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CASE CORNER:
The AWACS Interference Phenomenon

MARKET TRENDS:
FCC Electronic Filing Made Easy - Universal Licensing System (ULS)

REGULATORY RAP:
Microwave
Satellite

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Case Corner

The AWACS Interference Phenomenon
by Ken Ryan

The September 11th 2001 tragedy will have long-term, rippling affects on our lives and our businesses. The immediate aftermath has put the US in a state of high alert. Just one of the many ways in which our government has been protecting our nation from a repeat tragedy is by monitoring the skies. The Department of Defense has long had a mission to perform these types of tasks, and, since the terrorist attacks the US Air Force's 552nd Air Control Wing (ACW), along with a detachment from NATO, have been continuously patrolling the skies of America. 

Operation Noble Eagle, the defense of the United States, has been using the Airborne Warning and Control Systems, otherwise known as AWACS, as the primary airborne surveillance and warning system. AWACS uses an E-3 Sentry aircraft, which is a modified Boeing 707-320C plane. It has a pulse doppler radar, recognizable by its distinctive radome and is capable of detecting aircraft and missiles. It specializes in detecting low altitude objects. The ACW has 28 AWACs (not all are in operation in the US) and NATO has provided at least 5 aircraft since mid-October. AWACS aircraft are presently over many urban areas today. An unfortunate side effect is that the operation of these radars is causing interference into satellite earth stations receiving in the 4 GHz band. Most cable operators, broadcasters, and many "backyard" dishes use this band to receive video news and entertainment programming.

The look-down radar has a 360-degree view of the horizon, and at operating altitudes has a range of more than 320 km. The radar can detect and track air and sea targets simultaneously. In a tactical role, the E-3 can detect and track hostile aircraft operating at low altitudes over any terrain, and can identify and control friendly aircraft in the same airspace. In the strategic defense role, AWACS provides the means to detect, identify, track, and intercept airborne threats.

The frequency band of the AWACS radar is classified, but in general, operates in the 2700- 3700 MHz band. Receive C-band satellite earth stations operate in the 3700-4200 MHz. Since these two bands do not overlap, the primary means of interference coupling are in-band spurious emissions and out-of-band receiver front-end overload. The National Telecommunications and Information Administration (NTIA) is responsible for managing the Federal Government's spectrum use. They have recognized an interference problem for quite a while, and a few years ago performed an in-depth study to analyze and assess the problem (NTIA Report 94-313). Their studies showed that these radar are quite well filtered and do not produce harmful spurious emissions in the downlink satellite band. However, due to the wide-angle view of the high-powered AWACS transmitters and the line-of-sight conditions to the earth station's main beam at certain trajectories, the phenomenon of front-end overload can occur. This is exacerbated by the fact that many C-band downlinks typically have poor RF filtering on their receivers.

Front-end overload is a condition that exists when the receiver's filtering on the front-end amplifier is so broad that even out of band energy is captured and amplified. Earth stations use a Low Noise Amplifier (LNA) which is necessary to capture the low-power satellite signals. These devices are fairly inexpensive, have low noise figures, and have, unfortunately, very wide front-end filters, typically around 1000 MHz. The input power of the amplifier is increased by the amount of gain specified. A typical LNA would have 55 dB of gain, and a noise temperature of around 35K - about 0.4-dB noise figure. LNA's also have a maximum output power level, called the saturated output power. If too much power is in the front-end of the amplifier it will "drive it into saturation." Once an amplifier is overloaded it starts to misbehave. The most common problem associated with an overdriven amplifier is gain compression, which results in an overall reduction in output power levels. Another possible problem involves mixing products created within the satellite frequency band even though the interference is out of band. An LNA gain compression of 10 dB will eliminate most satellite signals and occurs across the entire band, affecting all receive signals.

Out-of-band emissions can be filtered with minimal impact on an earth station's operation. A pass-band filter is a good solution to the problem because it will pass the entire 500 MHz of the satellite band and suppress high-powered signals above and below the band.

The following figures are extracted from the above mentioned NTIA report and illustrate the gain response of a typical LNA, the response of an LNA in suppression, and the response of a good band pass filter.

Figure 1 - A typical LNA's response curve of gain and noise figure versus frequency.  As can be seen the gain response extends well beyond the satellite 500 MHz downlink, amplifying any signals above and below the desired band.

