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.
