Home >> July 2008 Edition >> ACTIONABLE INTELLIGENCE: Wideband MILSATCOM—Has Spectrum Monitoring Arrived?
ACTIONABLE INTELLIGENCE: Wideband MILSATCOM—Has Spectrum Monitoring Arrived?

by Bob Cooper, Senior Staff, Glowlink
and Michael Downey, CTO, Glowlink

Wideband MILSATCOM spectrum monitoring recently came into the 21st century with the initial fielding of the Wideband Global Spectrum Monitoring System (WGSMS) to the U.S. Military’s Camp Roberts in California, and Fort Buckner, Okinawa. Wideband SATCOM Operations Centers (WSOC) Follow-on installations are scheduled for Fort Meade, and Fort Detrick, in Maryland, and Landstuhl, Germany, WSOCs in the coming months.

The WGSMS, developed by Glowlink Communications Technology, is a component of the U.S. procured procured Military Wideband Satellite Communications (SATCOM) Operational Management System (WSOMS). WSOMS is based on a “System of Systems” architecture comprised of a suite of new, state-of-the-art systems that provide planning, management, and control of X- and Ka-band communications links traversing the Wideband Global SATCOM (WGS) and Defense Satellite Communications System (DSCS) satellites. WGSMS is a powerful Digital Signal Processing (DSP)-based system that provides signal detection and characterization functions, as well as the identification of unauthorized signals accessing the satellites.

A NewGen Of Spectrum Monitoring
WGSMS replaces the DSCS Automatic Spectrum Analyzers (DASA) that have been in use at the five WSOCs. DASA, developed in the late 1970s, has been the primary spectrum monitoring device for wideband SATCOM for more than 25 years. DASA provides conventional frequency domain monitoring capability via an automated spectrum analyzer-based system. DASA measures traditional Frequency Division Multiple Access (FDMA) link properties such as center frequency, channel percentage of power usage, and carrier power to noise density ratio (C/kT), while providing an unauthorized access (UA) detection capability.

While DASA has served the wideband community well, the addition of the WGS satellites to the wideband SATCOM constellation requires an expanded monitoring capability DASA is not capable of supporting. The capacity of a single WGS satellite will result in a nearly ten-fold increase in bandwidth over a DSCS satellite. This results in the need for a more powerful and faster monitoring capability than DASA is capable of providing. Interestingly, the founders of Glowlink were also members of the original DASA engineering team.

New Challenges
The WGS satellite provides greater bandwidth and also introduces a channelizer function to divide each communications channel into bandwidth segments. This creates “virtual” transponders for mapping communications links in an uplink coverage area to practically any downlink coverage area. While this results in incredible flexibility from a communications perspective, this technology presents a new challenge for spectrum monitoring.

Traditionally, spectrum monitoring is accomplished in the footprint of a downlink antenna providing visibility into the majority of the communications links traversing the satellite. However, the bandwidth mapping flexibility of the WGS, combined with 19 downlink antenna coverage areas limits the ability of the WSOC to be in the footprint of no more than a couple of the antenna coverage areas at any one time.

To overcome this limitation, the WGS satellite includes a Spectrum Information Gathering (SIG) feature that taps into the uplink segments of satellite bandwidth and routes them to a downlink antenna coverage area that illuminates the WSOC.

While this provides the ability to monitor the entire bandwidth of the satellite from a single coverage area, it also requires that the spectrum monitoring system be capable of taking the bandwidth segments and reassembling them into a usable spectrum.

The WGSMS provides the capability to track and acquire the SIG segments and digitally reassemble them into a viewable and measurable spectrum, providing frequency and time domain measurements. Thus, WGSMS is the world’s first system that performs synchronized monitoring, ushering in a new era in wideband MILSATCOM satellite communications.

In addition, WGSMS takes the uplink measurements, maps them from the uplink antenna through the channelizer to the appropriate downlink antenna, and then reconstructs a downlink spectrum that provides an operator with the propagated amplitude and frequency assignment for each of the links.

This feature takes the guess work out of determining how a link was routed through the satellite. Such allows the operator to easily correlate the relationship between the coverage area the transmit link is in with the coverage area the downlink is in.

“WGSMS is the world’s first system that performs synchronized monitoring, ushering in a new era in wideband military satellite communications”

“WGSMS is the world’s first system that performs synchronized monitoring, ushering in a new era in wideband MILSATCOM satellite communications.” In another area of break-through technology for MILSATCOM, WGSMS provides powerful, enhanced spectrum monitoring capability that combines frequency and time domain measurements, while achieving large gains in measurement cycle speeds over that of the DASA. WGSMS employs a high-speed digitizer with an instantaneous bandwidth of more than 72 MHz. WGMS allows the measurement of the entire 500 MHz bandwidth of a DSCS satellite to be completed in approximately 1/20th of the time the DASA takes.

