why BER is increasing with increasing SNR values?

[Usiddique]

Hi,

I have implemented very basic OFDM system to calculate BER. But BER is increasing as SNR increases.

Anyone can highlight the reason please??

 

[ChakerQ]

Hi,

When SNR increase, the noise power level decrease. So, the BER must decrease also.

For ofdm modulation, every subcarrier is a separate transmitter with modulation corresponding to the mapping choice.

For example, if you are using BPSK mapping, you must get BER function equal to 1/2*erfc(sqrt(Eb/No)).

If you have problem with code, you can post it and i see if i can help you.

Regards,

Chaker

 

[Usiddique]

Hi Chaker,

Thank you very much. I am trying to debug the code if i couldnot I do post..


Regards,
usman

 

[mejda]

Hi,

I 'm working on a DVB -T chain .the BER decreases as SNR inceases until a specific value of SNR(17-18db) onwards this limit the BER increases as SNR increases.
Anyone can explain this please??

 

[ChakerQ]

Hi Mejda,

Are you using matlab to simulate ?

It could be :
- a limited number of transmitted bits.
- your system is not stable.

Regards,

Chaker

 

[mejda]

Hi,
I m working with cocentric studio system and i simulate with matlab.In fact i have increased the number of simulated bits(from 1e7 to 1e8) to see this result!
sorry what do you mean by a non stable system?

 

[ChakerQ]

Hi,

- With SNR between 17 and 18 dB and the DVB-T communication system contain a convolutionnal code and Reed solomon code to correct errors, you are supposed to get no error with only 1e7 to 1e8 transmitted bits.
- non stable system, that is mean not correct. Try to simulate without noise and check if your system decode with 0 error.