In search of 6G Spectrum: Why, What & How!
Introduction
Welcome to the captivating world of the electromagnetic spectrum - an extraordinary resource entrusted to governments worldwide. At the heart of modern communication, the spectrum encompasses a vast range of electromagnetic frequencies, serving as the lifeblood for transmitting and receiving information across the globe. Regulators, in their role as custodians, carefully allocate specific bands of frequencies for diverse purposes, including mobile, satellite, broadcasting, military, Wi-Fi/Bluetooth, and more. Whether through auctions, coordinated sharing, or open/unlicensed authorizations, frequencies find their designated users, a dynamic process influenced by ever-evolving technology. Join us as we delve into the ever-changing landscape of spectrum use, exploring how carriers and licensees ingeniously harness this invaluable resource?
A. WHY: More spectrum for 6G?
A new generation of communications technology occurs when two driving forces align: one that stems from societal needs, the other when technologies are mature enough to address the need. With joint efforts from all over the world, ITU-R WP 5D successfully drafted the new Recommendation for IMT-2030 (6G), which was finalized at the 44th meeting in Geneva on 22nd June 2023. This is a fundamental milestone in the development of 6G. The following figure shows the approved set of Usage scenarios & capability list for 6G Radio interface technology framework. The inclusion of sensing & relevant capabilities including the positioning capability should in particular be noted.
There is a need to consider different methods for estimating spectrum needs for IMT-2030. This is due to the fact that the requirements of the different IMT-2030/6G use cases can be very divergent. Also, for IMT-2020, there were various methods: traffic forecast-based approach, application-based approach, and technical performance-based approach.?GSA , conducted a study (Document No. APG23-5/INF-26) that considers various data-rate requirements of different IMT-2030/6G use cases, hence providing a preliminary analysis of the spectrum needs for each application with straightforward, not overly complicated technical assessment methods. More accurate spectrum needs calculations would require many assumptions including country/deployment dependent (density of population, IMT-2030/6G penetration, etc.) data.?
In this summary Table above, the split is done to differentiate between cases where usage of IMT-2030/6G use cases is required for wide-area outdoors and/or with supported mobility versus the case where usage of IMT-2030/6G is for local-area/indoors.??
Each expected IMT-2030/6G use case will have different spectrum bandwidth needs due to different bit rate requirements, etc. The overall spectrum needs of IMT-2030/6G will need to correspond to the aggregated spectrum needs of the different IMT-2030/6G use cases.?
The aggregated spectrum needs required to enable mobility and outdoor application of the analyzed IMT-2030/6G use cases are estimated to be in the order of 1 GHz per network. If assuming typically 3-4 networks in a country, and that in the long term, existing mid bands spectrum will be re-used for IMT-2030/6G wide area use cases, the overall additional spectrum needs will approximately be 2 to 3 GHz for the analyzed wide-area use cases (corresponding respectively to the cases of 3 and 4 operators in a country).?
One interesting aspect is to review the current spectrum allocations for IMT and check if they can serve the required 6G spectrum goal. The FR2 range of frequency spectrum 24-71 GHz in particular looks promising for the new 6G spectrum requirements. In this context, the following should be noted.
For sensing-enabled high throughput outdoor coverage: The lower the frequency range the better from coverage and mobility perspectives as spectrum bands do not have the same propagation characteristics. On the other hand, the estimated spectrum needs of the local-area, indoor use cases are around tens of GHz, suitable for short-range types of usage in extremely high frequencies. So we would like to access if a band lower than FR2 can be used to provide outdoor wideband IMT2030 services aiding sustainable energy consumption at 6G RRU.
For the above reason, pressure on the mid-band spectrum is increasing and governments are looking for answers as to how to satisfy the demand for 5G. International agreements on the mid-band spectrum have long since been outstripped by national decisions in 5G markets while demand is growing fast.?
For indoor Tbps communication vision: The spectral efficiency offered by 5G (viz 30 bps/Hz is far less than the number required to enable Tbps communication using contiguous bands of 100-400 MHz. Hence, the only viable way with the current state of communication technology to enable indoor Tbps communication is to look out for contiguous bands of much higher bandwidths. Sub-THz frequency spectrum hence becomes a natural choice to explore for the same.
B. WHAT: New spectrum & challenges
The very first aspect which needs to be considered when trying to review the potential candidate bands for 6G communication technologies is the underlying physics of the propagation media (viz free space & its attributes).
