A marriage of the two worlds

The telecom networks space has been a battleground for decades, with the terrestrial and satellite worlds locked in relentless competition. Each has vied for supremacy, striving to assert dominance and position itself as the future of telecommunications.

The terrestrial world has been the elder brother of the two, which graduated from legacy analogue communications to bandwidth-efficient digital communications, incorporating technologies like Multi-Protocol Label Switching (MPLS) and Dense Wavelength Division Multiplexing (DWDM) to make wired communication high-speed in the core part of telecom network. Wireless technologies have evolved from 1G and 2G to the present ultra-high speed 5G technology, primarily used in the access part of the telecom network.

The satellite world, on the other hand, evolved from L-, S-, and C-band satellite systems by placing GEO satellites and providing Demand Assigned Multiple Access (DAMA) and Pre-Assigned Multiple Access (PAMA) voice and data circuits to remote areas not serviced by the terrestrial world. It graduated to LEO satellites in the 1990s, serviced by Iridium and Globalstar, enabling communication over satellite phones to individual users and gaining widespread popularity.

The Satellite World further graduated to Ku and Ka frequency bands to bolster more bandwidth for each satellite payload transponder. This migration helped in providing high-speed satellite broadband service for today’s communication requirements. Further, employing a string of LEO satellite constellations operated by a band of satellite brothers led by Starlink lowered the latency, thus resulting in improved user experience. The game-changer has been the cost of launching the satellite, which has decreased substantially, and the transponder bandwidth of the satellite, which has increased by leaps and bounds. The above two factors have ensured the re-emergence of LEO constellations for low-cost satellite broadband offered by multiple satellite operators.

NTN heralds a transformative shift in global communication, merging the strengths of satellite and terrestrial technologies well ahead of the arrival of 6G.

MARRIAGE OF CONVENIENCE

Over the decades, it has been realised that the terrestrial world can never provide full global coverage, even on the mainland. The return on investment, or the RoI, is the controlling factor in deterring the expansion of the terrestrial communication grid. As the human population concentrates around major cities, cellular networks are in clusters, and thus, vast stretches of areas in the hinterland experience poor connectivity.

NTN enables the Internet of Things (IoT) by supporting IoT applications optimised for low-power devices and those with minimal data exchange requirements.

The satellite world can potentially engross vast oceans, mountains, and scarcely populated hinterland in its global footprint. Utilising the GEO satellites or a constellation of dedicated LEO satellites can ensure global coverage to users. On the contrary, it also realises that it can never match the speeds of state-of-the-art terrestrial technology. Further, the satellite is a critical communication resource in the sky with no option to upgrade till the satellite dies its death and is replaced by its next better-performing avatar.

Hence, good sense prevailed, primarily to the credit of the satellite world. This allowed leveraging the strengths of both worlds to bridge the vulnerabilities of the other, thus ensuring a robust, seamless communication grid by marrying the two telecom worlds.

NEW KID ON THE BLOCK

The Non-Terrestrial Network (NTN) is the new kid on the block and promises to change how we communicate, much before 6G arrives. It is the marriage of convenience of the two telecom worlds. The name is misleading and sounds like it advocates satellite communication primarily. But, contrary to its name, its sole aim is to extend the coverage of terrestrial communication through existing satellite infrastructure.

Integrating terrestrial and NTN can extend telecom coverage, ensuring that remote areas lacking terrestrial infrastructure are adequately served.

The 3GPP has defined its technical specifications in Releases 17 and 18 and the bands of operation (see Spectrum For NTN). The global regulatory organisations, along with the GSMA and 3GPP, are finalising the frequency bands to augment and implement this new kid in their respective countries. Its USP: using mobiles and IoT devices to connect to LEO satellites and extend the coverage of terrestrial cellular networks.

BENEFITS OF THE MARRIAGE

Integrating terrestrial and NTN offers compelling advantages that benefit both systems and intrigue telecom users. The marriage of the two technologies can lead to extended coverage, ensuring that remote areas lacking terrestrial infrastructure or where deployment is economically unfeasible are  adequately served.

The system’s disaster resilience provides crucial backup communication during natural disasters and emergencies when terrestrial networks might be compromised. Global connectivity is especially ideal for industries that require consistent communication across vast and remote areas, such as maritime, aviation, and global supply chain tracking. Additionally, NTN enables the Internet of Things (IoT) by supporting IoT applications optimised for low-power devices and those with minimal data exchange requirements.

IMPLEMENTATION OF THE MARRIAGE

Two specific use cases illustrate the implementation of NTN. The first, NTN NB-IoT, uses LEO and GEO satellites to support low data rate NTN NB-IoT devices, compressed voice calls, and SMS as alternatives to terrestrial mobile communication. It also facilitates transmitting and receiving non-real-time data from remote locations across various industries, including agriculture, construction, forestry, and shipping.

The second, NTN NR Direct-to-Device (D2D), exclusively uses LEO satellites. This approach involves a ‘Cell on the Sky’ where NTN NR (base station) is implemented onto LEO satellites and High Altitude Platform Systems (HAPS), supporting higher-speed communications such as voice and video calls, media streaming, and mobile communication services to aircraft, high-speed railways, and ships. It also enables communication for the remote control of heavy machinery and autonomous vehicles, providing seamless coverage over land, sea, and air, thus supplementing the coverage of terrestrial base stations.

CHALLENGES OF THE MARRIAGE

Like every marriage, this integration also has its share of challenges. Communication with GEO satellites can experience higher delays of up to 500 milliseconds and significant path loss. The elliptical coverage and high altitudes of satellites cause variations in signal strength that must be considered in NTN design. Fast-moving NTN satellites produce a Doppler shift in the frequency of operation, requiring compensation by the user equipment.

The mobile nature of NTN cell sites leads to multiple handoffs, increasing the likelihood of dropped signals. This challenge is crucial to ensure that NTN complements rather than overlaps with cellular coverage, which could increase in-band interference. Other ongoing debates include cost, deployment challenges, competition, and radio spectrum allocation. Whether to use the same frequency for operation or an adjacent one is a constant topic among regulators and impacts regulation and actual device support of specific 5G NTN radio bands.

FOSTERING A STRATEGIC ALLIANCE

As the convergence between satellite and terrestrial networks gains momentum, several satellite operators, including Skylink, Sateliot, Skylo, and other European entities, have jumped onto the bandwagon, recognising it as a mutual gain, a win-win for both worlds. This collaboration allows satellite operators to tap into the extensive telecom user base while telecom operators can dramatically expand their global reach.

Globally, telecom operators remain cautious, aware that embracing this marriage is inevitable in extending their cellular coverage without installing thousands of additional cell towers. They also evaluate the implications of sharing their highly valued existing spectrum with satellite operators or persuading them to operate in adjacent bands.

Regardless of the specifics of this engagement, both sectors must deepen their understanding of each other to ensure a sustainable and fruitful partnership. For telecom users, this alliance promises exciting prospects as they stand to gain comprehensively from this strategic convergence.

It is an exciting time ahead. 

By Dr Sidharth Shukla

The author is the Head of Next Gen Tech, Networks Strategy, Bharti Airtel Ltd.

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