Future State of Global Navigation Satellite Systems (GNSS)
Expert Advice -- GNSS in the Year 2017 http://sidt.gpsworld.com/gpssidt/article/articleDetail.jsp?id=421287
By: John W. Lavrakas GPS World
What will GNSS service be like 10 years from now? Such a fascinating question, especially for those who have over recent years witnessed the explosion of GPS capabilities and applications!
For more than a decade, GPS has enriched our lives, bringing vast and unexpected improvements in transportation, communications, military effectiveness, scientific research, geographic data collection, business applications, and recreation.
Nonetheless, further steps are being taken to improve satellite navigation. GPS is being modernized to offer new signals and codes. The European Union's Galileo program is poised to introduce its new satellite navigation system by the year 2012, offering five levels of service. The Russian Federation is committed to updating GLONASS with new M- and K-class satellites offering additional capabilities for civil users. Even China has announced plans to offer a worldwide satellite navigation service, called Beidou Compass.
Billions of dollars, euros, and rubles are being spent on these initiatives, with three, perhaps four, Global Navigation Satellite Systems (GNSS) planned to be fielded in the next 10 years. How likely is it that all these systems will be fielded? What will service really be like in the year 2017? Let me try and look into the future to answer this question. I will consider three possible scenarios: a best-case scenario in which all schedules are met; a worst-case scenario in which no schedules are met; and a reasonable scenario, somewhere between the two, in which each program advances under typical rates of progress.
Best Case: Everyone Meets Their Dates
Under this best-case scenario, by 2017 GPS Block IIRM and Block IIF satellites have all been launched. The GPS Block III program is in the middle of deployment and is four years away from completion. Galileo has been operational for five years and GLONASS is fully operational. Let's take a look at each system individually and then at the total GNSS picture collectively.
GPS. Eight Block IIRM satellites will be deployed by 2008. Twelve Block IIF satellites will be deployed between 2008 and 2016. In addition to the L2C (dual-frequency) and M-code signals, these satellites provide the L5 safety-of-life (SOL) signal, necessary for aviation and other safety-of-life operations.
Block III satellites will be deployed between 2013 and 2021. These satellites have crosslink communication, resulting in near zero age of data and integrity monitoring/reporting capability. Block III satellites are required for dual-frequency full operational capability (FOC) and safety-of-life capability because only 20 Block II-class satellites with L2C will be purchased, and only 12 of those will have L5.
By following through on this schedule, the U.S. government launches on capability, without regard to the performance of existing satellites. Thus, if existing satellites are performing according to their specifications, and a new satellite with added capability is available, the new satellite will be launched. The net result is far more satellites on orbit than the minimum required to meet today's service commitments \u2014 in fact, more satellites than permitted under the current specified maximum of 32 signals. This scenario therefore assumes the control segment has been upgraded to accommodate the extra signals being broadcast.
To sum up, the GPS system has 35 satellites, all providing L1, M-code, and L2C signals. The L5 (safety-of-life signal) is available on 27 satellites, with full operational capability. Near zero age of data is available on 15 satellites due to crosslink communication on the Block IIIs.
Galileo. Thirty operational satellites are launched by 2012. In this best-case scenario, Galileo provides full operational capability with open service, safety-of-life, commercial service, and public regulated service on all 30 satellites.
GLONASS. GLONASS launches 24 K satellites by 2017. All 24 are equipped with L1, L2 (dual-frequency), and L3 (an L5 safety-of-life equivalent).
Awash in Signals. Under this best-case scenario, what kind of service does the world have in satellite navigation in 2017?
GNSS users employing hybrid technology are awash in quality signals, with 89 satellites on orbit (65 from GPS and Galileo alone). More than 25 satellites are in view at any one time (20-plus from GPS and Galileo alone). Aviation users, while not having a fully operational safety-of-life service, are able to operate dual frequency worldwide in test mode. Operational use of GNSS for landing is probably only a few years away.
GPS provides three signals at no cost to users. Half of the GPS III satellites have zero age of data, keeping range errors down. Integrity, while not completely assured without augmentation, is available on 15 of the satellites, giving a big boost to users worldwide.