The following figure captures the attenuation observed at various carrier frequencies due to free space propagation loss, fog, rain, and acute signal loss at the harmonics & overtones of resonance frequencies of atmospheric elements like Oxygen & water respectively.
New Spectrum:
It can be readily observed that the following two categories of frequency bands could be studied for potential IMT2030 identification in years to come based on their favorable channel conditions for free-space communication.
2. Parts of the sub-THz band spanning from 92 GHz to 275 GHz
So the potential 6G spectrum bands would look as follows:
As the Licensed spectrum (used for IMT services) can be easily re-farmed for new-generation communication technologies hence the 6G is expected to re-use the legacy 4G-5G low-frequency spectrum to fulfill the coverage capability confirming to the Ubiquitous connectivity usage scenario of IMT2030.
It should be noted that the 6G use cases applicable for each band are unique and depend upon the propagation characteristics of the band. Hence the role of each band-?Low, Mid & High- is critical, indispensable, and irreplicable in 6G journey.
In line with the above views, the Indian administration submitted its position (Document No. APG23-5-INP-31) supporting cm-Wave & sub-THz band in the APG23-5 meeting towards WRC23 A.I. 10 IMT candidate bands.
Challenges
Ka & Ku bands are the mainstay of Satellite broadband communication. Also, many administrations have allocated major chunks of this spectrum to defense services. Hence, any possibility of IMT identification in cm-Wave spectrum is dependent upon the studies to evaluate the possibility & conditions of spectrum sharing / co-existence of multiple co-primary services in this band.
Sub-THz 6G faces significant unresolved challenges. For the RF circuits, higher output power and efficiency, lower Noise Figure, and phase noise must be achieved, with even more advanced antenna beamforming solutions used to combat signal losses and limited link distance. Propagation channels at THz frequencies for both indoor and outdoor communications remain uncharacterized and largely depend on simulation rather than measurements, as channel-sounding techniques and measurement equipment are primitive.
The use of the sub-THz frequency range relies on the development of components and an equipment ecosystem. This requires time to reach maturity, starting from the lowest sub-THz frequencies and slowly moving upwards in frequency.
Licensed v/s Unlicensed spectrum:
The following table summarizes the aspects pertaining to the Licensed & Unlicensed allocation of frequency bands for given services in a region:
Spectrum sharing
With the increasing demand for low & mid-band spectrum, it is now clear that multiple communication services would need to share a common spectrum to fulfill their needs in the future. The WRC23 agenda item 1.2 6 GHz is a classic case where studies from various regions are trying to evaluate possible interference from IMT2020 deployment to the Geostationary satellites uplink (FSS E-to-s).
There are various possible methods of spectrum sharing among different communication technologies. While the Unlicensed technologies rely upon carrier sensing methodologies (CSMA-CD etc), The methodology used by Licensed technologies to share the same spectrum mainly focuses on interference protection of incumbent Primary service from the new co-primary service by studying the co-existence scenario as prescribed by ITU-R & then identifying the interference mitigation methods (for example - geographical separation/Protection distance or transmission mask for new technology to be deployed etc).
One possible sharing method is to allocate a block of spectrum to two or more services and then implement the sharing within administrations by geographically separating users in the different allocated services. This utilizes sharing by separation in the spatial coordinate of the spectrum. An example is the sharing between television broadcasting and terrestrial mobile services where geographical separation has facilitated sharing. The allocation tables contain a number of country footnotes that define a different service for use within a particular administration. These footnotes provide flexibility for countries to utilize an allocated service differently from the world or regional allocation. These footnotes define a de facto sharing arrangement among users who utilize the Table of Allocations and the administrations utilizing a service defined by the footnote. This type of sharing has the greatest possibility of success for terrestrial services. However, operations in adjoining administrations may be affected. It is more difficult to affect the sharing when one or both of the services involves a space or satellite communication service. The advantages and disadvantages of allocation footnotes need to be carefully considered.
C. HOW: IDENTIFY & HARMONIZE 6G SPECTRUM
As highlighted in Figure 1, the discussions towards regional identification of IMT bands would happen in WRC27. However, the primary candidate bands which would be discussed under various agenda items in WRC27 would be decided at the end of WRC23 meeting (A.I. 10) itself.
Following sections try to sum up the procedural details of spectrum identification and harmonisation at national & international stages.
Radio Regulations (RR)
The most important element for spectrum planning is the national table of frequency allocation (NFAP). It is important that this table be derived from the International Table of Frequency Allocations of the Radio Regulations (Art.5). Even though administrations may allocate frequencies according to their national needs, (remember frequencies do not honor boundaries).
