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FCC Proposes to Eliminate Spread Spectrum APC Requirement, Reduce Spread Spectrum Power Limit; Cleans Up Portions of Part 97

03/18/2010

In response to a 2006 ARRL Petition regarding spread spectrum issues, the FCC released a Notice of Proposed Rule Making (NPRM) on March 16 (WT Docket No 10-62), proposing to amend Part 97 to facilitate the use of spread spectrum communications technologies by eliminating the requirement that amateur stations use automatic power control (APC) to reduce transmitter power when the station transmits a spread spectrum (SS) emission and reducing the maximum transmitter power output when transmitting a SS emission. Through an Order attached to the NPRM, the Commission also made "certain non-substantive revisions" to the Amateur Service rules.

Notice of Proposed Rule Making

Spread spectrum techniques are methods by which the information signal of a particular bandwidth is intentionally spread in the frequency domain. At any point of bandwidth the SS emission occupies, either the power spectral density of the transmitted signal is reduced to a comparatively low level or the duration of a transmission on any frequency in the frequency segment is very brief. Consequently, stations in the same area can transmit SS signals without causing harmful interference to or experiencing harmful interference from each other or a station transmitting a non-SS signal over the same spectrum segment.

Back in 1985, the FCC authorized Amateur Radio stations to transmit SS emissions with a maximum transmitter power limit of 100 W PEP. To emphasize the experimental nature of spread spectrum as well as some of the potential benefits associated with it, the Commission authorized such transmissions on a secondary basis to other amateur service communications. At that time, the Commission noted that "to reduce the likelihood that SS transmissions from an amateur station could be made for the purpose of obscuring the meaning of a message, the Commission permitted only frequency hopping and direct sequence spreading techniques." Fourteen years later, the FCC eliminated restrictions on spreading techniques "to allow amateur stations greater flexibility and permit them to use the SS techniques used in other communications services." The Commission also required stations transmitting SS communications with a transmitter power greater than 1 W to utilize APC to limit the transmitter power in accordance with a specific formula (permissible power is determined by the use of the ratio, measured at the receiver, of the received energy per user data bit [Eb] to the sum of the received power spectral densities of noise [No] and co-channel interference [Io]; average transmitter power over 1 W shall be automatically adjusted to maintain an Eb/[No + Io] ratio of no more than 23 dB at the intended receiver).

In 2006, the ARRL petitioned the FCC, requesting that the APC requirement be eliminated, asserting that the APC provision has proven to be "virtually impossible" as it requires the operators of the transmitting stations to determine the transmitter power received at distant receivers and that this requirement has proven to be " something of a barrier to SS experimentation." The League further contended that the APC requirement could be eliminated without increasing the risk of harmful interference because: 

  • The station licensee or control operator of the station transmitting the SS emission would still be obligated under Section 97.313(a) of the Commission's Rules to use the minimum power necessary to conduct communications, and
  • Under Section 97.311(b) of the Commission's Rules, SS communications are already secondary to other Amateur Service communications. 

In the NPRM, the FCC agreed with the ARRL that the APC requirement "may be unnecessarily impeding Amateur Radio operators in advancing the radio art," but the Commission does not propose to simply eliminate the APC requirement. Noting that the purpose of the APC requirement is to limit interference to other stations, the FCC pointed out that commercial broadband Internet service providers operating in the 900 MHz and 2.4 GHz ISM bands argue that the APC requirement should be maintained in order to prevent interference to other users. They also referred to suggestions maintaining that if the APC requirement is eliminated, the FCC should lower the maximum power limit on amateur stations transmitting SS emissions so that interference is minimized.

Given these concerns, the FCC proposes to eliminate the APC requirement and reduce the maximum transmitter power output amateur stations may use when transmitting SS communications from 100 W to a peak of 10 W.

"We believe that this approach is consistent with both the ARRL's request that we eliminate a requirement that may be impossible to implement and the intent of the APC requirement to limit interference to other stations," the FCC stated in the NPRM. "We also believe that the proposed rule change would (1) encourage individuals who can contribute to the advancement of the radio art to more fully utilize SS technologies in experimentation, (2) balance the interests of all users in mixed-mode and mixed-service frequency bands until sharing protocols are sufficiently developed to avoid interference and (3) promote more efficient use of the radio spectrum currently allocated to the Amateur Service." The Commission is seeking comments on this proposal.

Order

In the Order, the FCC made amendments "to correct the Amateur Service rules or conform them to prior Commission decisions." These revisions will take effect once they are published in the Federal Register.

The FCC noted that when they authorized Novice class and Technician Plus class operators to transmit in certain portions of the 80, 40, 15 and 10 meter bands in 2006, they intended to limit those stations' power in those bands to 200 W PEP, "but the implementing amendment to Section 97.313(c) inadvertently applied that power limitation to all frequencies authorized to Novice and Technician Class licensees. We therefore correct Section 97.313(c) to clarify that the limitation applies only in those bands."

The Commission also revised Sections 97.301 and 97.303 related to the 40 and 60 meter and the 70 cm and 9 cm bands to conform to the Table of Frequency Allocations (Table), and to references within the relevant sections of the rules. They also revised the frequency sharing requirements in Section 97.303 "to limit the summary to those frequency bands that are allocated to the Amateur Service on a secondary basis, and to present the requirements more clearly."

In addition, the FCC moved transmitter power limit information from Section 97.303(s) to Section 97.313, the section concerning transmitter power standards. Section 97.103(c) was amended to delete the cross-reference to Section 0.314(x) that was removed in 1999. They also removed the entry "1260-1270 MHz" from Section 97.207(c) that lists the frequency bands authorized to amateur space stations "because footnote 5.282 to the Table limits the use of that segment to Earth station transmissions."

How to Make Comments on the NPRM

Pursuant to Sections 1.415 and 1.419 of the Commission's Rules, interested parties may file comments on the NPRM on or before 30 days after date of publication in the Federal Register and reply comments on or before 45 days after date of publication in the Federal Register. Based on previous experience, the ARRL expects publication of the NPRM and Order in the Federal Register sometime in early spring. Instructions on how to file comments on the NPRM only are listed on pages 6-7 in the NPRM.



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