Christian Sokolowski wrote: > Hi all, > > I use differential PSK with up to 4 bits per symbol. I tested transmission as > a simulation modelling the channel with AWGN noise and phase rotation. So > far, simulation works perfect (100% packets will be received correct) with > all modulation orders using Costas Loop for phase recovery and > Mueller&Mueller for clock recovery at the receiver. > > Problems occur when switching to the USRP board. I use Flex 2400 and TX and > RX > antennas are close to each other (near perfect propagation channel). In very > few cases (~5%) the receiver recovers the signal and correct packets will be > received. In most runs, no packet is received. Until now, I do not know if > the problem is due to some saturation effects (too high transmission power at > the amplifier) or if parameters of Costas Loop, Automatic Gain Control and > Mueller&Mueller clock recovery are set properly. I played with all those > parameters a lot, but without success. Can someone help? > > In general: Does Costas Loop need to be modified when differential PSK is > used? I read in the forum that the order needs to be 2 for BPSK and order 4 > used for QPSK in the block gr.costas_loop_cc(..., order)? What is the > purpose? > > If someone is interested, you can try with the following source code. I > appreciate any comments. > http://www.mobnets.rwth-aachen.de/~ade/cso/DPSK_code.zip > > the block "howto_psk_packet_sink.cc" is necessary to detect packets after > differential decoding at the receiver. One byte contains 1 to 4 bits ( which > is the symbol) depending on the modulation order. > > psk.py is extended to use 16PSK.
We have blocks that do DBPSK and DQPSK already (D8PSK sort of, but it's over-the-air operation is flaky). Check them out in gnuradio-core/src/python/gnuradio/blksimpl or you have use gnuradio-examples/python/digital/benchmark_tx.py -m [dbpsk, dqpsk] to run the transmitter. These should give you some help about the parameters used in the phase/frequency/timing sync block. Tom _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
