Sihan Wu

Publications

• 2.75

  Impact points

  Triptolide inhibits proliferation and invasion of malignant glioma cells.

  Haipeng Zhang, Wenbo Zhu, Xingwen Su, Sihan Wu, Yuan Lin, Jingjie Li, Youqiong Wang, Jingkao Chen, Yuxi Zhou, Pengxin Qiu, Guangmei Yan, Shujin Zhao, Jun Hu, Jingxia Zhang

  Journal of neuro-oncology. 05/2012;

  Malignant glioma is the most devastating and aggressive tumor in brain, characterized by rapid proliferation and diffuse invasion. Chemotherapy and radiotherapy are the pivotal strategies after surgery; however, high drug resistance of malignant glioma and the blood-brain barrier usually render chem... [more] Malignant glioma is the most devastating and aggressive tumor in brain, characterized by rapid proliferation and diffuse invasion. Chemotherapy and radiotherapy are the pivotal strategies after surgery; however, high drug resistance of malignant glioma and the blood-brain barrier usually render chemotherapy drugs ineffective. Here, we find that triptolide, a small molecule with high lipid solubility, is capable of inhibiting proliferation and invasion of malignant glioma cells effectively. In both investigated malignant glioma cell lines, triptolide repressed cell proliferation via inducing cell cycle arrest in G0/G1 phase, associated with downregulation of G0/G1 cell cycle regulators cyclin D1, CDK4, and CDK6 followed by reduced phosphorylation of retinoblastoma protein (Rb). In addition, triptolide induced morphological change of C6 cells through downregulation of protein expression of MAP-2 and inhibition of activities of GTPases Cdc42 and Rac1/2/3, thus significantly suppressing migratory and invasive capacity. Moreover, in an in vivo tumor model, triptolide delayed growth of malignant glioma xenografts. These findings suggest an important inhibitory action of triptolide on proliferation and invasion of malignant glioma, and encourage triptolide as a candidate for glioma therapy.
• 3.02

  Impact points

  Template effect of hydrolysis of the catalyst precursor on growth of carbon nanotube arrays.

  S H Liu, X W Zhao, T S Pan, S Wu, B Zeng, H Z Zeng, M Gao, Y Zhang, W Huang, Y Lin

  Journal of colloid and interface science. 02/2012; 374(1):34-9.

  Iron catalyst films for the growth of carbon nanotube (CNT) arrays are prepared using sol-gel technique during different hydrolytic periods. It is shown that the extent of hydrolysis of the catalyst precursor has strong impacts on the size and density of iron catalyst particles, which distributed on... [more] Iron catalyst films for the growth of carbon nanotube (CNT) arrays are prepared using sol-gel technique during different hydrolytic periods. It is shown that the extent of hydrolysis of the catalyst precursor has strong impacts on the size and density of iron catalyst particles, which distributed on surface of the film. The iron catalysts formed big clusters in the early stage of the hydrolysis, whereas the particle size decreased dramatically to approximate 20nm when the hydrolytic duration is as long as 150h. The reaction between the hydrolytic product of ethyl orthosilicate and the iron oxide particles effectively influence the structure of catalysts during the process of annealing precursor films and reducing the iron oxide particles into iron catalysts. We believe that the hydrolytic product limits the mobility of the catalyst particles, preventing them from aggregating into big clusters by Ostwald ripening. This catalyst film may be utilized to create a template to control the length and quality of CNTs.
• 2.10

  Impact points

  Assessing prostate cancer growth with citrate measured by intact tissue proton magnetic resonance spectroscopy.

