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Using 2^7-1 PRBS in a transceiver testing and get 10^-12 BER. Does this make sense ?

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DoYouLinux

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Hi all,

In a work of testing an OOK transceiver, I used 2^7-1 PRBS as digital input of the transmitter and I could measure the BER of lower than 10^-12 from the receiver. Does this make sense ? I mean, the length of the PRBS is less than the length of the BER.

Thanks a lot,

DYL
 

I'm not sure why you think there is any relationship between them. To check the BER you compare the PRBS at the transmitter with the same data at the receiver, it shouldn't matter what the data is. The PRBS is used so it covers all eventualities of data but in theory you could use any pattern you like. The low BER just means it was received with very few errors.

Brian.
 

Hi Brian,

Thanks a lot for your prompt answer. I have in mind is that, for example, if we assume that the full sequence of the 2^7-1 PRBS were to be represented by a 5-bit number, say 01110. After the first 5 bits has been generated by the PRBS generator, then the same sequence will be repeated. So, it will be 01110 01110 01110 and so on. So, it will become not a PRBS anymore, given that the bits are random only in the 5 bits. However, 10^-12 BER means that we need to input the error analyzer with more than 10^-12 bits and then check the error bits. But the PRBS length is much lower than the number of bits that 10^-12 BER used. So, I am confusing about this measurement. How does it imply clearly ...

DYL
 

I don't think the PRBS will produce the same pattern repeatedly, at least not for a long time. 2^7-1 is the length of the feedback chain used to generate the sequence but each number it produces will be close to random. The BER is a measure of incorrect bits received in the sequence but to check this, the receiving end has to know the same sequence as the sending end. 10^-12 is the number of bits which do not match, the sequence itself should be random and as with all PRBS systems will eventually repeat itself but that isn't an issue, it can repeat many times within the time you are checking for errors.

Brian.
 

Hi Brian,

Thanks a lot again for your explanation. That makes sense now :)

DYL
 

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