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Posted by Nicholas on May 13, 2010, 11:15 am


On Thu, 13 May 2010 08:05:27 -0700 (PDT), claudegps

>> On Thu, 13 May 2010 03:48:09 -0700 (PDT), claudegps
>> >> claudegps wrote:
>> >> >> I would like to create a home-made white noise generator to test the
>> >> >> sensitivity of a GPS receiver. It is a poor man's lobster, since I don't
>> >> >> want to buy a signal generator. Is there any simple way for me to create
>> >> >>    numerical white noise and save it in a data file?
>> >> > Matlab should have what you need to generate any "noise" and save it
>> >> > to a file.
>> >> > My question is: how do you plan to test the sensitivity of a GPS
>> >> > receiver using a file with noise?
>> >> Briefly speaking, the noise will be added to a standard signal.
>> >That is the problem :)
>> >You have to generate the noise in the same "format" of the standard
>> >signal.
>> >But the standard signal has already a centrain quantity of noise.
>> >If you have I/Q samples, I think you cant' simply "add" noise I/Q
>> >samples, but you need much more sophisticated way to add noise to
>> >standard signal.
>> >A shortcut that you could try could be randomaly change some I/Q
>> >samples of the standard signal, controlling the amount of noise added
>> >thru probability and random number genrator.
>> >If you set a low probability in the bit change, the added noise should
>> >be low.
>> >If you set a high probability in the bit change, the added noise
>> >should be high.
>> >But: I don't know it this works, I don't know how you could estimate
>> >the amount of noise added.
>> This entire topic sounds stinky to me.  I don't like the idea of
>> giving anyone information on how to build a gps signal jammer, and
>> then hand it to them in a format that can be distributed all over the
>> planet as an email attachment.
>You are totally missing the point here.
>Apart the fact that if you want to build a GPS signal jammer, there is
>enough informations everywhere...
>Here we are not *jamming* any GPS.
>The problem is to create noise to be added to *files* (digital samples
>of GPS IF stream coming from the front-end to baseband) to test GPS
>tracking algorithms (maybe also anti-jamming strategies...)
>No GPS is jammed, never! It's just a sort of post processing...
>Read(and understand) topic before posting ;)

I read and understood your topic. What I can't do is read and
understand your true motives.

Every gps manufacturer has equipment to do just the thing you ask for.
Why don't you call them and ask them how they do it. After all, isn't
this a simple "signal to noise experiment" you are trying to do? If
it is, the solution to your problem is trivial. Providing you know
your electronics and RF.


Posted by claudegps on May 13, 2010, 12:04 pm


> On Thu, 13 May 2010 08:05:27 -0700 (PDT), claudegps
> >> On Thu, 13 May 2010 03:48:09 -0700 (PDT), claudegps
> >> >> claudegps wrote:
> >> >> >> I would like to create a home-made white noise generator to test=
the
> >> >> >> sensitivity of a GPS receiver. It is a poor man's lobster, since=
I don't
> >> >> >> want to buy a signal generator. Is there any simple way for me t=
o create
> >> >> >> =A0 =A0numerical white noise and save it in a data file?
> >> >> > Matlab should have what you need to generate any "noise" and save=
it
> >> >> > to a file.
> >> >> > My question is: how do you plan to test the sensitivity of a GPS
> >> >> > receiver using a file with noise?
> >> >> Briefly speaking, the noise will be added to a standard signal.
--
> >> >That is the problem :)
> >> >You have to generate the noise in the same "format" of the standard
> >> >signal.
> >> >But the standard signal has already a centrain quantity of noise.
> >> >If you have I/Q samples, I think you cant' simply "add" noise I/Q
> >> >samples, but you need much more sophisticated way to add noise to
> >> >standard signal.
> >> >A shortcut that you could try could be randomaly change some I/Q
> >> >samples of the standard signal, controlling the amount of noise added
> >> >thru probability and random number genrator.
> >> >If you set a low probability in the bit change, the added noise shoul=
d
> >> >be low.
> >> >If you set a high probability in the bit change, the added noise
> >> >should be high.
> >> >But: I don't know it this works, I don't know how you could estimate
> >> >the amount of noise added.
> >> This entire topic sounds stinky to me. =A0I don't like the idea of
> >> giving anyone information on how to build a gps signal jammer, and
> >> then hand it to them in a format that can be distributed all over the
> >> planet as an email attachment.
> >You are totally missing the point here.
> >Apart the fact that if you want to build a GPS signal jammer, there is
> >enough informations everywhere...
> >Here we are not *jamming* any GPS.
> >The problem is to create noise to be added to *files* (digital samples
> >of GPS IF stream coming from the front-end to baseband) to test GPS
> >tracking algorithms (maybe also anti-jamming strategies...)
> >No GPS is jammed, never! It's just a sort of post processing...
> >Read(and understand) topic before posting =A0;)
> I read and understood your topic. =A0What I can't do is read and
> understand your true motives.

