Re: [Discuss-gnuradio] matched filter for BPSK produced by phase shifting

[Marcus Müller]

Hi Laur,

On 16.04.2016 18:30, Laur Joost wrote:

Hi all!

I need a clue where to start.

I have a signal that is BPSK that is modulated not by applying the filtered baseband to the in-phase component, but instead doing literal analog phase shifting.

The result is that the signal transitions between the -1 and 1 symbols not through zero, but instead along the unit circle.

Well, that's a good thing, envelope-wise :)

The transmitted baseband is RRC-filtered.

Wait, so you got

BPSK symbols (-1,+1,+1,-1...) --> RRC --> analog phase shifter?

Or how do I have to read that?
That would sound like you had two pulse shapers!

Cheers,
Marcus

My questions:

1. Is Raised Cosine even a valid Nyquist filter for such a signal? After all, the actual In-phase transition occurs not according to the RRC response, but according to the sine OF the RRC.

2. The response of such a modulator to a unit impulse is necessarily complex. From what I gather, the matched filter is then, also complex (time reversed and conjugated). How should I go about this in GnuRadio, given that the PFB Clock sync only takes real taps?

3. Or can I just take the real part of the matched filter and feed that to PFB Clock sync? The constellation will have a weird spread (see picture). Will that affect either Costas or PFB?

PS: The positioning of the constellation plots was not planned.

All the best,

Laur

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