ARRL

ARRL General Bulletin ARLB011 (2010)

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ARLB011 FCC Proposes to Eliminate Spread Spectrum APC Requirement,
and other actions

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ARRL Bulletin 11  ARLB011
From ARRL Headquarters  
Newington CT  March 18, 2010
To all radio amateurs 

SB QST ARL ARLB011
ARLB011 FCC Proposes to Eliminate Spread Spectrum APC Requirement,
and other actions

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.

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.

    * 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.

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."

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.  The NPRM can be found on
the web at,
http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-10-38A1.pdf.
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