Hi, The groups in our networking class have each built an ad-hoc wireless networks using a modified version of tunnel.py. For the next step we want them to develop routing in a multi-hop environment. In the code that we started them, we pretty much used the same transmit_ and receive_paths.
I figured the easiest way to simulate a larger-scale wireless deployment would be to decrease the TX amplitude, similar to putting an attenuator in between the antenna and the USRP. The two places that volume control is directly used are in setting the receiver gain and setting the transmitter amplifier. The receiver gain is simply set to its midpoint by default, and the amplifier is controlled by an application parameter (12000 by default). I measured packet reception rates transmitting 1000 small packets across the air, and I am not able to generate the kind of environment we need. For amplitudes above 800 or so, it's basically the case that around 950/1000 packets will be received, and then if I go much lower than that what happens is the majority of the first k packets are received and then after that another packet is never seen. K can vary as low at 10 and as high as 1000, but is typically in the 150-700 range. Something in the tracking or synchronization is going wrong, I think. Also, these problems seem to be very dependent on frequency in a strange way; if I send on 2.462G (802.11 Channel 11), I can near-zero loss rates around amplitude 500 even, but at 2.437G it's much higher. Since part of the class is enabling the students design their radios to flexibly change their behavior as a function of the environment, it's hard to design system parameters to make this an interesting task; it seems that some frequencies are just unusable. I'm using more or less the same code as tunnel.py/transmit_path.py/receive_path.py with GMSK modulation and bitrates varying between 125k, 250k, and 500k. Does anyone have suggestions as to how to fix this, and/or whether there is a better way to set up this environment? Sadly, I don't have enough lab space to e.g. actually distribute the machines around a large building. Thanks Dan _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
