[SLS-OPT] [EXTERNAL] Re: O3K channel model

Wed Apr 22 17:00:40 UTC 2020

Hello Jon,
Thank you for the presentation and the simple APD model. The algebra is OK.
In the proposed model the observations are homogeneous to  number of photons by bit. It might be easier, as Nicolo suggested,  to use in the simulations observations that are defined in power (watt). I added in the back-up slides (slides 9 and 10) the model in power as well. The correspondence between the two is simply ns=Rres/q*Ps*Ts.
I have a request: since we are going to do all the simulations again, I would like to ask that people compute the mutual information in their simulations. It is not complicated to do, and requires only few lines to be added in the code. Attached is a short note that describes how to compute mutual information.

Concerning the simulations at 1.22 Mbps, we have used with the colleagues from the French riviera observatory an APD to receive a 1Mbps signal, that had the following parameters:

-          Data sheet:

o   Noise Equivalent Power : 0.12 pW/√Hz  @ M = 10

o   Rres (1550 nm) = 0.95 A/W

o   Electrical filter: tchebychef 5th order @ 2MHz

o   RT = 47 kΩ,

o   M = 30 : APD amplification gain that was chosen

o   G_Ampli = 10 (transimpedance gain)

o   T_opt = 0.9: optical transmission lens before APD

o   Responsivity [Volt/Watt] from datasheet= Rres* RT* M* G_Ampli* T_opt= 1.2E7

-          Measurements

o   Responsivity [Volt/Watt] measured =1E7

o   Measured TIA noise spectral density = 0.045 pW/√Hz => 0. 45 pW*RT/ Responsivity = 2.1 E-16 A/√Hz

Note1: the APD was thermo-cooled at -20°C

Note2: with the same APD but an electric filter bandwidth of 16MHz the measured TIA noise spectral density was  0.2 pW/√Hz (closer to the datasheet)

Kind Regards,

Geraldine

De : SLS-OPT <sls-opt-bounces at mailman.ccsds.org> De la part de Jon Hamkins via SLS-OPT
Envoyé : mercredi 22 avril 2020 18:16
À : Nicolo Mazzali (external) <Nicolo.Mazzali at esa.int>
Cc : SLS-OPT at mailman.ccsds.org
Objet : Re: [SLS-OPT] [EXTERNAL] Re: O3K channel model

Thanks, Nicolò.  Yes, there is more than one way to do this, and we could have expressed things in terms of received watts.  The approach we took was to simplify the mean and variance expressions and use as few parameters as possible.  In this way, the mean depends only on rho (the fade) and ns (the mean number of absorbed photons per signal slot).  This makes it intuitively related to the photon counting model, and allows straightforward plotting using photons/bit, which is the common metric by which to measure optical coding performance.

One can do things in watts, and translate to n_s, if you find that more intuitive.  We didn't find that as convenient, however.  For example, if we had expressed the model so that the mean signal was Ps in incident watts, and used that as the free parameter in the simulations, the variance expressions would include an eta/ (h nu) term, which would require knowing the frequency and quantum efficiency.  That's not a problem, but it is two more parameters than are needed in the formulation we suggested.  We think it may be more easier to run simulations with the normalized model, and then plug in these other parameters later if you want to plot vs. received watts for an APD with a specific responsivity (or quantum efficiency and frequency).

Anyway, that was our thinking.

     ----Jon
Jon Hamkins
Lead Technologist
33   |   Communications, Tracking, and Radar Division
O 818-354-4764   |   M 626-658-6220

JPL   |   jpl.nasa.gov
On 4/22/2020 12:28 AM, Nicolo Mazzali (external) wrote:
Dear Jon,

Thanks for summarizing the channel model and the parameters' values.
In principle we are fine with them, but we would like to understand the motivation for having all the powers (i.e., the signal power and noise variances) normalized as dimensionless quantities, instead of having them in watts - which is probably more intuitive, at least from an engineering point of view. Could you please confirm that this is indeed the case and elaborate a bit on your choice?

Thanks a lot in advance!

Kind regards,

Modis for ESA - European Space Agency

Nicolò Mazzali, PhD
Communication Systems & Technologies Engineer

Telecommunications Section (TEC-ESC)
Radio Frequency Systems Division (TEC-ES)

Directorate of Technology, Engineering & Quality (D/TEC)

ESTEC
Keplerlaan 1, PO Box 299
NL-2200 AG Noordwijk, The Netherlands
nicolo.mazzali at esa.int<mailto:nicolo.mazzali at esa.int> | www.esa.int<http://www.esa.int/>
T +31 71 56 53215

From:        "Jon Hamkins via SLS-OPT" <sls-opt at mailman.ccsds.org><mailto:sls-opt at mailman.ccsds.org>
To:        "SLS-OPT at mailman.ccsds.org"<mailto:SLS-OPT at mailman.ccsds.org> <SLS-OPT at mailman.ccsds.org><mailto:SLS-OPT at mailman.ccsds.org>
Date:        15/04/2020 17:20
Subject:        [SLS-OPT] O3K channel model
Sent by:        "SLS-OPT" <sls-opt-bounces at mailman.ccsds.org><mailto:sls-opt-bounces at mailman.ccsds.org>
________________________________

Attached is the O3K channel model we discussed yesterday.  It also contains a suggestion for how to state the O3K coding performance.  I welcome your comments.  If we can agree to the model in the next week or so, each agency may be able to begin simulating with it and discuss some initial results at the May teleconferences.
A few notes:

  *   I am suggesting we study 10 Gsps, 78.125 Msps, and 1.22 Mbps, since those include the highest and lowest data rates and one in the middle.
  *   I don't have a good suggestion for the TIA noise density at 1.22 Msps.  Dirk, would you be able to supply a number?
  *   I have algebraically simplified the expressions for the means and variances.  You can compare the model to the expressions Dariush presented on yesterday (p. 5), and check my algebra.
  *   I have included the fading parameter as well.  Just set rho=1 if you want no fading.
     ----Jon
--
Jon Hamkins
Lead Technologist
33   |   Communications, Tracking, and Radar Division
O 818-354-4764   |   M 626-658-6220

JPL   |   jpl.nasa.gov [attachment "2020-04-15-O3K-channel-model.pptx" deleted by Nicolo Mazzali/estec/ESA]
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