Figure 2 – LNA in overload, as the out-of-band radar power level increases, the desired satellite signals become lower as a result of the LNA’s gain compression.  If the input is sufficiently powerful, all satellite signals will be too low to complete the link.

Figure 3 - Frequency Response of a Band Pass Filter. These BP filters are an effective and simple solution to AWACS, and other government radiolocation interference.

Comsearch has performed dozens of measurements at 4 GHz earth station facilities where interference from AWACS was identified. The use of a band pass filter has resolved the problem in all of these cases. A good band pass filter will introduce only about 0.5 dB of insertion loss and provide up to 90 dB of suppression 300 MHz from the satellite band edge.

AWACS may very well be the cause of increased downlink interference to many earth stations. Fortunately, experienced technicians can quickly identify and resolve the problem so that the interests of national security can proceed and commercial satellite operations can continue getting on with their business.

Regulatory Rap

MICROWAVE

Market Report
According to a recent report from Strategies Unlimited, commercial and industrial demand for broadband wireless access and cellular backhaul infrastructure lifted the microwave radio market to more than $3.3B in 2001, in spite of reductions in capital spending by North American carriers. Moving forward, the continued need for BB access and more cellular infrastructure could drive the microwave radio market to more than $5.5B during the next five years, for a CAGR of nearly 11%. The demand for both point-to-point and point-to-multipoint radios grew about 10% last year. The report also includes an outlook for RF modules and RF ICs, including revenue and ASP forecasts.

Nextel's Spectrum Reallocation Proposal
As a holiday gift to the Commission, Nextel submitted a White Paper outlining a reallocation of spectrum to correct the causes of interference between commercial wireless and public safety radio communications systems in the 800 MHz band. As part of this initiative, Nextel proposed to realign the 36 MHz of 800 MHz public safety/CMRS spectrum by creating two separate (adjacent) contiguous channel blocks: 20 MHz to Public Safety (channels 1 - 400), and 16 MHz (channels 401 - 720) to commercial digital wireless networks. To clear space for the public safety block, Nextel (the predominant incumbent commercial licensee with 18 MHz at 800 MHz) would relocate its licenses in channels 1 - 400 (8+ MHz of the total 20 MHz) to other spectrum at its own cost. Nextel will also contribute its 700 MHz Guard Band (4 MHz) and 900 MHz SMR licenses (4 of the 5 MHz SMR allocation at 900 MHz) to make spectrum available for relocating 800 MHz B/ILT incumbents and high-site (non-cellular) SMR incumbents from the new public safety block. In return for the 16 MHz Nextel would contribute for these purposes, Nextel would be licensed to replace spectrum as follows: (1) 6 MHz at 821/824 - 866/869 MHz (the current NPSPAC channels) made available by consolidating and expanding the Public Safety spectrum in channels 1-400; and (2) a 10 MHz contiguous block from the reserve Mobile Satellite Service ("MSS") spectrum at 2.1 GHz, reallocated for terrestrial CMRS service and licensed to Nextel on a nationwide basis. The proposal faces many hurdles as initial opposition comes from the displaced 800 MHz B/LT incumbents, mobile satellite companies that would be losing spectrum and PCS and cellular companies concerned about Nextel receiving a chunk of spectrum at 2.1 GHz without going through auction. http://wireless.fcc.gov/releases/011121-whitepaper_final.pdf

Federal Court Upholds FCC On 18 GHz Order
In the case of Teledesic v. FCC, the federal appeals court in the District of Columbia upheld the FCC's interpretations regarding rules in the 18 to 19 GHz band, requiring satellite providers compensate incumbent Fixed Service operators for relocating. The decision can be viewed at Teledesic v. FCC

More 18 GHz News
Now that the Commission has finalized the reallocation of the 18 GHz band to Fixed and Satellite services in the First Report and Order on Reconsideration in IB Docket 98-17, the FWCC is developing a rechannelization plan to increase efficient use of the spectrum. The Commissions reallocation plan removed the small bandwidth 5 MHz channel plan (commonly referred to as the 340 MHz split) from the Fixed Service, leaving them with a minimum channel bandwidth of 10 MHz. It also created an orphaned 40 MHz. The FWCC band plan looks to modify the remaining spectrum and add smaller bandwidth channels for efficient use of the spectrum.

