I could be wrong but I believe that block can work with a complex input or a real input. For the case of GMSK/MSK it should work on a real signal derived from the change in phase of the IQ(use gr_quadrature_demod_cf) not the IQ itself as is the case in regular QPSK. I believe the GMSK demo shows this. Filtering should not really matter in either case. If you want to recover OQPSK you might need to destagger the IQ stream for M&M to work, right?? MSK is really just OQPSK with sine pulse shaping in the IQ domain but since it is really a special case of FSK you can recover using FM detector or differential phase techniques.
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of George Nychis Sent: Friday, April 11, 2008 12:18 PM To: [email protected] Cc: Thomas Schmid Subject: [Discuss-gnuradio] M&M impl, its parameters,and why does it work for GMSK? Hi all, I've attempted to follow the M&M optimization algorithm paper, which GNU Radio implements, to try and select proper parameters for a O-QPSK / MSK implementation floating around that a UCLA group wrote: http://acert.ir.bbn.com/projects/gr-ucla/ I ask because it seems as though the PHY is not recovering from clock drift properly, which would be the goal of the M&M block. The blue in this graph is not important, but note the smearing on the right: http://cyprus.cmcl.cs.cmu.edu/tmp/graphs/zigbee_sample_dump9_unit_circl e_19v20.jpg That smearing is not recovered from properly by M&M and causes loss, as an example. This causes approximately anywhere from 5-15% frame loss over _coax_. So I was pointed to the M&M paper, to try and understand why its recovery is not working properly, looking to set proper parameters. The paper is here: http://ieeexplore.ieee.org/iel1/2220/8932/00392689.pdf But, if you read the first paragraph, it states that this algorithm is NOT for MSK, or GMSK for that matter: "We are assuming a system whose output comprises nom- inally synchronised data symbols subject to additive white Gaus- sian noise, where the transmitter and the receiver use Nyquist root raised-cosine filters." So, before I go any further... I was hoping someone could shed light on how this ends up working out for GMSK which does not use an RRC filter. Then, why would it not work with the MSK implementation? ;) I understand that GMSK is band-limited by the Gaussian filter, is this the significant difference? I suppose the overall question is the implications of using a CPM signal when the GR clock recovery block was written using an RRC filter. Thanks! George _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