Galileo is offering its full service on all 30 satellites. GLONASS users have the full 24-satellite service.
What I've just considered is the good news scenario, and what good news it is! Now, I'd like to look at a worst-case scenario.
Worst Case: Nobody Meets Their Dates
Under this scenario, GPS III is never funded. Galileo and GLONASS proceed with development but experience technical difficulties. For example I assume that each of the programs has had a launch failure (this is a worst case scenario, remember?). The GPS Block IIF program moves forward, but is not completed until 2018. Although delayed, Galileo is largely able to complete its constellation by 2017. GLONASS also experiences delays.
GPS. In this scenario, GPS Block III is never completely funded and no satellites are launched. The GPS Block IIF program is delayed from the 2008-2016 schedule to a 2010-2018 schedule. This includes a launch vehicle failure resulting in a one-year slip in new launches.
There are no more Block II/IIA satellites in service. Assuming Block IIRs have a 50 percent mortality rate, by the year 2017, only six remain. Eight Block IIRM satellites are completed and launched. Twelve Block IIF satellites are purchased, but only eight are launched by 2017 due to launch failure.
Under this scenario, L1 is available on all 22 satellites, the M-code and L2C signals are available on 16 satellites; and L5 is available on eight satellites.
Galileo. In this scenario, Galileo gets under way, but at a much slower pace. There have been problems in funding the initial program, and several years have been lost getting all the participants on board for the development of the operational phase. A launch failure has further delayed completion. For this scenario, it is assumed that five satellites are launched at a time.
Because of funding and technical issues, only a partial constellation has been launched. The first satellites were launched in 2009, followed by a one-year checkout, then a launch failure resulting in the loss of five satellites and delay of one year.
The original plan was 30 satellites launched in three years. In this scenario, 25 satellites are launched over six years, with the first launch occurring in 2009. Initial operational capabilities (IOC) provide open service, safety-of-life, and commercial service on all 25 satellites, but public regulated service isn't defined early enough to be incorporated into the first 10 satellites. It was only added to later satellites, for a total of 15.
GLONASS. Under this scenario, the constellation is sustained at lower levels due to inadequate funding and technical and programmatic difficulties. Launches continue at a rate of one per year with three satellites per launch. A launch failure further compounds deployment difficulties. GLONASS M satellite production ends when the K satellites become available in 2010.
Under this scenario, all original GLONASS satellites have died. All GLONASS M satellites have been launched, and three remain operational. Eighteen GLONASS K satellites have been launched starting in 2010, with a one-year delay because of launch failure.
All 21 satellites provide the L1 and L2 (dual-frequency) signals. The L3 safety-of-life signal is available on 18 satellites.
Hybrid Users Win. Under this worst-case scenario, in 2017 the world has a seriously degraded GPS service, with only 22 satellites on orbit. GPS-only users regularly have dilution of precision (DOP) holes lasting for long periods of time worldwide. Even though performance standards are being met, users are dropping GPS as their preferred system.
Galileo is offering its full service on a short constellation of 25 satellites. Like GPS, its service isn't quite complete, but service is adequate for most applications.
GLONASS users have dual-frequency service at the IOC level with 21 operational satellites on orbit.
Despite the shortcomings with individual systems, the GNSS users employing hybrid technology have more than enough quality signals, with 68 satellites on orbit (47 for GPS and Galileo alone) and more than 20 satellites in view at any one time (more than 15 satellites for GPS and Galileo alone).
Final Case: A Reasonable Outcome
I now consider a scenario that represents a reasonable outcome from today's planning. The schedule has been adjusted to reflect typical changes based on historical precedent.
For example, the U.S. government has delayed launches of the Block IIRM satellites from its original schedule, in part because the existing constellation continues to meet service goals and in part to save money. The U.S. government has been reluctant to turn off useful satellites even if the satellites are past their design life and have aging components, single points of failure, and reduced performance. This concept of launching only to replenish failed satellites is called "launch on need," which contrasts with the "launch on capability" strategy employed in the best-case scenario, and it forms the underlying launch strategy used in this scenario. In general, the government's approach is to sustain existing capability, not launch to support new capability.
