如何计算以 dB 为单位的接收信号强度 (RSS) 和路径损耗误差？答案

【问题标题】：How to calculate Received Signal Strength (RSS) and path loss Error in dB?如何计算以 dB 为单位的接收信号强度 (RSS) 和路径损耗误差？
【发布时间】：2019-01-30 10:58:25
【问题描述】：

假设测量RSS为“-70dBm”，预测RSS为“-68dBm，天线发射功率为” -12dBm”，

那么如果下面的等式是正确的？如果不是，如何计算？

错误 = |10 * log10 (70/12) - 10 * log10 (68/12)| = 10 * log10 (70/68)

现在我的测量值是 RSS in dBm，如何将其转换为 dB？

【问题讨论】：

感谢编辑。这里是RSS和RSSI的区别[dinomycle.blogspot.com/2011/04/…
不幸的是，“RSS”可能意味着很多东西。您已使用 RSS -tag 标记了您的问题（关于真正简单的聚合的问题）。您的问题可能会更好地标记为“无线”。那么这些领域的专家可以更好地找到您的问题。
@janih 非常感谢。这里的RSS是Wi-Fi的接收信号强度。

标签： networking rss communication wireless

【解决方案1】：

根据我的经验，这经常使人们感到困惑，因此需要进行彻底的解释。

“dBm”中的“m”表示相对于 1 毫瓦。它通常用于绝对测量，而“常规”dB 通常用于功率增益/损耗/差异。

Example:
in/tx   out/rx
1w      .5w

(1 milliwatt = 0.001)
10log(1/0.001) = 30dBm
10log(0.5/0.0001) = 27dBm
loss = 3dB


10log(1) = 0dB
10log(0.5) = 3dB
loss still is 3dB
(note there is an implied /1w here since the argument to log must be unit-less, e.g. 0.5w/1w = 0.5 "flat" (aka no units))

So in the context of power differences, the m does not matter.

Things to note:
1/2 of power lost == -3dB gain (or +3dB loss)
power gains/losses in series are added/subtracted when in dBs -vs- multipled/divided when in watts
0 watts == -infinity dB
0 dBm == 1 milliwatt
log here is base 10 (not 2 nor e)
reletiveGainOrLoss = 10^(valueOfGainOrLossInDb/10)
valueOfPowerInMilliwatts = 10^(valueOfPowerInDbm/10)


In your example, I'll presume by error you mean the error of the predicted loss relative measured loss:
predicted loss =
known transmission power - predicted RSS =
-12dBm - -68dBm = 
56dB

measured loss =
known transmission power - measured RSS =
-12dBm - -70dBm = 
58dB

error of predicted loss relative to measured loss =
|predicted loss - measured loss| = 
|56dB - 58dB| =
2dB (==2dBms, but for diffs we should drop the m) = 

Or more directly: 70 - 68 (so easy with dBs!)

This equates to a 63% error (or 58, depending on how it is done):
10^(-2dB/10) =
0.63
(10^(2dB/10) =
1.584893192461113

In millwatts:
10^(valueInDbm/10) =
10^(-70/10) = 0.0000001 milliwatts
10^(-68/10) = 0.000000158489319 milliwatts
10^(-12/10) = 0.063095734448019 milliwatts

As a sanity check:
(0.0000001/0.063095734448019 - 0.000000158489319/0.063095734448019) / (0.0000001/0.063095734448019) =
(0.000001584893192 - 0.000002511886428) / 0.000001584893192 = 
-0.000000926993236 / 0.000001584893192 =
-0.584893190707832
(note that doing it in watts is much more laborious! (not to even mention float errors))

回答您的其他问题：

Error = |10 * log10 (70/12) - 10 * log10 (68/12)| = 10 * log10 (70/68)

第一个等式是无意义的；如上所述：对于 dB，我们加/减 -vs- 乘/除。然而，第二个等式是正确的，基于日志规则之一：

log a + log b = log ab

【讨论】：

【解决方案2】：

当RSS在dBm时，路径损耗等于发送RSS和接收RSS之间的差，在这种情况下，路径损耗的单位是dB。

【讨论】：