如何使用RSSI改进蓝牙测距? [英] How to improve Bluetooth distance measuring using RSSI?

问题描述

对于我的项目，我需要估计智能手机和蓝牙模块之间的距离.估算不必很精确.我只需要确定误差为50cm的距离即可.

我确实以10厘米的距离步长测试了两个蓝牙模块的RSSI.我对每个步骤测量了5次RSSI，并获得了5次测量的平均值.平均值显示在下图中:

红色和蓝色线条类似于两个蓝牙模块.您可以看到结果不是很线性.造成这种情况的原因之一是干扰，因此我寻找了解决干扰问题的方法.我发现了两种方法:

• 信号噪声比(SNR):了解ibeacon距离

iBeacon信号强度(rssi)与已校准的发射机功率(txPower)的比率. txPower是在距1 meter远的rssi中的已知测量信号强度:解决方案

您正在遇到此技术的实际限制.在理想的条件下，短距离(2米以下)而不是10米以上的长距离，可能达到+/- 50 cm的估计精度.

我在此处写了一篇有关限制的更长的博客文章: http://developer.radiusnetworks.com/2014/12/04/fundamentals-of-beacon-ranging.html

要回答您的特定问题:

1. 否，没有实用的方法来知道单个RSSI测量的哪一部分来自信号以及哪一部分来自噪声.您可以对许多样本取平均值，如果发射机和接收机在样本间隔内保持静止，则可以部分消除噪声.

2. 您询问的技术确实可以为您提供距离估计，但是它们具有上述技术的局限性.

For my project I need to estimate the distance between a Smartphone and a bluetooth module. The Estimation doesn't have to be very precise. I only need to determine the distance with a margin of error of about 50cm.

I did test the RSSI of two bluetooth modules at distance-steps of 10 cm. I measured the RSSI 5 times for each step and got the average of the 5 measurements. The averages are shown in the graph below:

The red and blue lines resemble the two Bluetooth modules. You can see that the results are not very linear. One of the reasons for this is interference, so i searched for ways to tackle the interference issue. Two ways i found are:

• Signal Noise Ratio(SNR): Understanding ibeacon distancing

• ratio of the iBeacon signal strength (rssi) over the calibrated transmitter power (txPower). The txPower is the known measured signal strength in rssi at 1 meter away: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Signal-to-noise_ratio.html

However i don't really understand how the above techniques would be used to get more accuracy. For SNR i need the Noise value, how do i even get the Noise value?

For ratio rssi/txPower, I can get the txPower by simply measuring the rssi at 1 meter from the module. So I know all the needed values. But I don't know what to do from here on out. How do i use these values to get a more accurate distance estimations?

Are there any other techniques i can use to improve accuracy?

解决方案

You are running into the practical limitations on this technology. Getting estimation accuracy of +/- 50 cm may be possible under ideal conditions at short distances (under 2 meters) not at long distances of over 10 meters.

I wrote a longer blog post about the limits here: http://developer.radiusnetworks.com/2014/12/04/fundamentals-of-beacon-ranging.html

To answer your specific questions:

1. No, there is no practical way to know what part of a single RSSI measurement comes from signal and what part comes from noise. You can take an average over many samples, which partially removes noise if the transmitter and receiver are stationary over the sample interval.

2. The techniques you ask about do work to give you distance estimate, but they have the limitations of the technology described above.

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