Most countries follow a policy of assigning spectrum for terrestrial services through a process of auction. In India, the practice is perpetuating since 2010 when the 3G & BWA (Now 4G) spectrum was put to auction, and the outcome was a huge success. But when it comes to satellite spectrum, most countries allocate it through administrative means, and the process of auction is not implemented. In this note, we will make an attempt to analyze what is the reason for this difference in approaches, and at what point in time the approaches might align.
What is ITU’s Role?
Satellites need two important resources. A) A place to park itself in the sky (parking slots/orbits); B) An access to a frequency band to communicate with earth stations (orbital frequencies). Both these resources are intertwined with each other and are allocated by ITU based on meeting certain rules and regulations — which involve facilitating coordination with all nations. Why? The reason:- without going through such a process (involving a central agency), there will be chaos (total confusion) and therefore, the orderly growth of the sector will get hampered (orbital slots are scarce, and frequencies have to be separated out in space to prevent the satellites from interfering with each other).
Fortunately, this problem is not that severe in the case of terrestrial networks, as, unlike the satellites, the BTSs of the terrestrial networks can be separated out easily by tilting their RF beams downwards so that the radio waves emanating from them do not travel far enough to cause interference with networks of neighboring countries.
Most nations are members of the ITU (International Telecommunication Union) and agreements reached there has the status of an “international treaty” that all member countries are bound to respect.
Article 6 Para (CS 37) of the ITU constitution provides that the”
“Members States are bound to abide by the provisions of this Consitution, the Convention, and the Administrative Regulations in all telecommunication offices and stations established or operated by them which engage in international services or which are capable of causing harmful interference to radio services of other countries”
But ITU provides a large amount of flexibility to the participating member nations, by allowing each ITU Member State to be free to deviate from the Table of Frequency Allocations, but only to the extent that harmful interference is not caused to any other ITU Member State that is using the spectrum in accordance with Article 5 of the Radio Regulations. No 4.2 of the Radio Regulation states:-
“Member States undertake that in assigning frequencies to stations which are capable of causing harmful interference to the services rendered by the stations of another country, such assignments are to be made in accordance with the Table of Frequency Allocations and other provisions of these Regulations.”
Can Regulators Auction Satellite Spectrum?
The act of frequency assignment by ITU does NOT give a right to the satellite operator to start providing services in a country unless it is successful in securing permission (license) from the local government empowering it to do so. The reason is simple —All governments have the obligation to ensure — a) that their natural resources (spectrum) are most efficiently used; b) competitiveness of the market is preserved; c) services that are already running in the same band (having given equal primary status by ITU) are not interfered with; d) consumers interested are protected; e) security and integrity of the nation are preserved.
Hence, in order to meet the above objectives, if the local administration decides that the “auction” is the way to assign spectrum for providing satellite services then it is well within its right to do so.
Why is Satellite Spectrum Not Auctioned?
All satellite providers will like to share spectrum with each other, even though it tantamounts to opening the door to its own competitor — resulting in decreased market share and loss of pricing leverage due to more competition. Strange isn’t it? But there is a reason — The biggest enemy of satellite providers is “fragmentation of spectrum”. This is quite unlike their terrestrial counterparts who would like to have an exclusive right to their spectrum of operation — for ensuring business certainty and to reduce the cost of coordination. But for the satellite providers, these are much smaller challenges compared to the loss of capacity due to fragmentation of their spectrum. Let’s analyze -
Assume that you have X GHz of spectrum available for assignment, and you ask two terrestrial operators to share it among themselves, their individual capacity will go down by half (assuming both use it in the same geography with the same intensity). This means, that it is like assigning 50% of the X GHz individually to each of the terrestrial players. No?
Whereas if you make the same proposal to two satellite operators, their individual capacity will remain more or less the same (maybe go down by a little) when they share the full spectrum with each other, compared to the case when the spectrum is spitted into two halves and given individually to each of the operators. But why?
