Subject: [NEXTEL-1] Beware Of Unlicensed Operations

From: Marcelrf <[email-masked]>
Date: Wed, 18 Feb 2004 13:25:19 -0500

Beware Of Unlicensed Operations
Feb 16, 2004

By Leslie Taylor

Satellite industry officials need to gird themselves for another battle.
Still smarting from the Federal Communications Commission's (FCC)
decision to allow terrestrial multichannel video distribution and data
service (MVDDS) in the direct broadcast satellite (DBS) bands, the
industry now faces the FCC's initiative to allow unlicensed operations
in the 6525-6700 MHz and 12.75-13.25 GHz bands.

The FCC is letting unlicensed devices operate within large bands of
spectrum.  Recent examples include allowing Wi-Fi into the 5 GHz band
and ultra-wideband (UWB) operations across a large swath of bandwidth.
Now, the FCC is proposing that fixed-satellite service (FSS) operators
share a potentially unknown amount of spectrum with unlicensed devices.
You can't fault with the FCC for encouraging innovation, new services
and new methods of promoting spectrum sharing. Those goals are laudable.
However, the commission should not forget that its primary mission is to
ensure that licensed users of spectrum operate without unacceptable
interference. That responsibility includes ensuring that satellite
systems with primary allocations not face the risk of interference, loss
of capacity, or loss of future access to frequency bands because the FCC
wants to allow unlicensed operations to use a new "interference metric"
to determine whether the feared interference actually would occur.

What is this new "interference metric" and how should satellite
operators, manufacturers and users approach the commission's proposal?
And, what specifically is the commission's proposal?

FCC's Proposal

The commission, in ET Docket No. 03-327, proposes new technical rules
that would permit unlicensed devices (for purposes not yet identified)
to operate in the 6525-6700 MHz and 12.75-13.25 GHz bands. These bands
currently are allocated on a primary basis to FSS. Portions of the bands
also are allocated for other services, including radiolocation (used
primarily for U.S. government radars), terrestrial fixed services, cable
antenna relay systems and space science services. So, there is
considerable sharing going on in these bands already. In fact, in the
12.75-13.25 GHz band, the 2003 World

Radiocommunication Conference (WRC-03) liberalized the rules applicable
to FSS so that greater use of the band could be made for smaller
aperture earth stations. Previous international and U.S. domestic rules
had restricted operations in this band to large earth stations, thus
limiting the band's use as feeder links. Both the 6525-6700 MHz and the
12.75-13.25 GHz bands are considered the "extended C and Ku-bands" and
are subject to a number of restrictions in their use by FSS systems.
WRC-03's action to liberalize FSS operations in the 12.75-13.25 GHz band
followed several years of study to determine what technical rules could
best balance the interests of the co-primary spectrum users. Those
co-primary users included radiolocation, primarily relied on by the U.S.
government for military radars.

New Interference Metric

On the face of it, the FCC's technical proposal might seem reasonable.
Use of new tools to facilitate sharing should be taken seriously. The
FCC proposes that the unlicensed devices in the 6525-6700 MHz and
12.75-13.25 GHz bands, both satellite uplink bands, be restricted to
operation, on an individual device basis, with EIRP (Effective Isotropic
Radiated Power) levels as high as 30 dbm (the number of decibels
relative to 1 milliwatt) to 36 dbm. The commission works backwards to
get to these numbers. First, it looks at the interference trigger used
between FSS systems for coordination, e.g., a Delta T/T (an expression
of the amount of interference) of 6 percent. The FCC argues that the
cumulative effect of millions of devices, each operating at the
indicated EIRP levels, would not exceed a 5 percent Delta T/T. The
commission is correct that it is necessary to consider the aggregate
interference effect of such devices. The impact of one device on a
geostationary (GSO) satellite, in particular, would be impossible to
measure.  However, millions of devices would raise the noise floor, or
temperature, and potentially could impact the FSS uplink operations.

