On Thu, Jun 5, 2008 at 5:28 PM, Gregory Maxwell <[EMAIL PROTECTED]> wrote: > On Thu, Jun 5, 2008 at 3:25 PM, Steven Clark <[EMAIL PROTECTED]> wrote: > [snip] >> It should be a >> drop-in replacement for the existing demodulator in designs, except >> that the transmitted data needs to be differentially encoded (you will >> NOT, however, need a differential decoder on the receive side). > > Why? > > All the cases I can think of would be most logically implimented with > the same interface (encoded or non-encoded) on both the encoder and > decoders. > > If it's just an arbitrary decision then perhaps it should be changed > before it enters the tree and people build other radios expecting that > particular interface. >
It is not an arbitrary decision -- it is required. I do agree that it seems weird, but it is just a quirk of the way the math works out for a 2-bit differential detector that it removes a differential encoding in the process. The Simon & Wang paper explains it better than I can: "The dashed lines around the differential encoder indicate that it is present for a two-bit differential detector but absent for a one-bit differential detector at the receiver. As discussed in [16], this differential encoding operation is required for the two-bit detector in order that hard decisions made on the detector output reflect decisions on the true input data sequence and not a differentially decoded version of it as would be the case without the differential encoder at the transmitter input." If you can't get your hands on the Simon & Wang paper, let me know and I can send you a copy of it. -Steven _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
