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

[Laur Joost]

Thanks for the response, Marcus!

Analog phase modulator, is more correct I guess.

The RRC filtered signal goes into a signal generator's external modulation input, and I'm receiving the signal from the generator with USRP.

So: PRBS source (random devboard) -> RRC and DC offset (some IC) -> Phase modulation +- pi/2 (R&S SMHU signal gen) ->

-> USRP N210 -> GnuRadio -> PBKAC

is the current signal chain.

About the envelope:

Isn't "Special Case of QAM, not PM" what is usually understood as BPSK nowadays, when pulse shaping is applied? I've been looking for a relevant citation in textbooks, haven't found one...

Laur

2016-04-16 20:00 GMT+03:00 Marcus Müller <address@hidden>:

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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