Frequencies should be assigned to compatible services especially near the borders in order to avoid harmful interference.
Good planning is crucial for economic and social benefits. It can facilitate radiocommunication growth especially when the demand for spectrum increases, for preventing interference and for the identification of spectrum for future needs.
The foundation of international frequency management is the Radio Regulations (RR), the binding international treaty that determines how the radio frequency spectrum is shared between different services, including space services.
Covers terrestrial fixed and mobile radio services, satellite-based services, sound and video broadcasting, radio navigation, meteorological tracking and forecasting, space research, and Earth exploration, as well as amateur radio.
The RR encompasses over 2300 pages of texts and charts that specify how equipment and systems must operate to ensure the successful coexistence of services in today's increasingly crowded airwaves.
World Radiocommunication Conferences
ITU-R reviews and updates the RR through (WRCs), which meet every four years for a period of four weeks.
WRCs review the way specific portions of the radio spectrum are allocated, along with procedures for coordinating, notifying, and recording of frequency assignments and Plan modifications. WRCs bring together governments to negotiate and agree on the relevant modifications to the RR, typically to allow for the introduction of new radio services and systems.
Preparations for WRCs involve extensive studies and preparatory discussions among all stakeholders (government regulators, and public and private sector users of spectrum, as well as their equipment suppliers) at the national, regional, and worldwide levels. Many of these stakeholders also serve as members of national delegations at the conference itself. This multi-stakeholder approach ensures consensus, so the RRs provide a stable, predictable, and universally applied regulatory environment that secures trillions of dollars of long-term investments in radio systems.
The following figure details the composition of the 3 regions in which ITU-R classifies the globe in order to manage the spectrum harmonization in RRs.
As seen above the spectrum under consideration for IMT identification in each of the regions may vary. While some of the bands might be for global consensus.
WRC23 Preparations
A report of the CPM to the World Radiocommunication Conference 2023 (WRC-23) was prepared in response to Resolution 1399 (C20) of the ITU Council to assist those who will be involved in the preparations for and deliberations at WRC-23. The Report was prepared and approved by the Conference Preparatory Meeting (CPM) at its Second Session held in Geneva from 27 March to 6 April 2023. The Report is structured to follow the topics of the WRC-23 Agenda and its content follows the outline approved by the First Session of the CPM, which was held during the week following WRC-19.
In India National Preparatory Committee (NPC) Chairman steers the work of all five Working Groups. He looks into the study done by WGs as per provisions of Radio Regulations, ITU-R Reports, ITU-R Recommendations, and is bound to protect the existing assignments. NPC chairman will also ensure that the study done by WGs is transparent and all the stakeholders' views are heard. He steers the work of WGs in order to timely complete the studies on WRC23 agenda items. NPC Chairman will submit the report/recommendations to WPC Wing for further examination, approval, and submission to relevant APT/ITU meetings.
There are five working Groups (WG) corresponding to the five Conference Preparatory Meeting Report 23-1 chapters. Each working group is allocated agenda items as per CPM23-1 for WRC23. The Working Group chairman considers the existing users, future interests of stakeholders, Radio Regulations (RR), ITU-R Report, ITU-R Recommendation, the progress of studies at ITU-R etc. Working Group chairman advances the studies on agenda items for WRC23 considering the input contributions from stakeholders and by holding discussions on it with other stakeholders to update/form the national views. WG Chairmen submit progress reports/recommendations/draft contributions to NPC Chair at regular intervals as per NPC work plan/schedule.??
Potential 6G Spectrum sharing studies??in 7-24 GHz band???
- No allocations for satellite services in the portions of bands
- Sharing of the spectrum with FSS (Earth-to-space) is possible (similar to the previous study's outcome in WRC-19 AI 1.13 and WRC-23 AI 1.2)
- Sharing is feasible due to a limited number of EESS earth stations (similar to the previous study's outcomes in WRC-19 AI 1.13)?
? - Sharing might be challenging and to be considered on a case-by-case basis, as an exclusion zone might be needed for coexistence.
REFERENCES
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1 年Very intereting and well written.
Principal Engineer - 5G PHY Firmware at Marvell Semiconductor
1 年Good to hear from you Vinay and know about the practical challenges/regulations behind the spectrum identifications & allocations around the world.
Wonderful Session Vinay Shrivastava Sir.. Had a great time listening to you about spectrum details (Ganesha of Telecom) ??
Your presentation was very relevant, I enjoyed listening to your talk. but I think time allotted was short. Maybe you can write a detailed article on it.