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PNT Advisory Board on the Virtues of 30 Plus

Last fall, I wrote a column about the Civil GPS Service Interface Committee (CGSIC). Essentially, CGSIC is the forum for the civil community to communicate with the people who manage the GPS, and vice versa. In this column, I’d like to climb up the ladder, so to speak, and talk about the Space-Based Positioning, Navigation and Timing (PNT) National Executive Committee.

The PNT Executive Committee was established by the president to “advise and coordinate federal departments and agencies on matters concerning” GPS. Specifically, its functions, according to the website, are to develop a national space-based PNT strategy, develop a five-year national space-based PNT plan, and conduct an annual assessment of the adequacy of the federal government’s department and agency budgets and schedules.

Let me be clear, the Civil Global Positioning System Service Interface Committee (CGSIC) and NAVCEN are still together the clearinghouse for the public to communicate with the people who administer GPS and vice versa. That hasn’t changed. But monitoring PNT Committee activities, reading various presentations given by PNT Committee representatives, and reading minutes from PNT Committee advisory board meetings can give one a view into the thoughts of those who influence GPS policy.

A Case in Point.

Some of you in the user community have been around GPS for a decade or longer. You may recall that back in the 90’s, the U.S. government attitude towards other countries developing their own GNSS was quite cold and unsupportive.

Since then, this attitude has changed 180 degrees. The U.S. GPS folks are reaching out and embracing GNSS development elsewhere. Joint working groups have been established that include U.S. GPS representatives and technical folks from the various GNSS programs to promote compatibility and interoperability between GPS and these other GNSS.

There is no better example of this than when the United States and Russia formed the GPS-GLONASS Interoperability and Compatibility Working Group in December 2004. Remember that GPS and GLONASS were both deployed during the height of the Cold War, so no technical communication (at least non-adversarial) was possible at that time. Fast forward to 2007 when the Russian Space Agency indicated that GLONASS would be migrating towards CDMA so GLONASS would be compatible with GPS and other GNSS in development. This is a truly remarkable turnaround.

Last September at the Institute of Navigation (ION) GNSS conference, Alice Wong, Senior Advisor on GNSS with the U.S. State Department, discussed many of the international cooperation arrangements the United States has with countries developing a GNSS. She made two revealing and significant statements. “The number of space-based signal providers will grow from two countries (the United States and Russia) to at least six or more by 2020,” she said. The United States has recognized that although it may have set the gold standard for GNSS, it’s growing beyond what it can control. That leads to Wong’s second statement, which described the U.S. attitude towards GNSS development and operation.

Interoperable = Better Together than Separate

I didn’t intend for this to become a column on U.S. international GNSS policy, but rather to illustrate the tremendous amount of information and links to be found on the PNT.gov website.

Beside the presentations by PNT representatives, another part of the PNT.gov that’s very interesting to monitor is the PNT Advisory Board. NASA (National Aerospace and Space Administration) established the board on behalf of the PNT Executive Committee. The board members are non-government GPS experts who provide advice on GNSS from a technical as well as program and policy perspective. There are some well-known and well-qualified individuals on the board. Some you would know by name, such as Charlie Trimble (formerly of Trimble Navigation) and Brad Parkinson of Stanford University. But there are also many others from industries outside of surveying/construction that you may not recognize, but that represent significant industries or offer valuable perspectives.

The board meets at least twice a year and PNT.gov publishes minutes from the meetings. Reading the minutes from these meetings is an interesting look at how future GPS policy may be shaped.

The minutes from the March 2008 meeting (all 31 pages) are now available at PNT.gov. Please note that the board meetings aren’t limited to the PNT Advisory Board members. The meetings are open to the public, although audience members are asked not to interrupt the speakers. In the minute appendices, one can view a list of all who attended the March 2008 meeting.

In reading the minutes, one sees that a substantial part of the discussion centered on the optimal number of satellites and configuration of those satellites. To wit:

• Gerhard Beutler, President, International Association of Geodesy

“Further, he reported that the scientific community, organized in IAG, was committed to exploiting the full potential of all GNSS systems: this, he said, required combining all systems measurements in a single analysis; placing laser reflectors on all GPS/GNSS satellites; and expanding the GPS constellation to 30-plus equally-spaced satellites.”

