On 18.01.2011 23:37, JP234 wrote: > > Moeller: Yes I am trying to solve the near-far problem. I have used the > USRP radios to test the concept, and it works really well I am getting about > 55 - 60 dB suppression which is essentially equal to the practical dynamic > range of the ADCs for the USRP1. I would insert about 1 MHz of white > Gaussian noise at about 50 dB higher than a NBFM signal on the same > frequency band. There are still some problems with it though. I believe > for highly-nonstationary interfering signals (signals that are on and off > constantly with a short duration in between) it might not work.
The near-far problem is known for DSSS (direct sequence spread spectrum). I never heard of it in the context of NBFM. How can you reconstruct NBFM signals from below the noise floor? For on-off jammers or high-power TDMA interferers there are chances to get the weak signal in the quite moments (gated attenuation?). > However, my solution doesn't fix the problem where the ADC is completely > saturated, which according to wikipedia is the case for CDMA. Perhaps as I > continue studying, at some point I will extend my project to this level. I think you should read the appropriate literature, like Simon, Omura, Scholz "Spread Spectrum Communications Handbook" Wikipedia is not very detailed, a very good Encyklopedia, but not a substitute for a text book. > Marcus: The USRP most likely will not have enough logic cells to handle the > amount of programming I need to do =D. I have USRP1, and the 12-bit ADC is > also a limitation. It would also be more expensive for me to go with the I think it needs some other tricks than just adding a few bits of resolution. At first you should exactly define what you want. > higher USRPs because I need two receive inputs and a transmit port all > working at the same time while as for the Altera FPGA already comes with 2 > ADC inputs and 2 DACs, and it just needs an RF frontend, which would be a > nice homebrew project. ;) What's the bandwidth of the Altera ADC inputs? I guess it's not very wide. But with an open design RF frontend it would be easier to modify it, possibly with a circuit to protect it from saturation or destruction (gated attenuation for high-power or on-off jammers). _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