Under this scenario, Galileo has been up since 2015 (10 years after launch of GIOVE-A). It has been only two years since full operational capability. GLONASS has met its goal of full operational capability for dual-frequency service while full operational capability on safety-of-life service is still years away.
GPS. GPS follows through on commitments to complete the Block IIRM and Block IIF programs and to develop the Block III program, but deployment takes longer than originally envisioned. Six of the remain-ing Block IIR satellites are still in orbit. Existing Block II/IIA satellites have been removed from service, having all died off.
All eight Block IIRM and 12 Block IIF satellites have been launched.
One launch vehicle failure results in a one-year slip in the new GPS III launches, an assumption made because the GPS Block III program is using a new class-of-launch vehicle different from those employed in the Block II launches. GPS III has been funded, but is delayed because the current constellation is meeting commitments. Two GPS III satellites have been launched by 2017.
The L1 signal is available on all 28 satellites, while 22 of them have the M-code and L2C dual-frequency signals. The L5 safety-of-life signal is available on 14 satellites.
Galileo. Galileo moves forward, but at a slower pace than originally planned. There have been problems in funding the initial program, and several years have been lost getting all participants on board for development of the operational phase.
A full constellation is up, but the constellation was late because of funding and technical issues. The first satellites were launched in 2009, followed by a one-year checkout. Remember, the original plan was 30 satellites launched in three years. In this scenario, 30 satellites are launched over six years, starting in 2009 and completed in 2014.
As in the best-case scenario, Galileo provides full operational capability with open service, safety-of-life, commercial service, and public regulated service on all 30 satellites.
GLONASS. The constellation is complete, but not all improvements have been implemented. All original GLONASS (pre-GLONASS M) satellites have died. All GLONASS M satellites have been launched and 12 remain operational. Twelve GLONASS K satellites have been launched to sustain the constellation, starting in 2011, at a rate of two satellites per year by 2017.
The 24-satellite constellation consists of 12 GLONASS M satellites and 12 GLONASS K satellites. The L1 and L2 (dual-frequency) signals are available on all 24 satellites, and 12 satellites provide the L3 safety-of-life signal.
Expected Service. Under this reasonable scenario, what kind of service can we expect the world to have?
GPS provides service somewhat better than in 2007. Dual frequency (L2C) has initial operational capability, but full operational capability for both L2C and L5 (safety-of-life) is lacking. This situation will continue at least three more years as the U.S. government waits for enough Block IIR satellites to die off, creating room for replenishment with Block IIIs. Integrity is still years away with only two Block III satellites launched.
On the other hand, Galileo is offering its full service on all 30 satellites. GLONASS users have the full 24-satellite service with dual frequency on all satellites. The third civil frequency is available on only 12 satellites, and it will be years before this service is offered.
Galileo service is complete, offering three frequencies of service and guaranteed integrity, while GPS offers at best two frequencies. Since the standalone GPS user experiences a service only slightly better the service provided in 2007, and below the service levels of Galileo, most GNSS users by now have migrated to Galileo only, or hybrid GPS/Galileo technology.
The hybrid GNSS user is happy, of course, having access to 82 satellites on orbit (58 for GPS and Galileo alone) and more than 25 satellites in view at any one time (more than 15 for GPS and Galileo alone). Aviation users are relying on Galileo for dual-frequency operation, as well as using GPS receivers for single-frequency operation when augmented by the Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS).
GPS Eclipsed
Under this reasonable scenario, we have a most unexpected result, namely the GPS service has been eclipsed by both Galileo and GLONASS. How could this happen?
I see several reasons for this. In part, this has occurred because GPS satellites last so long. Historically their life spans are far greater than the design life of the satellite, and longer than the satellite life span of GLONASS. With the "launch on need" strategy employed by the U.S. government, however, it was only a matter of time before competitive services moved ahead of GPS. Unlike GPS, the two programs Galileo and GLONASS have essentially no service in 2007. They are building from scratch, and must move as quickly as possible to implement their service. This is not quite truly the case for GLONASS, since it has more than a dozen satellites in orbit and a complete ground control and monitoring capability in place. But even GLONASS has much work to do to launch a full set of modernized spacecraft to replace most of the first-generation satellites now in its fleet.
