Questiny Group

The “National Defense Authorization Act for Fiscal Year 2012” signed by President Obama signed at the end of 2011 included a section (Title IX, Subtitle B, Section 911) that directed that ” The Federal Communications Commission shall not lift the conditions imposed on commercial terrestrial operations in the Order and Authorization adopted on January 26, 2011 (DA 11–133), or otherwise permit such perations, until the Commission has resolved concerns of widespread harmful interference by such commercial terrestrial operations to covered GPS devices.”  In other words, LightSquared is prohibited from deploying their terrestrial base stations until it is determined that there are no impacts to “covered GPS devices” (i.e., military GPS receivers).  The Act goes on to order the Secretary of Defense to report to Congress every 90 days the results of testing that t if Military GPS receivers are effected by LightSquared operations.  This report is to be delivered to Congress every 90 days for two years.  Ouch!

Such legislation has some dire consequences for LightSquared.  Some background may be needed.  First, the FCC provides no protection for commercial receivers of any kind (other than to limit their own radiation through Type A and Type B certifications).  If a manufacturer builds a poor receiver that does not function, too bad for that manufacturer.  Also, there are no protections for commercial civilian GPS receivers.   the fact is that the GPS system is a DoD satellite navigation system, designed and operated by and for the military.  As far as I know, no federal agency or legislation protects the civilian use of GPS, and no tax dollars outside of the DoD’s budget goes to operate or maintain GPS.  If the DoD saw fit to turn GPS off, they could do so, and commercial users have no recourse.  No one believes such a thing would happen, but I understand that it is fully within the DoD’s right to do so.  This is why the Defense Authorization Act can only address “covered GPS devices.”  However, this creates quite a problem for LightSquared.

LightSquared has taken several steps to mitigate the interference to commercial GPS devices.  They have offered to reduce their power levels, operate on limited carriers for a period of time for manufacturers to improve their receivers and time for these improved receivers to diffuse into the market.  In addition, LightSquared has developed new filters to assist commercial precision GPS receivers that operate within the LightSquared spectrum.  All of these are the actions of a “good spectrum neighbor”, but unfortunately, they do not apply to the Military.  The Military has, and now must, conduct their own testing of these devices.  This means that LightSquared has to protect the US Military use of GPS before Congress will allow the FCC to license LightSquared. The consequence to LightSquared is that this will take time, and time is something I believe LightSquared is running short of.

It’s been reported that LightSquared needs additional funding to continue operations, and that these financial needs are becoming immediate.  If the Military can determine that LightSquared will not interfere with their receivers, then LightSquare might be granted a license to operate, paving the way for more funding.  But how long will this take?  I speculate that it could take the DoD more than 90 days just to identify the organizations impacted and the GPS equipment that should be tested.  Once that is decided, units would have to be procured and tested under conditions the US Military users accept.  To me, this sounds like a very long process.

For planning, let’s say the results are that there are some impacts the Military GPS devices, but they can be fixed with modifications to the GPS receivers (all big ifs).  Such modifications will have to conform to military procurement.  Military procurements take much longer civilian manufacturing.  Furthermore, such procurements are much more expensive, and many of the GPS devices are within classified equipment.  In times of declining defense budgets, where would the DoD find such money?  Under this scenario, LightSquared has limited options to mitigate the impacts and reduce any delays.

LightSquared might have a trump card, and I don’t know why they have not played it so far.  The card is this.  If GPS is so critical to Military Operations, then why can a civilian system affect its performance when it is operating well within its technical parameters and on an adjacent spectrum?  Doesn’t this mean that GPS is extremely vulnerable, and needs to be fixed anyway?  That may be happening.  I understand that GPS 3/R, the latest GPS replacement satellites, offers improved protection for Military users.  However, that still doesn’t ease the delay for LightSquared.  In the end, the “tyranny of the clock” may be working against LightSquared.