• Bard Parkinson, Stanford University

“Dr. Parkinson, panel chair, said the Independent Review Team (IRT) had identified the Big Five essential GPS performance criteria: assured availability, resistance to interference, accuracy, bounded inaccuracy (in particular, the limit on the “wild result”), and integrity.”

• Michael Shaw, director, National Coordination Office for Space-Based PNT

“Mr. Shaw commented that to meet a 30-satellite standard, 34 to 36 satellites would be required. Dr. Parkinson said he believed 33 would be sufficient; at present, he said, the commitment to 24 was not always maintained. Dr. Parkinson added that if the Federal government committed to 30, and didn’t always make it, ‘we would forgive you.’”

• Capt. Joe Burns, United Airlines

“Capt. Burns from United Airlines commented that the improvements in civil aviation expected from a space-based air traffic control system would not be realized with the current constellation. Dr. Parkinson urged civil aviation to undertake and make public a cost/benefit analysis on the subject: he asked Capt Burns how many satellites he believed were required. Capt. Burns said at least 27, preferably 30. Ms. Neilan said it appeared all present believed 30 satellites were needed. She asked Dr. Parkinson if his analysis had been intended to prompt persons at DoD to reconsider whether the 21 plus 3 constellation was indeed adequate to their needs. Dr. Parkinson said he did not know what affect his study might have.”

The discussion time spent on the number of optimal GPS satellites is positive and I think it speaks to the future of what we can expect. Even though we enjoy 31 satellites today, the DoD only guarantees a 24-satellite constellation. I also like the fact that Parkinson is staying on target with the same message of the Big Five that I first heard at the ION GNSS 2006 conference.

If you get a chance, take a break and read through the minutes. It’s worth the time.

 

The Mobile Frontier in Field Data Collection

The mobile phone business is going nuts. Makers are introducing powerful phones in groves. The sleek and stylish Motorola Razor is almost an antique now. Apple introduced their new iPhone G3 last week and Sprint is introducing the Instinct later this month, complete with streaming TV service. Blackberry is rumored to be coming out with a touch screen phone for Verizon. Nokia, well, they’re in the process of buying Navteq. Navteq map databases power the leading personal navigation devices (PNDs) like Garmin, Magellan and Navigon among others. ‘Nuff said.

2008/2009 is going to be the year(s) of the smartphone, with manufacturers packing more and more into mobile phones. I saw this at the CTIA Wireless 2008 conference in Las Vegas a couple of months ago. I was blown away by the absolutely huge exhibition booths setup by Nokia, Motorola, BlackBerry/Research in Motion, Samsung, LG, etc. Their booths were like small metropolitan areas within the exhibition center.

Okay, this is cool stuff, but how does this affect my business/organization?

Mobile phones are becoming powerful enough to rival some of the most powerful field data collection devices ever made. Certainly orders of magnitude more powerful than those hand-held bricks we used a decade or so ago.

Granted, most of the emphasis we see on the new mobile phones is geared towards the average consumer: texting, streaming video, e-mail, social networking, and web browsing. That’s where the huge volumes are, and that’s what gets the attention of the handset manufacturers and wireless service providers. Our industry is catching the attention of some software developers who are writing software for smartphones that can be very productive for field personnel. I think it is very early in this game and there is a lot of software yet to be released that will help us become more efficient in the field, though.

One software company who has recognized the potential in this area is a little-known company called Telenav out of Sunnyvale, Calif. Last I heard, they had about 400 people and were rated the no. 1 fastest growing company in Silicon Valley by Deloitte for the period 2002 to 2006 in the technology, media, telecommunications, and life sciences category.

