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Re: [Discuss-gnuradio] Benchmark scripts

From: Nick Foster
Subject: Re: [Discuss-gnuradio] Benchmark scripts
Date: Mon, 10 Jan 2011 13:16:04 -0800

On Mon, 2011-01-10 at 15:55 -0500, Thomas H Kim wrote:
> All, 
> I am testing 2x USRP1 with RFX2400 daughter cards with benchmark_rx
> and benchmark_tx scripts and have questions. 
> When I set the MCS to dbpsk, error rate I got was close to zero. 
> When I set it to dqpsk, d8psk, error rate is 100%. 
> When I set it to gmsk, certain daughter cards had close to 0 error
> rate, but certain swung from 0% to 100%. 
> I asked about it to Ettus research, they told me that it's likely to
> be due to frequency offset between the two boxes I have. 
> If it is true, 
> 1) how can I compensate the offset? 

Make a simple little FFT sink in GRC and use it on one of the USRPs to
determine the received signal offset from the other USRP while it is
transmitting. Or receive a signal from a signal generator of known
frequency and note the offset for both USRPs. Or transmit a signal from
each USRP and receive it using a different receiver and note the
difference between the frequencies of the received signals. Or vary the
frequency of either benchmark_rx or benchmark_tx via trial and error
until you get proper transmission/reception. You will probably find less
than 20kHz of offset at 2.4GHz.


> 2) Has someone used dqpsk, d8psk in 2.4MHz ISM band before? If so,
> what extra step is necessary? 
> Thanks, 
> Thomas 
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