I think it sad if LightSquared should succumb to the business pressure resulting from these delays.  LightSquared is the first real attempt at a hybrid satellite-terrestrial communications system.  It is my opinion that such systems are needed if a viable communications satellite industry continue in the United States.  Such a system does not have to operate on spectrum adjacent to GPS, but it will need access to spectrum amenable to dual terrestrial and satellite operation.

A article published today cited that the head of the FCC’s Office of Engineering and Technology, Julius Knapp, sent a letter to LightSquared and the GPS Council asking for more information on which devices were specifically interfered with by LightSquared, ane the effects of LightSquared’s new proposal to use only the lower portion of their licensed band (1,526 MHz to 1,536 MHz).  This is a valid, and not unexpected, question from the FCC especially since the Technical Working Group Report randomized the devices so that no correlation could be made between the device, device manufacturer and the test result.  This is understandable since the GPS receiver manufacturers likely want to preserve their proprietary performance from public disclosure to their competitors.  However, as Questiny looked at the data, we could not correlate the measured performance to the device characteristics.  For example, some of the receivers use automatic gain control (AGC) and 3-bit analog to digital convertors (A/Ds) , whereas other receivers use no AGC, and a 1-bit A/D.  The performance between these two devices is predictably differerent (the 1 bit A/D will be more sensitive to overload).  The figure shows the results of static tests performed for the General Navigation Class of GPS Receivers where the LightSquared power level was measured at the device such that the GPS carrier-to-noise level was reduced by 1 dB (or 25%).  As the figure shows, the range of power needed to create the same degradation across receivers varied by more than 70 dB (10 million time).  This is a huge difference in performance.  As the TWG only provided an index for the device, their technical characteristics could not be correlated to account for this range of performance difference.  (Note gaps in the measurements indicated devices that did not suffer any loss or were not tested.)

Regardless of the previous results of the TWG.  LightSquared essentially nullified their relevance when they proposed a new frequency plan on June 15.  Now, as expected, the FCC has ordered additional testing for this new LightSquared frequency plan, and they have reassured the GPS community that they will not impact the GPS performance.  As my colleague at TMF points out, this could put severe pressure on LightSquared vis-a-vis Sprint’s ability to back out of their deal should LightSquare be unable to raise additional capital and make their required payments.

Received Power (at Device) Required for 1 dB loss in GPS in C/N0 for General Navigation Devices

Today (June 9, 2011), FCC Chairman Julius Genachowski held a press conference stating that the FCC would protect GPS services, but that it was continuing to examine ways the two services could coexist.  As the article in Broadcast and Cable stated, “There continued to be an interference problem, they said, particularly in the upper portion of the band closest to GPS. While LightSquared’s proposal anticipates eventually using that spectrum as well, one FCC official said he did not see that happening anytime soon, and that the commission was focusing on the lower-band proposal.”  As also stated in the article, this is essentially a “proceed at your own risk” statement.  In other words, LightSquared’s business plan depends on rapid buildout of their network to derive free cash flow as soon as possible, but the FCC has essentially halted this until more testing can be completed for one-half of the spectrum for which LightSquared requested licensing and upon which they defined their business plan.  If I were an investor, this would dramatically increase my risk assessment for the LightSquared venture.

The Comerce Department’s telecommunication division has released a report stating that, “LightSquared should not commence commercial services per its planned deployment for terrestrial operations in the 1525 – 1559 MHz Mobile-Satellite Service (MSS) Band due to harmful interference to GPS operations.”  Strong words from a Government Agency.  Although, this is no real news since LightSquared’s own report to the FCC reached essentially the same conclusion.  The tests were so bad that LightSquared delayed the report two weeks to have time to prepare an alternate plan where they would delay operation in the upper portions of their licensed downlink band to minimize the impacts.   We have been conducting our independent review of the technical report delivered to the FCC, but at over 1000 pages, it will take some time.  There has much “banter” back and forth in a “He said, she said” game.  In reality, the truth is somewhere in the middle.  It is true that LightSquared is meeting the technical terms of their license.  It is true that the LS downlink transmissions will impact the current generation of GPS receivers, and it is also true that the GPS industry should have known that this was coming.  But such arguments are akin to children arguing on the playground.  The “adult” in this equation is, or should have been, the FCC.  In other areas the FCC, and their big brother-the International Telecommunications Union (ITU), demands progress be made toward the implementation of systems that use the spectrum.  For example, if satellite companies don’t meet progress milestones  on time, the can lose their license for a particular satellite slot.  For this spectrum, the satellite use was taken up rapidly, but the terrestrial component, or Ancillary Terrestrial Component (ATC), has languishes for years – the very period where GPS devices found their way into mainstream America.  In my opinion, this is where the fault lies. 

