Direct satellite connectivity to mobile

David Weinreich, Chair, Working Party 4B, ITU Radiocommunication Sector Study Group 4

Right now, direct-to-handset satellite communication is attracting consumers. It is also being considered by regulators. And as a very likely agenda item for the World Radiocommunication Conference in another four years, direct-to-handset is also being examined at the International Telecommunication Union (ITU) by study groups of the ITU Radiocommunication Sector (ITU–R).

The earliest promise of a mobile phone service

In the mid-to-late 1990s, the mobile-satellite service (MSS) segment was the first to show the promise of a true portable telephone service — where you could dial a number from almost anywhere, to connect with whoever you liked, anytime you wanted. This was the idea behind the so-called “Big LEO” (low Earth-orbit) systems of the time.

What the MSS proponents did not anticipate, of course, was the exponential growth and implementation of competing systems, initially called the Future Public Land Mobile Telecommunication Service (FPLMTS) and nowadays known as International Mobile Telecommunications (IMT).

A lack of customers soon led to financial difficulties and the eventual reorganization of MSS non-geostationary orbit (non-GSO) systems.

Today, however, we seem to have come full circle, with non-GSO MSS systems ready to soon provide direct-to-handset connectivity. This is due mainly to two new factors: the ability to construct smaller, more efficient spacecraft; and reduced launch costs.

The satellite component of IMT

With the onset of IMT services, the accompanying satellite component of IMT became inevitable.

Consequently, the ITU working party for MSS and other satellite systems — Working Party 4B in ITU–R Study Group 4 (Satellite Services) — developed ITU–R Recommendations for both the satellite components of the initial version of IMT and the follow-on IMT Advanced — commonly known as 4G.

At its recent June meeting, WP 4B approved steps to begin developing satellite radio interfaces for IMT 2030 — broadly equated with 6G mobile services. This work draws heavily on similar characteristics and documentation developed for the terrestrial element of IMT under ITU–R Study Group 5 (Terrestrial Services), Working Party 5D.

Technological developments

Direct-to-handset services will require new applications of current technologies. Due to the compactness of today’s cell phones, the antenna contained within is necessarily small. This means they offer relatively little antenna gain − just the ability to get enough satellite signal to make communication possible.

Coupled with this is the distance to and from the satellite over which the signal must travel. Given small antenna size, the satellite needs to be relatively near and is almost sure to be part of a low Earth-orbit constellation.

Advanced antenna techniques, possibly involving multi-beam, electronically configured adaptive arrays for both user terminals and spacecraft, are also likely be required.

Radio frequency issues

Which type of radio-frequency spectrum will be used to support direct-to-handset communication is important to know. Will it be terrestrial or satellite?

Both hold existing, worldwide allocations in the ITU Radio Regulations, and each offers advantages and disadvantages. The tricky part will be determining how to utilize the same spectrum for both satellite and terrestrial terminals simultaneously.

Major differences between terrestrial and satellite signal levels could create significant interference problems that need solving before direct-to-handset services can begin.

Tackling technical challenges

Regulatory bodies have already begun to tackle the anticipated problems and regulatory issues that might arise with the implementation of direct-to-handset services.

In North America, the US Federal Communications Commission has released a rulemaking inquiry requesting comments on how to provide “supplemental coverage from space” that would give users a single network solution. This would mean seamless connectivity, even when the user is beyond cellular coverage range.

In Europe, Project Team FM 44 of the European Conference of Postal and Telecommunications Administrations (CEPT) Electronic Communications Committee is considering the frequency management aspects of direct-to-handset. A forthcoming report may provide guidance on technical challenges, including how to address potential interference problems.

The scenario is also being considered in Asia and Australasia as various satellite operators initiate services with limited functionality, such as emergency-only connectivity to first responders.

All in one handset

Direct-to-handset IMT operation is coming soon. If, as hoped, it achieves a safe and productive landing, it will give users a full complement of expected mobile services with far greater range and versatility, all with a single handset.

*The views expressed in this article are those of the Chairman of Working Party 4B of ITU–R Study Group 4, and do not reflect the views or actions of any commercial entity.

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