 

You might have used its navigation product. Its flagship GPS navigation software provides the basis for navigation software that Sprint and others sell to their mobile phone customers. It provides many of the same functionality that today’s PNDs provide, such as voice-guided turn-by-turn navigation and points of interest (POI) lookup. The major difference between PNDs and mobile phone applications like Telenav is the up-front cost. PNDs cost from $100 to $1,000, whereas GPS navigation applications for your phone are sold on a subscription basis in the $10 month range. The subscription price in the industry has not settled yet. I think it will end up in the $2 to $3 per month range and/or come bundled with other services like social networking.

To give you an idea of the market reach, Telenav claims their software runs on more than 200 different mobile phones on 12 different wireless carriers in 22 different countries. Competitor Networks in Motion (NIM) claims to have the largest mobile phone subscriber base in North America. They claimed that on the day before Mother’s Day, May 10, it recorded nearly five million server transactions.

Onto Mobile Phone Applications Other Than GPS Navigation

What interests me about Telenav is that unlike most other mobile phone software companies, it is paying a lot of attention to mobile resource management (MRM). In fact, it claims to be the market leader in MRM for mobile phone users. Its flagship product for this market is Telenav Track. Tracking assets and people using GPS is commonplace these days, and there are many, many companies currently offering solutions. Last year, Trimble spent $500 million to acquire @Road, a company specializing in MRM, for example. What differentiates Telenav Track is that all the software runs on mobile phones.

More specifically, I’m really intrigued by the electronic forms aspect of MRM. Essentially, it’s taking a paper form, such as an inspection form, and programming it into an application on a mobile phone. Sound familiar? This is the same concept behind automating field data collection for surveying and construction. Just like 40 years old being the new 30, mobile phones are the new data collectors. Ok, you won’t see them replacing the data collector as you know it today, but I’m seeing a lot more crossover. More traditional field data collectors are now GSM/Wi-Fi capable and more mobile phones are becoming powerful field data collectors.

A case in point: in 2007, the City of New York dedicated 15 inspectors to travel through the city and search for maintenance problems such as potholes, graffiti and excess litter. Traditionally, the city had relied on citizens to report these problem areas, but detailed information and location was often incomplete. The city outfitted the inspectors with BlackBerry mobile phones with custom data collection software installed. The electronic form allows the inspector to record the necessary details while the GPS records the location of the problem area. Unlike traditional data collectors where the data is batched and downloaded later in the day, the data collected on a mobile phone is sent to the server in the office immediately.

The benefits are obvious. The electronic forms control the quality of the data collected by guiding the user through the inspection. The real-time aspect of data collection speeds up the entire process.

Higher quality data + real-time data = better decisions made faster.

Is Dual-Frequency GPS — As We Know It — Becoming Obsolete?

On Friday, May 16, 2008, the Office of Space Commercialization issued a Notice for Public Comment. In it, the U.S. Department of Defense (DoD) proposes to discontinue supporting P(Y) codeless/semi-codeless on both GPS L1 and L2 frequencies on modernized satellites (Block IIR-M, Block IIF and Block IIIA/B/C) beginning December 31, 2020. After 2020, legacy dual frequency receivers may still work, but the DoD would no longer assure that P(Y) power levels and the navigation message would remain the same. Therefore, the civil GPS community has no assurance that legacy dual frequency receivers will operate as before.

Essentially, this means that every dual frequency receiver designed in the 1980’s, 1990’s and many in the early 2000’s would become virtually obsolete. In the interest of disclosure, that includes my own legacy real-time kinematic (RTK) system.

I caution you … it is very easy to rush to judgment regarding this proposal. When I first read it, my first response was “Whoa, dude, no way!” However, it’s important to take a deep breath and work your way through the logic. Your conclusion may be the same as your initial response, but at least you’ve thought it through. That being said, you must also realize that this is the first action, in the history of GPS, which will render a massive amount of GPS equipment obsolete.

What is Codeless/Semi-codeless Processing?

On L1, there is C/A code and P(Y) code. C/A is for civilian use, P(Y) for military use. On L2, originally there was no civilian code, only P(Y) for military use.

