AT&T/SiriusXM Urge Opening of WCS Bands for LTE

Document asks FCC to prohibit mobile and portable transmitters in the WCS C and D blocks immediately adjacent to SDARS spectrum
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This article originally appeared in TV Technology.

Broadcasters may be interested in a compromise between SiriusXM Radio and AT&T that allows AT&T to make better use of the WCS bands through technology such as LTE, while providing protection to the Satellite Digital Audio Radio Service (SDARS). As spectrum becomes more crowded and the use of spectrum changes, the potential for interference between services operating on adjacent frequency bands increases. 

The FCC proposed a market-based approach for resolving adjacent band interference in a white paper I recently reviewed in RF Report. Another approach is for the two users to work together to develop a compromise that protects both of them. This appears to be the case here.

On June 15, AT&T and SiriusXM Radio sent the FCC a package of compromise proposals to allow AT&T to make better use of the 2.3 GHz WCS band. The joint letter noted: “The WCS band has been significantly underutilized since the Commission allocated the spectrum, due to the technical limitations imposed on WCS licensees to protect adjacent band operations and prolonged efforts to relax those limitations to allow more robust WCS use while protecting SDARS service.” 

It continued: “While the development of SDRS has not been constrained by technical rules, the SDARS licensees, now combined as SiriusXM, have endured years of uncertainty building and operating a terrestrial network under Special Temporary Authority, plus the significant uncertainty that the Commission might liberalize the rules governing WCS in a way that would threaten the ability of the over 22 million SDARS customers to receive a high-quality, high availability service.” 

The document asks the FCC to prohibit mobile and portable transmitters in the WCS C and D blocks immediately adjacent to SDARS spectrum. This, in effect provides a 5 MHz guard at each end of the SDARS band, while allowing WCS use for fixed services or base stations. 

SiriusXM and AT&T asked the FCC to exclude mobile and portable stations in the A and B blocks, and further removed from the SDARS spectrum, from the 50 mW/MHz power spectral density limit. Specifically, the companies “agree that technologies that employ and uplink protocol which avoids concentrating energy at the edge of the operating band (e.g. LTE, which uses Single Carrier FDMA with Proportionally Fair Scheduling) should be excluded from the power spectral density limits of 50 mW/MHz while retaining the maximum power level for portable and mobile devices at 250 mW EIRP.” 

The companies also asked the FCC to exclude mobile, portable and fixed CPE stations using frequency division duplex (FDD) technology from all uplink duty cycle limits. It isn't clear why this requirement is in the rules, as SiriusXM did not request it and FDD transmissions will have minimal impact on the AGC in Sirius XM receivers. SiriusXM said it believes that satellite radio operations can better coexist with WCS usage of FDD technology rather than TDD technology. Eliminating this restriction will maximize the performance of the WCS mobile broadband system while also maximizing protection of SiriusXM customers against AGC disruption. The companies also asked the FCC to permit FDD base operations in the lower WCS blocks. 

Regarding power levels, the companies agreed that no ground-level power flux density limit is required for base stations using FDD technology, but a ground power limit should be adopted. The agreed-upon maximums are -44 dBm for base and fixed transmitters operating in the WCS A or B blocks and -55 dBm for base and fixed transmitters operating in the C and D blocks. 

The letter states, “The Report & Order's prohibition on outdoor antennas for fixed CPE stations operating with 2 Watts per 5 MHz of less average EIRP and using the stepped emission mask threatens the viability of fixed applications.” It noted, however, that “SiriusXM remains concerned that increased OOBE [Out-Of-Band-Emission] levels from fixed CPE with outdoor antennas and the new stepped mask could have the potential for harmful interference to SDARS subscribers.”

As a compromise, AT&T and SiriusXM are proposing that fixed CPE stations operating at 2 Watts per MHz or less average EIRP, and using the stepped emission mask “be permitted to operate with professionally installed outdoor antennas in locations removed by 20 meters from roadways or in locations where it can be shown that the ground power level of -44 dBm in the A or B blocks or -55 dBm in the C and D blocks will not be exceed at the nearest road location.”

The letter contains additional requests regarding coordination, definition of harmful interference, and WCS build out requirements.

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