How to caracterize transfer function of signal chain

I am trying to caracterize a system consisting of a 1) pseudo random
generator (binary pulses, "on-off modulation") --> 2)laser diode --> light
beam --> reflection from surface --> 3)photodiode detector --> 4)amplifier


I would like to formulate at a model from measurements that mathematically
describe how the binary pulses are "shaped" thru the chain 2) to 4). 

I need to do this because I want to convolve my original binary on-off
sequence with the composite response of the signal chain 2) to 4). 
I want to use that shaped signal as the pattern to look for in a
correlator for detecting time differences. 

I am fairly new to DSP techniques so I would like to ask for some advice
on the following:

Q1) How do I set up a measuring system to measure the complete response of
the 2) to 4) chain? Do I for example use a step or a pulse input? Should
measure the response with a digital oscillocope that can store data to
file? Please give your suggestions. 

Q2) When I have gathered measurement data in discrete sample form (file on
my disk), how do I calculate the convolution coefficients to use on the
original binary sequence? 

Q3) How do I set up a correlator for testing this in Matlab? (What
functions do I use? Do you have a particular procedure or setup you use for
correlation experiments?)

Mike 

On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
> I am trying to caracterize a system consisting of a 1) pseudo random
> generator (binary pulses, "on-off modulation") --> 2)laser diode --> light
> beam --> reflection from surface --> 3)photodiode detector --> 4)amplifier

> Q2) When I have gathered measurement data in discrete sample form (file on
> my disk), how do I calculate the convolution coefficients to use on the
> original binary sequence?

This is a non-trivial problem. The reason is step 2,
where the light beam is emitted into some space and
reflected off some surface.

The exact behaviour of this step depends on a number of
factors, like the beam pattern of the diode, the surrounding
environment, the geometry of the set-up, the geometry of the
reflecting surface, the scattering properties of the reflecting
surface, and so on.

So you have two options: Either use a simple correlator
of whatever type you would have used in an optical fiber,
or set up a fully-fledged simulator where you simulate
the whole set-up in all its gory detail.

Rune

>On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
>> I am trying to caracterize a system consisting of a 1) pseudo random
>> generator (binary pulses, "on-off modulation") --> 2)laser diode -->
light
>> beam --> reflection from surface --> 3)photodiode detector -->
4)amplifier
>
>> Q2) When I have gathered measurement data in discrete sample form (file
on
>> my disk), how do I calculate the convolution coefficients to use on
the
>> original binary sequence?
>
>This is a non-trivial problem. The reason is step 2,
>where the light beam is emitted into some space and
>reflected off some surface.
>
>The exact behaviour of this step depends on a number of
>factors, like the beam pattern of the diode, the surrounding
>environment, the geometry of the set-up, the geometry of the
>reflecting surface, the scattering properties of the reflecting
>surface, and so on.
>
>So you have two options: Either use a simple correlator
>of whatever type you would have used in an optical fiber,
>or set up a fully-fledged simulator where you simulate
>the whole set-up in all its gory detail.
>
>Rune
>

Hello Rune, thank you for replying. 

The reflection from the reflective surface is assumed to be constant and
not varying (other than amplitude). 

What I need to do is to characterize (not simulate) the whole transmission
/ reception chain by empirical experimentation. In this way I dont need to
simulate anything, but meaasre. 

How do I set up a measuring setup? Do I use step response? How do I arrive
at a mathematical characterization of what the "channel and whole system"
does to my original on-off bit pattern. (lets look at one bit first only).

What function do I use from Matlab for this correlator? 

Mike 

On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> I am trying to caracterize a system consisting of a 1) pseudo random
> >> generator (binary pulses, "on-off modulation") --> 2)laser diode -->
> light
> >> beam --> reflection from surface --> 3)photodiode detector -->
> 4)amplifier
>
> >> Q2) When I have gathered measurement data in discrete sample form (file
> on
> >> my disk), how do I calculate the convolution coefficients to use on
> the
> >> original binary sequence?
>
> >This is a non-trivial problem. The reason is step 2,
> >where the light beam is emitted into some space and
> >reflected off some surface.
>
> >The exact behaviour of this step depends on a number of
> >factors, like the beam pattern of the diode, the surrounding
> >environment, the geometry of the set-up, the geometry of the
> >reflecting surface, the scattering properties of the reflecting
> >surface, and so on.
>
> >So you have two options: Either use a simple correlator
> >of whatever type you would have used in an optical fiber,
> >or set up a fully-fledged simulator where you simulate
> >the whole set-up in all its gory detail.
>
> >Rune
>
> Hello Rune, thank you for replying.
>
> The reflection from the reflective surface is assumed to be constant and
> not varying (other than amplitude).