While proposing specific rules, the commission seeks comment on the
appropriate interference temperature threshold that will afford
"sufficient" protection to licensed satellite operations, as well as
comment on the assumptions used in its link budget analysis on which it
based its proposed rules.
MSS Feeder Link Analogy

At WRC-03, and at the FCC, substantial spectrum has been made available
for unlicensed services (primarily Wi-Fi) in the 5 GHz band. Developing
the technical rules, which are embodied in the International Radio
Regulations and the FCC's regulations, was a very complex process,
involving much technical study over a period of years. Several ITU
Radiocommunication Sector (ITU-R) recommendations were developed to
address the operation of wireless local area networks (LANs) in the
5150-5250 MHz band. Within that band operate non-GSO mobile satellite
service (MSS) feeder links used primarily by Globalstar and ICO. Those
interested in the interference noise proceeding should take a look at
these ITU-R recommendations that include M. 1454, S. 1426 and S. 1427.
These recommendations provide methodologies for analyzing aggregate
interference into the MSS feeder links from terrestrial unlicensed
devices and provide for limitations on the EIRP of the individual
unlicensed devices. When this work initially was undertaken, there was
concern that even developing such rules would undermine the concept of
primary allocations, and by the back door, confer status to unlicensed
devices that they do not warrant. Historically, unlicensed devices
operate on a non-interference basis with respect to licensed devices.
However, now the FCC proposes a great leap forward. Not only will Wi-Fi
devices be accommodated in the 5 GHz and 2.4 GHz bands, but 175 MHz (in
the C-band) and 500 MHz (in the Ku-band) also will be made available for
unlicensed operations. The commission states that its "preliminary
analysis" shows that over 53 million devices in the C-band and over 369
million devices in the Ku-band can operate without exceeding the 5
percent Delta T/T into an individual spacecraft receiver. This analysis,
however, ignores several factors. First, what is the impact if devices
are clustered in small geographical locations, thus intensifying the
increase in the interference temperature into the spacecraft receiver?
Second, what is the impact of taking account of these devices in the
design, construction, cost and coordination of FSS systems with other
FSS systems, while these systems already must be engineered to share
with other co-primary service operations? Third, how does the commission
take into account the interference impact to satellite systems licensed
by other administrations? Fourth, does this proposal pre-empt the
international process because it would surely have multinational
implications in practice? Fifth, what happens if the projected numbers
(assuming they are correct) are exceeded? How does the FCC address the
enforcement of aggregate interference limits by unlicensed devices? The
commission already has experience with the difficulty of changing
direction once consumer devices are widely adopted.

With this proceeding, the commission has the potential to create a huge
constituency for unlicensed devices - the manufacturers, value-added
resellers and users. Such constituencies can be expected to wield
considerable political and economic clout. If satellite systems
experience interference, it is doubtful the commission could or would
act to require reduction in the power or number of the unlicensed
devices. For the FCC to cite the 5150-5250 MHz band as an example that
such sharing is feasible ignores the fact that it is far too soon to
assess the aggregate impact of millions of devices on satellite
receivers. Very few Wi-Fi devices are in operation in that band today.
Moreover, the MSS operators have faced considerable opposition within
the U.S. in putting forth technical papers into the international
process proposing mechanisms for measuring such aggregate interference.
The unlicensed community's objection to such papers is what would a
country do if the interference were too great, so why would we want a
method for measuring and identifying the source of the interference?

What is the impetus for the commission's proposal? The satellite bands
are the only ones in the interference noise proceeding for which the
commission proposes specific rules. The rest of the proceeding is at a
much more exploratory level. A Notice of Inquiry asks for comments about
many questions involving the operation of unlicensed devices in licensed
bands. There was no petition for rulemaking that spurred the
commission's action. One question is, what unlicensed devices are being
proposed for use in these bands? Another is, if these devices have
exhausted other available spectrum?

The satellite community should take the commission's proposal very
seriously and respond with technical analysis of the FCC's proposed
rules and underlying assumptions. In addition, the industry should
address the commission's policy arguments concerning the introduction of
unlicensed devices into additional frequency bands prior to the
operation of unlicensed devices in the 5 GHz band.  The U.S. government
should address the impact on its operations in these bands, particularly
the 12.75-13.25 GHz band. The U.S. Defense Department (DoD) worked hard
to craft rules to permit Wi-Fi into additional spectrum in the 5 GHz
band. However, the technical means adopted, including dynamic frequency
selection (DFS), has yet to be implemented, yet alone evaluated in
practice.

Spectrum sharing brings benefits to industry and users. However,
spectrum sharing, particularly with unlicensed devices, should be
introduced only after careful study, identification of the need for
spectrum by the devices, and showing that existing spectrum available
for unlicensed devices is not adequate to meet important public needs.
Spectrum sharing also should come only after careful consideration of
the impact of a new interference approach on licensed services operating
pursuant to primary allocations.

Leslie Taylor is a telecommunications consultant in Bethesda, Md. She
can be reached by phone at 301/229-9410 or by e-mail at [email-masked]
.

www.telecobweb.com

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