Back in the 1980’s, engineers in the commercial sector were trying to figure out a way to utilize L2 because it would significantly increase the receiver’s performance. Some really smart ones figured out how to track the encrypted P(Y) code on L1 and L2. Then they figured out how to cross correlate the measurements on L1 and L2 and voilà, the modern dual frequency receiver was born. This technique is used in virtually all dual frequency equipment sold today in the commercial (non-military) market.

All post-processing and RTK algorithms are based on using codeless/semi-codeless techniques of one sort or another.

Codeless/semi-codeless processing would not have been needed if L2C had been around on the original GPS satellites. In fact, even today there are only six satellites broadcasting L2C. Every satellite launched since 2005 (six of them to date) and each launched in the future will broadcast L2C, so eventually every satellite will.

What’s Being Proposed?

After December 31, 2020, the DoD proposes to discontinue supporting P(Y) on L1 and L2 for the commercial market on all modernized satellites (Block IIR-M, Block IIF, Block IIIA/B/C). Block IIA/IIR satellites will continue to operate as they do today. However, unlike today where Block IIA/IIR account for 25 of 31 operational satellites, the youngest Block IIR satellite will be 16 years old in 2020, if any still exist at all.

The DoD’s proposal assumes that most organizations will have upgraded their GPS equipment by 2020 and will be utilizing L2C (and other modernized signals), so that L1/L2 P(Y) codeless/semi-codeless processing won’t be needed any longer.

In their synopsis, the DoD states that GPS manufacturers have indicated that the user community needs approximately ten years to replace legacy GPS equipment with equipment capable of utilizing modernized GPS signals. You can read the DoD’s full proposal here. It contains a lot of pertinent background information.

Who’s Affected?

Unfortunately for those of us in the survey/engineering/construction/deformation monitoring/high-precision GIS industries, we would be the ones affected the most.

In real terms, this means that any dual frequency receiver not designed to use L2C will essentially become a paperweight after December 31, 2020. The receiver may still work after that date, but there is no assurance it will continue operating properly. The list of receivers affected is quite long and includes models from all major manufacturers, such as Trimble, Leica, Topcon, Magellan (Ashtech/Thales), and NovAtel among others. Check with the manufacturer of your equipment to determine if it is capable of utilizing L2C. If it’s not, then it’s considered a legacy receiver and would become obsolete.

Also, one should be careful and not assume that all receivers sold today are capable of utilizing L2C. Ask your dealer or the manufacturer of the equipment before your purchase.

No L1-only receivers, such as hand-held GPS units, car navigation systems, various tracking devices, GPS-enabled mobile phones, L1-only GPS mapping systems, and timing receivers are affected by this proposal. L1-only RTK receivers are not affected either. None of these use codeless/semi-codeless techniques. The exception is some of the newer GPS receivers designed for GIS data collection at the decimeter (or sub-foot) level. Although not actively marketed as such, these are dual frequency receivers and might be affected if this proposal is carried out.

It doesn’t take long for one to think about the thousands and perhaps tens of thousands of reference stations worldwide that will need to be replaced. Just the United States CORS (Continually Operating Reference Stations) network alone comprises more than 1,000 receivers. Granted, some are modernized receivers that may only need a minor update, but many others are legacy receivers that will need to be replaced or risk obsolescence. Those 1,000+ CORS receivers service thousands of users monthly. In April 2008 alone, the National Geodetic Survey reported that more than one million FTP requests were made for CORS data.

The DoD says that December 31, 2020 isn’t a “hard” date. In other words, GPS equipment using codeless/semi-codeless techniques may work just fine after December 31, 2020. What they are saying is that after December 31, 2020, they won’t guarantee they will not do something that will impact P(Y) code and subsequently prevent your receiver from performing like you’d expect.

Timing Is Everything

I think I understand the DoD’s logic. They are developing these modernized signals (L2C, L5, L1C) that should be commonplace by the time 2020 rolls around. Continued support of semi-codeless would interfere with some new features they want to play with on the military side of GPS. Why support the legacy stuff when the new stuff is better anyway?

