BER Tester V/s Standard PRBS Generator

[Sushank Chaudhary]

Hi,

I want to know what is the difference between BER Tester and standard PRBS Generator in the Optisystem. I am using OFDM modulation with 4 level QAM. I want to plot the graph of BER v/s SNR. For this i have inserted BER Tester in the layout but now the constellation, SNR are changed for the same data rate as measured with standard PRBS Generator ? May i know what is the reason for this ??

[Ahmad Mustafa]

Hi Shushank,

BERT is an analyzer tool where you can see the result of your digital output from a Photodiode. It could be Q factor, BER value or an Eye Diagram etc. A PRBS generator on the other side is a digital data source and you can not use it as a measurement tool.

Please read the User Manual and Component Instructions manual to read more about the functionality of PRBS Generator and BERT.

Does it help?

Cheers,
Ahmad

[Sushank Chaudhary]

Hi Ahmed,

BER tester can not measured the Q factor or digital output etc. Furthermore, PRBS generator is used for generation of randomly defined data which is not possible with BER tester. BER tester is used for only transmission of fixed sequence of data. BER tester is used for measuring the BER by sending known sequence of data through system and compared the received binary signal with the applied input binary sequence signal.

[Damian Marek]

Here is a little more information on the BER Test Set:

In the BER test set we provide multiple binary sequence generation options: a PRBS generator, User Defined sequence generation, or external Sequence. The PRBS and User Defined sequence generators are exact copies of the PRBS and User Defined sequence components respectively. HOWEVER, the default values for the number leading and trailing zeros is not the same. The PRBS generator inside the BER test set takes its number of leading and trailing zeros from the layout parameters and has default values of 0. The PRBS component defines the leading and trailing zeros within its own component and has default values of “(Time window * 3 / 100 ) * Bit rate”. This can make a big difference. Try setting them the same for a better comparison.

[Sushank Chaudhary]

Hi Damian, Thanks for your reply. I already tried that one. I put the leading and trailing zero inside the Bit error Test set under the script having formula “(Time window * 3 / 100 ) * Bit rate”. Then i compared it with standard PRBS generator with same data rate and measured the signal by using signal analyzer component. The binary signal generated by PRBS is random in nature, means if we simulate again it generate bits in different order but Bit error test component generate the same bits every time when it simulates. Also why the result are changes like constellation when using BER error test set instead of standard PRBS generator. With standard PRBS generator the result are showing 4 quadrants but with Bit error test set, the results are showing 9 quadrants. Any reason why ??

Attachments:

1. 

   with-bit-error-test-set.png
   

2. 

   With-standard-PRBS4.png
   

[Damian Marek]

Hi Sushank,

Thanks for pointing out this bug! The BER Test Set was not generating a new random seed for each calculation. It has been fixed and will be available in OptiSystem 13.0. For now, if you need to generate a random seed each calculation, you can set the BER Test Set, to choose “external component” and connect a PRBS component to it.

As for your other questions, can you please try sending an OptiSystem project file it will help us to understand. I can’t see your attached .bmp pictures either. Can you try .png or .jpeg?

Thanks

[Sushank Chaudhary]

Hi Damian, Thanks for your suggestion. I don’t find any option in BER tester regarding connecting external PRBS Generator ? Can you tell what is the procedure for that ? Also, why in M-ary modulation, when you are using high sequence length (For example-65536 as in case OFDM sample) OptiSystem is not capable for measuring the bit error rate ?

[Tech Support]

I’ve converted your files to PNG and reattached. Apparently, we need to fix some issues with attaching bitmaps.

[Sushank Chaudhary]

Thanks, Tech support 🙂

[Author]

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