  R Dittrich, J Kurth, E A Decelle, E M Defeo, M Taupitz, S Wu, C-L Wu, W S McDougal, L L Cheng

  Prostate cancer and prostatic diseases. 01/2012;

  Background:Annual PSA tests have led to a significant increase in the number of prostate cancer (PCa) cases diagnosed. This increased incidence has led to overtreatment of many patients, as current pathology often cannot distinguish latent from aggressive PCa. Studies have shown that the depletion o... [more] Background:Annual PSA tests have led to a significant increase in the number of prostate cancer (PCa) cases diagnosed. This increased incidence has led to overtreatment of many patients, as current pathology often cannot distinguish latent from aggressive PCa. Studies have shown that the depletion of zinc in prostate cells correlated with cell-line growth rates, and may therefore relate to the progression of PCa. Furthermore, as zinc is normally an inhibitor of citrate oxidation, the reduction of zinc in PCa may cause a decrease in citrate secretion levels in the glandular epithelia of PCa patients.Methods:Using high-resolution magic angle spinning proton magnetic resonance spectroscopy followed by quantitative histopathology, we investigate unit histo-benign prostate epithelial citrate concentrations in intact tissue samples obtained from 18 patients with pre-surgical PSA values less than 20 ng/ml. Using these data, we evaluate correlations between citrate concentrations and PSA velocities, densities and blood percent-free PSA.Results:We observe different linear patterns between citrate concentrations and histo-benign glandular epithelia from patients of different PSA velocities. More importantly, we obtain a significant correlation between PSA velocity, density and percent-free PSA, and citrate concentrations in unit volume of histo-benign epithelial glands of the peripheral zone.Conclusions:Low levels of citrate in unit volume represent rapidly increasing PSA values, and, therefore, may be used as an indicator of fast-growing PCa. Thus, tissue samples obtained at the time of biopsy may be evaluated for their citrate concentrations for the prediction of PCa growth rates, allowing for the implementation of alternative treatment options and reducing overtreatment.Prostate Cancer and Prostatic Diseases advance online publication, 31 January 2012; doi:10.1038/pcan.2011.70.
• 4.53

  Impact points

  MicroRNA 335 Is Required for Differentiation of Malignant Glioma Cells Induced by Activation of cAMP/Protein Kinase A Pathway.

  Minfeng Shu, Yuehan Zhou, Wenbo Zhu, Haipeng Zhang, Sihan Wu, Jingkao Chen, Guangmei Yan

  Molecular pharmacology. 12/2011; 81(3):292-8.

  Glioma is the most common malignant cancer affecting the central nerve system, with dismal prognosis. Differentiation-inducing therapy is a novel strategy that has been preliminarily proved effective against malignant glioma. We have reported previously that activation of cAMP/protein kinase A (PKA)... [more] Glioma is the most common malignant cancer affecting the central nerve system, with dismal prognosis. Differentiation-inducing therapy is a novel strategy that has been preliminarily proved effective against malignant glioma. We have reported previously that activation of cAMP/protein kinase A (PKA) pathway is capable of inducing glioma cell differentiation, characterized by astrocyte-like shape and dramatic induction of astrocyte biomarker glial fibrillary acidic protein (GFAP). However, little progress has been made on molecular mechanisms related. Here we demonstrate that microRNA 335 (miR-335) is responsible for the glioma cell differentiation stimulated by activation of cAMP/PKA pathway. In the cAMP elevator cholera toxin-induced differentiation model of rat C6 glioma cells, miR-335 was significantly up-regulated, which was mimicked by other typical cAMP/PKA pathway activators (e.g., forskolin, dibutyryl-cAMP) and abolished by PKA-specific inhibitor (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i] [1,6]benzodiazocine-10-carboxylic acid, hexyl ester (KT5720). In an assay measuring gain and loss of miR-335 function, exogenetic miR-335 resulted in induction of GFAP, whereas miR-335 specific inhibitor antagomir-335 violently blocked cholera toxin-induced GFAP up-regulation. It is noteworthy that in human U87-MG glioma cells and human primary culture glioma cells, miR-335 also mediated cholera toxin-induced differentiation. Taken together, our findings suggest that miR-335 is potently required for differentiation of malignant glioma cells induced by cAMP/PKA pathway activation, and a single microRNA may act as an important fate determinant to control the differentiation status of malignant gliomas, which has provided a new insight into differentiation-inducing therapy against malignant gliomas.
• 7.14

  Impact points

  MiR-135a functions as a selective killer of malignant glioma.

