Hello!

I am trying to generate GPS signals with USRP B210 SDR. I have made a source "from workspace" where are values ones and zeros. There are 30690000 values, with sample time 1/1023000, which is the GPS L1 signal rate (1,023 MHz). Next block is "ideal rectangular pulse filter" with Pulse Length=4, which i have left in from examples i have found online( i'm not sure, if i really need this). Next block is BPSK modulator baseband with default settings. Next block is "Buffer" with size 1000 and final block is "SDRu Transmitter", with Fc-1575.42e6 Hz, LO offset-0 Hz, Gain-5 dB, Master Clock Rate- 20.95104e6 Hz, Interpolation- 512 and everything else is default.

When i run the model, my GPS evaluation software (U-center) receives gibberish. Intermittent signal and pseudo satellites. Occasionally, it finds the satellite code, which i generate. (In the source block there is PRN #01 and NavData for 30 seconds)

My question is, that why my simulation transmits such gibberish signal? As far as i have searched for this answer, the problem should be with mismatching sample rates? Anyone could explain me, how the DSP and SDR Tx sample times are related? How should i configure them? Also i have issues with running the simulation in real time, as i need to acquire the generated signal with u-center, where it should "see" legit GPS satellite information.

Mihkel.

Hi Mihkel,

I can confirm Marcus' suspicions.  The rectangular pulse filter will destroy your data.

The BPSK modulator block needs binary (0/1) input.

Hth,
Mike

From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] On Behalf Of Marcus Müller via USRP-users
Sent: Wednesday, April 26, 2017 2:04 PM
To: usrp-users@lists.ettus.com
Subject: Re: [USRP-users] B210 and Simulink sample times

Hi Mihkel,

don't know Simulink overly well, but "ideal rectangular pulse filter" sounds like a moving average - and that would completely destroy your data.

So, I don't think this is going to work. Not sure you need an extra "buffer" block.

Best regards,

Marcus

On 04/26/2017 12:25 PM, Mihkel M via USRP-users wrote:

Hello!

I am trying to generate GPS signals with USRP B210 SDR. I have made a source "from workspace" where are values ones and zeros. There are 30690000 values, with sample time 1/1023000, which is the GPS L1 signal rate (1,023 MHz). Next block is "ideal rectangular pulse filter" with Pulse Length=4, which i have left in from examples i have found online( i'm not sure, if i really need this). Next block is BPSK modulator baseband with default settings. Next block is "Buffer" with size 1000 and final block is "SDRu Transmitter", with Fc-1575.42e6 Hz, LO offset-0 Hz, Gain-5 dB, Master Clock Rate- 20.95104e6 Hz, Interpolation- 512 and everything else is default.

When i run the model, my GPS evaluation software (U-center) receives gibberish. Intermittent signal and pseudo satellites. Occasionally, it finds the satellite code, which i generate. (In the source block there is PRN #01 and NavData for 30 seconds)

My question is, that why my simulation transmits such gibberish signal? As far as i have searched for this answer, the problem should be with mismatching sample rates? Anyone could explain me, how the DSP and SDR Tx sample times are related? How should i configure them? Also i have issues with running the simulation in real time, as i need to acquire the generated signal with u-center, where it should "see" legit GPS satellite information.

Mihkel.

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