The first issue I thought of is what the status of the GPS constellation will be in 2020. Today, GPS users have 31 satellites to work with. As high-precision users, we need every one of those. Just last week, I was stuck in the middle of a GPS fieldwork day waiting for a sixth satellite to come into view so I could continue my RTK work.

The DoD is still only committed to a 24-satellite constellation, but they’ve been spoiling us with 30 or more for quite awhile now. It would be hard to go back.

So, of course, I started doing the math to guesstimate how many satellites will be operational in 2020, based on information provided in the DoD’s proposal and other sources. The DoD’s proposal states that they expect 24 satellites to be broadcasting L2C by 2016 and 24 satellites will be broadcasting L5 by 2018. We know that eight Block IIR-M satellites were built and twelve Block IIF satellites will be built. We also know that, as announced last month, eight Block IIIA, eight Block IIIB and eight Block IIIC satellites will be built. From this information, one can deduce that in 2016 the constellation will look something like this:

• 8 ea. Block IIR-M satellites broadcasting L1 C/A, L2C
• 12 ea. Block IIF satellites broadcasting L1 C/A, L2C, L5
• 4 ea. Block IIIA satellites broadcasting L1 C/A, L2C, L5, L1C

The above lists and the ones following the paragraph below are the civil signals. Of course we can assume that each satellite is still broadcasting military P(Y) code and M-code on L1/L2.

Based on the exceptional life span of legacy Block IIA/IIR GPS satellites, there would still be approximately six to eleven of them still broadcasting L1 C/A code. By 2018 we can deduce that the remaining four Block IIIA satellites and four new Block IIIB satellites will have been launched, giving a total of 24 satellites broadcasting L5. The constellation would look something like this:

• 8 ea. Block IIR-M satellites broadcasting L1 C/A, L2C
• 12 ea. Block IIF satellites broadcasting L1 C/A, L2C, L5
• 8 ea. Block IIIA satellites broadcasting L1 C/A, L2C, L5, L1C
• 4 ea. Block IIIB satellites broadcasting L1 C/A, L2C, L5, L1C

There should also be a handful of remaining Block IIR satellites available for service that are still broadcasting L1 C/A code.

If I’ve done the math right and the DoD keeps this schedule, that’s not bad; not bad at all. In 2016, there would be somewhere between 30 and 35 operational satellites. In 2018, there would be somewhere around 37 operational satellites. In terms of sheer numbers, that’s equal to or better than where we are today.

After working through this, I think it’s obvious that we will be better off than we are today with respect to the satellite constellation. As I’ve written before, triple frequency receivers (L1, L2, and L5) will be far superior to today’s dual frequency receivers that utilize codeless/semi-codeless techniques. If you add Galileo on top of that, it’s a no-brainer. I look forward to the day that I’m in the field and have 20 or more GPS/Galileo satellites in view when just last week I was struggling to find six.

Lastly, in case you missed it ,the DoD stated that if the new satellite schedule were delayed, they would reassess the codeless/semi-codeless sunset date.

It’s All About the $$$

Alas, at the end of the day, this is where it’s going to hurt the user community the most.

I think nearly everyone’s heard of the Spring 2009 sunset date for analog television in the US. On that date, full-power television stations will stop broadcasting on analog channels, rendering analog television sets obsolete. Congress was so concerned about consumer backlash that they are subsidizing analog-digital conversion boxes to the tune of $890 million, based on a price of $50 to $70 each. To put it in perspective, that doesn’t even cover the cost of 3-meter L1/L2 antenna cable.

We are going to get hit in the wallet … hard.

An argument in support of all this states that triple frequency GPS equipment will be much cheaper at that time. I agree it will be cheaper, but we are still talking about tens of thousands of dollars. The survey/engineering/deformation monitoring/high-precision GIS market is relatively limited in size, is highly technical, and requires complex software, training, and technical support. It’s not like spending $150 at WalMart for a Garmin receiver that you can figure out without reading a manual.

Another argument in support of the DoD’s proposal is that 12 years gives us plenty of time to enjoy a solid return on investment (ROI) on our current equipment. While I follow that logic, I’ve seen a lot of GPS equipment in the field that is 15 years to 20 years old. The stuff just keeps working.