Under this reasonable-outcome scenario, three systems now provide various levels of service, which used to be provided by just one system. What, then, is the effect on users?
For some, there is little change in 2017. For others, they are beginning to adjust the source of their satellite navigation service. Users in surveying, marine navigation, agriculture, and precision mining shift to Galileo Open Service to take advantage of the dual frequency.
Recreational users \u2014 boaters, hikers, sports clubs, youth groups, and automobile navigation users \u2014 are content to keep using their GPS receivers, lacking incentive to dispose of them. They have already made their investment and the service is more than adequate for their needs.
European and other national commercial vehicle operations are now using Galileo commercial service.
Commercial transportation, taxis, emergency vehicles, and geographic data collectors are switching to Galileo/GPS hybrids to get better availability of service.
Aviation users are still relying on receiver autonomous integrity monitoring with fault detection and exclusion for en route through non-precision approach, but have expanded to include Galileo as well as GPS operation. U.S. aviators use WAAS for non-precision approach, while European aviators use EGNOS. Commercial aviators rarely if ever use hybrid aviation receivers. These receivers are probably not yet certified by 2017 or, if the units are certified, it will be several years before they appear in significant numbers.
The future for GNSS is quite promising. Table 1 shows that the service provided for the hybrid user in 2017 is always good, regardless of how pessimistic the scenario. Even under the worst-case scenario, there are no fewer than 68 satellites are on orbit, with more than 20 satellites in view. Dual-frequency operation is available. While safety-of-life service may not be fully operational, an initial capability is very much available to users. The addition of the Chinese Beidou system would only further improve service for the hybrid user.
Whichever way each of the three systems advances, in 10 years we will have a rich global capability for positioning, navigation, and timing.
Users will no longer rely on a single system. Instead, they will employ multiple systems to obtain the best service for their needs. Depending on a single system is risky and reduces performance. Having access to a diversity of systems results in improved accuracy and increased availability, reliability, and integrity. As long as systems are compatible, users can obtain the positioning and timing service they need without significant increase in cost or risk.
Under each of the scenarios I've considered, all three satellite navigation systems survive. They are all supported by their respective governments and provide a steady service to their users.
Surprisingly, GPS could lose its place as the dominant satellite navigation service by 2017. It will still be used by millions worldwide, but it will now share the role of providing this most valuable service to users across the globe. Because of this, the GNSS providers would be wise to review their current policy toward satellite navigation. Rather than assuming their service to be a standalone service, at least from a civilian standpoint, they should consider key issues and steps to integrate their service into the larger hybrid GNSS world. Issues to consider include monitoring of foreign GNSS services, performance assessment of hybrid services, and sharing of information (including notification and characterization of detected service anomalies and performance data). Steps to consider would be development of hybrid monitoring capabilities and implementation of information dissemination protocols.
Of course, no one can accurately predict the future. What actually happens will be the result of decisions and actions taken by the organizations that support each of these navigation systems. We can only be grateful for the tremendous resources and commitment each organization is applying to provide these valuable services that benefit all of us. It surely isn't an easy task, but the rewards justify the effort and investment.
JOHN W. LAVRAKAS is president of Advanced Research Corporation, where he provides consulting and research and development services on satellite navigation. He is the current president of the Institute of Navigation. Over his 26-year career, he has provided technical support to GPS initiatives such as Integrity Failure Modes and Effects Analysis, Civil Performance Monitoring, and GPS Operations Center. He has also supported development of the GPS Control Segment, GPS user equipment for military range applications, GPS performance analysis capabilities, and GPS-based commercial asset location systems.
See: http://sidt.gpsworld.com/gpssidt/article/articleDetail.jsp?id=421287
posted by Robert W. @ 6:37 AM
