问题 问答题 简答题

LTE中的物理资源特点及分配方式是什么?

答案

参考答案:

LTE下行采用正交频分复用(OFDM)调制,上行采用单载波频分多址(SC—FDMA)调制,可以提供比2G、3G更灵活的资源分配方式。LTE定义频域上连续12个子载波(频域占180KHz)和时域上一个时隙(0.5ms)构成的时频资源为一个资源块(RB,Resource Block)。时域上两个连续的RB构成一个RB对(RB pair),RB对是LTE系统资源调度的最小单位。LTE物理资源的特点是,资源颗粒度小,可灵活配臵,调度周期短。

LTE系统有两种资源分配方式:一种是集中式的资源分配;一种是分布式的资源分配。集中式资源分配,可以通过选择一段较优的连续资源分配给用户,获得频域上的调度增益,多个用户各自选择自己较优的频段传输,也能获得多用户分集增益。分布式资源分配,用户的资源均匀分配在整个带宽上,能够避免用户的所有数据传输都经历深度衰落等,可以获得频率分集的增益。LTE下行传输既支持集中式资源分配,也支持分布式资源分配,上行传输只支持集中式的资源分配。

阅读理解

任务型读写

     Chinese parents are being urged to pay more attention to their children's nutrition, after a study

revealed that unscientific ways of feeding babies and a lack of trace elements are the two biggest threats

to youngsters'health. Experts drew these conclusions from a two year study into the nutrition and health

situation of children under six in ten cities including Beijing, Shanghai and Guangzhou. 

     Started in 2003 by the China National Children's Center, the survey includes 8043 children, equally

divided between the sexes. It shows 37 percent of surveyed children have baby food earlier than the

recommended age of four to six months old, with another 35percent taking it later, which in return brings

about a nutrition difference as these children grow up.  "Our children above four to six months old fall

behind foreign children in terms of their physical well?being," said Zhao Shunyi, head of the center.  She

called on Chinese parents to pay more attention to their children's nutrition after they stop breast feeding

at six months old.      

     Trace elements

     The survey also shows more than half of the children above six months old are deficient in five trace

elements which are crucial to their physical development-magnesium, copper, calcium, iron and zinc. 

"Lack of zinc will lead to low level of intelligence," said Dou Xiaowei, vice director of the National Center

for Child Nutrition Quality Supervision and Testing. "Parents had better choose baby food with plentiful

trace elements, especially calcium, iron and zinc."

     Zhao said, "The center is urging the government to strengthen child food production management by

revising related  laws.  Child food producers should be advised to market products with rich trace

elements."  

 

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