On 09/12/2014 10:50 AM, Malcolm Robb wrote: > Salvatore, > I have tried that, and it doesn't work very well whilst sampling at 2 Mhz > because the bit rate is also 2 Mhz. You can't even reliably correct for phase > based on the pre-amble, because it's 10100001010000. If you're spot on in > phase, the 0's are analogue values ranging from 0 to limit, and the 1's are > limit to +127. Limit depends on the signal strength, and is usually set to > around 1/3rd average peak amplitude. If you happen to be exactly 90 degrees > out in the sampling, the 1''s smear equally across two adjacent sample > periods, so you get 11110001111000, where the 1's are half the true peak > amplitude. If you sample exactly in phase then you get good signal level > difference between the 0's and 1's. As the phase drifts the difference > between a 1 and a 0 drops. Since you have to have a level detector somewhere > to decide between a 0 and 1, at some point/phase the difference between a 0 > and a 1 becomes indistinguishable. The stronger the signal, then the further > off phase you can recover it, but there will always be a proportion of > signals that cannot be - and I estimate that to be 30% at my location. > > Correct me if I'm wrong, but usually you recover the phase (e.g. by comparing against the pre-amble) and then you turn I/Q so that information is only e.g in I. That's one (complex) multiplication.
Regards, Alexander