  S Wu, Y Lin, D Xu, J Chen, M Shu, Y Zhou, W Zhu, X Su, P Qiu, G Yan

  Oncogene. 12/2011;

  Glioma is the most common and fatal primary brain tumor. Thus far, therapeutic strategies to efficiently and specifically antagonize glioma are limited and poorly developed. Here we report that glia-enriched miR-135a, a microRNA that is dramatically downregulated in malignant glioma and correlated w... [more] Glioma is the most common and fatal primary brain tumor. Thus far, therapeutic strategies to efficiently and specifically antagonize glioma are limited and poorly developed. Here we report that glia-enriched miR-135a, a microRNA that is dramatically downregulated in malignant glioma and correlated with the pathological grading, is capable of inducing mitochondria-dependent apoptosis of malignant glioma by regulating various genes including STAT6, SMAD5 and BMPR2, as well as affecting the signaling pathway downstream. Moreover, this lethal effect is selectively towards malignant glioma cells, but not neurons and glial cells, through a novel mechanism. Our findings suggest an important role of miR-135a in glioma etiology and provide a potential candidate for malignant glioma therapy.Oncogene advance online publication, 5 December 2011; doi:10.1038/onc.2011.551.

• Sub-25nm FinFET with advanced fin formation and short channel effect engineering

  T. Yamashita, V.S. Basker, T. Standaert, C.-C. Yeh, T. Yamamoto, K. Maitra, C.-H. Lin, J. Faltermeier, S. Kanakasabapathy, M. Wang, [......], M. Colburn, M. Hane, D. Mcherron, V.K. Paruchuri, B. Doris, R.J. Miller, H. Bu, M. Khare, J. O'Neill, E. Leobandung

  VLSI Technology (VLSIT), 2011 Symposium on; 07/2011

  FinFET devices achieving N/P Ion values of 1250/950 uA/um at 100 nA/um at 1V, 1300/1000 uA/um with self-heating correction, are demonstrated, using a dual work function gate-first process flow at 100 nm gate pitch and 40 nm fin pitch. Ring-oscillator (RO, FO = 3) functionality has been demonstrated,... [more] FinFET devices achieving N/P Ion values of 1250/950 uA/um at 100 nA/um at 1V, 1300/1000 uA/um with self-heating correction, are demonstrated, using a dual work function gate-first process flow at 100 nm gate pitch and 40 nm fin pitch. Ring-oscillator (RO, FO = 3) functionality has been demonstrated, showing excellent Vdd scalability. We have also demonstrated logic scan chain functionality and yield improvement by optimizing the gate stack process. An optimized SIT process has been developed to improve short-channel characteristics in devices with a small number of fins in a narrow active area, which is also critical for manufacturability improvement. Various conformal doping techniques for NFET/PFET are optimized to improve device performance.
• 3.14

  Impact points

  Reply to Comment on 'Unconventional gap state of trapped exciton in lead sulphide quantum dots'.

  J E Lewis, S Wu, Xiaomei Jiang

  Nanotechnology. 06/2011; 22(23):238002.

  This is a reply to a comment on our previously published paper.
• 1.42

  Impact points

  Circuits and System Design of RF Polar Transmitters Using Envelope-Tracking and SiGe Power Amplifiers for Mobile WiMAX

  Yan Li, J. Lopez, D.Y.C. Lie, K. Chen, S. Wu, Tzu-Yi Yang, Gin-Kou Ma

  Circuits and Systems I: Regular Papers, IEEE Transactions on. 06/2011;