The assumption might be good enough, but since you talk
about a surface, and not a point reflector, the net effect
is that the recieved signal might experience interference
bewteen rays reflected off the near end of the surface, and
rays reflected off the near end of the surface.

Rune

>On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> I am trying to caracterize a system consisting of a 1) pseudo
random
>> >> generator (binary pulses, "on-off modulation") --> 2)laser diode
-->
>> light
>> >> beam --> reflection from surface --> 3)photodiode detector -->
>> 4)amplifier
>>
>> >> Q2) When I have gathered measurement data in discrete sample form
(file
>> on
>> >> my disk), how do I calculate the convolution coefficients to use on
>> the
>> >> original binary sequence?
>>
>> >This is a non-trivial problem. The reason is step 2,
>> >where the light beam is emitted into some space and
>> >reflected off some surface.
>>
>> >The exact behaviour of this step depends on a number of
>> >factors, like the beam pattern of the diode, the surrounding
>> >environment, the geometry of the set-up, the geometry of the
>> >reflecting surface, the scattering properties of the reflecting
>> >surface, and so on.
>>
>> >So you have two options: Either use a simple correlator
>> >of whatever type you would have used in an optical fiber,
>> >or set up a fully-fledged simulator where you simulate
>> >the whole set-up in all its gory detail.
>>
>> >Rune
>>
>> Hello Rune, thank you for replying.
>>
>> The reflection from the reflective surface is assumed to be constant
and
>> not varying (other than amplitude).
>
>The assumption might be good enough, but since you talk
>about a surface, and not a point reflector, the net effect
>is that the recieved signal might experience interference
>bewteen rays reflected off the near end of the surface, and
>rays reflected off the near end of the surface.
>
>Rune
>

Certainly, but thats where the correlator comes in. The transmitted signal
will be amplitude modulated and if there are two reflections, a little
delayed in time, the correlator will be able to detect those two signals
and will be giving out two correlation peaks. I may use both or just one of
them as the received peak. There is no need for extremely high time
resolution. 

Still. I wonder if somebody could help me with how to measure the transfer
function of the system? 

Mike 

On 19 Jul, 12:03, "Dsp1000" <rezycle....@gmail.com> wrote:
> >On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >> I am trying to caracterize a system consisting of a 1) pseudo
> random
> >> >> generator (binary pulses, "on-off modulation") --> 2)laser diode
> -->
> >> light
> >> >> beam --> reflection from surface --> 3)photodiode detector -->
> >> 4)amplifier
>
> >> >> Q2) When I have gathered measurement data in discrete sample form
> (file
> >> on
> >> >> my disk), how do I calculate the convolution coefficients to use on
> >> the
> >> >> original binary sequence?
>
> >> >This is a non-trivial problem. The reason is step 2,
> >> >where the light beam is emitted into some space and
> >> >reflected off some surface.
>
> >> >The exact behaviour of this step depends on a number of
> >> >factors, like the beam pattern of the diode, the surrounding
> >> >environment, the geometry of the set-up, the geometry of the
> >> >reflecting surface, the scattering properties of the reflecting
> >> >surface, and so on.
>
> >> >So you have two options: Either use a simple correlator
> >> >of whatever type you would have used in an optical fiber,
> >> >or set up a fully-fledged simulator where you simulate
> >> >the whole set-up in all its gory detail.
>
> >> >Rune
>
> >> Hello Rune, thank you for replying.
>
> >> The reflection from the reflective surface is assumed to be constant
> and
> >> not varying (other than amplitude).
>
> >The assumption might be good enough, but since you talk
> >about a surface, and not a point reflector, the net effect
> >is that the recieved signal might experience interference
> >bewteen rays reflected off the near end of the surface, and
> >rays reflected off the near end of the surface.
>
> >Rune
>
> Certainly, but thats where the correlator comes in. The transmitted signal
> will be amplitude modulated and if there are two reflections, a little
> delayed in time, the correlator will be able to detect those two signals
> and will be giving out two correlation peaks.