I’ve been amazed that my RTK system, based on 12-year-old technology, still cranks up like it did the first time I used it. Maybe it’s more of an emotional feeling than anything else, but as much as I work through the logic, it’s hard to swallow that my $40,000 system has a date with the trash bin.

I know codeless/semi-codeless dual frequency GPS is the core technology for thousands of small to medium sized businesses around the world. Outside of vehicles, GPS equipment may have been the largest capital investment for them. For those who made that purchase in the last couple of years, the codeless/semi-codeless obsolescence is not something they want to hear about even if it is 12 years away.

The U.S. Department of Commerce has done a quick survey and prediction, to get a rough idea of the dollar-value of equipment that will need to be upgraded sometime toward the 2020 time frame. Its figure for the economic impact is $1.3 billion to $1.7 billion dollars per year if semi-codeless were taken away today. That’s the estimated value of at least 200,000 semi-codeless receivers out in the field today, a figure that it
acknowledges to be conservative, by the way.

According to the DoC analyst, if semi-codeless were taken away in five years, in the year 2012, using some growth rates and extrapolating, the estimate would grow to between 373,000 and half a million users worldwide, and the economic loss on a worldwide basis would be between $3.6 billion and $4.8 billion; within the U.S. alone, that portion would be between $1.1 billion and 1.9 billion.

These figures formed the rationale for a proposed decision to push the discontinue date out to 2020, to give manufacturers and the user base adequate time to re-equip for using L2C and L5. Incidentally, a full-length interview on this topic with a senior DoC analyst and advisor to the National Coordination Office for Space-Based Positioning, Navigation, and Timing will appear in the July print edition of GPS World magazine.

I don’t have an answer on the money issue. For the manufacturers and dealers, it’s going to a salesman’s dream, not unlike Y2K and GPS Week Rollover were. For the user community, it’s going to taste sour no matter how it goes down.

You Have Your Chance: the DoD Is Listening

It’s important to note that the DoD is seeking comments from everyone around the globe. The potato farmer in Argentina, the land surveyor in Australia, the geodetic surveyor in the United States, and the engineer in Denmark are all encouraged to comment. GPS is a tool that knows no boundaries.

Col. Mark Crews, the U.S. Air Force GPS Chief Engineer, says the GPS Wing is keenly interested in public comment on the proposal. The Air Force estimates there are approximately 250,000 worldwide users of dual frequency receivers that use P(Y) codeless/semi-codeless.

“We are trying to do everything absolutely the right way in pre-notifying everybody in the world. If anybody has any concerns, please notify us,” said Crews. “We are taking every precaution to transition semi-codeless users to civil coded signals in a stable, measured, and transparent manner by 2020. That’s why we’re taking action now to pre-notify semi-codeless users worldwide and ask for their input by means of the Federal Register’s request for comments.”

Crews further says that the Air Force recognizes that that dual frequency GPS receivers are a “huge business.” It recognizes that these receivers “play an extremely positive role in survey, agriculture, and all high-accuracy augmentation systems. We are bending over backwards until we have at least two other civil signals, being L2C and L5, on 24 satellites in time for people to transition,” he said.

The US Department of Commerce (DoC), on behalf of the DoD, is seeking public comments on the codeless/semi-codeless sunset proposal. Time is short though. You have until June 16, 2008 to submit your comments. I think that’s a mistake; it’s not enough time. They should allow at least 90 days so the word has a chance to spread.

All comments submitted are a matter of public record and can be viewed by anyone at http://www.space.commerce.gov/gps/semicodeless/. As of June 1, 2008, there have been no comments posted and we are half way through the 30-day comment period already.

That concerns me.

Clarifications/Corrections to The Last Column Regarding L5

In my last column I included a listing of satellite models and signals they broadcast. An astute reader was quick to point out two omissions, and I discovered an error as well. First, I neglected to list P(Y) on L1, which is especially important to note, given the subject of this newsletter.

