[Sls-ocm] ITU and Link budget

Mon Apr 11 13:49:41 EDT 2011

Dear OCM All,

Here are some infos to prepare our discussion on ITU docs during the OCM meeting (May, 18th).

I found the following ITU recommendations related to free-space optical comms:
- SA.1742, Technical and operational characteristics of interplanetary and deep-space systems operating in the space-to-Earth direction around 283 THz
- SA.1805, Technical and operational characteristics of space-to-space telecommunication systems operating around 354 THz and 366 THz
- P.1621, Propagation data required for the design of Earth-space systems operating between 20 THz and 375 THz
- P.1622, Prediction methods required for the design of Earth-space systems operating between 20 THz and 375 THz
- P.1814, Prediction methods required for the design of terrestrial free-space optical links
- P.1817, Propagation data required for the design of terrestrial free-space optical links

The ITU recommendations mentioned by Enrico (SA.1742 and SA.1805) base their link budgets on the following papers:
[1] B. J. Klein and J. J. Degnan, "Optical Antenna Gain. 1: Transmitting Antennas," Appl. Opt. 13, 2134-2141 (1974)
[2] J. J. Degnan and B. J. Klein, "Optical Antenna Gain. 2: Receiving Antennas," Appl. Opt. 13, 2397-2401 (1974)

Whereas I think everybody agrees with the Tx-gain definition given in [1], the Rx-gain definition provided in [2] may not be consensual. In particular, the Rx-Gain includes the "losses at the detector", which makes the Rx-gain depend also on the detection technique and possibly on the turbulence parameter r_0. E.g., the Strehl loss would thus be included in the Rx-Gain. (As you know<http://cwe.ccsds.org/sls/docs/SLS-OCM/Meeting%20Materials/2011_05_Berlin/FSO_LinkBudgetConventions_Proposal_20110324.pdf>, I personally prefer to avoid the concept of Rx-gain).

Note also that the ITU recommendation P.1814 bases its link budget on the "geometrical attenuation" (which we also call "free-space coupling loss") formulated as the ratio of two surfaces. So, ITU seems flexible regarding link-budget formulations.

Regards,

Nicolas
Chair of SIG OCM

________________________________
From: Enrico.Vassallo at esa.int [Enrico.Vassallo at esa.int]
Sent: 06 April 2011 11:26
To: Perlot, Nicolas
Cc: sls-com at mailman.ccsds.org; Gian.Paolo.Calzolari at esa.int
Subject: Fw: [Sls-ocm] Concept book + Link budget convention

Dear Nicolas,

I do not want to challenge your reasons for proposing the use of directivity instead of gain, and the relevant link terminology.

However, I would like to point out that other bodies like the ITU do use gain and free-space loss also for optical links. In my opinion, it would not be a good idea if CCSDS were not to use the same terminology of ITU. We have always tried to be consistent with ITU in the RFM WG.

Please check recommendations ITU-R SA.1742 and SA.1805 on 238 THz and 354/366 THz communications. For ITU copyright reasons, I cannot forward them. I trust you can get them from DLR frequency management office.

Regards, Enrico
----- Forwarded by Enrico Vassallo/esoc/ESA on 06/04/2011 11:16 -----
From:

Gian Paolo Calzolari/esoc/ESA

To:

Enrico Vassallo/esoc/ESA at ESA

Date:

28/03/2011 14:52

Subject:

Fw: [Sls-ocm] Concept book + Link budget convention

________________________________

per te che sei un esperto di link budget

----- Forwarded by Gian Paolo Calzolari/esoc/ESA on 28-03-2011 14:51 -----
From:

<Nicolas.Perlot at dlr.de>

To:

<sls-com at mailman.ccsds.org>

Date:

27-03-2011 22:11

Subject:

[Sls-ocm] Concept book + Link budget convention

Sent by:

sls-com-bounces at mailman.ccsds.org

________________________________

Dear Lasercom People,

1) Regarding the last version of our "concept book" that I provided in February, I did not receive the feedback that I had wished from ESA, NASA, CNES. However I received some comments, so I uploaded a new version on CWE with the proposed changes highlighted in yellow:
http://cwe.ccsds.org/sls/docs/SLS-OCM/Draft%20Documents/OCM_ConceptBook_Draft_20110325.doc

2) I'd like to propose a convention for link budget calculation/display in our field of free-space optics. Please read the attached document (3 pages), be open-minded and let me know what you think.

Regards,

Nicolas Perlot
Chair of SIG OCM

_____________________________________________
From: Perlot, Nicolas
Sent: Dienstag, 15. Februar 2011 13:52
To: 'sls-com at mailman.ccsds.org'
Subject: Spring meeting in Berlin and Inputs for Concept Book

Dear Lasercom people,

  *   CCSDS Spring meeting in Berlin is approaching (May 16th- 20th). So far, limited info is available:
http://public.ccsds.org/meetings/DispForm.aspx?ID=101

  *   About our Concept (White) Book:
  *   A new version of our Concept Paper is available at http://cwe.ccsds.org/sls/docs/SLS-OCM/Draft%20Documents/OCM_ConceptBook_Draft_20110211.doc
Changes were made according to point 7)c. of the last-meeting minutes. Also, propositions were made according to point 7)e. on the following sections:
§ 3.3. Inappropriate technical solutions
§ 3.4. Possible working areas within space laser communications
  *   So far, I have received no inputs from ESA, NASA or CNES. In addition to the new sections §3.3 and §3.4 where suggestions would be appreciated, several sections have been identified where agencies shall provide their views. Please return the document with your respective inputs by March 18th (one month time):
  *   NASA: pls, review and complete
§ 4.2.2
§ 4.3.1
§ 4.3.2
§ 4.3.3
  *   ESA: pls, review and complete
§ 4.2.1.1
§ 4.2.1.2
§ 4.2.1.4
§ 4.3.1
§ 4.3.2
§ 4.3.4
  *   CNES: pls, review and complete
§ 4.2.3.1
§ 4.2.3.2

  *   I also recall the action items on NASA/JPL from our Spring 2011 meeting:
  *   Describe figures and tables in §7.4 and §7.5 of the Concept Book.

Best regards,

Nicolas Perlot

--
Nicolas Perlot, Ph.D.
Digital Networks Section,
Optical Communications Group

German Aerospace Center (DLR)                 phone: ++49/8153/281836
Institute of Communications and Navigation    fax:   ++49/8153/282844
Oberpfaffenhofen, P.O. Box 11 16              email: nicolas.perlot at dlr.de<mailto:nicolas.perlot at dlr.de>
82234 Wessling, Germany                       http://www.dlr.de/KN/KN-DN/

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