**Before the**

**FEDERAL COMMUNICATIONS COMMISSION**

**Washington, D.C. 20554**

)

In the Matter of )

)

Petition of Spacenet, Inc. for a )

Declaratory Ruling that Section 25.134 )

of the Commission\'s Rules Permits )

VSAT Remote Stations in the Fixed )

Satellite Service to Use Network Access ) RM-9864

Schemes that Allow Statistically Infrequent )

Overlapping Transmissions of Short )

Duration, or, in the Alternative, )

For Rulemaking to Amend that Section )

)

**ORDER**

Adopted: December 6, 2000 Released: December 7, 2000

By the Chief, International Bureau:

**I. INTRODUCTION**

1 By this Order, we deny a petition for declaratory ruling filed by
Spacenet, Inc. (Spacenet). Spacenet requests a declaratory ruling that
the Commission\'s rules allow networks of very small aperture terminals
(VSAT networks) \"to employ access schemes that entail statistically
infrequent overlapping transmissions of remote earth stations.\"[^1] We
recognize, however, that, due to confusion about the rule at issue, some
operators may already be using these access techniques. We grant all
these operators a waiver on our own motion, so that they may continue to
serve their customers. Consequently, by today\'s actions, we eliminate
uncertainty over the interpretation of the Commission\'s VSAT rules. We
also preserve the *status quo* until the Commission can complete a
forthcoming rulemaking proceeding to consider fully the issues raised by
Spacenet.

**II. BACKGROUND**

2 The Commission\'s rules permit parties to obtain a single or
\"blanket\" license for a large number of technically identical small
aperture antenna earth stations operating in the Ku-band.[^2] These
systems consist of one or more hub stations transmitting via a satellite
to technically identical remote small aperture antennas. These systems
are referred to as very small aperture antenna terminal (VSAT)
networks.[^3] VSAT networks employ different techniques to prevent or
limit the transmissions to and from their remote earth stations from
interfering with each other and with adjacent satellite networks. To
this end, most VSAT networks originally used frequency division multiple
access (FDMA), which assigns different portions of the Ku-band
frequencies to different remote earth stations.[^4] Subsequently, VSAT
system operators developed techniques that enabled some remote earth
stations to share frequency bands. One of these techniques is called
time division multiple access (TDMA), in which each remote earth station
is assigned a different time to transmit and receive information.
Another, code division multiple access (CDMA), prevents interference
between remote earth stations by assigning a different digital code to
different earth stations.

3 The access technique that is the subject of Spacenet\'s petition is
called the \"slotted Aloha\" technique.[^5] In this technique, the hub
earth station synchronizes all remote VSAT stations so that they
transmit only in discrete time slots, typically tens of milliseconds in
duration.[^6] Unlike the TDMA techniques, however, Aloha permits two or
more remote earth stations to transmit simultaneously. Aloha relies on
statistical probability calculations to limit the number and duration of
simultaneous transmissions. When two or more remote earth stations in
Spacenet\'s VSAT network transmit simultaneously, those transmissions
can \"collide,\" and the resulting power level caused by these
collisions exceeds the level specified in the Commission\'s rules during
the time period of simultaneous transmission, although for no more than
tens of milliseconds.[^7] Increasing the power levels of a transmission
increases the possibility that it will cause unacceptable interference
to other satellite systems. According to Spacenet, however, because the
collisions in its VSAT network are infrequent and of short duration,
they do not cause unacceptable interference to adjacent satellite
systems.[^8]

4 Many of the requirements applicable to VSAT networks appear in Section
25.134 of the Commission\'s rules.[^9] Section 25.134(a) states that, to
qualify for routine licensing, VSAT remote earth stations must operate
with an input power density no higher than -14 dBW/4 kHz.[^10] Section
25.134(b) states that VSAT network license applicants planning to use a
power spectral density higher than -14 dBW/4 kHz must submit additional
information in their applications, including an Adjacent Satellite
Interference Analysis (ASIA), to demonstrate that use of the higher
power level will not cause unacceptable interference into adjacent
satellite systems.[^11] In addition, Section 25.134(c) requires
operators of VSAT networks to coordinate with operators of subsequently
launched satellites, and to lower the VSAT power levels to those
specified in Section 25.134(a) if a coordination arrangement cannot be
reached.[^12]