  This paper discusses the circuits and system design methodology of a highly-efficient wideband RF polar transmitter (TX) using the envelope-tracking (ET) technique for mobile WiMAX applications. Monolithic power amplifiers (PAs) are designed and fabricated in IBM 0.18 μm SiGe BiCMOS technology, and ... [more] This paper discusses the circuits and system design methodology of a highly-efficient wideband RF polar transmitter (TX) using the envelope-tracking (ET) technique for mobile WiMAX applications. Monolithic power amplifiers (PAs) are designed and fabricated in IBM 0.18 μm SiGe BiCMOS technology, and a linear-assisted switch-mode envelope amplifier is applied to modulate the PA supply voltage to form the core of the RF polar TX. Nonlinearities caused by bandwidth limitation of the envelope amplifier and timing misalignment have been investigated. When driven by WiMAX 64QAM 8.75 MHz signals, the overall PAE of our ET-based polar TX system reaches 30.5% at 17 dBm average output power, while also meeting the stringent WiMAX linearity specs without using any predistortion. When the decresting algorithm using the soft limiter is applied to the baseband, the overall PAE increases to 33%, at the expense of a higher EVM of 4.9%. Based on measurement results, our ET-based polar TX system has demonstrated excellent efficiency with good linearity for high peak-to-average ratio (PAR) broadband signals when compared with the recent literature on state-of-the-arts polar TX designs.
• 4.16

  Impact points

  Targeting oncogenic miR-335 inhibits growth and invasion of malignant astrocytoma cells.

  Minfeng Shu, Xiaoke Zheng, Sihan Wu, Huimin Lu, Tiandong Leng, Wenbo Zhu, Yuehan Zhou, Yanqiu Ou, Xi Lin, Yuan Lin, Dong Xu, Yuxi Zhou, Guangmei Yan

  Molecular cancer. 05/2011; 10:59.

  Astrocytomas are the most common and aggressive brain tumors characterized by their highly invasive growth. Gain of chromosome 7 with a hot spot at 7q32 appears to be the most prominent aberration in astrocytoma. Previously reports have shown that microRNA-335 (miR-335) resided on chromosome 7q32 is... [more] Astrocytomas are the most common and aggressive brain tumors characterized by their highly invasive growth. Gain of chromosome 7 with a hot spot at 7q32 appears to be the most prominent aberration in astrocytoma. Previously reports have shown that microRNA-335 (miR-335) resided on chromosome 7q32 is deregulated in many cancers; however, the biological function of miR-335 in astrocytoma has yet to be elucidated. We report that miR-335 acts as a tumor promoter in conferring tumorigenic features such as growth and invasion on malignant astrocytoma. The miR-335 level is highly elevated in C6 astrocytoma cells and human malignant astrocytomas. Ectopic expression of miR-335 in C6 cells dramatically enhances cell viability, colony-forming ability and invasiveness. Conversely, delivery of antagonist specific for miR-335 (antagomir-335) to C6 cells results in growth arrest, cell apoptosis, invasion repression and marked regression of astrocytoma xenografts. Further investigation reveals that miR-335 targets disheveled-associated activator of morphogenesis 1(Daam1) at posttranscriptional level. Moreover, silencing of endogenous Daam1 (siDaam1) could mimic the oncogenic effects of miR-335 and reverse the growth arrest, proapoptotic and invasion repression effects induced by antagomir-335. Notably, the oncogenic effects of miR-335 and siDAAM1 together with anti-tumor effects of antagomir-335 are also confirmed in human astrocytoma U87-MG cells. These findings suggest an oncogenic role of miR-335 and shed new lights on the therapy of malignant astrocytomas by targeting miR-335.
• 2.66

  Impact points

  Activation of a pro-survival pathway IL-6/JAK2/STAT3 contributes to glial fibrillary acidic protein induction during the cholera toxin-induced differentiation of C6 malignant glioma cells.

  Minfeng Shu, Yuxi Zhou, Wenbo Zhu, Sihan Wu, Xiaoke Zheng, Guangmei Yan

  Molecular oncology. 03/2011; 5(3):265-72.

