"Oli Filth" <[email protected]> wrote in message
news:LrAOf.27232$[email protected]..
> Davy said the following on 05/03/2006 11:55:
>> Hi all,
>> I have build a simulation system to test my Error Correcting Code.
>> And now I add modulation/demodulation module.
>>
>> When I apply BPSK and QPSK to system, I found their BER versus SNR
>> curve almost identical, is it right in theory?
>>
>> My code rate is 0.9, code length >10000.
>>
>> BTW, I found BPSK and QPSK have identical uncoded BER versus SNR curve,
>> is above similar?
>>
>
> QPSK can be regarded as a pair of orthogonal BPSK systems, i.e. the real
> component is one BPSK system, the imaginary component is the second BPSK
> system. Because they are orthogonal, they don't interfere (to a good
> approximation), hence the BER curves are largely equivalent.
>
If you plot Eb/No vs probability of bit error.

But you expect to see same PeBit for QPSK when the SNR is 3.01 dB higher
than for BPSK because, at the same symbol rate, they occupy the same
bandwidth and the signal energy needs to be twice as big for QPSK to have
the same energy per bit as BPSK.

Best of luck - Mike