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I am researching NZ's Radiocommunications Regulations for satellite services, which specifies the RF bands reserved for general use. However, different bands have been reserved for different types of service, particularly MSS and FSS. Am I correct in understanding that MSS refers to satellite communications with mobile users, while FSS refers to communications with fixed users?

I have found some sources that imply FSS refers to communication with geostationary satellites (ie. it's the satellites that are fixed) but others imply the classifications only refer to the Earth-based communications equipment. Furthermore, others seem to imply that FSS refers to satellites with which communication is continuously available (ie. geostationary satellites, or a constellation network).

As an example, would a satellite operator with a fixed ground station who is communicating with a CubeSat in LEO (multiple 10-minute contact passes per day) be considered FSS or MSS (or both, or neither)? If it is possible for that ground station to be easily moved (ie. plugged in somewhere else), does that change the classification?

My apologies if this is an amateur-ish question - I am still trying to understand the world of radiocommunications and the corresponding regulations.

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    $\begingroup$ Can you provide references to the sources you did find? $\endgroup$
    – Ludo
    Dec 11, 2023 at 7:48
  • $\begingroup$ @Ludo this Gazette notice from the NZ government is the main source that I'm trying to decode. The special conditions (section 5 of the notice) are particularly confusing to me - special condition 5 implies that Earth Stations in Motion may be used for the purpose of FSS, which leads me to believe that FSS does not refer to fixed ground stations $\endgroup$
    – moooligan
    Dec 11, 2023 at 21:39
  • $\begingroup$ @Ludo furthermore, this Public Information Brochure implies in section 4.1.2 that the licence covered by the Gazette notice in the previous comment does not cover 'fixed ground station facilities' $\endgroup$
    – moooligan
    Dec 11, 2023 at 21:42
  • $\begingroup$ @Ludo however, the ITU Radio Regulations (Volume 1, Article 1, Section 3, 1.21) defines fixed-satellite service to be 'between earth stations at given specified fixed points' $\endgroup$
    – moooligan
    Dec 11, 2023 at 21:47
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    $\begingroup$ I didn't find a definitive answer so leaving a comment for now. Going by this report the distinction is fuzzy. MSS are for mobile use (e.g. handheld devices, cars, etc.), while FSS are intended fixed (can be transportable, but are not intended to be operational while being moved). The linked report is a discussion on if stations on mobile platforms (I'm thinking drilling rigs etc.) are MSS or FSS. As far as I understand it (no expert), your understanding is correct and your example ground station would be an FSS in this context (even if it can be moved). $\endgroup$
    – Ludo
    Dec 12, 2023 at 15:16

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The definitions of FSS and MSS are summarised in the ITU handbook on Small Satellites - which may be a good resource for you in any case - as:

There has been an increasing number of small satellites telecommunication space missions using fixed-satellite service (FSS) and mobile-satellite service (MSS).
According to the terminology and technical characteristics of Chapter I of Radio Regulations, fixed-satellite service is defined in No. 1.21 of the RR as a radiocommunication service between earth stations at given positions when one or more satellites are used. Mobile-satellite service is defined in No. 1.25 of the RR as a radiocommunication service between mobile earth stations and one or more space stations, or between space stations used by this service, or between mobile earth stations by means of one or more space stations.
For fixed-satellite service, the earth stations are fixed in a given position, and they can operate with both GSO and Non-GSO satellites. For mobile-satellite service, the earth stations are mobile, and they can similarly operate with both GSO and Non-GSO satellites.

(section 4.6 on page 94).

The text references the Radio Regulations, which provides the formal definitions (Vol I, chapter 1):

1.21 fixed-satellite service: A radiocommunication service between earth stations at given positions, when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be operated in the inter-satellite service; the fixed-satellite service may also include feeder links for other space radiocommunication services.

and

1.25 mobile-satellite service:
A radiocommunication service:
– between mobile earth stations and one or more space stations, or between space stations used by this service; or
– between mobile earth stations by means of one or more space stations.
This service may also include feeder links necessary for its operation.

As this report shows, the distinction is not always clear: for example, is a station on a maritime platform (e.g. a drilling rig) mobile or fixed.

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    $\begingroup$ I didn't get too far into my amateur radio licenses, but one of my impressions was that the question on the regulator's minds in defining FSS and MSS is "if you break the radio laws, are we going to have to hunt you down or are you going to be breaking the law in a well-defined place" $\endgroup$
    – Erin Anne
    Dec 13, 2023 at 19:43
  • $\begingroup$ @ErinAnne It's much more technical reasons. For one, traditional FSS have large, pointed dishes with narrow beamwidths, so uplink frequencies can be reused over the same sky, compared with MSS with omni uplinks (e.g. Iridium). That also means FSS is less sensitive to terrestrial interferers than MSS, so that's a factor for frequency planning. Issues like foliage penetration, multipath fading from a moving vehicle, and cost, favor lower frequencies for MSS, whereas bandwidth means you go higher on FSS. $\endgroup$
    – user71659
    Dec 14, 2023 at 1:15
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I can't say that I know the answer to this for sure, but I have some experience in the satellite communications and, if I had to guess, I say that the distinction exists because of the overhead associated with establishing and maintaining a link.

First, I think it might be helpful to think of the terms as:

  • Fixed-user-"Satellite Service" (FSS), and
  • Mobile-user-"Satellite Service" (MSS)

With fixed user equipment, the user equipment can, upon being turned on, patiently scan the sky to find a satellite. When its found one it can initiate communications, download information about the dynamics of satellites in the constellation (information called "ephemeris"), and then software algorithms can plan out how to apportion bandwidth so that the user's equipment will receive service. After these initialization steps are completed, the overhead associated with providing service will drop significantly. Alternatively, with a GEO satellite, the installer can just get the user equipment oriented correctly once during installation.

With mobile user equipment, it is harder to get away with a long period of time for initializing the service. The overhead associated with maintaining service is also higher, as obstructions are more dynamic, orientation is more dynamic, and users' positions are constantly in flux.

In practice, there are a range of use cases with varying amounts of overhead, but for regulatory purposes its probably useful to organize them all into two main buckets: FSS and MSS.

Regulators probably ask an operators to estimate how many customers they can support in the case where all are FSS customers as well as the case where all are MSS customers (and maybe some blends as well) to give regulators a sense of the operator's system's capabilities and how well it performs.

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