RPU Band Meeting Notes
Low Earth Orbit Satellite Operators Seeking 455 MHz
by Dave Wilson
Thanks to everyone who provided me with information about their usage of 455-456 MHz, and thanks to Dane Ericksen for supplying me with a copy of the comments that SBE filed in the WRC-2000 process related to this issue. Here's an update on the status of the issue.
Over a year ago (10/14/97) the FCC released a Notice of Proposed Rule Making in ET Docket 97-214 proposing, in part, to allocate 455-456 MHz to the Mobile Satellite Service for uplink operations. The FCC proposed that these MSS uplinks be allocated on a co-primary basis with Broadcast Auxiliary users. Both NAB and SBE, among others, filed comments objecting to this allocation. The satellite companies filed comments supporting it. The FCC has not yet published a decision in this docket.
Every few years there is a large international meeting at which governments from all over the world get together to coordinate their radio frequency allocation efforts. This meeting is called the World Radiocommunication Conference (WRC) and the next one is scheduled for 2000 (WRC-2000). The FCC is in the middle of a year-or-so long process of planning for WRC-2000. It has an advisory committee that is contemplating what the U.S. position should be on various issues at WRC-2000. This advisory committee has a number of smaller informal working groups (IWGs), each of which is studying some specific issues. One of these working groups, IWG-2, is studying the "Mobile Satellite Service Below 1 GHz."
The International Telecommunications Union (ITU) is an arm of the United Nations which publishes technical reports and makes recommendations regarding telecommunications issues. One of the reports it publishes in preparation for WRCs is called the Conference Preparatory Meeting (CPM) Report. The CPM Report being prepared now will be used by the participants at WRC-2000. The CPM Report is produced through the ITU process, so it is an international effort. Leading up to WRC-2000 various ITU committees are meeting in order to provide input to this report. The ITU committee that is addressing the 455 MHz issue is called Working Party 8D. There was an international meeting of Working Party 8D October 19-30. At this meeting, the U.S. submitted a document, prepared by a satellite proponent, which purports to demonstrate that MSS systems can share the spectrum at 455-456 MHz without interfering with broadcast RPU operations. Included in this document was some draft text for the CPM report to be used at WRC-2000. [I have attached this draft text to the end of this email message.]
Last Friday (11/20/98) there was a meeting of the FCC's IWG-2 at which the same study claiming to demonstrate that MSS systems can share 455-456 MHz without interfering with RPU operations was briefly discussed. Now that the satellite folks have some draft language in the CPM Report for WRC-2000 which indicates that MSS/RPU sharing might be possible, they would like the U.S. to push for a worldwide frequency allocation for MSS systems at 455-456 MHz. Also at Friday's meeting, several sets of comments were distributed which address the issue of potential MSS/land mobile sharing in the 450-470 MHz band. These comments were received by the FCC in response to a public notice that it released on June 15, 1998 (DA 98-1125). The comments filed by SBE in response to this public notice were not among those distributed. I was told that the members of the committee were unaware that SBE had filed comments. One of the FCC advisors to this committee, Alex Roytblat, said that he would see if he could track down the SBE comments and have them available for distribution at the next meeting, scheduled for February 11, 1999.
That's the status as of now. Clearly, broadcasters need to pay attention to what's going on in IWG-2 in order to ensure continued interference-free and unrestricted use of 455-456 MHz. Last week, when I asked for information about how people are using 455-456 MHz for RPU operations, I was trying to check a hypothesis that the number of times that RPUs are operated on a 24-hour per day basis in this band would be enough to completely prevent an MSS system from having any access to the band for days, maybe weeks at a time. If this were the case, then clearly MSS/RPU sharing would not be advisable since the MSS system couldn't go for days without access to the band. While I did receive a lot of useful information, I did not receive enough to confirm or reject this hypothesis.
Thanks again to everyone for their input.
DRAFT CPM TEXT RE: 455 MHZ
"An analysis was performed at 455 MHz to evaluate frequency sharing between FDMA narrowband uplinks in the non-GSO mobile-satellite service and a specific terrestrial system operating in a mobile service band. The non-GSO MSS network modeled had 48 satellites with Earth-to-space links from mobile earth stations with antenna heights of 3 m. The satellite network was assumed to use a dynamic channel assignment technique to avoid channels that were actively being used by terrestrial systems, and it was assumed that this channel assignment technique was 99.8 percent effective in detecting active remote pickup unit (RPU) channels for the terrestrial systems modeled. The specific terrestrial system was a RPU linked to a sound broadcasting station, in an urban noise environment (assumed to be -138 dBW). The remote unit antenna height was 15 m and the base station receiving antenna height was 60 m. The simulation results showed that the probability of interference was 0.00015% (due to one interfering non-GSO MSS system). This is equivalent to a single short, one-half second, interference event every 4 days, assuming that the RPU is operating continuously for that period. If the RPU only operated for 2.5 hours per day, then the average interval between short, one-half second, interference events would be a month. The results show that for the particular sharing scenario analyzed the RPU channel availability was degraded by much less than a 99% availability reduced to 98.9%."
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Edited by Gary Stigall. Updated 1-Dec-98.