**Before the**

**Federal Communications Commission**

**Washington, D.C. 20554**

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| In the Matter of                 | *  | MM Docket No. 01-145         |
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| Request for Declaratory Ruling   | ** |                              |
| Removing the Commission's        |    |                              |
| Minimum Carrier Tone Requirement | *  |                              |
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| Multipoint Distribution and      | ** |                              |
| Instructional Television Fixed   |    |                              |
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**DECLARATORY RULING AND ORDER**

**Adopted: September 25, 2001 Released: September 26, 2001**

By the Chief, Mass Media Bureau:

**I. INTRODUCTION**

1\. The Commission, by the Chief, Mass Media Bureau, acting pursuant to
delegated authority, has before it a request for declaratory ruling
filed by Cisco Systems, Inc. ("Cisco")[^1] pursuant to Section 1.2 of
the Commission's Rules, 47 C.F.R. § 1.2. Cisco requests that the
Commission amend its rules to eliminate the requirement that a minimum
of 256 QAM-modulated carriers be used with Orthogonal Frequency Division
Multiplexing ("OFDM")[^2] modulation in the Multipoint Distribution
Service ("MDS") and the Instructional Television Fixed Service ("ITFS").
For the reasons set out below, we are granting Cisco's petition.

**II. BACKGROUND**

2\. On July 9, 1996, the Commission adopted a declaratory ruling which
permits MDS and ITFS stations to use Vestigial Sideband Modulation
("VSB") and Quadrature Amplitude Modulation ("QAM") on a regular basis
so long as they meet certain technical requirements.[^3] In a subsequent
rulemaking, the Commission expanded the list of permissible MDS and ITFS
modulations to include Code Division Multiple Access ("CDMA") and
Quadrature Phase Shift Keying ("QPSK").[^4] On August 31, 1998, Clarity
Wireless, Inc. ("Clarity")[^5] filed a Petition for Declaratory Ruling
requesting that the Commission further expand the list of permissible
MDS and ITFS emissions to include OFDM. In support of its petition,
Clarity submitted the results of laboratory tests evaluating the
technical characteristics of two different OFDM waveforms, one with 256
carriers, each modulated by a 4-QAM signal, and one with 4096 carriers,
each modulated by a 64-QAM signal. These tests demonstrated that both of
the OFDM emissions complied with the Commission's spectral mask
requirements and would present no greater interference potential than
other, previously authorized, digital emissions. On March 19, 1999, the
Commission granted the Clarity petition and authorized the use of OFDM,
with the condition that a minimum of 256 QAM-modulated carriers must be
utilized.

3\. In its petition, Cisco requests that the Commission remove the
condition that a minimum of 256 QAM-modulated carriers must be used for
OFDM. Cisco states that its earlier use in laboratory tests of a lower
limit of 256 carriers was meant to generate "worst case OFDM signals
whose power spectral density completely filled the spectral mask in the
Commission's rules." Cisco argues that the use of fewer than 256
carriers should be permitted because the potential for interference from
such OFDM signals will be no greater than the interference from OFDM
signals using 256 or more carriers.[^6] The ability to use fewer than
256 carriers, Cisco argues, would "allow MDS/ITFS network designers to
make important bandwidth and design trade-offs to meet customer
bandwidth and cost requirements." This would occur because of the direct
linkage between the number of carriers and the bandwidth occupied by
those carriers, *i.e.*, as fewer carriers are utilized, less bandwidth
is needed.

4\. In response to the Commission's Public Notice requesting comment on
Cisco's request for a declaratory ruling,[^7] comments were filed by
Wireless Communications Association International ("WCAI"), Wi-LAN, Inc.
("Wi-LAN"), and the Catholic Television Network ("CTN"). Reply comments
were filed by Cisco Systems. WCAI and Wi-LAN fully supported the Cisco
request, citing advantages to the removal of the limitation in the
number of carriers permitted for OFDM and urging the Commission to
remove this limitation. Wi-LAN also urged the Commission to permit, in
addition to QAM modulation of OFDM carriers, Binary Phase Shift Keying
("BPSK") and Quadrature Phase Shift Keying ("QPSK") modulation of the
OFDM carriers.[^8] CTN, while also supporting removal of the carrier
limitation, expressed concerns about the interference potential of OFDM
emissions with fewer than 256 carriers, and asked that the removal of
the limitation be accompanied by an amendment to the Commission's rules
which would, in their view, prevent such interference from occurring.

5\. Specifically, CTN is concerned that "lower level QAM spectral energy
may concentrate in certain portions of a 6 MHz channel," and that
"unless there is a randomizer . . . in the digital encoder, then it is
possible in a steady state for the spectral energy to concentrate and
increase in amplitude." CTN argues that even if "a lower level QAM
signal met the 45 dB D/U co-channel interference ratio in its spread out
state, the D/U ratio may degrade to an interference-causing sub-45 dB
during steady state video modulation conditions." To remedy this
concern, CTN suggests that the Commission adopt one of two requirements
for sub-256 carrier OFDM, either: (a) "the proposed transmission meets
the 45 dB D/U interference ratio as to all relevant co-channel stations
for the worst case digital spectral energy signature;" or (b) "the
digital encoder include a randomizer that ensures the spectral energy is
spread over the entire channel bandwidth." In reply comments addressing
CTN's proposed new requirements for OFDM, Cisco disputes CTN's
contention that any new rules are needed, arguing that existing
Commission rules already fully address the issues raised by CTN.