  Differentiation-inducing therapy has been proposed to be a novel potential approach to treat malignant gliomas. Glial fibrillary acidic protein (GFAP) is a well-known specific astrocyte biomarker and acts as a tumor suppressor gene (TSG) in glioma pathogenesis. Previously we reported that a traditio... [more] Differentiation-inducing therapy has been proposed to be a novel potential approach to treat malignant gliomas. Glial fibrillary acidic protein (GFAP) is a well-known specific astrocyte biomarker and acts as a tumor suppressor gene (TSG) in glioma pathogenesis. Previously we reported that a traditional biotoxin cholera toxin could induce malignant glioma cell differentiation characterized by morphologic changes and dramatic GFAP expression. However, the molecular mechanisms underlying GFAP induction are still largely unknown. Here we demonstrate that an oncogenic pathway interleukin-6/janus kinase-2/signal transducer and activator of transcription 3 (IL-6/JAK2/STAT3) cascade mediates the cholera toxin-induced GFAP expression. Cholera toxin dramatically stimulated GFAP expression at the transcriptional level in C6 glioma cells. Meanwhile, phosphorylation of STAT3 and JAK2 was highly induced in a time-dependent manner after cholera toxin incubation, whereas no changes of STAT3 and JAK2 were observed. Furthermore, the IL-6 gene was quickly induced by cholera toxin and subsequent IL-6 protein secretion was stimulated. Importantly, exogenous recombinant rat IL-6 can also induce phosphorylation of STAT3 concomitant with GFAP expression while JAK2 specific inhibitor AG490 could effectively block both cholera toxin- and IL-6-induced GFAP expression. Given that the methylation of the STAT3 binding element can suppress GFAP expression, we detected the methylation status of the critical recognition sequence of STAT3 in the promoter of GFAP gene (-1518 ∼ -1510) and found that it was unmethylated in C6 glioma cells. In addition, neither DNA methyltransferase1 (DNMT1) inhibitor 5-Aza-2'-deoxycytidine (5-AZa-CdR) nor silencing DNMT1 can stimulate GFAP expression, indicating that the loss of GFAP expression in C6 cells is not caused by its promoter hypermethylation. Taken together, our findings suggest that activation of a pro-survival IL-6/JAK2/STAT3 cascade contributes to cholera toxin-induced GFAP expression, which implies that a survival-promoting signal may also play a differentiation-supporting role in malignant gliomas.

• Extrinsic or Intrinsic Motivation of E-Negotiation Experiments' Participants

  G.E. Kersten, S. Wu, C. Oertel

  System Sciences (HICSS), 2011 44th Hawaii International Conference on; 02/2011

  Motivation of the negotiation experiments participants affects their behavior and performance. We asked students participating in online experiments to assess the subjective importance of seven objectives associated with the negotiation. Based on the responses we identified three types of motivation... [more] Motivation of the negotiation experiments participants affects their behavior and performance. We asked students participating in online experiments to assess the subjective importance of seven objectives associated with the negotiation. Based on the responses we identified three types of motivation. We also identified four participants' profiles which differ in the assessment of the significance of the motivations. The implications of the relationship between profiles, motivation, and the process and its results is discussed.

• World's first monolithic 3D-FPGA with TFT SRAM over 90nm 9 layer Cu CMOS

  T. Naito, T. Ishida, T. Onoduka, M. Nishigoori, T. Nakayama, Y. Ueno, Y. Ishimoto, A. Suzuki, W. Chung, R. Madurawe, S. Wu, S. Ikeda, H. Oyamatsu

