[Discuss-gnuradio] OQPSK for IEEE 802.15.4

[Luis Simoes]

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