After coming up with some scripts to generate thousands of 200-byte random files and attempt to transfer them over a GMSK link, I isolated 5 of 10,000 'files' that cause the packet to be dropped (when the MTU is big enough to hold the entire 200 bytes- which should be all the time)- most likely due to repeated zeros or ones that cause a loss of sync. Upon debugging the output after the whitener, it does appear that there are instances of around 12-zeros in the packets that don't work.
It seems that a reasonably simple solution would be to replace or augment the whitener with an 8b/10b encoding (per Widmer/Franaszek's 5b/6b+3b/4b) which also would allow for a beginning and end of packet comma symbol for synchronization. The 8b/10b could replace the whitener completely, but I read that passing it through the whitener and then the 8b/10b yields better spectral properties/dc balance. I found dozens of Verilog/VHDL implementations by googling, but none in software. I computed some tables and was part way into making some code but am at a couple of question marks that need to be answered. 1) If I do somehow finish this (I'm not that great at Python just yet, though am very familiar with other languages- so I can definitely finish with the help of google), would this be something that would be committed to the tree (eg- do Matt/Eric/Johnathan, etc think this is the appropriate solution) 2) if (1), what is the bit and byte order over the wire for GMSK so that I can make sure I formulate the characters/packets in the right order. 3) if (1), someone more familiar could probably implement this in minutes or perhaps a couple of hours, whereas it'll take me the better part of a day or two- is anyone interested in helping me reduce the number of question marks and think through doing this correctly? Another viable option might be applying the TMDS method (XOR/XNORing) creatively to this medium. The way I read it, the clock signal is only for frequency reference so I don't see a reason why we cant use TMDS on a clock-less medium if we don't care about blanking periods, etc. Please let me know if I'm off my rocker or if I'm pointing in the right direction. I look forward to your thoughts/comments. -- View this message in context: http://www.nabble.com/8b-10b-for-GMSK-tf3169223.html#a8791437 Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
