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I am using an IQ-based digital demodulator circuit IC to receive and decode BPSK signals. It is designed for ordinary BPSK signals, which have [ 0º , 180º ]. However, the signals I am intending to receive are also binary, but the symbols are [ +60º , -60º ].

Will the demodulator work in this circumstances?

Thank you.

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  • \$\begingroup\$ BPSK always have the constellation points separated by 180°; so whatever your 120°-separated constellation is, it's not BPSK, imho. From the top of my head, there's no way to distort a signal inadvertedly so that this happens "reliably", so are you sure? Is it possible you mean "BPSK with a 60° Phase offset, ie. [60°, 240°] "?? Or do you really have a synchronous system that always produces your +-60° symbols? That sounds very unlikely, since it's terribly inefficient w.r.t. error robustness & average power, and on top of that, it's harder to implement than BPSK. \$\endgroup\$
    – Marcus Müller
    Commented Mar 5, 2017 at 21:32
  • \$\begingroup\$ Hi @MarcusMüller. Yes, I am sure. We are talking about the ARGOS system,a satellite-based system which collects, processes and disseminates environmental data from fixed and mobile platforms worldwide. These are the specs of the system. As I said, I have a IQ digital BPSK 0º/180º circuit implemented to demodulate. My question is, will it work for those signals? \$\endgroup\$
    – Filipe Taveiros
    Commented Mar 6, 2017 at 16:48

1 Answer 1

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For 0/180, if you track the carrier (RF, IF) phase, you'll only need a single-phase local-phase reference.

For +60/-60, for optimal BER you'll need inphase and quadrature, so you set up matched filters with precise phasing. Keep in mind these are not orthogonal symbols.

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  • \$\begingroup\$ Hi @analogsystemsrf, thanks for the answer. However, as I said, I have a BPSK 0º/180º IQ digital circuit implemented to demodulate. My question is, will it work for +60º/-60º signals? \$\endgroup\$
    – Filipe Taveiros
    Commented Mar 6, 2017 at 16:49
  • \$\begingroup\$ What does "work" require? As Marcus Mueller explains, +-60 is not optimal for Bit Error Rate. But with high SNR, you may succeed. If your symbol decoder requires orthogonal symbols, expect trouble. If sloppy symbols, with sloppy constellation and lots of ISI, are OK, you may succeed. \$\endgroup\$
    – analogsystemsrf
    Commented Mar 14, 2017 at 3:18

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