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Chengshi Zhao,Kyungsup Kwak IEEE 2010 IEEE Transactions on Vehicular Technology VT Vol.59 No.4
<P>Conflict-free power allocation for secondary users (SUs) in cognitive networks is a challenging problem because the accessible spectrum of the SUs is shared with the primary users (PUs). The problem becomes particularly difficult when the objective is to achieve maximum network capacity considering the mutual interference between the PUs and the SUs. In this paper, we specify the case with a single SU and multiple PUs, where both the SU and the PUs are orthogonal frequency-division multiplexing (OFDM) modulated. The power allocation for the subcarriers of the SU is modeled into a constrained optimization problem, where the mutual interference between the SU and the PUs is comprehensively formulated as restrictions on the SU's transmission power. As a result, the proposed modeling scheme restrains the interference to the PUs, as well as maximizing the capacity of the SU. A novel iterative power-loading algorithm with low computational complexity is proposed to realize the power loading. On this basis, a suboptimal integral-bit-loading algorithm is further presented. In a simplified scenario, simulation results are exhibited to confirm the efficiency of the proposed power and bit-loading algorithms. Finally, the influence of the mutual interference on the SU's power/bit loading and the system capacity is illustrated.</P>
Recent Update of Embolization of Postpartum Hemorrhage
Chengshi Chen,Sang Min Lee,김종우,신지훈 대한영상의학회 2018 Korean Journal of Radiology Vol.19 No.4
Postpartum hemorrhage (PPH) is a life-threatening condition and remains a leading cause of maternal mortality. Transcatheter arterial embolization (TAE) is an effective therapeutic strategy for PPH with the advantages of fast speed, repeatability, and the possibility of fertility preservation. We reviewed the vascular anatomy relevant to PPH, the practical details of TAE emphasizing the timing of embolization, and various clinical conditions of PPH according to a recent literature review.
Joint sensing time and power allocation in cooperatively cognitive networks
Chengshi Zhao,Kyungsup Kwak IEEE 2010 IEEE communications letters Vol.14 No.2
<P>The jointly optimal allocation of sensing time and power for a two-user amplify-and-forward overlay cognitive network is developed by maximizing the averaged aggregate throughput of the secondary network. In particular, observing that the sensing duration lies within a strict interval, the jointly optimal strategy of sensing time and power allocation is proved to be tractable by sequential optimization.</P>
Novel UWB Transceiver for WBAN Networks: A Study on AWGN Channels
Chengshi Zhao,Zheng Zhou,곽경섭 한국전자통신연구원 2010 ETRI Journal Vol.32 No.1
A novel ultra-wideband (UWB) transceiver structure is presented to be used in wireless body area networks (WBANs). In the proposed structure, a data channel and a control channel are combined into a single transmission signal. In the signal, a modulation method mixing pulse position modulation and pulse amplitude modulation is proposed. A mathematical framework calculating the power spectrum density of the proposed pulse-based signal evaluates its coexistence with conventional radio systems. The transceiver structure is discussed, and the receiving performance is investigated in the additive white Gaussian noise channel. It is demonstrated that the proposed scheme is easier to match to the UWB emission mask than conventional UWB systems. The proposed scheme achieves the data rate requirement of WBAN; the logical control channel achieves better receiving performance than the logical data channel, which is useful for controlling and maintaining networks. The proposed scheme is also easy to implement.
Rayleigh-Quotient and Iterative-Threshold-Test-Based Blind TOA Estimation for IR-UWB Systems
Bin Shen,Chengshi Zhao,Taiping Cui,곽경섭 한국전자통신연구원 2010 ETRI Journal Vol.32 No.2
This letter proposes a non-coherent blind time-of-arrival (TOA) estimation scheme for impulse radio ultra-wideband systems. The TOA estimation is performed in two consecutive phases: the Rayleigh-quotient theorem-based coarse-signal acquisition (CSA) and the iterative-threshold-test-based fine time estimation (FTE). The proposed scheme serves in a blind manner without demanding any a priori knowledge of the channel and the noise. Analysis and simulations demonstrate that the proposed scheme significantly increases the signal detection probability in CSA and ameliorates the TOA estimation accuracy in FTE.