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Federal Register / Vol. 86, No. 158 / Thursday, August 19, 2021 / Proposed Rules
are consistent with those stipulated by the ETSI standard EN 305 550. This standard has been in existence since 2014, thus these limits have been tested and deployed in other geographic regions with similar spectrum allocations. In fact, ETSI released an updated draft of this standard in 2017
and did not recommend changes to the limits. Thus, it appears that these proposed power levels have been successful in providing an environment that supports robust sharing of the 60
GHz spectrum among various users as the Commission is proposing to allow here. The Commission seeks comment on this view. The Commission also seeks input on the development status of the draft 2017 ETSI EN 305 550
Standard with respect to the technical parameters the Commission is proposing herein. The Commission understands that ETSI is undertaking a major revision of EN 305 550 to address receiver performance parameters, which the 2014 Harmonized version did not address. The Commission seek comment on the status of this revision and what changes to the specification are anticipated. In light of this ongoing revision, are changes to the Commissions proposed rules warranted? To develop a comprehensive record, the Commission seeks input on current or planned standards, both domestic and international, regarding operation of FDS devices in the 5771
GHz band, or any subset frequency band thereof. In addition, because radar resolution is generally dependent on bandwidth, the Commission seeks comment on whether the proposed rules will provide the sufficient resolution over the ranges needed for the applications envisioned for radars in the 60 GHz band.
Peak vs. Average Power Limits. The Commission notes that, except for fixed FDS devices that contain their operating bandwidth within the 61.061.5 GHz band, the existing rules for FDS devices do not specify an average power limit, but instead only a peak or maximum power limit, unlike the power limits for 60 GHz communications devices, where the Commission specifies both an average EIRP and a peak EIRP of 3 dB
above the average limit. The Commission observes that 60 GHz FDS
and radar devices will mostly use constant-amplitude continuous-wave CW, frequency-modulated continuous wave FMCW, or pulse/impulse transmissions. If the limits are applied only during active transmission i.e., only over the chirp or pulse duration, then the peak and the average signals will be equivalent. The Commission
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further notes that by specifying the limits only in terms of average power, potential measurement instrument desensitization phenomena can be avoided. The Commission proposes to define the power limits for FDS/radar devices in terms of average power and seek comment on the benefits of such a measurement. Are there consequences to specifying average power measurements rather than peak with respect to the potential to cause harmful interference to authorized users, or for unlicensed radar systems to coexist with unlicensed communications systems?
Those who believe that such a change might result in harmful interference should estimate the costs of such interference. Would this change impact passive EESS users in the 5759.3 GHz band? Are there are other possible FDS/
radar modulation techniques that would make requiring a peak power limit necessary?
The existing rules do not place a duty cycle restriction on 60 GHz devices.
Similarly, the ETSI EN 305 550 standard does not stipulate a duty cycle limit for 60 GHz short-range devices; however, the standard does specify requirements for 60 GHz receivers to ensure that they can adequately handle interferer signals.
The Commission imposed a 10% duty cycle limit in the Google Waiver Order and subsequent waivers for 60 GHz FDS
devices operating under higher emission limits than permitted in the rules. This 10% duty cycle is based on a maximum 3.3 ms transmission time in every 33 ms interval and was derived from Googles 2018 final agreement with stakeholders from the WLAN communications industry whose technology operates in the 60 GHz spectrum. The Commission proposes to require the same duty cycle restriction as that imposed in the multiple waivers.
However, the Commission notes that in some of the waiver requests, parties asked for a longer transmission time frame. The Commission further notes certain parties recommend modifying the duty cycle restriction adopted in the waivers to read that any radar off-time period between two successive radar pulses that is less than 2 ms shall be considered on time for purposes of computing the duty cycle. These parties express concern that the duty cycle requirement in the waivers will not promote coexistence with communications applications, including AR/VR/XR communication devices which require very high data throughput and very low latency. They point out that the 10% duty cycle requirement could lead to certain radars transmitting very short bursts in microsecond durations followed by similarly
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short silent periods also in the microsecond durations during the entire total 33 ms interval. This would result in interspersed, non-contiguous microsecond short silent intervals during which 60 GHz AR/VR communication devices may have difficulty accessing the spectrum due to the briefness of the radars quiet intervals; yet, when added together, the total amount of transmission time and silent intervals would comply with the 10% on, 90%
off definition of a 10% duty cycle.
On the other hand, other parties indicate that regulatory guarantees of such latency targets would substantially degrade performance of FMCW radars, which generally need to transmit frequent chirps to prevent velocity aliasing and span a sufficient burst time to enable good velocity resolution.
These parties argue that a duty cycle rule restricting radars to guarantee that at least 99% of WiGig packets experience on-air latency of no more than a few milliseconds would be unnecessary due to radars low transmission power, low potential to generate interference, and antenna directionality, as well as propagation loss in the 60 GHz band. A regulatory latency target will have a similar impact on pulse radars as well, as the radars observable maximum velocity and velocity resolution both depend on the pulse repetition frequency. As such, should duty cycle be defined differently for radar systems with different modulation techniques FMCW, pulse, etc. operating on different time scales?
On the other hand, in view of these apparent limitations with respect to maximum velocity and velocity resolution, is duty cycle a suitable parameter for regulation? Can limiting peak and average power within a defined band be a better approach than specifying a duty cycle? If regulating the duty cycle is necessary, then how should it be defined? The Commission seeks comment and technical input on appropriate parameters for regulation including definition/characterization of the duty cycle with respect to radar devices. The Commission seeks input on this issue to maximize the efficiency of both communications and radar operations without unduly degrading the operating environment for unlicensed users of the band or causing harmful interference to authorized users in the band. The Commission also seeks comment on whether radar signals could mimic the spectrum access protocols of communications devices to appear like any other communication signal thereby making a duty cycle restriction unnecessary. The
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