  VLSI Technology (VLSIT), 2010 Symposium on; 07/2010

  World's first monolithically integrated Thin-Film-Transistor (TFT) SRAM configuration circuits over 90nm 9 layers of Cu interconnect CMOS is successfully fabricated at 300mm LSI mass production line for 3-dimensional Field Programmable Gate Arrays (3D-FPGA). This novel technology built over the ... [more] World's first monolithically integrated Thin-Film-Transistor (TFT) SRAM configuration circuits over 90nm 9 layers of Cu interconnect CMOS is successfully fabricated at 300mm LSI mass production line for 3-dimensional Field Programmable Gate Arrays (3D-FPGA). This novel technology built over the 9^th layer of Cu metal features aggressively scaled amorphous Si TFT having 180nm transistor gate length, 20nm gate oxide, fully silicided gate, S/D, all below 400C processing essential to not impact underlying Cu interconnects. Low temperature TFT devices show excellent NTFT/PTFT transistor I_on/I_off ratios over 2000/100 respectively, operate at 3.3V, E-field scalable, and are stable for SRAM configuration circuits. We believe this 3D-TFT technology is a major breakthrough innovation to overcome the conventional CMOS device shrinking limitation.

• Efficiency enhancement and linearity trade-offs for cascode vs. common-emitter SiGe power amplifiers in WiMAX polar transmitters

  Yan Li, J. Lopez, D.Y.C. Lie, K. Chen, S. Wu, Tzu-Yi Yang

  Circuits and Systems (ISCAS), Proceedings of 2010 IEEE International Symposium on; 07/2010

  In this paper, a monolithic RF cascode SiGe power amplifier (PA) design capable of enhancing its power-added efficiency (PAE) is demonstrated. Four RF switches are adopted at the bases of the common-emitter transistors, which can be turned on/off in response to the desired output power. Simulations ... [more] In this paper, a monolithic RF cascode SiGe power amplifier (PA) design capable of enhancing its power-added efficiency (PAE) is demonstrated. Four RF switches are adopted at the bases of the common-emitter transistors, which can be turned on/off in response to the desired output power. Simulations show that by utilizing device size variation, our cascode PA achieves higher gain and PAE compared to conventional fixed-size cascode PA in the low power region; in addition, it also provides more output power and higher average PAE than single-stage common-emitter PAs. We also studied and compared the linearity performance of our cascode PAs vs. single-stage common-emitter PAs in a RF polar TX using an envelope tracking (ET) technique. We found that even through self-biasing for the common-base device can improve the output distortion of cascode PAs, a single-stage common-emitter SiGe PA designed for comparison is still considerably more linear than cascode PAs. Therefore, more careful system linearization design will be critical when the cascode PAs are adopted in RF polar transmitters (TXs), especially for broadband wireless applications such as mobile WiMAX studied here.

• Cooperative Sensing and Compression in Vehicular Sensor Networks for Urban Monitoring

  X. Yu, H. Zhao, L. Zhang, S. Wu, B. Krishnamachari, V. O. K. Li

  Communications (ICC), 2010 IEEE International Conference on; 06/2010

  A Vehicular Sensor Network (VSN) may be used for urban environment surveillance utilizing vehicle- based sensors to provide an affordable yet good coverage for the urban area. The sensors in VSN enjoy the vehicle's steady power supply and strong computational capacity not available in traditiona... [more] A Vehicular Sensor Network (VSN) may be used for urban environment surveillance utilizing vehicle- based sensors to provide an affordable yet good coverage for the urban area. The sensors in VSN enjoy the vehicle's steady power supply and strong computational capacity not available in traditional Wireless Sensor Network (WSN). However, the mobility of the vehicles results in highly dynamic and unpredictable network topology, leading to packet losses and distorted surveillance results. To resolve these problems, we propose a cooperative data sensing and compression approach with zero inter-sensor collaboration overhead based on sparse random projections. The algorithm provides excellent reconstruction accuracy for the sensed field, and by taking advantage of the spatial correlation of the data, enjoys much smaller communication traffic load compared to traditional sampling algorithms in wireless sensor networks. Real urban environment data sets are used in the experiments to test the reconstruction accuracy and energy efficiency under different vehicular mobility models. The results show that our approach is superior to the conventional sampling and interpolation strategy which propagates data in an uncompressed form, with 4-5dB gain in reconstruction quality and 21-55% savings in communication cost for the same sampling times.