WGSMS provides the basic frequency domain measurements of center frequency, percentage of power, and C/kT and includes time domain measurements that allow signal characterization functions for the determination of modulation and coding attributes. The WGSMS time domain measurement capability provides special features, such as signal under carrier (SunCarTM) detection, which detects the presence of interference under another carrier or communications link as part of its routine monitoring function. Prior to the WGSMS, low-level signals interfering with communications links were not detectable without switching the desired carrier, or link off-air, to see if any signal energy remained.

The WGSMS not only detects the presence of the unwanted signal, it also determines the impact to the primary signal while providing characterization of the unwanted signals to assist an operator in determining its potential origin.

Another state-of-the-art feature of the WGSMS is its ability to automatically assess the health of a satellite to prevent catastrophic failure, such as transponder saturation. Traditionally, power balancing a communications network on the DSCS satellite required a controller to compare channel percentage of power used against the power levels of all of the links in that channel. Under certain conditions, rain fade and equipment degradation compensation could result in subtle channel compression that, if undetected, could result in full channel saturation.

Operators could find themselves inadvertently raising links that were in alarm without knowing that the channel was in compression. The result of the power raise would put the channel into further compression, which in turn would lead to even more links in alarm. The cycle would continue until it became obvious that the channel was saturated but, all too often, not before impacting the communications links.

The WGSMS introduces a Transponder Operating Point (TOPTM) feature that monitors the operating point automatically and alerts the operator at the onset of compression prior to any link degradation. This allows a much more deliberate power balancing process where the operator is knowledgeable of the operating point of the channel and can perform power balancing without adversely affecting the communications links.

Vital, Seamless Integration
Prior to WGSMS, some vendors have been touting the need to buy an “integrated system” from a single source. While this may sound appealing on a surface level, the customer often ends up in an “all eggs in one basket” predicament. This severely limits future options and places them at the risk of being held “captive” by a single vendor. Perhaps even worse is that the customer ends up being trapped with expensive and second-best, or even third-best, products in each product category.

To help the customer avoid this pitfall, and to accomplish its MILSATCOM mission, the WGSMS is designed with an open architecture and standard protocols so it can readily interface to a variety of other WSOMS elements. The WGSMS can be configured to monitor either a DSCS or WGS satellite via a configuration plan developed by the communications planners and managers located in the wideband SATCOM management sites. The monitoring plan will contain all of the communications links, earth terminal, and satellite attributes necessary to properly configure the WGSMS for performing spectrum monitoring in support of the radio frequency (RF) transmission control mission.

For monitoring the DSCS, the WGSMS will be configured for in-beam monitoring. The configuration plan will provide the only data necessary for the WGSMS to monitor the DSCS spectrum. For the WGS, the WGSMS can be configured for in-beam or for synchronized monitoring using the WGS SIG. When configured for WGS in-beam monitoring, the configuration plan is the only information that the WGSMS needs. For synchronized monitoring, the WGSMS will receive the configuration plan containing the same information as the in-beam plan and also receive the Global Satellite Configuration Control Element (GSCCE) information, which includes the crucial data required by WGSMS to carry out synchronized monitoring tasks.

Comprehensive System Views
WGSMS’s open architecture design allows all of the aforementioned capabilities to be accessed from a diverse set of external users via other WSOMS elements and clients, such as the WSOMS Remote Access System (RAS). Not only will multiple operators in the WSOC be capable of accessing the WGSMS from any of the Objective DSCS Operations Control System (ODOCS) workstations, remote users at the WSOMS management sites will be able to access satellite and communications link performance gathered by WGSMS via the RAS. Through this comprehensive pan-system view, executive managers of WGS and DSCS are able to ensure the satellites and the communications links traversing them are fully operating within established parameters.

WGSMS is sponsored and operated by the US Army, who is also responsible for the life cycle management of the system. In addition to the five WSOCs, the WGSMS will be deployed in the near future to Fort Gordon, Fort Monmouth, and the Johns Hopkins University Applied Physics Lab (JHU/APL), while the RAS clients will be deployed at WSOMS management sites worldwide.

About the authors
Bob Cooper is a senior technical staff at Glowlink Communications Technology, Inc. He has over 25 years of MILSATCOM experience spanning both the DSCS and WGS satellites. He joined Glowlink after devoting more than 20 years to wideband satellite planning, control and monitoring systems development and operations for the U.S. Army.

Email: Bob.Cooper@glowlink.com

Michael Downey is a Co-Founder and Chief Technology Officer of Glowlink Communications Technology, Inc. He is a recognized leader in signal processing, interference detection and geolocation technologies. Mr. Downey earned his BSEE from California State University, Sacramento, and his MSEE from Santa Clara University, Santa Clara, California.

Email: Michael.Downey@glowlink.com