A QUESTION OF PRECLUSION

The impact of the first Two-Way Filing Window on the ITFS licensee

T. Lauriston Hardin, P.E.

MSI BWA Center of Excellence

Introduction

With the adoption of the Two-Way Order, the landscape of the MDS and ITFS market has changed dramatically.  New service sets, new ways of reaching students and new methods for distant learning are all available.  To make way for the provision of these new two-way services, the operator or licensee must plan a new network, prepare the associated applications under the Two-Way Rules, and file those applications with the Commission.  That process can take time and resources which may strain the operator or licensee to the point where they cannot reasonably be ready with applications for the first filing window.  Thus a dilemma is raised.  Will the ITFS entity who does not file applications in the first two-way filing window be precluded from later desired filings due to applications which are filed in the first window?

Brief Overview of Two-Way Rule Changes

It is clearly evident to even the causal observer that the rule changes associated with the Two-Way Order are complex.  More specifically, the rule changes associated with the prediction of interference due to upstream transmissions are complex.  That is a significant statement.  One must remember that save the rule changes associated with allowing boosters, the downstream transmission rules are changed very little.  In the case of the booster rule changes, they are a help, not a hindrance and do not add in any appreciable way to the complexity of system design or application preparation.  Moreover, under the Two-Way Rules, the burden of non-interference remains squarely on the shoulders of the entity filing the application.

In the case of upstream transmissions, the Rules have become complex and the interference environment is much more complicated.  The reason for this complexity is to provide as much flexibility as possible for two-way operation while still guaranteeing the present level of interference protection.  This issue should not be overlooked because it is part of the answer to the preclusion question.  For their present operations, ITFS operators have the same protection which they have always enjoyed – without interruption.

How Could Preclusion Occur?

For the sake of this discussion, preclusion will be defined as the inability of an ITFS entity to file applications for two-way operation after the first filing window due the fact that their new applications would cause predicted interference to facilities applied for in the first filing window.  In a simple example, the later filed application is predicted to cause interference to the hub location of the previously filed application.  As in this example, preclusion is generally the result of predicted interference in accordance with the Two-Way Rules.

How does interference occur?  Generally, there are two types of interference – cochannel and adjacent channel – and the levels of desired-to-undesired signal level which constitute interference are different from each.  However, the mechanism for determination of those levels is the same.  Those levels are 45 dB D/U for cochannel interference and 0 dB D/U for adjacent channel interference either downstream or upstream.  These are the same levels which have existed from the start of the ITFS service and the levels which have been used in the past for the design and operation of ITFS systems.  The major differences in a two-way environment are there can be significantly more sources of interference, namely the response stations or customer locations, and there are now upstream transmission collection points, or hubs, which are new and more difficult locations to afford co- and adjacent channel protection.

In the two-way operational environment, the preclusion issues generally revolve around the response station hubs.  These are the upstream interconnection points to the network and the signals which are being received by these hubs are lower in signal level and, therefore, more subject to interference and the resulting corruption of their data.  The placement of these hubs relative to the ITFS entity’s PSA is the determining factor in the first order analysis of preclusion possibilities.

Hubs within the PSA

As a practical matter, no cochannel or adjacent channel operators will be able to place a hub within another station’s PSA without the consent of that licensee.  This rests on the fact that due to the requirement that an application for a response station hub must specify a Response Service Area (RSA) which defines the area in which response stations may be placed.  It is tantamount to impossible to define an RSA within the PSA boundary of another co- or adjacent channel station without predicting interference in accordance with the Rules.  As such, preclusion will not be possible in this case.

Hubs outside of the PSA

The area outside the ITFS entity’s PSA can be divided into two areas – areas near the PSA border and areas distant from the PSA border.  In the case of hubs placed in close proximity to the PSA border, again it will be very difficult to place a co-channel hub in this area due to the same interference rules cited above.  However, in the case of an adjacent channel operation, it is possible to place a hub in that area so long as its associated RSA does not overlay the PSA.  What is the practical implication of this adjacent channel situation?

The existence of an adjacent channel hub near the PSA border of another station should have very little impact on the future channels of the other station from a hub placement standpoint since the RSAs of the two stations will not overlap.  This is based on the assumption that the stations have not exchanged consents over this overlap.  As such, there should generally be no issue of preclusion in this case.  However, the existence of the adjacent channel hub in close proximity to the other station’s PSA may have two effects worthy of consideration.  First, the existence of the response stations associated with the hub may cause some increase in the noise floor of the hub the other station may someday propose.  This increase is probably minor but could have some effect on the operating range of the hub along certain azimuths.  Second, the existence of the hub may limit the placement of and the amount of downstream power authorized to a booster location which may be filed later in the PSA by the other station.  This issue in this case is that the hub must be afforded protection.  This could come up in the situation where the later filing ITFS entity desires to place a booster very near the border of its PSA and also very near the hub of the other station.  The probability of these situations appears to be low but should be kept in mind.

Predatory Filings

The foregoing discussion assumed that all licensees and operators are preparing system designs and applications based on a desire to operate viable two-way systems.  Unfortunately, that may not always be the case.  If a party wants to create an application with the sole purpose of impeding the plans of an adjacent market licensee, while despicable, it is possible.  One could create a hub location on the border of a neighboring PSA which has a defined RSA with radius of less that one-mile, very low response station heights and a very high hub.  This hub would prove very difficult to protect.  As with the rules prior to the Two-Way Order, there will always be loopholes and other mechanisms which unscrupulous individuals will be able to employ.  Vigilance is the only answer in this case.

The Preclusionary Impact of Expected Filings in the First Window

From the information generally available in the industry, it appears that the vast majority of filings being prepared for the first window will be employing MDS-1 and MDS-2(2A) channels for upstream and some of the other commercial channels for downstream in a sectorized, supercell configuration.  The implications of this are clear.  There should be very little practical possibility of ITFS preclusion in the first window due to the fact that very few upstream applications, with their associated hubs, will be filed either co- or adjacent channel to any ITFS channels.  As such, it is reasonable to expect no significant preclusionary impact in the first filing window. 

Certainly, this paper is not meant to be nor does it purport to be an exhaustive study of the issue of preclusion or every possible situation in every market.  However, the general outlines forwarded herein are believed to have broad applicability.

June 14, 20000

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