• Energy Efficient Algorithms for the RFID Estimation Problem

  Tao Li, S. Wu, Shigang Chen, M. Yang

  INFOCOM, 2010 Proceedings IEEE; 04/2010

  RFID has been gaining popularity for inventory control, object tracking, and supply chain management in warehouses, retail stores, hospitals, etc. Periodically and automatically estimating the number of RFID tags deployed in a large area has many important applications in inventory management and th... [more] RFID has been gaining popularity for inventory control, object tracking, and supply chain management in warehouses, retail stores, hospitals, etc. Periodically and automatically estimating the number of RFID tags deployed in a large area has many important applications in inventory management and theft detection. The prior work focuses on designing time-efficient algorithms that can estimate tens of thousands of tags in seconds. We observe that, for a RFID reader to access tags in a large area, active tags are likely to be used. These tags are battery-powered and use their own energy for information transmission. However, recharging batteries for tens of thousands of tags is laborious. Unlike the prior work, this paper studies the RFID estimation problem from the energy angle. Our goal is to reduce the amount of energy that is consumed by the tags during the estimation procedure. We design several energy-efficient probabilistic algorithms that iteratively refine a control parameter to optimize the information carried in the transmissions from the tags, such that both the number and the size of the transmissions are minimized.
• 0.75

  Impact points

  Entropy-based robust spectrum sensing in cognitive radio

  Y. Zhang, Q. Zhang, S. Wu

  Communications, IET. 04/2010;

  Sensitivity to noise uncertainty is a fundamental limitation of current spectrum sensing strategies in detecting the presence/absence of primary users in cognitive radio (CR). Because of noise uncertainty, the performance of traditional detectors such as matched filter, energy detector and even cycl... [more] Sensitivity to noise uncertainty is a fundamental limitation of current spectrum sensing strategies in detecting the presence/absence of primary users in cognitive radio (CR). Because of noise uncertainty, the performance of traditional detectors such as matched filter, energy detector and even cyclostationary detectors deteriorates rapidly at low signal-to-noise ratio (SNR). Without accurate estimation of noise power, an absolute /SNR wall/ exists in traditional detectors below which robust detection is impossible, no matter how long the observations are. To counteract the effect of noise uncertainty in low SNR, the authors propose a blind frequency-domain entropy-based spectrum sensing scheme. The entropy of the sensed signal is estimated in the frequency domain with probability space partitioned into fixed dimensions. The authors prove that the entropy of noise is a constant and the proposed scheme is thus intrinsically robust against noise uncertainty. Monte Carlo experiments are carried out to verify the robustness and further show that the proposed scheme outperforms classical energy detector and cyclostationary detector in low SNR region with 6 and 4/dB performance improvement, respectively. In addition, the sensing time is reduced to about 75/ by the proposed scheme compared to energy detector under the same detection performance.

• A multistandard, multiband SoC with integrated BT, FM, WLAN radios and integrated power amplifier

  C.P. Lee, A. Behzad, B. Marholev, V. Magoon, I. Bhatti, D. Li, S. Bothra, A. Afsahi, D. Ojo, R. Roufoogaran, [......], S. Mak, J. Castaneda, K. Kim, Zhenhua Liu, S. Bouras, K. Chien, V. Chandrasekhar, P. Chang, E. Li, Zhimin Zhao

  Solid-State Circuits Conference Digest of Technical Papers (ISSCC), 2010 IEEE International; 03/2010

