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What is the appropriate procedure to be followed to examine the efficiency or to identify limitations of the FEC algorithm, which is currently implemented in the Unet audio?

I wanted to analyze how efficiently the current FEC algorithm in the Unet audio works, specifically how many bits of errors it can correct and what its limitations are.

For that, I have tried to use BER (Bit Error Rate) as a metric to check the performance of FEC under various situations using the count of errors in the received data from the BER value.

I have used two laptops for this experiment as there is a very minimal probability of getting errors using a single laptop. I was able to observe the errors in the received data (using BER) when phy[].fec was set to zero, and when I turned on the FEC, it resolved all those errors (BER = 0/144). Then, I introduced some ambient noise by playing music while transmitting data so that it would interfere with the actual data and add some noise to it, simulating a realistic underwater scenario. This resulted in a lot of errors in the received data even after applying FEC.

Here are the screenshots of the two Unet audio shells used for data transmission. In this case, a standard test frame is transmitted to compute the BER for the frame (phy[].test is set to true):

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The first TxFrameReq is sent without any noise, and the later one is sent in the presence of some noise.

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As depicted in the images above, when some noise is added during data transmission, errors occur in the received message, and data is corrupted even though the FEC is set on.

So, I would like to know if the above method is an appropriate and justified one to analyze the efficiency and get the limitations of the FEC in the Unet audio. If otherwise, it would be really helpful if you could suggest a method to do the same.

Andrej Istomin
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Poojitha Surla
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1 Answers1

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What you have done is to enable test mode and disable FEC to measure BER without error correction. Then to enable FEC and check that the BER goes to 0. That is a reasonable way to check FEC performance if you can control the your environment well (so that the error distribution is stationary).

An alternative approach is to use the FECDecodeReq to pass in simulated received bits with controlled bit errors, and check if the FEC is able to recover it. To do this, you'll need to capture a frame encoded with a FEC, but decoded without FEC (but with frameLength set up to capture the received code word fully), with a high enough SNR that there are no errors. Then you can set up FEC and pass those bits in using FECDecodeReq, and it should generate a RxFrameReq for you. You can pass in bits with some errors, and it should correct those for you, yielding 0 BER for the RxFrameReq when error correction works.

Mandar Chitre
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  • Is there any other metric (like BER) that could be used for estimating the FEC performance in Unetstack? – Poojitha Surla Feb 24 '23 at 13:53
  • I am unclear as to what you want the metric to measure. – Mandar Chitre Feb 25 '23 at 17:43
  • BER, for example, tells us the total number of errors that still exist after forward error correction, giving us an insight into the performance of the FEC used there. Similarly, are there any other parameters in Unetstack that are often used to assess how any FEC is working? – Poojitha Surla Mar 06 '23 at 04:51
  • If fec works to correct errors, UnetStack gives you an RxFrameNtf and reports how many errors were there before correcting. If it fails to correct, CRC check fails and you get a BadFrameNtf instead. You can you these to estimate FEC performance. – Mandar Chitre Mar 07 '23 at 05:26