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.

--
Oli