No. There will not be two rays. There will be one beam,
that reflects off the surface. Light scattered from the
whole footprint of the beam will interfere at the receiver.

Rune

On Jul 19, 3:03&#4294967295;am, "Dsp1000" <rezycle....@gmail.com> wrote:
> >On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >> I am trying to caracterize a system consisting of a 1) pseudo
> random
> >> >> generator (binary pulses, "on-off modulation") --> 2)laser diode
> -->
> >> light
> >> >> beam --> reflection from surface --> 3)photodiode detector -->
> >> 4)amplifier
>
> >> >> Q2) When I have gathered measurement data in discrete sample form
> (file
> >> on
> >> >> my disk), how do I calculate the convolution coefficients to use on
> >> the
> >> >> original binary sequence?
>
> >> >This is a non-trivial problem. The reason is step 2,
> >> >where the light beam is emitted into some space and
> >> >reflected off some surface.
>
> >> >The exact behaviour of this step depends on a number of
> >> >factors, like the beam pattern of the diode, the surrounding
> >> >environment, the geometry of the set-up, the geometry of the
> >> >reflecting surface, the scattering properties of the reflecting
> >> >surface, and so on.
>
> >> >So you have two options: Either use a simple correlator
> >> >of whatever type you would have used in an optical fiber,
> >> >or set up a fully-fledged simulator where you simulate
> >> >the whole set-up in all its gory detail.
>
> >> >Rune
>
> >> Hello Rune, thank you for replying.
>
> >> The reflection from the reflective surface is assumed to be constant
> and
> >> not varying (other than amplitude).
>
> >The assumption might be good enough, but since you talk
> >about a surface, and not a point reflector, the net effect
> >is that the recieved signal might experience interference
> >bewteen rays reflected off the near end of the surface, and
> >rays reflected off the near end of the surface.
>
> >Rune
>
> Certainly, but thats where the correlator comes in. The transmitted signal
> will be amplitude modulated and if there are two reflections, a little
> delayed in time, the correlator will be able to detect those two signals
> and will be giving out two correlation peaks. I may use both or just one of
> them as the received peak. There is no need for extremely high time
> resolution.
>
> Still. I wonder if somebody could help me with how to measure the transfer
> function of the system?
>
> Mike- Hide quoted text -
>
> - Show quoted text -

You want to get a step response for each components in the chain, I
guess? You can send a fairly good (good rise time) signal to the input
and measure the output, plot them, and interpolate the plot to the a
step response.

>On Jul 19, 3:03=A0am, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> >> I am trying to caracterize a system consisting of a 1) pseudo
>> random
>> >> >> generator (binary pulses, "on-off modulation") --> 2)laser diode
>> -->
>> >> light
>> >> >> beam --> reflection from surface --> 3)photodiode detector -->
>> >> 4)amplifier
>>
>> >> >> Q2) When I have gathered measurement data in discrete sample
form
>> (file
>> >> on
>> >> >> my disk), how do I calculate the convolution coefficients to use
on
>> >> the
>> >> >> original binary sequence?
>>
>> >> >This is a non-trivial problem. The reason is step 2,
>> >> >where the light beam is emitted into some space and
>> >> >reflected off some surface.
>>
>> >> >The exact behaviour of this step depends on a number of
>> >> >factors, like the beam pattern of the diode, the surrounding
>> >> >environment, the geometry of the set-up, the geometry of the
>> >> >reflecting surface, the scattering properties of the reflecting
>> >> >surface, and so on.
>>
>> >> >So you have two options: Either use a simple correlator
>> >> >of whatever type you would have used in an optical fiber,
>> >> >or set up a fully-fledged simulator where you simulate
>> >> >the whole set-up in all its gory detail.
>>
>> >> >Rune
>>
>> >> Hello Rune, thank you for replying.
>>
>> >> The reflection from the reflective surface is assumed to be
constant
>> and
>> >> not varying (other than amplitude).
>>
>> >The assumption might be good enough, but since you talk
>> >about a surface, and not a point reflector, the net effect
>> >is that the recieved signal might experience interference
>> >bewteen rays reflected off the near end of the surface, and
>> >rays reflected off the near end of the surface.
>>
>> >Rune
>>
>> Certainly, but thats where the correlator comes in. The transmitted
signa=
>l
>> will be amplitude modulated and if there are two reflections, a little
>> delayed in time, the correlator will be able to detect those two
signals
>> and will be giving out two correlation peaks. I may use both or just
one =
>of
>> them as the received peak. There is no need for extremely high time
>> resolution.
>>
>> Still. I wonder if somebody could help me with how to measure the
transfe=
>r
>> function of the system?
>>
>> Mike- Hide quoted text -
>>
>> - Show quoted text -
>
>You want to get a step response for each components in the chain, I
>guess? You can send a fairly good (good rise time) signal to the input
>and measure the output, plot them, and interpolate the plot to the a
>step response.
>