Ultra-WideBand
As reported by the Los Angeles Times, the controversial ultra-wideband proceeding at the FCC could be coming to a close, and insiders are expecting the FCC to approve the use of the technology at its next open meeting. Ultra-wideband can be used for very-high-speed wireless Internet access and to facilitate such other applications as home radar and improved collision avoidance systems. Airlines, the wireless industry and some parts of the government have offered sharp opposition to ultra-wideband technology, claiming it will cause interference with their communications systems.

The Defense Goes On The Offensive
In an effort to protect radio spectrum used by the Defense Department, Defense Secretary Donald Rumsfeld has hired a telecommunications industry executive to focus on protecting that electromagnetic spectrum. Steven Price, former president and chief executive officer of LiveWire, has been hired as a deputy assistant secretary of Defense for spectrum and command, control and communications policy. This marks the first time that spectrum issues have risen to the deputy assistant secretary of Defense level.

FCC Allocates Additional Spectrum For New Wireless (ET Docket No. 00-221)
On December 21, 2001, the FCC adopted a Report and Order and a Memorandum Opinion and Order reallocating 27 megahertz of spectrum transferred from Federal Government use for new flexible services. The reallocated spectrum is in the 216-220 MHz, 1390-1395 MHz, 1427- 1429 MHz, 1429-1432 MHz, 1432-1435 MHz, 1670-1675 MHz, and 2385-2390 MHz bands. These actions also preserve the primary status of Wireless Medical Telemetry Services and elevated Low Power Radio Services in the 216-217 MHz band, which include auditory assistance and law enforcement applications, to primary status. Additional information can be found at http://www.fcc.gov/Bureaus/Engineering_Technology/News_Releases/2001/nret0108.html

FCC Announces New Filing Address for Paper Documents and New Fax Number for General Correspondence - (DA 01-2919)
Effective December 18, 2001, ALL hand-delivered or messenger-delivered paper filings for the Commission's Secretary must be sent to a new location in downtown Washington, DC. All hand deliveries must be held together with rubber bands or fasteners. Any envelopes must be disposed of before entering the building. Delivery options are as follows:

In light of recent events in Washington, DC, resulting in unforeseeable and understandable disruption of regular mail delivery, the FCC is providing a means for the public to fax general correspondence to the Commission, such as inquiries about the Commission's activities, status inquiries, fee-related questions, and any other correspondence that is not an official filing addressed to the Commission's Secretary. The public may now fax correspondence to the Commission at 202-418-0188. If possible, please include the following information in the addressee block of the correspondence.

• The Commission's full name and address (445 12th Street, SW, Washington, DC 20554).
• The name of the Commission Bureau or Office to which the correspondence is directed.
• The name and room number of the FCC staff person to whom the correspondence is directed.

As noted above, this fax number for general correspondence must not be used for official filings addressed to the Commission's Secretary.

FCC Announces Changes in Filing Procedures at the Gettysburg Office - (DA 01-2620)
As a precautionary measure, effective immediately and until further notice, the following procedure is in place:

• The staff at the Gettysburg office's filing counter at 35 York Street will not accept documents enclosed in envelopes.
• Originals and copies of each official filing must continue to be addressed to the Commission and held together with rubber bands or fasteners. As usual, "stamp and return" copies will be provided as long as they clearly accompany each individual filing.
• Documents intended to be received by specific staff persons within Bureaus and Offices must be clearly labeled on the first page of the document or with a cover sheet indicating the destination. As appropriate, originals and copies must be held together with rubber bands or fasteners.
• Filings requesting confidential treatment under the Commission's rules must also be filed without envelopes. As long as the request for confidential treatment is clearly indicated on the first page of the filing, the staff at the filing counter will enclose the filing in a Commission envelope labeled "confidential" to signal that the filing contains material that is subject to a request for confidential treatment.
• The Gettysburg office will work with specific Bureaus and Offices, as appropriate, to handle bulk filings in accordance with the precautionary measures described above.