As the deployment of the ATC component of this spectrum languished, the FCC could have taken steps to either remove the allocation as an MSS/ATC band, to an MSS-only spectrum, or revoke the licenses of those who did not meet their milestones.  The fact that they did not take pro-active action to avoid this problem is their failing of leadership.  Now the FCC will likely claim that they cannot adjudicate the business plans of Companies by granting and revoking licenses, but this is a false claim.  They do that all the time with other spectrum license holders.  So the FCC “dropped the ball” on this one.  So what.  Every organization has it faux pas’, but it’s the recovery that matters.  Now is the time for the FCC to take a leadership position.  They need to step in and stop the wrangling, name calling, and wanton waste of treasure from all who are seeking a solution in their favor.  In short, the FCC needs to re-allocate this spectrum.  It’s not ideal, it may not even be right, but it is necessary. 

Millions of GPS devices exist and are relied upon.  That is a fact.  These devices were not designed to accomodate high power transmissions in adjacent spectrum.  Also a fact.  LightSquared had rights to that adjacent spectrum.  Also a fact.  However, LightSquared got their too late.  It sucks to be late.  LightSquared has a legitamate claim to spectrum, and LightSquard’s desires are in line with overall policy of the current Administration and the FCC.   The FCC needs to find other spectrum that will accommodate the growth of wireless.  The market questions of bandwidth and mobility have been answered-consumers will by as much bandwidth as they can get, and they will take as much of that bandwidth on the road with them as they can.  Now the FCC needs to get on with the business at hand and develop a better National spectrum policy that provides the spectrum resources that satisfy that market.

On June 30, 2011, LightSquared™ officially submitted the final report from the Technical Working group tasked with analyzing the impact of LightSquared’s deployment on the GPS community. In addition, LightSquared™ officially recommended that they defer their immediate plans to use the upper 10 MHz of their downlink spectrum (1545.2 MHz-1555.2 MHz), and operate solely on the lower 10 MHz portion (1526 MHz – 1536 MHz). LightSquared™ cited the correct source of the impact as to the filtering in the GPS receivers allowing the LightSquared™ signals to enter and distort within the GPS receiver. LightSquared™ also correctly noted that the use of only the lower 10 MHz LTE carrier will dramatically reduce the interaction between the GPS receivers and the LightSquared™ towers. Our calculations show that the distance for a given degradation is reduced by about 5x when the upper carrier is inoperative. For example, the distance for a 2 dB receiver desensitization (i.e., reduction in C/No or Eb/No) is reduced from approximately 5 km to under 1 km in free-space (no shadowing by buildings or effects from the Earth).

Figure 1. Receiver Desensitization Distance

Figure 2 shows the impact of the reduction of the upper carrier on the intermodulation power spectral density, and it’s dramatic reduction around the 0 frequency point (the location of the L1 GPS carrier). This characterizes the impact on the GPS-only receivers; it does not address the precision GPS receivers whose front-end filters intentionally include the adjacent MSS band to receive location augmentation information over satellites (such as Inmarsat). We will examine this impact next.

Figure 2a. Single carrier intermodulation power spectral density (-61 dBm)

Figure 2b. Intermodulation power spectra for dual LightSquared carrier operation

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Most notably, in the recommendation is the GPS signal degradation employed to assess impacts. LightSquared considered a 6 dB loss in C/N0 as acceptable if the GPS receiver still functioned, whereas the GPS portion of the TWG, thought that a loss of 1 dB in C/N0 was a significant impact to the performance of the GPS receiver.  Arguments for either side can be made, and this is another area for our investigation into the technical results published today.  It should be noted that for satellite systems, the International Telecommunications Union (ITU) uses a 6% dT/T criteria which is equivalent to a 0.25 dB degradation in C/No!

