By Parag Naik,
CEO, Saankhya Labs
September 4 2016: The Dynamic Spectrum Alliance (DSA) which Saankhya Labs is a proud member of – asked me as an Indian entrepreneur innovating on spectrum to write an article on demystifying whitespaces in India. I was only too happy to oblige. Earlier on in this year, Professor H Nwana, Executive Director of the DSA (and former boss of UK Spectrum Poicy at renowned regulator Ofcom), in welcoming the Indian Government’s move to issue eight experimental licenses in the 470-582 MHz band, noted:
“These eight licenses will also bring a great deal of innovation to engender in India from native companies such as Bengaluru-based Saankhya Labs, who develop world-beating software defined radio chipsets covering this band. The 470-582 MHz band will be key to bridging the digital divide in India, a country with more than 800 million people who are not connected to the Internet, 68% of which are living in rural areas.” Prof Nwana and the DSA are right, and this brief article proceeds to address some of the key myths about whitespaces, particularly for the Indian context.
In the past decade India embarked and successfully completed “Aadhar”, the world’s largest social identification programme. This has led to fewer leakages in the subsidy scheme meant for the unprivileged.
The Government of India has now embarked on the “Digital India”, a program to narrow down the digital exclusivity and the urban-rural digital divide. It aims to connect 500K villages and more mofussil towns. The advantages of such a program have been debated in multiple fora and the conclusion about its utility is forgone.
The backbone of this program is nationwide optical fibre and in some cases high throughput satellites (HTS); however, the radio technologies to provide the “last mile” and “last meters” have been in question. Among the candidates, white spaces in the TV bands (TVWS) have been proposed as one of the preferred technologies. There have been several debates on its merits and demerits. A lot has been said by consultants but there has never been a deep dive. This is an attempt to dispel the myths from a practitioner.
This article focuses on the technologies associated with the implementation of the Digital India program and the ‘myths’ that have been doing the rounds.
Myth 1: There is no white space in India
In India, unlike in the US and Europe, there are no private terrestrial broadcasters. The only broadcaster is the Government-owned Doordarshan (DD). Since there is no analog switch off, for the moment the 470-646 MHz spectrum is vacant. Given this, it might seem from a semantic perspective that there is no white space. But this in extremely narrow definition of White spaces.
White spaces are more than just empty channels between two active broadcast channels. White Spaces also refer to a set of technologies that use cognitive and advanced signal processing to enable efficient and dynamic access of spectrum that incidentally uses the UHF/VHF spectrum. Given the ITU resolution, white space devices are by definition secondary users and need to adhere to far stricter norms for spectral emissions. In India, Xerox has become synonymous with the photocopier. Similarly white spaces encompass more than just spectral occupancy.
Myth 2 : White spaces are access technologies to connect phones or laptops to the fibre backhaul
As an engineer, to me the distinction between access and backhaul spectrum sounds semantic as both are frequencies! However from an operator perspective access spectrum is an expensive resource that has to be utilized fully and efficiently. This makes sense. Given that the 700 MHz spectrum is priced quite high it is natural for operators to oppose “giving away” spectrum in the 470 MHz range for “free” (unlicensed).
As a semiconductor vendor supplying chipsets for white spaces, this should be music to my ears. However for a TVWS chipset to get into a cell phone, the cost structures must be that of Wi-Fi modules and to get to those economies of scale it would take quite a while. There has been talk of implementing a tri-band Wi-Fi chipset that supports 802.11ac and 802.11af in a single chip. From an economics standpoint it would not work as the margins for low end Wi-Fi chipsets are few 10 cents. Furthermore designing a small form-factor, high gain antenna at reasonable price points in the 470 MHz band is a huge challenge if not impossible.
Further cellular networks use a spectrum reuse of three to mitigate interference and reduce receiver costs. In an access network it makes sense to keep the receiver complexity low. However in backhaul networks, which are less sensitive to pricing interference, mitigation techniques to improve overall throughput can be implemented. In the interim I believe that white space is suited to be a backhaul or “middle mile” technology that compliments the operator’s access spectrum especially for 2G/3G and Wi-Fi small cells in rural areas.
Myth 3: Spectral efficiency of white space technologies is poor
This is far from the truth and people raising these questions implicitly assume that Wi-Fi based CSMA/CD MAC protocols will be used for deploying white spaces. The more polite a protocol, the lower its spectral efficiency. Other MAC protocols such as OFDMA/TDM and standards like 802.22 are spectrally more efficient while retaining politeness to an extent. In fact some of these are better than LTE in the uplink.
A centrally coordinated data base that ensures “fairness” for competing users and operators ensures the best of fairness and spectral efficiency. Also in certain network architectures it becomes difficult to implement traditional MIMO due to the nature of the terrain. When pitched as a back-haul spectrum, there are other ways to improve spectral efficiency to about 15 bits/Hz which is far greater than the current LTE networks.
Myth 4: Channel bonding to increase data rates
Channel bonding is the easy way out to increase data throughputs especially when spectrally inefficient schemes are used. It works well for licensed spectrum and in the higher bands such as 5 and 6 Hz where there are swathes of spectrum. In the UHF band spectrum is limited to about 120 Mhz in India. Therefore highly spectrally efficient schemes are imperative and traditional Wi-Fi and LTE type efficiency is not going to fly for large scale nationwide deployments. More so because of the spectrum reuse factor. Current cellular networks have a spectrum reuse of three which means that for every 1 Hz of spectrum, 3 Hz of spectrum is needed to actually deploy networks. The ideal is to get to a single frequency network. SFN networks usually put a heavy workload on the receivers and are therefore more likely to be implemented in a backhaul network than an access network
Myth 5: Small Cell for urban, Macro cells for rural
There is no single network architecture that fits all. Where fibre POP’s are abundant it makes sense to use small cells as the reuse factor increases, throughputs increase and the overall cost of ownership is lowered.
Given that the fibre POP’s in the rural areas are limited and the range offered by macro cells, it looks logical to use macro cells. However cellular 3g/4g macro cells consume about 1 kW of power and are extremely expensive. This is one of the reasons operators are not able to service their service obligation that results in lots of LUT (low utilization towers).
TVWS based backhauls change all of that. Pitching it as a backhaul alternative gives both cap-ex and ope-ex advantages. Operators can now provide 3g/4g services to rural areas.
Parag is a serial entrepreneur with over 24 years of industry experience, out of which 16 years have been in high technology startups. At Saankhya he has been the CEO since April 2014. He co-founded Saankhya and was the CTO and VP Marketing between 2007-2014 contributing to the product roadmaps and designing Saankhya SDR architecture. He is a named inventor on 19 US and India patents in the areas of CPU/SDR architecture, Digital Communications, Signal Processing and Hardware-Software Co-design/ Code generators.
The Dynamic Spectrum Alliance is a global organization advocating for laws and regulations that will lead to more efficient and effective spectrum utilization. The DSA’s membership spans multinationals, small- and medium-sized enterprises, and academic, research, and other organizations from around the world, all working to create innovative solutions that will increase the amount of available spectrum to the benefit of consumers and businesses alike.