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. --------------------------------------------------------------------- Christian Sokolowski Office: +49(0)-240-7575-7043 RWTH Aachen FAX: +49(0)-240-7575-7050 Wireless Networks Dept Kackertstrasse 9 E-mail: [EMAIL PROTECTED] D-52072 Aachen Web: http://www.mobnets.rwth-aachen.de --------------------------------------------------------------------- _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
