Need For Spectrum Sharing In A Productive And Optimal Way By The TSPs

A TSP should share interband spectrum with only one TSP in an LSA. Post sharing, there should be at least two independent wireless access networks in the LSA. TRAI recommended that TSPs should be allowed to import the required network equipment in respect of shared frequency bands

As the demand for mobile services is increasing, demand for spectrum is also increasing. Since spectrum is a limited natural resource, it is necessary to ensure efficient and optimal utilisation. Spectrum sharing is one of such techniques which can be exploited by Telecom Service Providers (TSPs) to provide additional network capacities in places where there is network congestion due to spectrum crunch.

Unlicensed spectrum is used for provision of Wi-Fi services to enterprises and to households. Demand for this spectrum is also increasing because of the surge in availability of new apps and services.

Use of the same spectrum by different users at different timings or at different geographical locations will increase the spectrum utilisation efficiency. With proper space/frequency coordination and putting restrictions on maximum power that can be radiated by one service, both the services working in the same frequency band can coexist. Better off-axis radiation pattern of the antennas of base stations of the two services can reduce the interference and helps in siting the base stations of the two services close by.

For example altimeters in the aircrafts operate in the 4200-4400 MHz band. Aircrafts use the altimeters, in low visibility condition, to land. 5G mid band spectrum ranges from 3300- 4200 MHz. So there is a possibility of a 5G signal interfering with the altimeter signal. So effective coordination is required between the airport authority and 5G operators in those countries which use 5G at 4200 MHz. In the US, they have banned the use of this band by 5G operators near airports. In India, NFAP (National Frequency Authorisation Plan) allocation for 5G is from 3300 to 3800 MHz only (there is a guard band of 400MHz). We have also put restrictions on the maximum power emissions by 5G BTSs near airports and on proximity between airports and 5G BTSs so that the altimeters will not be interfered with out of band emissions from 5G BTSs.

Licensed spectrum is the standard for 5G networks but since spectrum is scarce, particularly in low and mid band ranges, solution would be to allow TSPs to share the available spectrum.

Intraband and interband spectrum sharing

Spectrum sharing can be of two types viz.1) Intraband spectrum sharing and 2) Inter-band spectrum sharing

Intra-band frequency sharing is the sharing of airwaves between two operators within a specific band. Based on TRAI (Telecom Regulatory Authority of India) recommendations, DOT permitted Intraband band spectrum sharing and issued guidelines on 24.09.2015.

Inter-band spectrum sharing is the pooling and sharing of airwaves between two or more operators in multiple bands. In April 2024, TRAI recommended that inter-band spectrum sharing should be allowed to better utilise spectrum resources in the country. According to TRAI, inter-band access spectrum sharing between access service providers may be implemented either by way of pooling of access spectrum held by the participating access providers in different frequency bands through common radio access networks. It can also take place by allowing the partnering access service providers to use each other’s radio access networks operating in the shared frequency bands in the Local Service Area (LSA). A TSP should share interband spectrum with only one TSP in an LSA. Post sharing, there should be at least two independent wireless access networks in the LSA. TRAI recommended that TSPs should be allowed to import the required network equipment in respect of shared frequency bands.

Authorised Shared Access (ASA) of Spectrum

TRAI recommended that DOT should explore the possibility of implementing ASA technique- based spectrum sharing. Under ASA, the spectrum assigned to government agencies or other entities (non-TSPs) for IMT (International Mobile Telecom) services can be assigned to TSPs as secondary users. This is because the utilisation of spectrum by govt agencies/non TSP may not be optimum across frequency, space and time.

Dynamic Spectrum Sharing (DSS)

DSS is “two or more radio services adjusting their respective operations to achieve efficient utilisation of the same frequency range in time or space such that they can provide their intended services in a cost effective manner with minimal performance degradation to their respective operations”. This is an emerging technology and will bring innovation. It is an antenna technology that permits two services (say 4G LTE and 5G technology) to be used in the same frequency band. It allocates bandwidth to the services based on the changing levels of usage while minimising the interference and maximises spectral efficiency.

DSS is highly effective in a Cognitive Radio (CR) network. A CR network is aware of itself, of what is happening within and around in the environment and can make decisions by mapping what is known at any given point against a table of predefined objectives. It can manage radio resources to prevent interference between two services. The basic foundation of DSS are RF spectrum, Software Defined Radio (SDR) and Network Slicing optimised for specific types of services or different customers. DSS allows both the services to share the same antenna, Radio Frequency units and Spectrum. It increases spectral efficiency by allowing low priority unlicensed users to share the spectrum of high priority licensed users. DSS is also ideal for IOT because its dynamic nature is appropriate to the wide diversity of proliferating IOT systems and networks, as it allocates the spectrum on the fly to ensure IOT devices have the bandwidth and reliable communication channels to work efficiently and guarantee the transmission of large amounts of data.

However, uptake of DSS depends on motivating those operators already holding spectrum to share it by giving financial incentives. It will also require valuation of spectrum sharing and need for investment in new technologies.

NSA (Non Stand Alone) 5G shouldn't be mistaken for DSS. While NSA creates a 5G network with 4G infrastructure using dual connectivity, DSS permits 4G LTE and 5G NR to coexist in the same frequency band. Airtel and Vi have gone for NSA 5G implementation.

Spectrum sharing is a technically complex operation. The TSPs desirous of sharing the spectrum, which has been used exclusively by the incumbent TSP, have to ensure that their operations do not interfere with the incumbent’s performance and parameters.

Wayforward

The National Digital Communication Policy (NDCP) 2018 recognises spectrum as a key natural resource for public benefit to achieve India’s socio economic goals. NDCP 2018 aims to further liberalise the spectrum sharing (along with leasing and trading) regime in the country. Also the Telecom Act 2023 provides that the central government may permit sharing of assigned spectrum.

Hope DOT accepts the recommendations of TRAI on interband spectrum sharing, leading to better spectrum utilisation. It is also hoped that ASA based spectrum sharing is implemented so that the present under utilised spectrum will be utilised optimally. With the rollout of 5G networks, DSS will play an important role in achieving optimal utilisation of spectrum and unlocking the potential of low- band, mid-band and mmWave spectrum. Hope this technology will mature soon!

‘Use it or share it’ rule, will lead to productive use of spectrum. Spectrum sharing enables the TSPs to expand the services and bridge the Digital Divide. It will reduce the spectrum price, ultimately lowering the tariffs, benefitting the consumers.

References:

1. TRAI recommendations on Telecom Infra sharing, Spectrum Sharing and Spectrum Leasing

2. ‘Spectrum Sharing is becoming a necessity for the success of 5G’ by Martyn Warwick, Telecom TV.

(The author is a former Advisor, Department of Telecommunications (DoT), Government of India)