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Transmit Power Optimization for Cooperative Beamforming in Uplink MIMO Ad-hoc Networks
Younghyun Jeon,Seungjoo Maeng 대한전자공학회 2017 대한전자공학회 학술대회 Vol.2017 No.1
In Ad-hoc networks, one great interest is its combination with multiple-input multiple-output (MIMO) transmission techniques. On this work, we consider a specific type of Ad-hoc networks called reverse-link MIMO Ad-hoc network (RMAN) and maximize the data rate with a power consumption constraint using cooperative beamforming techniques. Based on mathematical analysis, we design an algorithm which constructs optimal orthogonal weight vectors according to channel feedback and controls the transmission power according to a QoS-pricing value level. In simulation results, we show the validity of the analysis and the data rate performance of our proposed algorithm. We also show that the data rate of each link converges to a stationary point.
Jeon, Younghyun,Song, Changick,Lee, Sang-Rim,Maeng, Seungjoo,Jung, Jaehoon,Lee, Inkyu IEEE 2017 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.16 No.5
<P>In this paper, we study a joint spatial division multiplexing (JSDM) beamforming scheme, which enables large-scale spatial multiplexing gains for massive multi-input multi-output downlink systems. In contrast to the conventional JSDM, which employs a block diagonalization method as a pre-beamformer, we aim to maximize sum-rate by applying minimum-mean-squared error (MMSE) approaches when designing a pre-beamformer and a multi-user precoder sequentially. First, to suppress inter-group interference, we design the pre-beamformer, which minimizes an upper bound of the sum mean-squared-error in the large-scale array regime. Then, to mitigate same-group interference, we present the multi-user precoder based on the weighted MMSE (WMMSE) optimization method, which requires the same channel state information overhead as the conventional JSDM. Also, in order to reduce the computational complexity, we compute deterministic equivalents of the WMMSE beamforming parameters to generate the beam-formers by employing asymptotic results of large system analysis. Through simulation results, we confirm that the proposed two-step beamforming methods bring substantial performance gains in terms of sum-rate over the conventional JSDM schemes especially in a low and medium signal-to-noise ratio regime with comparable complexity.</P>
Molecular imaging with terahertz waves.
Oh, Seung Jae,Choi, Jihye,Maeng, Inhee,Park, Jae Yeon,Lee, Kwangyeol,Huh, Yong-Min,Suh, Jin-Suck,Haam, Seungjoo,Son, Joo-Hiuk Optical Society of America 2011 Optics express Vol.19 No.5
<P>We demonstrate a highly sensitive THz molecular imaging (TMI) technique involving differential modulation of surface plasmons induced on nanoparticles and obtain target specific in vivo images of cancers. This technique can detect quantities of gold nanoparticles as small as 15 µM in vivo. A comparison of TMI images with near infrared absorption images shows the superior sensitivity of TMI. Furthermore, the quantification property of TMI is excellent, being linearly proportional to the concentration of nanoparticles. The target specificity issue is also addressed at the ex vivo and cell levels. The high thermal sensitivity of TMI can help extend photonic-based photothermal molecular imaging researches from the in vitro level to the in vivo level. The TMI technique can be used for monitoring drug delivery processes and for early cancer diagnosis.</P>
Cha, Soonyoung,Hong, Yoochan,Yang, Jaemoon,Maeng, Inhee,Oh, Seung Jae,Jeong, Kiyoung,Suh, Jin-Suck,Haam, Seungjoo,Huh, Yong-Min,Choi, Hyunyong American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.39
<P>The conducting polymer polyaniline (PANI) has a wide range of optoelectronic applications due to its unique electronic and optical characteristics. Although extensive works have been performed to understand the equilibrium properties, the nature of the charge type that governs its nonequilibrium optical response has been barely understood; a number of studies have debated the nature of photogenerated charge type in PANI, specifically whether it is polaron or exciton based. Here, we report experimental evidence that the charge relaxation dynamics of PANI are dominated by excitons. Utilizing ultrafast spin-resolved pump–probe spectroscopy, we observed that PANI charge dynamics are strongly spin-polarized, exhibiting a spin Pauli-blocking effect. Investigations including both spin-independent and spin-dependent dynamics reveal that there is no spin-flip process involved in charge relaxation. This provides compelling evidence of an exciton-dominated photoresponse in PANI.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-39/jp408800j/production/images/medium/jp-2013-08800j_0006.gif'></P>
Nanoparticle-enabled terahertz imaging for cancer diagnosis
Oh, Seung Jae,Kang, Jinyoung,Maeng, Inhee,Suh, Jin-Suck,Huh, Yong-Min,Haam, Seungjoo,Son, Joo-Hiuk The Optical Society 2009 Optics express Vol.17 No.5
<P>This paper demonstrates the principle of the nanoparticle-contrast-agent-enabled terahertz imaging (CATHI) technique, which yields a dramatic sensitivity of the differential signal from cancer cells with nanoparticles. The terahertz (THz) reflection signal increased beam by 20% in the cancer cells with nanoparticles of gold nano-rods (GNRs) upon their irradiation with a infrared (IR) laser, due to the temperature rise of water in cancer cells by surface plasma ploritons. In the differential mode, the THz signal from the cancer cells with GNRs was 30 times higher than that from the cancer cells without GNRs. As the high sensitivity is achieved by the surface plasmon resonance through IR laser irradiation, the resolution of the CATHI technique can be as good as a few microns and THz endoscopy becomes more feasible.</P>