Hi Eric, The Tx_gain set is set to 15 dB by default. I tried with 5 dB and 30 dB, varied it in the full range. The Tx_amplitude is set to 0.5 by default. I varied it from 0.1 to 1.
I saw the received spectrum using "usrp2_fft.py" and there is substantial separation between noise floor and PSD peak, yet benchmark_rx fails to receive any packet for rates < 250 kbps at 5 GHz. Thanks for answering the other questions, it did help understanding USRP2 better. Also, how to perform benchmark_rx/tx in BERT mode ( from digital-bert folder) ? looks like the scripts are written for USRP1. I was under the impression that 3.2 ver. supports USRP2 fully. How to modify them to make it work on USRP2 ? Srinivas Graduate Student, WINLAB, Rutgers University, NJ On Thu, Jul 16, 2009 at 6:00 PM, Eric Blossom <e...@comsec.com> wrote: > On Thu, Jul 16, 2009 at 03:30:26PM -0400, Srinivas wrote: > > Hi All: > > > > I am new to GNU Radio and I am experiencing a few anomalies. My > experimental > > setup is as follows: > > > > - I am using USPR2 with GNU Radio ver. 3.2 installed on an Intel 64-bit > Quad > > Core machine with GigEthernet. > > - I am using XCVR2450 daughter card and the latest firmware on the > USRP2s. > > - I am running benchmark_rx.py and benchmark_tx.py using two USPR2s. > > - I have wired the two USRPs using a 60 dB attenuator. > > > > My Observations: > > - The maximum bit rate I could achieve was 12.5 Mbps corresponding to > > samples/symbol = 2 and interpolation and decimation factor set to 4 > > - The minimum bit rate I could see was 120 Kbps in the 2.4GHz band and > 250 > > Kbps on the 5GHz band. > > The bit rates should not vary depending on the frequency. The > appropriate gain required to achieve a given bit rate may be dependent on > frequency band on the XCVR2450 (2.4 vs 5 GHz). > > > > I have the following questions: > > > > 1. What is the minimum and maximum bit rates that USPR2 can support ? > > Not to be glib, but the correct answer is "it depends". > It depends on at least: > > * modulation > * any additional s/w decimation/decimation that you add. > * system h/w configuration (cpu, cache, power saving mode, memory > bandwidth..., other things on the bus, other things on the > ethernet, the particular peripherals in your pc, ...) > * system o/s configuration > * are you using gr.enable_realtime() ? > > > > My immediate guess for minimum bitrate is that it depends on the ADC/DAC > > sampling rates, samples/symbol and interpolation and decimation factor. > So > > with least interpolation (4) and least Samples/Sym (2), the calculations > > give 12.5 Mbps (for GMSK - 1bit/sample/Hz). > > The maximum bit rate is limited by the host processor; whether it can > churn > > out as many packets as the USPR2 wants in a second. > > > > Is my analysis correct ? > > Uhh, if you want the minimum bit rate, you'd want the maximum > interpolation (that is, the minimum bandwidth of the complex baseband). > > > 2. Why does the minimum bit rate depend on the carrier frequency ? > > It shouldn't. > > > I tried changing the Tx amplitude and Tx gain at 5G but it still didn't > > change anything. > > By "didn't change anything" do you mean that when you measured the > output with a spectrum analyzer or o'scope, there was no change? If > so, what values were you passing to the set_gain method? Are they > within the values returned by gain_range() and/or gain_min(), > gain_max()? > > > > 3. How to perform benchmark_rx/tx in BERT mode ( from digital-bert > folder) ? > > Looks like the scripts are written for USRP1. How to modify them to make > it > > work on USRP2 ? > > > > Can anyone please help me resolve these issues ? > > Did this help? ;-) > > > Thanks, > > Srinivas > > Graduate Student, > > WINLAB, Rutgers University, NJ > > Eric >
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