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RE: [Discuss-gnuradio] M&M impl, its parameters, and why does it work fo
From: |
Long, Jeffrey P. |
Subject: |
RE: [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK? |
Date: |
Fri, 11 Apr 2008 12:45:38 -0400 |
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: address@hidden
[mailto:address@hidden On Behalf Of
George Nychis
Sent: Friday, April 11, 2008 12:18 PM
To: address@hidden
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
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- [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK?, George Nychis, 2008/04/11
- RE: [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK?,
Long, Jeffrey P. <=
- Re: [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK?, George Nychis, 2008/04/11
- RE: [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK?, Long, Jeffrey P., 2008/04/11
- Re: [Discuss-gnuradio] M&M impl, its parameters, and why does it work for GMSK?, Bob McGwier, 2008/04/11
- RE: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for GMSK?, Long, Jeffrey P., 2008/04/11
- Re: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for GMSK?, Bob McGwier, 2008/04/11
- RE: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for GMSK?, Long, Jeffrey P., 2008/04/11
- Re: [Discuss-gnuradio] M&M impl, its parameters, and why does itwork for GMSK?, Bob McGwier, 2008/04/11