Abhay Karandikar, Former Chairman, TSDSI, and Director, Indian Institute of Technology Kanpur

Abhay Karandikar, Former Chairman, TSDSI, and Director, Indian Institute of Technology Kanpur

In recent years, there has been significant growth in cellular mobile infrastructure in India. Today, broadband connectivity in the country is primarily enabled through the cellular network. However, despite the exponential growth of cellular mobile subscribers, universal penetration of rural bro­adband connectivity remains elusive. “Con­­­n­ecting the unconnected” population me­ans addressing requirements such as accessibility, affordability, low energy consumption, fixed access/low mobility support, and wide coverage.

The specifications of cellular mobile te­chnology are being primarily driven by the Th­ird Generation Partnership Project (3GPP) es­ta­blished by the standards development or­ga­nisations (SDOs) of Europe, the US, Kor­ea, Japan and China in the 1990s. At the time, India had no SDO and no presence in global standards specifications for 2G and 3G. In 2014, the Telecommunica­tions St­a­n­­­dards Develop­ment Society of India (TSDSI) was form­ed as India’s SDO. The TSDSI beca­me an organisational partner of 3GPP only in 2015. Since then, Indian en­ti­ties have been participating actively in specification development activities.

The International Telecommunication Union (ITU) outlined its vision and requir­e­ments for 5G mobile broadband net­works in the International Mobile Tele­commu­ni­cations-2020 (IMT-2020) standards. Some of the key performance indicators (KPIs) in IMT-2020 are a peak downlink data rate of 20 Gbps, user experienced data rate of 100 Mbps, over-the-air latency of 1 ms, connection density of 106 devices per square km, spectral efficiency of 30 bit/s/Hz and vehicular speeds of up to 500 km per hour. With these KPIs, the 5G cellular standards are focused more on the use cases and requirements of urban areas in developed countries.

To address rural connectivity in India, the Government of India launched an ambitious project called BharatNet, which is expected to provide fibre connectivity to all gram panchayats (GPs) in India. From the distribution of the distance between villages and their corresponding GP offices in India, one can surmise that a radius of 3 km fr­om the cell site would cover 60 per cent of villages while a radius of 6 km from the cell site would cover over 90 per cent of villages. There­fore, a wireless technology that can support a cell radius of around 6 km can address the problem of broadband access for over 90 per cent of villages. The original rural en­hanced mobile broadband (eMBB) configuration with a cell radius of around 1 km would be able to cover only a small area ar­ound a cell site. Cells with such small radii would increase the backhaul and cell site infrastructure requirements, and create an economically unviable solution.

To address this, TSDSI members in­troduced low mobility large cell (LMLC) as a new sub-configuration of the rural eMBB test environment. Unlike the other rural bro­adband use cases of IMT-2020 and the ear­lier IMT-Advanced system, LMLC does not focus on high speed mo­bility. LMLC was eventually incorporated as a mandatory re­quirement in IMT-2020 by the ITU in 2017.

3GPP developed its Release 15 specifications with Radio Interface Technology (RIT) in mind to address the IMT-2020 requ­ire­ments. With the goal of addressing the LMLC requirements of IMT-2020, TSDSI members proposed a new radio waveform (pi/2-BPSK) to increase the uplink coverage. This new radio waveform has a low peak-to-average-power ratio, and is re­silient to the non-linearities of power amplifiers. However, this was accepted only as an optional feature in the 3GPP Release 15 specifications. Since 3GPP did not include it as a mandatory feature in the Re­lea­se 15 specifications, the TSDSI then decided to submit its own RIT called 5Gi as a candidate technology for IMT-2020. The TSDSI’s RIT was essentially an enhancement of the 3GPP Release 15 specifications, with pi/2-BPSK radio waveform and some other minor tweaks. The ITU submitted this to the TSDSI in July 2019. It was evaluated during 2019-20 and was finally approved as part of the IMT-2020 5G family of standards in November 2020.

After about a year, 3GPP agreed, on Dec­ember 17, 2021, to incorporate the TSDSI’s new radio waveform in its future specifications release, Release 17, thus en­abling the merging of 5Gi with 3GPP’s 5G specifications.

In this journey, the research teams of TSDSI members, led by IIT Madras, IIT Hyderabad and CeWiT, played a significant role. The Government of India and the De­partment of Telecommunications pro­­­vi­ded immense support to the TSDSI leadership and members in steering their proposals in the global fora. The merger of the 5Gi standard with 3GPP has enabled a si­ngle common specification for the IMT-2020 5G fa­mily of standards. This also sym­bolises the acceptance of Indian requ­ir­ements and contributions in global 5G stan­dards. While the TSDSI was a late en­trant in 5G, we have an opportunity to con­tri­bute to 6G, as the glo­bal community has st­ar­ted work on 6G. More concerted effo­rts, however, need be made in the coming years to in­fluence 5G and 6G technologies to add­ress the Indian requirements. This will help est­a­­blish an ecosystem of Indian companies and organisations with ownership of next­-gen­eration wireless technologies, lead­ing to ful­­filment of the vision of Atmanirbhar Bharat.