[CMC] Fw: CESG action on low rate wireless frequency trade

[Nestor.Peccia at esa.int]

FYI
----- Forwarded by Nestor Peccia/esoc/ESA on 05/02/2014 16:45 -----

From:   Chris Taylor/estec/ESA
To:     Martin Pilgram <martin.pilgram at dlr.de>, 
Cc:     CCSDS Secretariat <tomg at aiaa.org>, Nestor Peccia/esoc/ESA at ESA, 
Jean-Francois Dufour/estec/ESA at ESA
Date:   05/02/2014 16:09
Subject:        CESG action on low rate wireless frequency trade


Dear Martin, I had look again at the Magenta and Green books. In fact both 
contain justifications for the recommendation to use the 2.4 GHz band. 
In the Magenta book you will find an annex D: JUSTIFICATIONS FOR THE 2.4 
GHz BAND PREFERENCE. 
You should also take a look at section 6 in the supporting Green book. 
Here is a summarized response from Jean Francois Dufour the WG lead.
Dear Chris,
Here are some summaries of trade-offs we performed during the creation of 
the LDR Magenta Book concerning the promotion of the 2.45GHz frequency 
band.
[900-915MHz band Rules and Radar Band] Outside the United States, 
operation between 900 and 915MHz requires a license, and in Europe systems 
operating in this band must compete with a radar band, so the license is 
generally only available on an ?at risk? basis. This implies that the 
operator cannot restrict the operation of an (unlicensed?) interfering 
system but can be shut down if he interferes with anyone else who is 
licensed in that band. This incurs a risk to guaranteed operation. Under 
ITU regulations, the 900-928MHz band is not to be used outside Region 2 
(Americas), especially in areas that use the GSM 900 band, with the 
exception of Australia and Israel. 2.45GHZ is open ISM band (802.15.4 is 
2.400-2.495).
[Antenna Size] Antennas for lower frequency radiation must be larger than 
antennas for higher-frequency radiation in order to achieve the same 
efficiency and gain. Hence, antennas for communication nodes operating in 
the UHF bands (868 MHz and 900-915 MHz) will generally be much larger than 
antennas for nodes operating in the 2.4 GHz band.
[Compatibility to Oversized Cavity Propagation Theory] To be able to use 
our simulation tools, the oversized cavity theory dictates the need for a 
wavelength 10 times smaller than the spacecraft cavity size. 2.45GHz 
offers more capability in that regard. Also, the UHF wavelength is 
approximately 0.3 meters, which is of the same order as the size of many 
spacecraft cavities. In such environments, UHF propagation is likely to be 
influenced by resonant mechanisms. The 2.4 GHz wavelength is approximately 
12.5 cm, so multiple-antenna techniques can be readily utilised, even by 
small devices, to provide spatial diversity and/or multiplexing gain in 
reverberant environments.
[Availability] Due to the international acceptance of other 2.4GHz systems 
such as 802.11b, g, and n, radios and antennas for this band are readily 
available commercially. Radios for 868-915MHz are less common. As a lot of 
intended low-data rate sensors will be spun in from the commercial 
Industry, this importance of this criterial is not to be underestimated.
[Co-existence and Number of Channels] Additionally, with more frequencies 
available in the 2.4GHz band, there is more opportunity for selection to 
avoid co-channel or adjacent channel interference.


[Higher Frequencies] By the way, it may be interesting to know that as we 
are looking at a WWG High Data Rate Wireless Book (to be confirmed this 
Spring), we are also looking at other frequencies. An example is the 
IEEE802.11ac (500Mbps) running in the 5GHz band, while their has been 
discussions on the 60GHz band for short distance Gbps+ wireless 
communications. ESA is also running tests on Ultra-Wideband wireless 
technologies (typically frequencies at noise level, therefore 
theoretically possible to use between 3GHz and 10GHz). Therefore the 
frequency discussion will remain a topic in the next discussions.


In general, the compatibility with the spacecraft depends on the EMC 
specification. As there is as many EMC spec that of spacecraft, it is 
impossible to propose a generic statement. For example, for existing 
spacecraft as VEX, the 802.15.4 emitter need to be limited to -18dBm in 
order to ensure less than the EMC specification. On the other hand, 
802.15.4 emitter at 0dBm is compatible with Telecom spacecraft EMC 
specification.
Nevertheless, the WWG has decided to provide guidance through this Magenta 
Book and promote the frequency that made the most sense at the time of 
writing. The WWG of course welcomes any CCSDS member to provide inputs in 
this field.



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