问题 问答题 简答题

简述什么是孤岛效应?怎么引起的?如何解决?

答案

参考答案:

(1)孤岛效应就是在无线通信系统中,因为复杂的无线环境,无线信号经过山脉、建筑物、以及大气层的发射、折射,或基站安装位置过高,以及波导效应等原因,引起在远离本小区覆盖的区域外形成一个强场区域。

(2)引起孤岛效应的主要原因有以下方面:天线挂高太高;天线方位角、下倾角设置不合理;基站发射功率太大;无线环境影响。

(3)调整方法主要有以下几个方面:调整工程参数;调整功率;优化邻区配置。

选择题
单项选择题

More than 40 million Americans between the ages of 5 and 18 attend schools throughout the United States. About 2 million school-age children are taught at home. While home schooling offers an alternative to the school environment, it has become a controversial issue.

Many public school advocates take a harsh attitude toward home schoolers, perceiving their actions as the ultimate slap in the face of public education and a damaging move for the children. Yet, as public school officials realize they stand little to gain by remaining hostile to the home-school population, the hard lines seem to be softening a bit. Some public schools have moved closer to tolerance, and,even in some cases, are seeking cooperation with home schoolers. " We are becoming relatively tolerant of home schoolers. Let’s give the kids access to public school so they’ll see it’s not as terrible as they’ve been told, and they’ll want to come back, " says John Marshall, an education official.

Perhaps, but don’t count on it, say home-school advocates. Some home schoolers oppose that public school system because they have p convictions that their approach to education—whether fueled by religious belief or the individual child’s interests and natural pace—is best. Other home schoolers contend " not so much that the schools teach heresy, but that schools teach whatever they teach inappropriately." "These parents are highly independent and strive to ’take responsibility’ for their own lives within a society that they define as bureaucratic and inefficient. " says Van Gallon.

But Howard Carol, spokesman for America’s largest teachers union, argues that home schooling parents are trying to hide their children from the real world, says Van Gallon. " Maybe we are going to run into people with problems, people that have a drug problem, people that have an alcohol problem, and teenage pregnancy. We have many problems that happen in our society and many of the children are victims. But shielding the children from the real mix of what happens every day is denying them something that they are going to need later in life. " Mr. Carol also questioned the competence of parents as teachers though he admitted that some home schoolers do better academically. " We want to make sure that a student is not denied the full range of curriculum experiences and appropriate materials, especially now with the new technology that is being introduced and the costs involved there. "

" The success of home schooling has been documented in standardized test scores administered by public school officials, " says Frank Bernet, the executive director of the National Association of College Admission Councilors. " I know why they are doing it, but I wonder why they can’t work with school officials and teachers to make the school what they want it to be. " The response from home schoolers: " We have tried that. NOW it’s time to strike out on our own. \

The author writes this passage to show that()

A. public school is becoming more and more inefficient

B. public school is still preferred by the majority

C. home schooling becomes an alternative to public schools

D. opinions differ over home schooling