Verictor, thank you for your suggestion. 

What do you mean by a fairly good rise time? Is that a fast rise time? 

What I am actually looking at making is a laser range finder that will
work against leaves & vegetation. For example, measure the range to the top
of a tree. 

Does anyybody on this group have any experience with laser range finders
and applied DSP techniques? 

Mike 

On Jul 21, 4:52&#4294967295;am, "Dsp1000" <rezycle....@gmail.com> wrote:
> >On Jul 19, 3:03=A0am, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
> >> >> >> I am trying to caracterize a system consisting of a 1) pseudo
> >> random
> >> >> >> generator (binary pulses, "on-off modulation") --> 2)laser diode
> >> -->
> >> >> light
> >> >> >> beam --> reflection from surface --> 3)photodiode detector -->
> >> >> 4)amplifier
>
> >> >> >> Q2) When I have gathered measurement data in discrete sample
> form
> >> (file
> >> >> on
> >> >> >> my disk), how do I calculate the convolution coefficients to use
> on
> >> >> the
> >> >> >> original binary sequence?
>
> >> >> >This is a non-trivial problem. The reason is step 2,
> >> >> >where the light beam is emitted into some space and
> >> >> >reflected off some surface.
>
> >> >> >The exact behaviour of this step depends on a number of
> >> >> >factors, like the beam pattern of the diode, the surrounding
> >> >> >environment, the geometry of the set-up, the geometry of the
> >> >> >reflecting surface, the scattering properties of the reflecting
> >> >> >surface, and so on.
>
> >> >> >So you have two options: Either use a simple correlator
> >> >> >of whatever type you would have used in an optical fiber,
> >> >> >or set up a fully-fledged simulator where you simulate
> >> >> >the whole set-up in all its gory detail.
>
> >> >> >Rune
>
> >> >> Hello Rune, thank you for replying.
>
> >> >> The reflection from the reflective surface is assumed to be
> constant
> >> and
> >> >> not varying (other than amplitude).
>
> >> >The assumption might be good enough, but since you talk
> >> >about a surface, and not a point reflector, the net effect
> >> >is that the recieved signal might experience interference
> >> >bewteen rays reflected off the near end of the surface, and
> >> >rays reflected off the near end of the surface.
>
> >> >Rune
>
> >> Certainly, but thats where the correlator comes in. The transmitted
> signa=
> >l
> >> will be amplitude modulated and if there are two reflections, a little
> >> delayed in time, the correlator will be able to detect those two
> signals
> >> and will be giving out two correlation peaks. I may use both or just
> one =
> >of
> >> them as the received peak. There is no need for extremely high time
> >> resolution.
>
> >> Still. I wonder if somebody could help me with how to measure the
> transfe=
> >r
> >> function of the system?
>
> >> Mike- Hide quoted text -
>
> >> - Show quoted text -
>
> >You want to get a step response for each components in the chain, I
> >guess? You can send a fairly good (good rise time) signal to the input
> >and measure the output, plot them, and interpolate the plot to the a
> >step response.
>
> Verictor, thank you for your suggestion.
>
> What do you mean by a fairly good rise time? Is that a fast rise time?
>
> What I am actually looking at making is a laser range finder that will
> work against leaves & vegetation. For example, measure the range to the top
> of a tree.
>
> Does anyybody on this group have any experience with laser range finders
> and applied DSP techniques?
>
> Mike- Hide quoted text -
>
> - Show quoted text -

Idealy a step response needs the input to be rise immediately so that
later on you can get the impulse response, right? But in real life, it
is not an easy job to find very short rise time stimulus.