5 On April 5, 2000, Spacenet filed a petition for declaratory ruling or
rulemaking requesting that the power levels generated by the Aloha
access technique during transmission collisions do not violate Section
25.134 of the Commission\'s rules. Spacenet\'s petition was placed on
public notice on April 28, 2000. Hughes Network Systems (Hughes) and
PanAmSat Corporation (PanAmSat) filed comments, and ALOHA Networks, Inc.
(ALOHA Networks) filed electronic comments. Spacenet and Hughes filed
replies.[^13]

**III. DISCUSSION**

**A. Aloha Access Technique**

6 As Spacenet describes the slotted Aloha technique, the VSAT network
operator first derives the proportion of time slots occupied by exactly
one transmission.[^14] Then, the VSAT network operator uses statistical
methods to determine the probability of two or more transmissions from
remote terminals \"colliding\" at various peak network loads.[^15] By
this method, the VSAT network operator can adjust the number of
transmissions to limit the number of anticipated \"collisions.\" This
methodology is discussed in detail in Appendix A to this Order.

7 Spacenet maintains that VSAT operators have used multiple access
techniques like Aloha for years.[^16] Spacenet requests us to declare
that the slotted Aloha technique is consistent with Section 25.134 of
the Commissions\' rules, provided that:

> \(i\) each station individually satisfies the power density limits of
> Section 25.134(a);
>
> \(ii\) the probability P of k stations transmitting, for k greater
> than 1, is below the limit defined by P\[k\] = (0.38/k!)\*e^(-0.38)^,
> and
>
> \(iii\) the maximum duration of any single collision is less than 100
> milliseconds.[^17]

In the alternative, Spacenet requests a rulemaking to add these
requirements to Section 25.134.[^18]

8 PanAmSat agrees with Spacenet that the Commission should clarify or
amend its rules to permit random access techniques, provided that the
probability of collisions is within a defined range.[^19] PanAmSat
argues further that the Commission\'s VSAT rules have become outdated,
and that the Commission should increase the power level limits to
reflect technological advances.[^20] Hughes questions whether any action
is required to clarify Section 25.134, but agrees that, if clarification
is necessary, a declaratory ruling is better than a rulemaking
proceeding.[^21] Hughes argues, however, that the second requirement in
Spacenet\'s proposed rule is unnecessarily detailed, and could
unreasonably restrict the flexibility of VSAT operators to adapt their
networks to future technological developments.[^22] Hughes proposes the
following requirement as an alternative: \"(ii) the total average power
radiated toward the target satellite by all the remote earth stations in
the network, using an averaging period of one second, is less than that
of a single remote earth station transmitting continuously.\"[^23]
Spacenet supports PanAmSat\'s proposal to relax the power level
standards in a future proceeding, but opposes delaying action on its
petition while considering PanAmSat\'s proposal.[^24] Finally, Spacenet
expresses support for Hughes\'s proposed rule as an alternative to its
own proposal.[^25]

9 We decline to adopt any declaratory ruling at this time because both
Spacenet\'s and Hughes\'s proposals raise issues that require further
analysis. Sections 25.134(a) and (b) establish finite limits for
individual earth station antenna input power densities.[^26] When
signals from two or more earth stations within a VSAT network collide,
the resulting power level exceeds the limits specified in Sections
25.134(a) and (b), and so the Aloha method, and variants such as slotted
Aloha, cannot be construed to comply with the letter of Section 25.134
if each terminal transmits at the maximum power density limit. This
result is discussed in more detail in Appendix A.