  A fully integrated SoC compliant with 802.11 a/b/g/ssn, BT, and FM standards is presented. Shared blocks include LNA, PA, crystal, bandgap, and RCAL. The WLAN, BT, and FM receivers achieve sensitivities better than -76 dBm (54 Mb/s/2.4 Ghz), -91 dBm, and 1 uV_rms, respectively.... [more] A fully integrated SoC compliant with 802.11 a/b/g/ssn, BT, and FM standards is presented. Shared blocks include LNA, PA, crystal, bandgap, and RCAL. The WLAN, BT, and FM receivers achieve sensitivities better than -76 dBm (54 Mb/s/2.4 Ghz), -91 dBm, and 1 uV_rms, respectively. The WLAN and BT transmitters achieve linear output powers of 21 dBm and 10 dBm, respectively.
• 2.07

  Impact points

  Effects of conducting layers on surface acoustic wave in AlN films on diamond

  C. C. Sung, Y. F. Chiang, R. Ro, R. Lee, S. Wu

  Journal of Applied Physics. 01/2010;

  The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the c... [more] The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band.

• A de-cresting technique for polar transmitters using Envelope-Tracking (ET) and SiGe power amplifiers for mobile-WiMAX

  Yan Li, Dongri Meng, J. Lopez, D.Y.C. Lie, K.C.J. Chen, S. Wu, Tzu-Yin Yang

  Microwaves, Communications, Antennas and Electronics Systems, 2009. COMCAS 2009. IEEE International Conference on; 12/2009

  A decresting algorithm for mobile WiMAX has been developed using time domain clipping and filtering processes for a polar transmitter (TX) using envelope-tracking (ET) and a monolithic SiGe power amplifier (PA). RF/Analog/Digital system and circuits co-design simulations have been performed for mobi... [more] A decresting algorithm for mobile WiMAX has been developed using time domain clipping and filtering processes for a polar transmitter (TX) using envelope-tracking (ET) and a monolithic SiGe power amplifier (PA). RF/Analog/Digital system and circuits co-design simulations have been performed for mobile WiMAX with 64 QAM OFDM modulation format. It is found that higher power-to-average ratio (PAR) decresting can improve the adjacent channel power ratio (ACPR) and the overall TX system efficiency, but at the cost of its EVM degradation. Our system simulations show that careful design of signal decresting can improve the overall polar TX system efficiency from 28.1% to 30.3% while the TX output can still meet the stringent WiMAX TX mask and EVM specs.
• 3.15

  Impact points

  Design of Highly Efficient Wideband RF Polar Transmitters Using the Envelope-Tracking Technique

  J. Lopez, Yan Li, J.D. Popp, D.Y.C. Lie, Chia-Chang Chuang, K. Chen, S. Wu, Tzu-Yin Yang, Gin-Kou Ma

  Solid-State Circuits, IEEE Journal of. 10/2009;

  This paper discusses the design issues of highly efficient and monolithic wideband RF polar transmitters, especially the ones that use the envelope-tracking (ET) technique. Besides first reviewing the current state-of-the-art polar transmitters in the literature, three focus topics will be discussed... [more] This paper discusses the design issues of highly efficient and monolithic wideband RF polar transmitters, especially the ones that use the envelope-tracking (ET) technique. Besides first reviewing the current state-of-the-art polar transmitters in the literature, three focus topics will be discussed: 1) the system-on-a-chip (SoC) design considerations of the monolithic polar transmitter using ET versus EER (envelope elimination and restoration); 2) the design of highly efficient envelope amplifier capable of achieving the high efficiency, current, bandwidth, accuracy and noise specifications required for wideband signals; and 3) the design of high-efficiency monolithic Si-based class E power amplifiers (PAs) suitable for ET-based RF polar transmitters. A design prototype of a polar transmitter using ET and a monolithic SiGe PA that passed the stringent low-band EDGE (Enhanced Data rates for GSM Evolution) transmit mask with 45% overall transmitter system efficiency will be given; the simulated data of the entire polar transmitter system is also compared against the measurement. Further investigations on how to solve the technical challenges to successfully implement linear and high-efficiency ET-based polar transmitter for broadband wireless applications such as WiBro/WiMAX are also discussed.