TRAI rejects broadcasters' demand for 100 MHz guard band in 5G auction; suggests ways to avoid interference

In its recommendations sent to Department of Telecom (DoT), Telecom regulator TRAI on Monday went ahead with suggesting the auction of the C-band spectrum between 3300-3670 MHz as prescribed by the ministry.

TRAI had, in 2018, recommended auctioning 3300-3600 MHz band for 5G services which was later increased to 3300-3670 MHz by DoT.

During the consultation process initiated by the regulator, the broadcasters had objected the addition of 70 MHz. The satellite broadcasters’ reservation was to maintain 100 MHz guard band between IMT/5G and broadcasting services to avoid any interference.

In its recommendation, the regulator has suggested that there is a need to make use of high-quality bandpass filters operating in 3700-4200 MHz range.

“Therefore, DoT should ask the Ministry of Information and Broadcasting (MIB) to take appropriate action and sensitize the MSOs, DTH operators, and other users to ensure the use of high-quality bandpass filters operating in 3700-4200 MHz range to avoid interference from IMT stations.

In order to avoid unwanted out of band emissions of the IMT stations falling within the FSS operating band 3700-4200 MHz, DoT should prescribe for having a sharp Spectrum Mask for IMT transmitters with an out-of-band PFD limit, the regulator said,

Acknowledging the broadcasters’ concerns, TRAI said that some of the stakeholders having interest in broadcasting and satellite have raised their concerns regarding possible interference due to reduction of guard band between IMT and satellite services from 100 MHz to 30 MHz.

Submissions made by these stakeholders are:

a) This allocation of frequencies to 5G services beyond the current NFAP-18 upper limit of 3600 MHz will lead to serious disruption of Satellite services for media and broadcast in the 3700-4000 MHz band. Today over 600 licensed satellite channels over India operate in this band. The disruption occurs due to the following reasons:

(i) The power received from satellite at receiver LNB (Low Noise Block) is much lower (~60 dB lower) than that of 5G Terrestrial signals which operate at a very heavy power level. This leads to the overloading of the LNBs of satellite Antennas and no signal can then be received.

(ii) Simultaneous use of the band by Satellite and Terrestrial 5G services is not possible.

b) The impact of reducing 100 MHz guard band to 30 MHz has two implications:

(i) Filters of 3700-4200 MHz, even if used, cannot filter out these out of band emissions as these falls in the 3700-4200 MHz band.

(ii) LNB Overdrive: The LNBs used in Cable Headends, which are typically designed for 3400-3900 MHz, would get overdriven (saturated) due to high terrestrial transmissions. This overdrive could have been prevented by the use of filters of 3700-4200 MHz but with Out of Band Emissions (OOBE) falling in the pass band of filters, the interference will lead to complete loss of signals.

c) Telecom Service Providers and DPOs (Cable operators, MSOs, DTH operators) be mandatorily required to install band pass filters in order to ensure that minimum disruption to broadcasting services.

One of the stakeholders submitted that C-Band Satellite downlink is being used by Prasar Bharati for Networking and Distribution. Any interference from IMT will also affect the C-Band Satellite Downlink reception by the receiving ends be it DD Centers, DD DTH, Other DTH Operators/MSOs/LCOs who are using the C-Band Downlink of DD Services for mandatory carriage on their platforms.

As regards the issues raised by some of the stakeholders that allocation of frequencies to 5G services beyond 3600 MHz will lead to serious disruption of Satellite services for media and broadcast in the 3700-4000 MHz band, it is noted that traditionally Fixed Satellite Service (FSS) earth stations operated in the 3400-4200 MHz C-band spectrum range. In India, this frequency range was mainly used for receiving the broadcasting channels and television channels by MSOs and DTH operators.

As the entire range 3300/3400-4200 MHz was being used earlier for C-Band satellite receive earth stations, the traditional bandpass filter deployed at receiving antenna covers the entire range 3400-4200 MHz. IMT emissions in the 3300-3670 MHz are likely to saturate the Low Noise Block (LNB) of the FSS earth station which traditionally operates in the 3400-4200 MHz, even if the mobile 5G signal is having a 30 MHz band gap with satellite frequencies. However, this interference issue can be resolved if the satellite receive earth stations, being deployed by MSOs and DTH operators, make use of sharp cut-off bandpass filters operating in 3700-4200 MHz range.

Further, in order to avoid unwanted Out of Band Emissions (OOBE) of the IMT stations falling within the FSS operating band 3700-4200 MHz, TSPs should be mandated for having a sharp Spectrum Mask for IMT transmitters with an out-of-band PFD limits. Considering the interference concerns raised by the stakeholders, TRAI through its letter dated 22nd February 2022, referred the matter to DoT, which in its response through letter dated 10th March 2022 mentioned that coexistence studies are being carried out which address DoS analysis regarding co-existence of satellite and IMT services in C-band, considering 30 MHz guard band between IMT and TV received terminals in 3700-4200 MHz. DoT further mentioned that as per the outcome of the study so far, it has been concluded that introduction of a cavity filter on the Television Receive-Only (TVRO) systems can make these systems co-exist with IMT/5G.

Further, the interference to broadcasting signals in C-band from 5G testing was experienced by one of the stakeholders in the month of December 2021. TRAI received a complaint from one of the stakeholders (M/s Sai Vision Cable network) regarding interference to broadcasting signals in C-band from 5G trails. The complaint was forwarded to DoT to examine the matter. DoT got the matter examined and submitted its response vide letter dated 10th March 2022, wherein it was mentioned that M/s Sai Vision Cable network has 8 no. of teleports and they operate around 3300-4200 MHz. To mitigate interference from 5G signals, they are now using 5G filter. It was further mentioned that it has been concluded that introduction of a cavity filter on the TVRO systems can make this system coexist with IMT/5G.

In view of the above, the Authority recommends that:

a) As the IMT emissions in the 3300-3670 MHz may saturate the Low Noise Block (LNB) of the FSS earth station which traditionally operates in the 3400-4200 MHz, there is a need to

make use of high-quality bandpass filters operating in 3700-4200 MHz range. Therefore, DoT should ask the Ministry of Information and Broadcasting (MIB) to take appropriate action and sensitize the MSOs, DTH operators, and other users to ensure the use of high-quality bandpass filters operating in 3700-4200 MHz range to avoid interference from IMT stations.

b) In order to avoid unwanted out of band emissions of the IMT stations falling within the FSS operating band 3700-4200 MHz, DoT should prescribe for having a sharp Spectrum Mask for IMT transmitters with an out-of-band PFD limit.

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