10 We also decline to adopt a declaratory ruling at this time because it
would not adequately address cases where the bandwidth used by the earth
station(s) causing interference to other earth stations is wider than
the bandwidth used by the victim earth station(s) of the interference.
Assuming the transmission bandwidth for the interfering earth stations
is a few hundred kHz, the potential interference resulting from
co-channel carrier collisions to a victim earth station operating over a
wider bandwidth (*e.g.*, greater than ten times the interfering
bandwidth) may corrupt only a fraction of the victim earth station's
transmission data. The victim's corrupted data would likely be recovered
by the error correction techniques employed by the victim satellite
system. Thus, this issue is not as problematic as might be thought.
However, if the victim earth station(s) is operating in a narrower
bandwidth or approximately the same as the interfering earth station,
the victim earth station's transmission data would be significantly
degraded, possibly beyond recovery. The narrow-bandwidth problem can be
compounded as satellite-based voice/data traffic increases.

11 Instead of addressing the issues raised by the Aloha access technique
in this proceeding, the Commission will address these issues in a
forthcoming rulemaking. In that proceeding, the Commission will also
examine the current power limit rules, as PanAmSat requests.[^27]

12 Nevertheless, based on our review of Spacenet\'s calculations, and
the record we have developed on Spacenet\'s random access technique, we
find that Spacenet has shown persuasively that its random access
technique does not, at this time, cause harmful interference to other
satellite systems. Accordingly, we find that Spacenet has shown good
cause for a waiver of Sections 25.134(a) and (b) for purposes of
continuing to use its Aloha random access technique. Further, because of
confusion and to prevent disruption in service, we grant all VSAT
operators a waiver, on our own motion, for purposes of continuing to use
any multiple access techniques VSAT operators are using at the time this
Order becomes effective. The waiver we grant here will remain in effect
only until the upcoming rulemaking on this and other related issues
takes effect, and does not prejudge any decision in that rulemaking
proceeding. These VSAT operations will then be subject to implementation
of the final rulemaking decision.

**B. Probability Distribution**

13 ALOHA Networks maintains that Spacenet used the wrong probability
formula for slotted Aloha networks. ALOHA Networks projects that the
number of collisions is three times greater than Spacenet\'s estimate.
According to ALOHA Networks, the probability formula Spacenet used
applies only to unslotted networks.[^28] Spacenet maintains that ALOHA
Networks is mistaken in asserting that its probability function
underestimates the number of collisions.[^29] Spacenet also maintains
that, if its system had the potential to cause unacceptable
interference, then space station operators would have opposed its
petition.[^30] Finally, Spacenet maintains that ALOHA Networks\'
probability equation would limit the number of collisions more than
necessary to prevent interference, and so would render its slotted Aloha
system commercially nonviable.[^31]

14 Because we are not granting Spacenet\'s petition for declaratory
ruling, we need not address the probability formula for projecting the
number of collisions here. Rather, the Commission will examine
probability formulas, if necessary, in the context of its rulemaking.

**IV. ORDERING CLAUSES**

15 Accordingly, IT IS ORDERED, pursuant to Section 1.2 of the
Commission\'s rules, 47 C.F.R. § 1.2, that the petition for declaratory
ruling filed by Spacenet, Inc. on April 5, 2000, IS DENIED.

16 IT IS FURTHER ORDERED, pursuant to Section 1.3 of the Commission\'s
rules, 47 C.F.R. § 1.3, that current operators of VSAT networks ARE
GRANTED a waiver of Section 25.134 of the Commission\'s rules, 47 C.F.R.
§ 25.134, for purposes of continuing to use any multiple access
techniques being used at the time this Order becomes effective, pending
a Commission rulemaking addressing the use of such techniques.

17 This Order is issued pursuant to Section 0.261 of the Commission\'s
rules on delegated authority, 47 C.F.R. § 0.261, and is effective upon
release.

