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

Jon Hamkins Jon.Hamkins at jpl.caltech.edu
Wed Apr 22 16:16:04 UTC 2020

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 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)*
> 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>
> To: "SLS-OPT at mailman.ccsds.org" <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>
> ------------------------------------------------------------------------
> 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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