Radio spectrum covers the range of electromagnetic frequencies from 3 Hz to 3,000 GHz. Lower frequencies in this range can cover long distances but are less effective for high-capacity services. In contrast, higher frequencies are ideal for transmitting large amounts of data, but only over shorter distances. Frequencies in the middle, typically between 300 MHz and 6 GHz, strike a balance, providing sufficiently high-capacity services over medium distances, making them particularly well suited for wireless communication services.

The terahertz (THz) band, positioned between 100 GHz and 30 THz (between microwaves and infrared waves), is also known as the sub-millimetre band. It offers significantly larger bandwidths, ranging from tens of giga-hertz to several terahertz, and is well suited for nanoscale cells. THz communication systems are highly directional, more energy efficient and less susceptible to free-space diffraction. They have lower latency and can effectively address the capacity limitations of current wireless systems.

Emerging technologies are now exploring the use of THz radiation for high speed point-to-point wireless data links. As a result, communications in the THz band are expected to play a crucial role in the development of upcoming 6G wireless mobile communications, paving the way for ultra-high bandwidth communication paradigms. The combination of large THz bandwidths, massive antenna arrays and densification driven by machine-type communications will significantly enhance communication system performance.

Background

Earlier, the government regulated telecommunications primarily through the Indian Telegraph Act, 1885, and the Indian Wireless Telegraphy Act, 1933. In December 2023, Parliament enacted the Telecommunications Act, 2023, to amend and consolidate the laws related to the development, expansion and operation of telecommunication services and networks, spectrum assignment, and other related matters. Under the new act, individuals seeking to use spectrum must obtain an assignment from the government unless exempted. The government may assign spectrum for testing, trials, experimentation and demonstration purposes to support emerging technologies, including the creation of regulatory sandboxes through administrative processes.

Currently, the government manages spectrum use through the National Frequency Allocation Plan [NFAP] 2022, which provides a regulatory framework for various services, such as cellular mobile, Wi-Fi, broadcasting, navigation and emergency communications. The NFAP 2022 aligns with the International Telecommunication Union’s (ITU) Radio Regulations and governs the use of radio frequencies from 8.3 kHz to 275 GHz in India. For frequencies beyond 95 GHz, most allocations are designed for radio astronomy and satellite-based services, with no allocations beyond 275 GHz. In addition, the NFAP 2022 allocates about 57 per cent of the spectrum between 95 GHz and 275 GHz to fixed and mobile services on a primary basis.

Against this backdrop, the Telecom Regulatory Authority of India (TRAI) released a consultation paper in September 2023 titled “Open and De-Licensed Use of Unused or Limited-Use Spectrum Bands for Demand Generation for a Limited Period in the Tera Hertz Range”. An online open house discussion on the consultation paper was held with stakeholders on March 8, 2024. Based on the comments and counter-comments received from stakeholders during the consultation process, and further analysis, TRAI has formulated its recommendations.

Salient features of recommendations

Separate experimental licence for spectrum in the 95 GHz-3 THz range

To support the development of emerging radiocommunications technologies, promote research and development (R&D), and facilitate testing and experimentation in wireless communications, the Department of Telecommunications (DoT) committee recommended the creation of a new experimental radio licence category – Spectrum-Terahertz Applications License (STAL). This licence would apply to the experimentation and demonstration of equipment operating exclusively on frequencies above 95 GHz. Further, the committee suggested opening the spectrum from 95 GHz to 3 THz for experimental use under STAL, aiming to make experimentation more attractive and drive innovation in this spectrum range.

In line with this, TRAI recommended introducing a new experimental authorisation called the “Tera Hertz Experimental Authorisation” (THEA) to promote R&D, indoor and outdoor testing, technology trials, experimentation and demonstrations in the 95 GHz-3 THz range. Any Indian entity, including academic institutions, R&D labs, government bodies, public sector units, technology parks, telecom service providers, incubators and manufacturers, would be eligible to obtain THEA.