**III. DISCUSSION**

6\. We agree with Cisco that no purpose is served by continuing the
limitation on the minimum number of carriers which can be utilized for
OFDM. The channelization rules for MDS and ITFS permit the use of a very
wide range of bandwidths, from tens of kHz to tens of MHz, and it is
important that licensees have available to them the flexibility to use
the particular digital emissions and bandwidths that meet their
operational needs. Removal of the 256 carrier limitation from OFDM would
enable licensees to choose from a significantly wider range of
bandwidths and data rates than is now permissible with OFDM, *e.g.*, for
bandwidths on the order of 50-100 kHz, as few as 4 to 8 carriers may be
optimum, whereas for bandwidths on the order of 750 kHz to 1.5 MHz, 64
to 128 carriers may be optimum.

7\. With respect to CTN's interference concerns, while we concur that
"symbol patterns" may occur with the use of OFDM emissions having fewer
than 256 carriers, it is also true that this phenomenon occurs when more
than 256 carriers are used and that such a concentration of power in a
segment of a wider channel is simply a transient form of the more
general occurrence of power spectral non-uniformity commonly associated
with some digital emissions. However, we believe that Cisco has
adequately demonstrated that this non-uniformity, if and when it occurs,
will not have any adverse impact on the potential for harmful
interference in MDS and the ITFS systems, in that the range of OFDM
emissions which will now be permitted are already fully addressed by the
interference protection and power spectral density provisions of our
rules. Specifically, all forms of OFDM are subject to the existing rule
requirements for interference protection of MDS and ITFS stations, such
as Section 21.902[^9], as well as subject to the existing rule
requirements governing emissions with respect to power spectral density,
both uniform and non-uniform, such as Section 21.904(e).[^10] We
therefore are granting Cisco's request to remove the 256 carrier
restriction from OFDM and we reject CTN's request that additional
requirements be placed on OFDM emissions with fewer than 256 carriers.

**IV. ORDERING CLAUSES**

8\. Accordingly, IT IS ORDERED that under the authority contained in
Section 4(i) of the Communications Act of 1934, as amended, 47 U.S.C.
§154(i), and Section 554(e) of the Administrative Procedure Act, 5
U.S.C. §554(e), the Petition for Declaratory Ruling submitted by Cisco
Systems, Inc. IS GRANTED to the extent specified above. This Declaratory
Ruling and Order shall be effective upon its release and shall remain
effective pending adoption of rules specifically governing the use of
digital emissions in MDS and ITFS in a future rulemaking proceeding.
*See* 47 C.F.R. §§1.4(b)(2) and 1.103. Nothing in this Declaratory
Ruling and Order shall prejudice the outcome of such a rulemaking
proceeding.

9\. IT IS FURTHER ORDERED that the staff of the Mass Media Bureau shall
send copies of this Declaratory Ruling and Order by certified mail,
return receipt requested, to the parties who filed formal comments and
reply comments in response to the Commission's June 5, 2001 Public
Notice.

> FEDERAL COMMUNICATIONS COMMISSION
>
> Roy J. Stewart
>
> Chief, Mass Media Bureau

[^1]: *Petition for Declaratory Ruling*, filed March 13, 2001 ("Cisco
    Petition").

[^2]: OFDM is a digital emission consisting of multiple carriers within
    a single authorized bandwidth or channel, each of which is modulated
    with a portion of the information being transmitted in the bandwidth
    or channel. The signal modulating each carrier is itself a digital
    emission, such a QAM. The amplitudes and spacings of the carriers is
    such that the spectral energy of each carrier is significantly
    attenuated at the frequencies of each of the two adjacent carriers.

[^3]: *Digital Declaratory Ruling*, 11 FCC Rcd 18839 (1996).

[^4]: *Amendment of Parts 21 and 74 of the Commission's Rules to Enable
    Multipoint Distribution Service and Instructional Television Fixed
    Service Licensees to Engage in Fixed Two-Way Transmissions*, 13 FCC
    Rcd 19112 (1998), *recon.*, 14 FCC Rcd 12764 (1999), *further
    recon.*, 15 FCC Rcd 14566 (2000).

[^5]: Cisco acquired Clarity effective November 2, 1998.

[^6]: In a Technical Appendix to their Petition, Cisco cites data
    evaluating the peak-to-mean envelope power ratio (PMEPR) of OFDM
    signals with differing numbers of carriers as an indicator of
    relative interference potential and finds that the PMEPR of a
    128-carrier signal is less than that of a 256-carrier signal.

[^7]: *Pleading Cycle Established for Comments on Request for
    Declaratory Ruling to Remove Minimum Sub-Carrier Requirement for
    Orthogonal Frequency Division Multiplexing Modulation in Multipoint
    Distribution and Instructional Television Fixed Services*, Public
    Notice, MM Docket No. 01-145, DA 01-1582 (released June 5, 2001).

[^8]: Wi-LAN's request is partially moot because QPSK modulation, when
    it was added to the list of permissible emissions in Rule Section
    21.905, was considered to be the functional equivalent of the 4-QAM
    emission. Therefore, we consider that QPSK is covered under the QAM
    emission for purposes of modulating carriers in an OFDM emission.

[^9]: 47 C.F.R. § 21.902 sets out the 45 dB co-channel and 0 dB adjacent
    channel D/U requirements and the --73 dBW/m^2^ flux density contour
    limit, as well as adjustments in these parameters based on
    bandwidths used.

[^10]: 47 C.F.R. § 21.904(e) sets out the procedure for calculating
    transmitter power for emissions with non-uniform power spectral
    density. When applied to OFDM emissions, any non-uniformities in
    transmitted power spectral density arising from "symbol patterns"
    *(i.e*., concentrations of power in one part of the occupied
    channel) or other causes, transient or persistent, must be taken
    into account in determining permissible power levels and calculating
    interference in accordance with Section 21.902.