Browsing by Author "Wang, Cheng"
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Item High rate space-frequency codes for MIMO-OFDM systems(University of Delaware, 2010) Wang, ChengIn the recent years, multiple-input multiple-out (MIMO) technology has attracted lots of attention because it significantly increases the data throughput (mul- tiplexing gain) and link reliability (diversity gain) without additional bandwidth or transmission power. Orthogonal frequency division multiplexing (OFDM) technology has been developed into a popular scheme for wideband digital communications since it is an efficient and effective techniques to deal with frequency-selective fading as well as achieving high speed data transmissions. The combination of the MIMO and OFDM, i.e. MIMO-OFDM system, has been widely recognized as the next generation broadband wireless system. In order to achieve both spatial and frequency diversities in MIMO-OFDM system, space-frequency (SF) codes have been proposed in the literature. In this thesis, we first look into the development of SF codes and various methods to achieve full diversity. Then we briefly describe the full-diversity layered space-time codes and propose an idea of high-rate full diversity space-frequency codes for a multiuser MIMO-OFDM system.Item An invisible soil acidification: Critical role of soil carbonate and its impact on heavy metal bioavailability(Nature Publishing Group, 2015-07-31) Wang, Cheng; Li, Wei; Yang, Zhongfang; Chen, Yang; Shao, Wenjing; Ji, Junfeng; Cheng Wang, Wei Li, Zhongfang Yang, Yang Chen, Wenjing Shao & Junfeng Ji; Li, WeiIt is well known that carbonates inhibit heavy metals transferring from soil to plants, yet the mechanism is poorly understood. Based on the Yangtze River delta area, we investigated bioaccumulation of Ni and Cd in winter wheat as affected by the presence of carbonates in soil. This study aimed to determine the mechanism through which soil carbonates restrict transport and plant uptake of heavy metals in the wheat cropping system. The results indicate that soil carbonates critically influenced heavy metal transfer from soil to plants and presented a tipping point. Wheat grains harvested from carbonates-depleted (due to severe leaching) soils showed Ni and Cd concentrations 2–3 times higher than those of the wheat grains from carbonates-containing soils. Correspondingly, the incidence of Ni or Cd contamination in the wheat grain samples increased by about three times. With the carbonate concentration >1% in soil, uptake and bioaccumulation of Ni and Cd by winter wheat was independent with the soil pH and carbonate content. The findings suggest that soil carbonates play a critical role in heavy metal transfer from soil to plants, implying that monitoring soil carbonate may be necessary in addition to soil pH for the evaluating soil quality and food safety.