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设计wifi热点的时候需要进行什么计算吗？

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设计wifi热点的时候需要进行什么计算吗？

因此可能会有墙壁、需要更大的天线等。在为 wifi 热点选择合适的天线/无线网卡之前，我可以进行哪些计算？或者整个“设计 wifi 热点”只是一个近似的猜测？是否有任何物理计算？[这样我就可以购买一根刚好适合这项工作的天线]

答案1

来源：http://www.tp-link.com/en/support/calculator/

无线电信号的大部分功率都会在空气中损失。即使在完全真空中，无线电波也会损失部分能量，因为总有一部分能量会辐射到链路轴以外的方向。自由空间路径损耗 (FSPL) 测量的是自由空间中没有任何障碍物的功率损耗。因此，对于最终用户来说，了解发射器和接收器之间的大致距离非常重要，同时要保持不同数据传输速率下的一定链路质量。

FSPL depends on two parameters: First is the frequency of radio signals；Second is the wireless transmission distance. The following formula can reflect the relationship between them.

FSPL (dB) = 20log10(d) + 20log10(f) + K

d = distance
f = frequency
K= constant that depends on the units used for d and f
If d is measured in kilometers, f in MHz, the formula is:

FSPL (dB) = 20log10(d)+ 20log10(f) + 32.44

From the Fade Margin equation, Free Space Path Loss can be computed with the following equation.

Free Space Path Loss=Tx Power-Tx Cable Loss+Tx Antenna Gain+Rx Antenna Gain - Rx Cable Loss - Rx Sensitivity - Fade Margin

With the above two Free Space Path Loss equations, we can find out the Distance in km.

Distance (km) = 10(Free Space Path Loss – 32.44 – 20log10(f))/20

The Fresnel Zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. You want a clear line of sight to maintain strength, especially for 2.4GHz wireless systems. This is because 2.4GHz waves are absorbed by water, like the water found in trees. The rule of thumb is that 60% of Fresnel Zone must be clear of obstacles. Typically, 20% Fresnel Zone blockage introduces little signal loss to the link. Beyond 40% blockage the signal loss will become significant.

FSPLr=17.32*√(d/4f)

d = distance [km]
f = frequency [GHz]
r = radius [m]

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