What is a laser range finder? I don't know about that. You mean use
laser's reflection to determine the arrival time so that you can
decide the object's dimension? Just a side question to your
application. You don't have to answer my question.

>On Jul 21, 4:52=A0am, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >On Jul 19, 3:03=3DA0am, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> >On 18 Jul, 15:03, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> >> >On 18 Jul, 13:42, "Dsp1000" <rezycle....@gmail.com> wrote:
>> >> >> >> I am trying to caracterize a system consisting of a 1) pseudo
>> >> random
>> >> >> >> generator (binary pulses, "on-off modulation") --> 2)laser
diode
>> >> -->
>> >> >> light
>> >> >> >> beam --> reflection from surface --> 3)photodiode detector
-->
>> >> >> 4)amplifier
>>
>> >> >> >> Q2) When I have gathered measurement data in discrete sample
>> form
>> >> (file
>> >> >> on
>> >> >> >> my disk), how do I calculate the convolution coefficients to
use
>> on
>> >> >> the
>> >> >> >> original binary sequence?
>>
>> >> >> >This is a non-trivial problem. The reason is step 2,
>> >> >> >where the light beam is emitted into some space and
>> >> >> >reflected off some surface.
>>
>> >> >> >The exact behaviour of this step depends on a number of
>> >> >> >factors, like the beam pattern of the diode, the surrounding
>> >> >> >environment, the geometry of the set-up, the geometry of the
>> >> >> >reflecting surface, the scattering properties of the reflecting
>> >> >> >surface, and so on.
>>
>> >> >> >So you have two options: Either use a simple correlator
>> >> >> >of whatever type you would have used in an optical fiber,
>> >> >> >or set up a fully-fledged simulator where you simulate
>> >> >> >the whole set-up in all its gory detail.
>>
>> >> >> >Rune
>>
>> >> >> Hello Rune, thank you for replying.
>>
>> >> >> The reflection from the reflective surface is assumed to be
>> constant
>> >> and
>> >> >> not varying (other than amplitude).
>>
>> >> >The assumption might be good enough, but since you talk
>> >> >about a surface, and not a point reflector, the net effect
>> >> >is that the recieved signal might experience interference
>> >> >bewteen rays reflected off the near end of the surface, and
>> >> >rays reflected off the near end of the surface.
>>
>> >> >Rune
>>
>> >> Certainly, but thats where the correlator comes in. The transmitted
>> signa=3D
>> >l
>> >> will be amplitude modulated and if there are two reflections, a
little
>> >> delayed in time, the correlator will be able to detect those two
>> signals
>> >> and will be giving out two correlation peaks. I may use both or
just
>> one =3D
>> >of
>> >> them as the received peak. There is no need for extremely high time
>> >> resolution.
>>
>> >> Still. I wonder if somebody could help me with how to measure the
>> transfe=3D
>> >r
>> >> function of the system?
>>
>> >> Mike- Hide quoted text -
>>
>> >> - Show quoted text -
>>
>> >You want to get a step response for each components in the chain, I
>> >guess? You can send a fairly good (good rise time) signal to the
input
>> >and measure the output, plot them, and interpolate the plot to the a
>> >step response.
>>
>> Verictor, thank you for your suggestion.
>>
>> What do you mean by a fairly good rise time? Is that a fast rise time?
>>
>> What I am actually looking at making is a laser range finder that will
>> work against leaves & vegetation. For example, measure the range to the
t=
>op
>> of a tree.
>>
>> Does anyybody on this group have any experience with laser range
finders
>> and applied DSP techniques?
>>
>> Mike- Hide quoted text -
>>
>> - Show quoted text -
>
>Idealy a step response needs the input to be rise immediately so that
>later on you can get the impulse response, right? But in real life, it
>is not an easy job to find very short rise time stimulus.
>
>What is a laser range finder? I don't know about that. You mean use
>laser's reflection to determine the arrival time so that you can
>decide the object's dimension? Just a side question to your
>application. You don't have to answer my question.
>

Hi again. 

Thanks for your post regarding step response. 

A laser range finder is a laser distance (range) measuring device.
It will give you distance to an object you shine light on as a binary or
analog output. There are two main methods to use: Time of flight of the
laser beam and phase difference detection. The latter is better on short
distances but has some challenges associated with it. It is a more advanced
version of the latter I am looking at. 

All experts on this list: anybody with laser range finder experience?

Mike