> FEDERAL COMMUNICATIONS COMMISSION

Donald Abelson

Chief, International Bureau

**APPENDIX A**

**Technical Analysis of Spacenet\'s Aloha Random Access Scheme**

**I. Spacenet\'s Proposed Rule**

Spacenet proposed adding a new paragraph (e) to Section 25.134.
Spacenet\'s proposed rule is as follows:

1.  Each station individually satisfies the antenna input power density
    limit of the rule;

2.  The probability P of k stations simultaneously transmitting, for k
    being greater than 1, is below the limit defined by

> P{k} = (0.38 ^k^) \* exp (-0.38) / k!)
>
> where the channel load G is set for 0.38 as a numerical constant; and

3.  The maximum duration of any individual collision is less than 100
    milliseconds.

Spacenet's proposed Section 25.134(e)(1) merely restates an existing
requirement. Proposed Section 25.134(e)(3) does not appear to be
controversial based on the record in this proceeding. Accordingly, we
will direct our attention to proposed Section 25.134(e)(2).

Proposed Section 25.134(e)(2) raises two questions: (1) What is the
probability that a \"collision\" of transmissions from two or more earth
stations will occur? and (2) How much do power levels increase during a
collision? We address these two issues below.

**II. Probability of Collisions**

Spacenet based its probability determination on a Poisson probability
distribution, such that, for the standard Aloha approach,

\(1\) S = G\*e^(-2G)^

where S is throughput, G is channel loading, and e is a constant equal
to approximately 2.73. The Poisson probability distribution is similar
for the slotted Aloha approach

\(2\) S = G\*e^(-G)^

We replace the \"-2G\" term with \"-G\" because the collision-vulnerable
period in the slotted-Aloha approach is half of that in the standard
Aloha approach.

The probability of a collision of transmissions is P{k}, where k is the
number of stations transmitting simultaneously. According to the
equation in Spacenet\'s proposed Section 25.134(e)(2), setting the
channel loading G equal to 0.38, the following results:

**Table 1: Probability of Collisions**

  ----------------------- ----------------------- -----------------------
  Number of Earth         Probability of          Probability of
  Stations Transmitting   Collision involving N   Collision in Percentage
  Simultaneously          transmissions P(N)      Terms

  0                                               

  1                       0.260                   26%

  2                       0.049                   4.9%

  3                       0.00625                 0.625%

  4                       0.00059                 0.059%

  5                       0.00005                 0.005%
  ----------------------- ----------------------- -----------------------

The probability of collision for six or more stations is remote and so
we can ignore it.

**III. Excessive Power Emissions**

In a multiple access scheme such as slotted ALOHA, a carrier collision
occurs when two or more stations are transmitting simultaneously on the
same frequency. If we assume that each transmitter in the network is
operating at the maximum authorized power level, then a single
transmitter would not cause any increase over the maximum authorized
power level. In other words, there would be a 0 dB increase in potential
interference. A two-transmission collision, however, would double the
potential interference (*i.e.*, cause a 3.0 dB increase in power), and a
three-transmission collision would triple the potential interference
(*i.e.*, cause a 4.77 dB increase in power). The increase in power level
is

\(3\) 10\*log(N)

where N is the number of colliding transmissions. Clearly, the potential
for interference to adjacent satellite operations increases whenever a
collision takes place.

Table 2: Power Increases Caused by Collisions

  ----------------------------------- -----------------------------------
  Number of Colliding Transmissions   Power Increase in dB

  1                                   0

  2                                   3.0

  3                                   4.7

  4                                   6.0

  5                                   7.0
  ----------------------------------- -----------------------------------

Spacenet argues that we should discount high power levels for the low
probability of occurrence. Specifically, Spacenet argues that the Net
Power Increase (NPI) should be --5.85 dB for a single-station
transmission, -10.09 dB for a two-station collision, and so on. Based on
this, Spacenet claims that Over-Time Net Power Increase (ONPI) from two
simultaneously transmitting remote stations is 4.20 dB below the
emission of a single station transmitting constantly at the maximum
authorized power under the current Rule. By using ONPI, Spacenet
demonstrates the inbound carrier collisions over time do not generate
excessive emission in violation of the Commission's Rules.

