A Digital Predistortion Scheme Exploiting Degrees-of-Freedom for Massive MIMO Systems

The primary source of nonlinear distortion in wireless transmitters is the power amplifier (PA). Conventional digital predistortion (DPD) schemes use high-order polynomials to accurately approximate and compensate for the nonlinearity of the PA. This is not practical for scaling to tens or hundreds of PAs in massive multiple-input multiple-output (MIMO) systems. There is more than one candidate precoding matrix in a massive MIMO system because of the excess degrees-of-freedom (DoFs), and each precoding matrix requires a different DPD polynomial order to compensate for the PA nonlinearity. This paper proposes a low-order DPD method achieved by exploiting massive DoFs of next-generation front ends. We propose a novel indirect learning structure which adapts the channel and PA distortion iteratively by cascading adaptive zero forcing precoding and DPD. Our solution uses a 3rd order polynomial to achieve the same performance as the conventional DPD using an 11th order polynomial for a 100x10 massive MIMO configuration. Experimental results show a 70% reduction in computational complexity, enabling ultra-low latency communications.Comment: IEEE International Conference on Communications 201

Erosion-induced CO2 flux of small watersheds

Soil erosion not only results in severe ecological damage, but also interferes with soil organic carbon formation and decomposition, influencing the global green-house effect. However, there is controversy as to whether a typical small watershed presumed as the basic unit of sediment yield acts as a CO2 sink or source. This paper proposes a discriminant equation for the direction of CO2 flux in small watersheds, basing on the concept of Sediment Delivery Ratio (SDR). Using this equation, watersheds can be classified as Sink Watersheds, Source Watersheds, or Transition Watersheds, noting that small watersheds can act either as a CO2 sink or as a CO2 source. A mathematical model for calculating the two discriminant coefficients in the equation is set up to analyze the conditions under which each type of watershed would occur. After assigning the model parameter values at three levels (low, medium, and high), and considering 486 scenarios in total, the influences are examined for turnover rate of the carbon pool, erosion rate, deposition rate, cultivation depth and period. The effect of adopting conservation measures like residue return, contour farming, terracing, and conservation tillage is also analyzed. The results show that Sink Watersheds are more likely to result in conditions of high erosion rate, long cultivation period, high deposition rate, fast carbon pool turnover rate, and small depth of cultivation; otherwise, Source Watersheds would possibly occur. The results also indicate that residue return and conservation tillage are beneficial for CO2 sequestration. (C) 2012 Elsevier B.V. All rights reserved.Geography, PhysicalGeosciences, MultidisciplinarySCI(E)EI0ARTICLE101-11094-9

Emigration from China in Comparative Perspective

Comparative research on international migration has increasingly focused on immigrant integration rather than the process of emigration. By investigating the different streams of Chinese migration to the United States and Europe, as well as the different stages of Chinese migration to the United States, this study examines the way in which both receiving and sending contexts combine to shape the process of emigration. Using data from a 2002–2003 survey of emigration from China's Fujian Province, we demonstrate that under restrictive exit and entry policies and high barriers to migration (i.e., clandestine migration from Fuzhou to the United States), resources such as migrant social capital, political capital (cadre resources), and human capital all play a crucial role in the emigration process. However, the roles of these resources in the migration process are limited when migration barriers are sufficiently low and when local governments adopt proactive policies promoting emigration (i.e., legal migration from Mingxi to Europe). Comparisons over time suggest that the importance of migrant social capital, political capital, and human capital has strongly persisted for Fuzhou-US emigration, as a result of tightening exit and entry policies. Despite these marked differences between Fuzhou and Mingxi emigration, the results also point to two general processes that are highly consistent across settings and over time—the cumulative causation of migration and the advantage conferred by traditional positional power (cadre status)