On 16th of May 2025, Ministry of Communication under Government of India, has published the draft rules for the Use of Low Power and Very Low Power Wireless Access System including Radio Local Area Network in Lower 6 GHz band (Exemption from Licensing Requirement). ^[1] This shall ultimately lead to opening up of 500 MHz of bandwidth from lower 6 GHz band for unlicensed usage in India in near future.

Frequency spectrum from 5150 MHz and 7125 MHz band are distributed in eight Unlicensed National Information Infrastructure (U-NII) radio band by the US Federal Communications Commission (FCC). U-NII 1 through 4 are for 5 GHz WLAN, and 5 through 8 are for 6 GHz WLAN (802.11ax) use. U-NII 2 is further divided into three subsections. ^[2]

U-NII 5 Ministry of Communication, GoI, has published the draft rules on 16th May 2025 for unlicensing the 500 MHz bandwidth, which is a part of U-NII 5 band (range 5925-6425). U-NII 5 has 24 channels of 20 MHz, 12 channels of 40 MHz, 6 channels of 80 MHz and 3 channels of 160 MHz.

Following are the regulatory requirements for 6 GHz unlicensed usage in India -

Other operational restrictions:
(i) All kinds of use are prohibited on Oil platforms
(ii) Indoor use is prohibited on Land vehicles (e.g., cars, trains) and boats, aircrafts except when flying above 10,000 feet.
(iii) Communication with and control of Drones and Unmanned Aerial Systems is prohibited.

EIRP, PSD and Out-of-Band Emission (OOBE)

I. EIRP (Effective Isotropic Radiated Power) represents the maximum power that an antenna can radiate in a particular direction, considering all the components of the transmission system. It’s a key metric used to ensure that wireless transmissions comply with regulatory power limits.
EIRP is not just the power output of the Wireless router. It involves various other parameters as discussed below :
EIRP (dBm) = Transmitter Power (in dBm) + Antenna Gain (in dBi) − Cable Loss (in dB)
Example -
Transmitter Power: 20 dBm (100 mW)
Antenna Gain: 5 dBi
Cable Loss: 1 dB
EIRP =20+5−1= 24 dBm
In summary, EIRP provides a standardized way to measure the "strength" of the Wi-Fi signal as it effectively leaves the antenna, taking into account all the gains and losses in the transmission path. It's a key factor for both network performance and regulatory compliance.

II. PSD (Power Spectral Density) typically expressed in units like dBm/MHz, describes how the total transmit power of a Wireless device is distributed across its operating frequency band. Think it in this way:

• Total Power (EIRP): This is the overall "strength" of the signal that's radiated, as discussed above. It's like the total amount of water coming out of a hose.
• Bandwidth: This is the width of the frequency channel that the Wi-Fi signal uses (e.g., 20 MHz, 40 MHz, 80 MHz, 160 MHz). It's like the diameter of the hose.
• PSD: This tells you how that total power is spread out over that bandwidth. It's like how much water is flowing per unit of hose diameter.

PSD has become particularly relevant with the introduction of Wi-Fi 6E (operating in the 6 GHz band). In 2.4 GHz and 5 GHz, focus was often on a constant EIRP regardless of the channel width. However, with Wi-Fi 6E, the approach has shifted to a constant PSD.

• Constant EIRP: If you doubled the channel bandwidth, the total power remained the same. This meant that the power per unit of frequency (PSD) actually decreased. This could lead to a Signal-to-Noise Ratio (SNR) penalty for wider channels, making them less effective than narrower channels in some scenarios. As per Juniper Networks, 80 MHz channels has to pay a penalty of 6 dB SNR in comparison with 20 MHz channel, and thus posing a challenge in using wider channels for high density deployments. ^[3]
• Constant PSD: If you will double the channel bandwidth, the total EIRP will also double. This is because you're maintaining the same power density across the wider spectrum. This helps to maintain a consistent SNR across different channel widths, making wider channels (like 80 MHz and 160 MHz, which are more common in 6 GHz) much more viable for high-density deployments and high-throughput applications without a significant signal quality penalty.

Relationship between EIRP and PSD:
There's a direct relationship between EIRP and PSD, as the total power is essentially the integral of the power spectral density over the bandwidth. A simplified relationship is:
EIRP (dBm) = PSD (dBm/MHz) + 10 * log10(Channel Width in MHz)

For a given PSD limit, a wider channel allows for a higher total EIRP. In nutshell, while EIRP tells us the overall strength of the Wi-Fi signal, PSD provides a more granular view of how that power is distributed across the frequency spectrum.

III. Out-of-Band Emissions: Out-of-band emissions (OOBE) are unwanted emissions that occur outside the assigned frequency band or channel of a transmitting device. These emissions are tightly regulated to prevent interference with adjacent channels and services. Maximum EIRP Density for OOBE is the maximum power per unit bandwidth (typically in dBm/MHz) that is allowed to be radiated by a device in the out-of-band region.