OQPSK for IEEE 802.15.4

Hi all,

I will implement a ZigBee transceiver on Gnuradio using channels in the
2.4GHz
ISM band. I studied a bit the IEEE standart and I could observe that
ZigBee
uses DSSS channel encoding with 32 chips long random noise sequences and
an
offset QPSK modulation scheme. The offset between In-phase and
quadrature
streams is a half symbol duration. Does anybody have an idea how to
build a
phase detector and decision device for this modulation in Gnuradio?
What’s
about the costas loop for QPSK detection? Is this loop able to trigger
the
offset fast enough or should I build two phase detection loops, one for
each
stream (I & Q). After having the two streams what could be the best way
to
achieve symbol recovery? And , as last question for the moment, in
transmission mode how can I build a delay for the offset needed? DSSS is
not
a big deal and I think that I will write a block with simple mapping
tables.

I am still designing the application and some tips would be very
precious to
start implementation by the right way.
I appreciate any advise or tip and I’d like to thank all of you in
advance.

Luis

Hi Luis,

I implemented exactly that. Here is the code:

http://acert.ir.bbn.com/projects/gr-ucla/

Thomas

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