The reason for these two different outcomes is due to the fact that terrestrial and satellite networks have different capabilities when it comes to harnessing the full capacity of the assigned spectrum. Terrestrial networks have a higher capability (exponentially more) compared to their satellite counterparts. Why? This is due to higher frequency reuse capability driven by a smaller cell radius, made possible by the RF signal’s ability to attenuate much faster on the ground than in free space. However, the satellite networks have limited spectrum reuse capabilities, due to the satellite numbers being significantly less compared to the BTS numbers of the terrestrial networks and their (satellite’s) RF beams on ground have a very large foot print compared to that of a terrestrial BTS’s coverage.
Hence, satellite operators can live very well with the need to coordinate (using complex interference management) between themselves, rather than allowing their spectrum to get fragmented by auctions. But this inference might change as and when the intensity of satellite networks grows significantly, as more players enter the space, especially with the purpose of offering high-speed broadband services.
How do Satellite Networks Coordinate?
The first level of coordination happens at the ITU level (as mentioned earlier), however, the next level of coordination happens at the country level. This is to make sure that coordination is not done arbitrarily, but anchored upon certain rules so as to ensure that players are not disadvantaged, and can plan their investments properly and in the framework of full transparency. And spectrum (natural resource of the country) is put to good use and not wasted.
On 15th Dec 2021, FCC released a proposal with the purpose of refining the earlier rules for coordinating and sharing spectrum between NGSO FSS systems. The purpose is to facilitate satellite broadband competition. FCC’s existing default spectrum sharing rule (being refined) mandates band splitting to deal with inline interference between the satellite system by measuring the noise temperature infused by the interfering system. As soon as this metric goes beyond a threshold value (6%), the band splitting between system get triggered, otherwise, the individual satellite systems have access to the full spectrum. The need for such refinement was felt to mitigate the uncertainty being faced by the existing satellite operators in face of the new entrants. The existing operators have made huge investments, and they need some certainty in the environment in which they function. This is mandatory to keep the sector healthy and the interests of the investors stay alive.
Similar attempts are in place by other regulators over the world, and therefore, it echoes the point (stated earlier) that regulators have the full right and need to make rules of operations for satellites in order to facilitate orderly growth of the sector and to ensure spectrum is efficiently used in line with the interest of the country and its people.
What are the Frequencies Assigned to Satellites?
The following table list all the frequencies that are assigned to satellite operators intending to offer NGSO services.
In order to estimate the number of players operating in a band, we must have the capability to view these assignments overlapped on top of each other. With this intent, I put together a tool (link embedded) that provides the user with that capability. This tool also overlaps the 5G bands of interest (26/28 GHz and E Band). The screenshot of the tool for the Ka-band is below.
One can see that two types of satellite usages of the Ka-band are overlapping on the 28 GHz band of 5G interest (27.5 to 28.5 GHz). These are:- Uplink (earth to space) for Gateways and Uplink (earth to space) for the user terminals. Gateways of all operators fully overlap the 28 GHz band, but use terminal overlap is very less, except for Telesat and OB3 — who fully overlap the band (27.5 to 28.5 GHz). In other words, except for Telesat and OB3, the satellite operators must not have any interest in the block (27.5 to 28.5 GHz) from a user terminal point of view now (may be in futue).
What did TRAI Recommend For 27.5 to 28.5 GHz?
TRAI in its recommendation dated 11th April 22 (Page 322) said the following:-
6.7(a) As the mmWave spectrum is going to be used for capacity requirements, its deployment is not likely to be ubiquitous rather it is more likely to be kind of hotspots or urban microcells. Therefore, IMT Stations and Satellite Earth Stations Gateways (Earth to Space) can co-exist in the 27.5–28.5 GHz frequency range. The Satellite Earth Station Gateway should be permitted to be established in the frequency range 27.5 to 28.5 GHz at uninhabited or remote locations on case to case basis, where there is less likelihood of 5G IMT services coming up.
