Multi-output) communication scenarios. Numerical results show that the proposed new dynamic transmission-mode selection scheme generally achieves higher average spectrum efficiency than the conventional and existing cross-layer design.
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