Second, I listed Block I/II/IIA as one group. There are no Block I/II operational satellites any longer. There is only Block IIA/IIR. For complete clarification and for no other reason than I’ve intended to do this for awhile now, I’ve provided a comprehensive table of operational GPS satellites below.

Lastly, I stated last time that there are 26 Block IIA/IIR satellites broadcasting. There are actually 25. Below is a complete list of operational satellites.

PRN	MODEL	OPERATIONAL	PLANE/ SLOT	CIVIL SIGNALS	MILITARY SIGNALS
9	Block IIA	July 20, 1993	A1	L1 C/A	L1 P(Y), L2 P(Y)
31	Block IIR-M	Oct. 13, 2006	A2	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M
8	Block IIA	Dec. 18, 1997	A3	L1 C/A	L1 P(Y), L2 P(Y)
7	Block IIR-M	Mar. 15, 2008	A4	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M < /td>
25	Block IIA	Mar. 24, 1992	A5	L1 C/A	L1 P(Y), L2 P(Y)
27	Block IIA	Sept. 30, 1992	A6	L1 C/A	L1 P(Y), L2 P(Y)
16	Block IIR	Feb. 18, 2003	B1	L1 C/A	L1 P(Y), L2 P(Y)
30	Block IIA	Oct. 1, 1996	B2	L1 C/A	L1 P(Y), L2 P(Y)
28	Block IIR	Aug. 17, 2000	B3	L1 C/A	L1 P(Y), L2 P(Y)
12	Block IIR-M	Dec. 13, 2006	B4	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M
5	Block IIA	Sept. 28, 1993	B5	L1 C/A	L1 P(Y), L2 P(Y)
None	None	None	B6	None	None
6	Block IIA	Mar. 28, 1994	C1	L1 C/A	L1 P(Y), L2 P(Y)
3	Block IIA	April 9, 1996	C2	L1 C/A	L1 P(Y), L2 P(Y)
19	Block IIR	April 5, 2004	C3	L1 C/A	L1 P(Y), L2 P(Y)
17	Block IIR-M	Nov. 13, 2005	C4	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M
None	None	None	C5	None	None
29	Block IIR-M	Jan. 2, 2008	C6	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M
2	Block IIR	Nov. 22, 2004	D1	L1 C/A	L1 P(Y), L2 P(Y)
11	Block IIR	Jan. 3, 2000	D2	L1 C/A	L1 P(Y), L2 P(Y)
21	Block IIR	April 12, 2003	D3	L1 C/A	L1 P(Y), L2 P(Y)
4	Block IIA	Nov. 22, 1993	D4	L1 C/A	L1 P(Y), L2 P(Y)
24	Block IIA	Aug. 30, 1991	D5	L1 C/A	L1 P(Y), L2 P(Y)
None	None	None	D6	None	None
20	Block IIR	June 1, 2000	E1	L1 C/A	L1 P(Y), L2 P(Y)
22	Block IIR	Jan. 12, 2004	E2	L1 C/A	L1 P(Y), L2 P(Y)
10	Block IIA	Aug. 15, 1996	E3	L1 C/A	L1 P(Y), L2 P(Y)
18	Block IIR	Feb. 15, 2001	E4	L1 C/A	L1 P(Y), L2 P(Y)
32	Block IIA	Dec. 12, 1990	E5	L1 C/A	L1 P(Y), L2 P(Y)
None	None	None	E6	None	None
14	Block IIR	Dec. 10, 2000	F1	L1 C/A	L1 P(Y), L2 P(Y)
15	Block IIR-M	Oct. 31, 2007	F2	L1 C/A, L2C	L1 P(Y), L1M, L2 P(Y), L2M
13	Block IIR	Jan. 31, 1998	F3	L1 C/A	L1 P(Y), L2 P(Y)
23	Block IIR	July 9, 2004	F4	L1 C/A	L1 P(Y), L2 P(Y)
26	Block IIA	July 23, 1992	F5	L1 C/A	L1 P(Y), L2 P(Y)
None	None	None	F6	None	None