**Table 3: Power Increases Caused by Collisions, Spacenet\'s Approach**

+-----------------+-----------------+-----------------+-----------------+
| Number of Earth | Probability     | Power Increase: | Net Power       |
| Stations        | P(N)            | 10log(N) \[dB\] | Increase        |
| Transmitting    |                 |                 | Adjusted for    |
| Simultaneously  |                 |                 | Probability of  |
|                 |                 |                 | Occurrence:     |
|                 |                 |                 |                 |
|                 |                 |                 | 10log(P(N)) +   |
|                 |                 |                 | 10log(N) \[dB\] |
+-----------------+-----------------+-----------------+-----------------+
| 1               | 0.260           | 0               | -5.85           |
+-----------------+-----------------+-----------------+-----------------+
| 2               | 0.049           | 3.0             | -10.09          |
+-----------------+-----------------+-----------------+-----------------+
| 3               | 0.006           | 4.7             | -17.52          |
+-----------------+-----------------+-----------------+-----------------+
| 4               | 0.001           | 6.0             | -24.00          |
+-----------------+-----------------+-----------------+-----------------+

By summing all the net power increases adjusted for probability of
occurrence, we obtain

\(4\) ONPI = 10log\[10^-5.85/10^ + 10^-10.09/10^ + 10^-17.52/10^ +
10^-24.00/10^\]

[\~]{.underline} -4.2 dB

We can draw two relevant observations from Spacenet\'s proposal. First,
we recognize that Spacenet\'s showing assumes that the described events
are taking place randomly under a Poisson distribution and the network
traffic is being held to a 38% load, which yields about 26% throughput
(or efficiency). Based on these assumptions, we can obtain a set of
probabilities of carrier collisions and draw certain conclusions. For
example, at 38% load, the probability of a three-carrier collision is
0.6%, which we are willing to dismiss as *de minimis*. However, if the
load is doubled to about 75%, the probability of a three-carrier
collision becomes 3.3%, which may be difficult to dismiss as *de
minimis*. Therefore, in Spacenet\'s approach, Spacenet must be able to
maintain the 38% channel load at all times so that the number of
undesired carrier collisions can be controlled within the network.

Second, Spacenet claims that interference is not an issue because the
ONPI is 4.2 dB less than the total power emission from a single
continuously transmitting earth station. We do not agree. This by itself
is not sufficient to comply with the Commission\'s rules. Specifically,
we are concerned that the power overruns due to collisions could lead to
excessive emissions that may cause harmful interference to neighboring
satellites in the orbit, (even though the probability of occurrence is
low and the total time of occurrence are brief) if there is a
significant deviation from the parameters represented in Spacenet's
Petition. During the very instance of a carrier collision, short burst
of excessive emissions are generated, and the resulting power level will
likely violate the Commission\'s rules if each network station is
operating at maximum permitted power level. The Commission rule places a
limit on power density, rather than a threshold that may be exceeded.
Consequently, the Commission has responsibility to ensure that these
excessive emissions will not interfere with the operation of neighboring
satellites in orbit even for brief instances.

[^1]: Spacenet Petition at 1.

[^2]: For purposes of this Order, the \"Ku-band\" denotes the 11.7-12.2
    and 14.0.14.5 GHz frequency bands.

[^3]: Routine Licensing of Large Networks of Small Antenna Earth
    Stations Operating in the 12/14 GHz Frequency Bands, 51 Fed. Reg.
    15067 (Apr. 22, 1986) (*1986 VSAT Order*); Routine Licensing of
    Earth Stations in the 6 GHz and 14 GHz Bands Using Antennas Less
    that 9 Meters and 5 Meters in Diameter, Respectively, for Both Full
    Transponder and Narrowband Transmissions, Declaratory Order, 2 FCC
    Rcd 2149 (Com. Car. Bur. 1987) (*1987 VSAT Order*). *See also* 47
    C.F.R. §25.134.