The application and granting process for THEA would be online, requiring applicants to outline how their experiments could lead to innovative devices or services, along with providing an interference analysis. Certain application parameters, such as frequency, emissions type, power and location, must be publicly disclosed. Applicants seeking spectrum allocated for passive use must justify why alternative bands are unsuitable and acknowledge plans to transition long-term use to appropriate bands. A single point of contact should be designated to ensure compliance.

According to TRAI, THEA would be valid for up to five years, extendable in five-year increments. While applicants may request any frequency within the 95 GHz-3 THz range, no exclusive rights will be granted. Assignments will be on a non-interference basis and non-protection basis (NIB/NPB), with no protection from incumbent users.

Authorisation and assignment-exempt operations in the 116-123 GHz, 174.8-182 GHz, 185-190 GHz and 244-246 GHz frequency ranges

In its report, the DoT committee highlighted international practices for unlicensed frequency bands. The US Federal Communications Commission (FCC) has designated four frequency bands – 116-123 GHz, 174.8-182 GHz, 185-190 GHz and 244-246 GHz – as unlicensed, allowing their use without a licence. Meanwhile, the UK’s Ofcom has made the 116-122 GHz, 174.8-182 GHz and 185-190 GHz bands available on NIB/NPB. The European Conference of Postal and Telecommunications Administrations has also recommended the 122.0-122.25 GHz and 244-246 GHz bands for unlicensed use.

Taking into account the committee’s insights on THz spectrum, the government tasked TRAI with developing recommendations for the terms and conditions, including technical parameters, to permit licence-exempt operations within the 116-123 GHz, 174.8-182 GHz, 185-190 GHz and 244-246 GHz frequency ranges. The aim was to ensure that both passive and active services within these ranges are adequately protected.

In response, TRAI recommended that authorisation and assignment-exempt operations be permitted in these frequency bands in India. Initially, the technical specifications outlined by the FCC’s electronic code of federal regulations should be adopted for these operations in the 116-123 GHz, 174.8-182 GHz, 185-190 GHz and 244-246 GHz bands. These specifications can be modified if necessary, based on inputs from the Telecom Engineering Center (TEC), the technical arm of DoT, to better suit India’s requirements.

Authorisation and assignment of exempt operations in the 77-81 GHz range for automotive radar applications

The report released by the DoT committee on Tera Hera Hertz Spectrum outlined several key observations regarding the 40-95 GHz bands. It noted that the government is in the process of formulating regulations for the V band (57-66 GHz) and E band (71-76 GHz/81-86 GHz). In addition, the 76-77 GHz frequency band has been delicensed for the use of very low-power radio frequency devices, such as short-range radar systems. To facilitate vehicle-to-everything (V2X) communication, DoT has established a dedicated committee. The 76-77 GHz and 77-81 GHz bands are currently utilised for long-range radar and short to medium-range radar applications in V2X technologies respectively. In this context, TRAI sought stakeholder comments on whether licence-exempt operation should be permitted in the 77-81 GHz band for automotive radar applications.

Based on these developments, TRAI has made the following recommendations:

  • The 77-81 GHz frequency range should be made available for authorisation and assignment-exempt operations for automotive radar systems in India.
  • The technical parameters outlined in the ITU’s recommendation on “System characteristics of automotive radars operating in the frequency band 76-81 GHz for intelligent transport system applications” should be adopted for these operations.

Conclusion

Unlike millimetre wave communications, THz communications can leverage the higher bandwidths available in the THz spectrum to achieve terabit-per-second data rates without the need for additional spectral efficiency enhancement techniques. Due to their shorter wavelengths, THz communication systems offer several advantages, including higher link directionality, reduced susceptibility to free-space diffraction and inter-antenna interference, smaller system size, and greater resistance to eavesdropping. The THz band has the potential to support higher user densities, improved reliability, lower latency, improved energy efficiency, enhanced positioning accuracy, better spectrum utilisation, and increased adaptability to different propagation scenarios.

However, several challenges must be addressed for the widespread adoption of THz communications, such as high propagation losses and power limitations, which restrict communication to very short distances.

Niha