Testing GPS algorithms, I think. Ask the OP :)

> Every gps manufacturer has equipment to do just the thing you ask for.

No, I'm not asking anything. I'm helping the OP

> Why don't you call them and ask them how they do it. =A0After all, isn't
> this a simple "signal to noise experiment" you are trying to do? =A0If
> it is, the solution to your problem is trivial. =A0Providing =A0you know
> your electronics and RF.

No, your still missing the point here.
The RF data is already sampled and the OP needs to add (controlled)
noise on the sampled files that he already has. (at least that is my
understanding)
This mean working on files, not on RF signals with a noise generator.

Do you find a trivial solution to this problem?


Posted by Nicholas on May 13, 2010, 12:13 pm


On Thu, 13 May 2010 09:04:28 -0700 (PDT), claudegps

>> On Thu, 13 May 2010 08:05:27 -0700 (PDT), claudegps
>> >> On Thu, 13 May 2010 03:48:09 -0700 (PDT), claudegps
>> >> >> claudegps wrote:
>> >> >> >> I would like to create a home-made white noise generator to test the
>> >> >> >> sensitivity of a GPS receiver. It is a poor man's lobster, since I
don't
>> >> >> >> want to buy a signal generator. Is there any simple way for me to
create
>> >> >> >>    numerical white noise and save it in a data file?
>> >> >> > Matlab should have what you need to generate any "noise" and save it
>> >> >> > to a file.
>> >> >> > My question is: how do you plan to test the sensitivity of a GPS
>> >> >> > receiver using a file with noise?
>> >> >> Briefly speaking, the noise will be added to a standard signal.
>> >> >That is the problem :)
>> >> >You have to generate the noise in the same "format" of the standard
>> >> >signal.
>> >> >But the standard signal has already a centrain quantity of noise.
>> >> >If you have I/Q samples, I think you cant' simply "add" noise I/Q
>> >> >samples, but you need much more sophisticated way to add noise to
>> >> >standard signal.
>> >> >A shortcut that you could try could be randomaly change some I/Q
>> >> >samples of the standard signal, controlling the amount of noise added
>> >> >thru probability and random number genrator.
>> >> >If you set a low probability in the bit change, the added noise should
>> >> >be low.
>> >> >If you set a high probability in the bit change, the added noise
>> >> >should be high.
>> >> >But: I don't know it this works, I don't know how you could estimate
>> >> >the amount of noise added.
>> >> This entire topic sounds stinky to me.  I don't like the idea of
>> >> giving anyone information on how to build a gps signal jammer, and
>> >> then hand it to them in a format that can be distributed all over the
>> >> planet as an email attachment.
>> >You are totally missing the point here.
>> >Apart the fact that if you want to build a GPS signal jammer, there is
>> >enough informations everywhere...
>> >Here we are not *jamming* any GPS.
>> >The problem is to create noise to be added to *files* (digital samples
>> >of GPS IF stream coming from the front-end to baseband) to test GPS
>> >tracking algorithms (maybe also anti-jamming strategies...)
>> >No GPS is jammed, never! It's just a sort of post processing...
>> >Read(and understand) topic before posting  ;)
>> I read and understood your topic.  What I can't do is read and
>> understand your true motives.
>Testing GPS algorithms, I think. Ask the OP :)
>> Every gps manufacturer has equipment to do just the thing you ask for.
>No, I'm not asking anything. I'm helping the OP
>> Why don't you call them and ask them how they do it.  After all, isn't
>> this a simple "signal to noise experiment" you are trying to do?  If
>> it is, the solution to your problem is trivial.  Providing  you know
>> your electronics and RF.
>No, your still missing the point here.
>The RF data is already sampled and the OP needs to add (controlled)
>noise on the sampled files that he already has. (at least that is my
>understanding)
>This mean working on files, not on RF signals with a noise generator.
>Do you find a trivial solution to this problem?

Not to make a *data file* of this. Only to do it in Real Time. Of
course, to do it in Real Time will cost some money if precise
measurements are required.

