Re: Clock synchronization problem of modulated signal: How to set the parameters to make the synchronization effect better?

Hi!
On 03.06.21 10:28, 能书能言 wrote:
>   I am trying to modulate an unconventional signal. Its constellation points are not as
> beautiful as QPSK or QAM.

So, what are they? This might be very relevant to synchronization aspects. Especially
important: is the average of all your symbols after source coding and channel coding still 0?


> then use "polyphase arbitrary resampler" for pulse shaping,

Unusual choice! You'd almost always want to use an interpolating FIR filter for this.

What is the pulse shape you're using? This defines which synchronization algorithms can work.

> because some constellation points are too close, the distinction is not very obvious. I
> want to know how to set the parameters to achieve a better synchronization effect?

This really depends on your constellation! You'll have to tell us more about it.

It's also an indication for why your constellation might not be a good idea, if this is
what you see at the receiver:
You're literally telling us "there's a high probability that the receiver mistakes one
symbol for another", which means that you're not making good use of the channel, i.e. the
mutual information between output and input of your channel is not as high as possible.

So, I assume you use that constellation for some other reason, some constraint that we
don't know: Often, such constraints do have influence on synchronization!
I think you'll want to tell us *why* you chose that constellation.

> In addition, I also need to add frequency offset and multipath effects later. According
> to the CMA equalizer in the "QPSK Modulation and Demodulation Tutorial",it only works on
> signals that have a constant amplitude, or modulus. What other existing ones can be easily
> removed Any method or module for frequency phase shift and multipath effect of any signal?

Well, equalization is very system-dependent; when simple statistical properties like
(e.g., constant envelope for CMA) don't work, then you need something specific to sense
your channel. We don't know enough about your system, and its motivation, to advise here.
For example, I wonder: Maybe pilot symbols are a good idea? But what about the constraints
that led to your special constellation, are they in conflict with that? Maybe FBMC or OFDM
solve the multipath problem more elegantly? ...

Best regards,
Marcus