Satellite based connectivity in BharatNet

Bharat Broadband Network Limited (BBNL) has been mandated by the Government of India to set up the flagship BharatNet project. A total of approx. 2.6 lakh Gram panchayats spread over more than 7000 blocks and 700 districts of the country are being covered by laying incremental fiber between the block and the GPs. The digital infrastructure of the middle mile, thus created is made available to the service providers (TSP/ISP/MSO/LCOs) at a nominal price, who in turn use it to provide affordable high-speed broadband to rural citizens and institutions. It is expected that the affordable broadband access will unleash plethora of opportunities in rural hinterland, which still houses more than two-thirds of the country’s workforce but contributes less than half to the national income.

Keeping in mind the enormous future requirement of bandwidth, BharatNet prefers to use OFC as a medium of connectivity, but other media such as radio and satellite are also being used to connect remote, inaccessible locations where OFC laying is either not possible or economically unviable.

In India, the usage of satellite technology started in early 80s along with the other countries. The earlier satellites were geo-stationary (located at about 36000 km above equator) with a single beam covering large geographical area, and were suitable for voice services but had low data throughput capacity (a few kilobits). ISRO launched many geo-stationary satellites for providing telecommunication/broadcasting services in various frequency bands S-band, C-band, Extended C-band, and Ku band.

The satellite technology has evolved over the years. The present high throughput satellites (HTS) with multiple beams are capable of providing terabits of data throughput. The beams can be steered over a particular geographical location to provide more data bandwidth over that area. ISRO has launched high throughput multi-beam, geo-stationary satellites (GSAT-19, GSAT-11, GSAT-29) in the last 2-3 years, which are capable of providing data throughput of about 30 Gbps capacity over India. Handheld satellite phones are available. The price of data BW has also come down 4-5 times from about ₹9 lakhs per Mbps per annum to about ₹2.11 lakhs per Mbps per annum.

Under BharatNet, approximately 7000 sites are planned to be connected through satellite across 26 Indian states and UTs. Most of these sites are in North Eastern region, J&K, Ladakh, HP, Uttarakhand, Sikkim, Islands, LWE areas like Chattisgarh, Odisha, Jharkhand and other states through the satellite beam available in the region. As of now, more than 4000 sites have been commissioned using satellite.

The network has VSATs (1.2 dia antenna) at GP sites connected in a star topology to four satellite gateways (9.1 dia antenna) at Ranchi, Ahmedabad, Delhi and Bengaluru, through satellite beams available in the region. The baseband equipment of gateways and the VSAT equipment use the latest technology DVB-S2X which is the most suitable for digital broadband type of services. The gateways are equipped with routers, network management systems and are connected to Internet nodes through Internet Lease Line (ILL). The VSATs at GP sites are equipped with Wi-Fi access points, solar panels, UPS so that Internet based services can be provided to the public at those remote places.

The satellites are ISRO’s high throughput satellites, GSAT-11 and GSAT-19. The satellites operate in Ka and Ku frequency bands i.e. the transmission from and to gateways are in Ka frequency band and the transmission from and to remote GP site (VSAT) is in Ku frequency bands. ISRO is also launching multi-beam GSAT-20 satellite with 48.5 Gbps capacity over India which shall operate in Ka and Ku frequency band, for the first time. The use of Ka frequency band provides large amount of spectrum/bandwidth in comparison to other frequency bands.

Although geo-stationary satellites are capable of high data throughputs but the latency is of the order of 600 milliseconds (ms), which may not be suitable for applications requiring low latency. Therefore, the latest trend in the satellite technology is to create constellation of satellites at much lower earth orbits, in order to provide higher data throughputs with low latency networks. One such constellation of satellites located at medium earth orbits (MEOs) at about 8000-12000 km over earth, provide higher data throughput with low latency (about 150 ms).

Another large constellation of satellites (thousands) at lower earth orbit (LEOs) at about 1000-2000 km above earth are also being launched, which are capable of providing much higher throughputs with very low latency (less than 50 ms) and thus are comparable with optical fibre. MEOs are already available for commercial usage and LEOs are likely to be available for commercial usage from year 2022 onward. The price of the data bandwidth provided through satellites has also come down drastically and is comparable with cellular mobile communication networks for the end users. In future, the combination of geo-stationary satellites, MEOs and LEOs shall be used, depending upon the applications/usage.