I already found a pre-made signal generator for this on the WWW
(Russian made), and then you need to rent a Spectrum Analyzer. Too
much money IMO. Unless you work for a government agency which can
fund the project.

So you can record the output from the spectrum analyzer, but not a 1.5
GHz signal on any recording equipment that I know of.

If you know of some kind of recording equipment that can lay down a
1.5 GHz signal, please advise.

Lg


Posted by claudegps on May 13, 2010, 12:30 pm


[cut]
> >Do you find a trivial solution to this problem?
> Not to make a *data file* of this. =A0Only to do it in Real Time. =A0Of
> course, to do it in Real Time will cost some money if precise
> measurements are required.

Rigth, but this is a solution to another problem. Not the one we are
discussing in this thread :)

> I already found a pre-made signal generator for this on the WWW
> (Russian made), and then you need to rent a Spectrum Analyzer. =A0Too
> much money IMO. =A0Unless you work for a government agency which can
> fund the project.
> So you can record the output from the spectrum analyzer, but not a 1.5
> GHz signal on any recording equipment that I know of.

> If you know of some kind of recording equipment that can lay down a
> 1.5 GHz signal, please advise.

Depends on which type of recording you need.
If you need the I/F stream, a RF frontend will be enough...

Posted by Johnson on May 14, 2010, 2:34 pm


claudegps wrote:
>> On Thu, 13 May 2010 08:05:27 -0700 (PDT), claudegps
>>>> On Thu, 13 May 2010 03:48:09 -0700 (PDT), claudegps
>>>>>> claudegps wrote:
>>>>>>>> I would like to create a home-made white noise generator to test the
>>>>>>>> sensitivity of a GPS receiver. It is a poor man's lobster, since I don't
>>>>>>>> want to buy a signal generator. Is there any simple way for me to create
>>>>>>>> numerical white noise and save it in a data file?
>>>>>>> Matlab should have what you need to generate any "noise" and save it
>>>>>>> to a file.
>>>>>>> My question is: how do you plan to test the sensitivity of a GPS
>>>>>>> receiver using a file with noise?
>>>>>> Briefly speaking, the noise will be added to a standard signal.
>>>>> That is the problem :)
>>>>> You have to generate the noise in the same "format" of the standard
>>>>> signal.
>>>>> But the standard signal has already a centrain quantity of noise.
>>>>> If you have I/Q samples, I think you cant' simply "add" noise I/Q
>>>>> samples, but you need much more sophisticated way to add noise to
>>>>> standard signal.
>>>>> A shortcut that you could try could be randomaly change some I/Q
>>>>> samples of the standard signal, controlling the amount of noise added
>>>>> thru probability and random number genrator.
>>>>> If you set a low probability in the bit change, the added noise should
>>>>> be low.
>>>>> If you set a high probability in the bit change, the added noise
>>>>> should be high.
>>>>> But: I don't know it this works, I don't know how you could estimate
>>>>> the amount of noise added.
>>>> This entire topic sounds stinky to me. I don't like the idea of
>>>> giving anyone information on how to build a gps signal jammer, and
>>>> then hand it to them in a format that can be distributed all over the
>>>> planet as an email attachment.
>>> You are totally missing the point here.
>>> Apart the fact that if you want to build a GPS signal jammer, there is
>>> enough informations everywhere...
>>> Here we are not *jamming* any GPS.
>>> The problem is to create noise to be added to *files* (digital samples
>>> of GPS IF stream coming from the front-end to baseband) to test GPS
>>> tracking algorithms (maybe also anti-jamming strategies...)
>>> No GPS is jammed, never! It's just a sort of post processing...
>>> Read(and understand) topic before posting ;)
>> I read and understood your topic. What I can't do is read and
>> understand your true motives.
>
> Testing GPS algorithms, I think. Ask the OP :)
>
>> Every gps manufacturer has equipment to do just the thing you ask for.
>
> No, I'm not asking anything. I'm helping the OP
>
>> Why don't you call them and ask them how they do it. After all, isn't
>> this a simple "signal to noise experiment" you are trying to do? If
>> it is, the solution to your problem is trivial. Providing you know
>> your electronics and RF.
>
> No, your still missing the point here.
> The RF data is already sampled and the OP needs to add (controlled)
> noise on the sampled files that he already has. (at least that is my
> understanding)
> This mean working on files, not on RF signals with a noise generator.
>
> Do you find a trivial solution to this problem?
>
Yes, you are absolutely right.


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