So the TRAI has concluded that Satellite Gateways of all operators whose frequencies overlap with the 27.5 to 28.5 GHz can coexist with 5G IMT. But what about the user terminals (especially of Telesat & OB3)? How will those coordinate with the gateways and the 5G IMT deployed concurrently on this spectrum band (27.5 to 28,5 GHz)?
Can Satellite & 5G coexist in the 27.5 to 28.5 GHz band?
The biggest issue seems to be the need to coordinate between the 5G equipment (especially BTS) with the satellites tuned to the user terminals, as we know that Gateways are not an issue at all as the TRAI had concluded. Why? Unlike the case of gateways, the user terminals can’t be placed at remote locations. They probably it will be all over the place, and in some cases even overlapping with the 5G equipment. But there could be one more issue, i.e the need for coordination between the gateways and the user terminals of the satellite operators working in the same block of spectrum. This they have to do anyway, irrespective of whether 5G is there or not.
So how do we manage the interference between a 5G equipment and the satellites in reception mode — trying to lock into the RF signals emanating from the satellite user terminals? This we can do easily by ensuring that all satellite BTSs RF beams point downwards and none point directly to the satellites, and it will work perfectly (with no cross-border interference) as most satellites stop receiving signals when they go below a certain angle of elevation. However, there is also a chance of the satellite user terminals interfering with the 5G BTSs and handheld terminals too, as 5G equipment transmits and receives in the same spectrum band, quite unlike the satellite operators who use this band to uplink RF signals of gateways and user terminals to the satellite hanging on the sky.
Since the satellite beams are narrow, and the RF beams from the 5G BTSs will never point upwards in the sky, it is clear that both 5G and Satellite can coexist in the same band. Of course, the 5G user terminals are still there, but they are less of a problem as their signals are of low power and will never reach the satellite to cause interference.
What could be the best assignment strategy for the 27.5 to 28.5 GHz band?
The best assignment strategy could be to auction ONLY this block (27.5 to 28.5 GHz) where both 5G and satellite interest coexists.
And then leave the coordination issue between the 5G and Satellite to be managed by the operator himself.
As no significant IMT interest exists as of now in other spectrum blocks (Ku and portions of Ka), these blocks can be assigned administratively as band splitting will result in a huge capacity loss for the satellite operators.
And since the gateways will be allowed to function outside auction in the same spectrum band, the satellite operator’s interest stays protected.
Therefore, the 1 GHz (27.5 to 28.5 GHz) can be split into two blocks of 500 MHz each and put to auction, and the flexibility should be given to the winner for the using the acquired spectrum for providing both satellite services and 5G services depending upon his business needs. In this way, the conflict of interest between 5G and Satellite can be totally mitigated, and the spectrum can be used more efficiently. As regards the gateways are concerned, they are anyways not a big issue as mentioned earlier (these can be located in remote areas). Anyways, as per TRAI’s recommendation, these gateways should be allowed to share the same spectrum block facilitated by the regulator.
Conclusion
It is clear from the above discussion that it is not wise to auction all kinds of spectrum up for providing satellite services. As this will drastically reduce the their overall data throughput capacities. However, for the 27.5 to 28.5 GHz a different approach (of auction) can be adopted, as band fragmentation into two halves (from the point of user terminal) will not reduce satellite networks capacities, as there are only two players whose allocated frequencies (for user terminals) are overlapping with the band 27.5 to 28.5 GHz where IMT interest exists. Also, gateways will not be impacted at all, and will have full access to the whole block of spectrum as these will not be part of auctions.
Following this approach will have many advantages :- a) Satellites networks can contribute to providing services unhindered; b) 5G can leverage the economies of scale of deployment in 28 GHz band of many countries (USA, Korea & Japan); c) Spectrum can be more effciently used, which otherwise will lie fallow if only satellite alone is allowed to operate; d) Government will be able to collect some revenue; e) No need to mandate complex rules of coordination in this band. In the end it is win-win for all.
(Views expressed are of my own and do not reflect that of my employer)
PS: Find the list of other relevant articles in the embedded link.
