On 08/09/2011 11:12 PM, shantharam balasubramanian wrote: > Hello Tom, Marcus and Martin, > > Thanks a lot for your replies. One of the objective of our experiment > is find to the capacity of a path, i.e, we want to transmit a random > binary sequence between two USRP nodes. We want to find the maximum > data transfer rate (in bit/sec) with a "small" bit error rate / > probability of error. > Tom said, "The way things are in our benchmark code, a single bit > error means that an entire packet is lost." Based on this statement, I > have the following questions: > > 1. From Tom's reply, it seems like the benchmark_Rx and benchmark_Tx > programs already have error correction coding blocks in themselves. > Therefore, it is hard for us to calculate the bit error rate and find > the capacity of the path. Is there any program in gnuradio repository > that does not employ error correction codes? > The benchmark stuff doesn't, as far as I know, have FEC in it.
> 2. In our experiments, we have received packets that has some bit > error rate (e.g. 15% bit error rate, 20% bit error rate, etc.). If a > single bit error means that an entire packet is lost, do you know why > that phenomenon occurs? (i.e. some packets get lost but some other > packets have small erroneous bits) > > Your feedback will be very appreciated. > > Thanks > > > I think Tom was referring to single-bit errors in the so-called "access code" at the beginning of the frame. If there are bit errors there, then the frame is necessarily discarded, since it's not *recognized* as a valid frame. But apart from that, if the frame sequence is valid, then the packet is "recognized", and punted up through the RX packet callback mechanism, which means there could still be bit errors in the payload section of the packet. In the "real world" this would still cause the packet to be discarded entirely, because the FCS (CRC-32, usually) at the end of the packet wouldn't validate, and somewhere between the PHY and MAC layer, it would get discarded. This is all from my having spent 10 minutes looking at the code--I don't have as deep an understanding of it as Tom. -- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