FCC Auctions

Auction 42: Multiple Address Spectrum - Closed on November 27, 2001. Spectrum was lightly bid with only 878 of the more than 5,000 available licenses sold. The top bidders are as follows:

Company                                # of Licenses                       Total Bids
MilkyWay Communications          476                               $1,010,000
Microwave Data Systems             168                                 $ 181,000
Paging Systems, Inc                     38                                 $ 113,100
TeleBEEPER of New Mexico          58                                  $ 59,100
Telephone & Two-Way                   40                                  $ 40,400
Wisconsin Electric                        33                                  $ 33,000
Other 7 Bidders                             65                                 $ 67,100

Additional information can be reviewed at: http://wireless.fcc.gov/auctions/42/

Auction 43: 220, 800 and 900 MHz Service licenses - Auction began January 10, 2002 and includes the following:

220 MHz - A total of 4 licenses will be available in the Phase II 220 MHz Service. Two licenses will be offered in Economic Areas (EAs), and two licenses in Economic Area Groupings (EAGs). Each channel encompasses a base frequency and a mobile frequency which are 1 MHz separated. Licensees will be able to provide voice, data, paging and fixed communications.

800 MHz SMR - A total of 23 General Category licenses will be awarded in this auction. Each channel encompasses a base frequency and a mobile frequency which are 45 MHz separated. Licensees may provide analog or digital services used for voice communications, paging, data and facsimile services. The SMR marketplace is allowing new acknowledgment paging and inventory tracking, credit card authorization, automatic vehicle location, fleet management, remote database access and voicemail.

900 MHz LMS - A total of 42 licenses will be available in the Location and Monitoring Service: 2 licenses will be auctioned in Block A, 39 licenses will be auctioned in Block B, and 1 license will be auctioned in Block C. LMS systems utilize non-voice radio techniques to determine the location and status of mobile radio units. Multilateration LMS systems are authorized to transmit status and instructional messages, either voice or non-voice, so long as they are related to the location or monitoring functions of the system.

Additional information can be found at: http://wireless.fcc.gov/auctions/43/factsheet.html

SATELLITE

Some Good News for Emerging Satellite Services
As of early January 2002, both XM Radio and DirectWay have reported strong sales in the initial rollout of their respective new nationwide satellite services. Hughes Network Systems has announced that it has surpassed 100,000 subscribers for DirectWay, its direct-to-home two-way broadband satellite service. XM Satellite Radio, the first satellite radio service to serve the United States, recently exceeded 30,000 paid subscribers in the two months since its debut. Sirius Satellite Radio, the other satellite radio broadcaster, has grossed approximately $158 million in a public stock offering. Sirius will be launching service on February 14, 2002 in Houston, Denver, and Phoenix.

On The Other Hand…
On January 5, Alcatel, the telecommunications systems vendor, announced that it is postponing plans to deploy the SkyBridge satellite broadband system. Alcatel has had difficulty in raising the $6 billion needed to fund the project. Alcatel has said they will re-examine the deployment of the internet-in-the-sky service when the market improves.

Lockheed Martin Corporation, on the heels of announcing it was dropping the Astrolink Ka-band satellite system, has announced plans to restructure the Lockheed Martin Global Telecommunications (LMGT) businesses. They said that LMGT's Systems & Technology line of business and its COMSAT General telecommunications unit will be realigned with the Space Systems business area. Other operations will be incorporated into segments of Lockheed Martin, some will be sold, and others eliminated.

FCC Activity
On October 9, 2001 the FCC authorized mobile satellite service in the United States using the Inmarsat satellite system. The Commission found that Inmarsat; formerly an intergovernmental satellite organization, which privatized in April 1999, satisfied the privatization criteria of the ORBIT Act. The authorizations are conditioned upon Inmarsat compliance with the ORBIT Act requirement that it conduct an Initial Public Offering (IPO). As a result of the Commission's action, U.S. customers will be able to use the Inmarsat satellite system for a variety of aeronautical, maritime and land mobile satellite communications services, including voice, data, facsimile and high-speed Internet.

Full-Band, Full-Arc Proceeding (IB Docket No. 00-203)
Based upon overwhelming industry sentiment against the proposals put forth by the Commission in IB Docket 00-203, it appears that the proceeding will be dropped by the Commission in the coming weeks. The Fixed Wireless Coalition Committee (FWCC) initiated the rulemaking proceeding in an effort to resolve inequalities in the way that fixed microwave and satellite earth stations are coordinated and licensed. However, the Commission's ultimate proposal was found to be unworkable by both fixed and satellite interests.