[^4]: Satellite systems used this access technique even before the
    Commission developed its VSAT policies. *See* Satellite Business
    Systems, 62 FCC 2d 997, 1083 (para. 247) (1977).

[^5]: With the \"unslotted Aloha\" technique, remote earth stations in
    the VSAT network can transmit randomly at any time, meaning that the
    transmissions are not synchronized in time or duration. The
    \"unslotted Aloha\" technique is distinguishable from the \"slotted
    Aloha\" technique, in which remote earth stations transmit in
    specific time slots, which means that the transmissions are
    synchronized but not coordinated. In other words, the remote earth
    stations transmitting in a given time slot can transmit regardless
    of whether there are other earth stations transmitting in the same
    time slot. G. Maral, *VSAT Networks* at 144-45 (John Wiley and Sons,
    ed. 1995).

[^6]: Spacenet Petition at 6.

[^7]: Spacenet maintains that the duration of an inbound transmission is
    typically between 15 and 50 milliseconds. Spacenet Petition at 8.

[^8]: Spacenet Petition at 7.

[^9]: 47 C.F.R. § 25.134.

[^10]: 47 C.F.R. § 25.134(a).

[^11]: 47 C.F.R. § 25.134(b).

[^12]: 47 C.F.R. § 25.134(c).

[^13]: In addition, Spacenet filed an *ex parte* statement on September
    15, 2000.

[^14]: This proportion is derived by the following formula: S =
    G\*e^(-G)^, where S is the utilization or throughput per slot, G is
    the load or average transmissions per slot, and e is Euler\'s
    number, a constant equal to approximately 2.73. Spacenet Petition at
    6.

[^15]: Spacenet Petition at 5-7.

[^16]: Spacenet Petition at 8-10. *See also* PanAmSat Comments at 2.

[^17]: Spacenet Petition at 9.

[^18]: Spacenet Petition at 11.

[^19]: PanAmSat Comments at 1-2.

[^20]: PanAmSat Comments at 2-3.

[^21]: Hughes Comments at 2-4.

[^22]: Hughes Comments at 3-4.

[^23]: Hughes Comments at 4-5. *See also* ALOHA Networks Comments
    (recommending amending Section 25.134 to permit VSAT networks to
    exceed the power limits by no more than one second per hour when the
    network is operated at peak load for one hour).

[^24]: Spacenet Reply at 5.

[^25]: Spacenet *Ex Parte* Statement at 1.

[^26]: 47 C.F.R. § 25.134(a), (b).

[^27]: PanAmSat Comments at 2-3.

[^28]: Aloha Network Comments at 1-2. Hughes maintains that the Aloha
    Network\'s approach has \"technical validity,\" but argues that the
    language of its proposed rule is more flexible, and so more workable
    in practice. Hughes Reply at 1-3. Specifically, ALOHA Network
    criticizes Spacenet for using a Poisson probability distribution
    rather than a binomial distribution. The binomial distribution, one
    of the more common statistical distributions, is designed for cases
    like determining the probability of flipping a coin and getting
    heads a certain number of times in a row. More generally, for each
    trial, there are only two possible outcomes, the probability of each
    outcome is known, and the probability does not vary from trial to
    trial. The Poisson distribution is designed for cases where the
    probability of an event occurring is very low, but the number of
    opportunities for such occurrences are very high. Examples are
    estimating the number of people who will contract a rare disease in
    a population of several million, or the number of atoms that will
    undergo radioactive decay in a large amount of uranium.

[^29]: Spacenet Reply at 6.

[^30]: Spacenet Reply at 6-7.

[^31]: Spacenet Reply at 7.