The final technical report contains more than 600 pages of technical documentation and test results.  This will take some time to review.

Analysis of LightSquared™™ Terrestrial Carriers on GPS Receivers

Keith R. Barker, Questiny Group, Inc.

Monday LightSquared™ offered to move its spectrum from the current location to mitigate their impact on existing GPS receivers.  This is the first admission that no real solution existed to this problem.  Details are sketchy at this moment, but in an article published by Wireless Week, they stated that, ” LightSquared™ plans to use spectrum leased under an existing contract with Inmarsat instead of its own L-band spectrum until it can figure out how to use its own bandwidth without affecting GPS.  The company also said its base stations will transmit their signals at half-strength to further minimize interference.”  That article went on to state that, “The Inmarsat spectrum slated to be used by LightSquared™ runs from 1526 MHz to 1536 MHz and is located further away from bands used by GPS receivers, which run from about 1559 MHz to 1610 MHz, helping to reduce the likelihood that LightSquared™’s transmitters will knock out GPS service.”  The article quoted the Company as stating that even this fix would not remove the impact to all of the precision GPS receivers currently deployed.

The article suggests that LightSquared™ is giving up on a two-carrier configuration in their spectrum.  In their FCC filing, LightSquared™ proposed a phased deployment plan.  The last phase, Phase 2, used two 10 MHz wide LTE carriers located at 1,526-1,536 MHz and 1,545.2-1,555.2 MHz.  Each of these carriers were opertated at an effective radiated power of 32 dBW.  The plan suggested by LightSquared™ appears to drop plans to use the upper carrier (1,545.2-1,555.2 MHz), and to cut the power of their carriers to 32 dBW.

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An article was published in the Light Reading Mobile web-site today regarding LightSquared’s interference issues with GPS receivers.  (http://www.lightreading.com/document.asp?doc_id=208849).  Essentially, the article states that the GPS community is requesting the FCC look for new spectrum for LightSquared.  This is really no surprise.  With millions of existing GPS receivers in the hands of voters, how could this really end any differently.  Forget the fact that LightSquared is technically meeting all of their regulatory requirements, or the fact that the GPS receiver manufacturers knew that the adjacent spectrum was allocated for terrestrial towers (requiring them to use better front-end filters).  This result was dictated by the GPS manufacturers building receivers that allowed energy from the frequency band adjacent to Radio Navigation band to leak into their receivers, and in the end, I suspect that millions of GPS receivers (in the hands of voters) will trump the technical ligitimacy of LightSquared.

Soon Questiny Group will publish a white paper showing our analysis of the interference between LightSquared and GPS.  Early results of that  analysis show that there is nothing that LightSquared can really do about the problem as the interference is manifested within the GPS receivers themselves.  This leaves the only option one of finding new spectrum for LightSquared-no easy task.

Another aspect adding to this drama is the financial terms LightSquared has agreed to.  As a post in by TMF Associates blog (http://tmfassociates.com/blog/2011/06/) pointed out last Friday, if LightSquared does not deploy their network soon, they default on their financial terms.  This could add to the pressure LightSquared is under to find a resolution to the interference issue (i.e., look for other spectrum).

Yesterday we completed our first quarterly technical review with the Navy SPAWAR on the development of our Land-Mobile SATCOM Network Simulator (LMSNS).  The review went very well, and the Navy was impressed with the progress we have made on the software design and development.  They were especially impressed with the degree of flexibility that our performance simulator will provide while at the same time allowing users to build up models over time, adding complexity as they uncover more details of the system they are trying to simulate.  This is important to them as many of the performance modeling tools they have require complete inputs to run.  These complete inputs can mean hundreds or thousands of entries into the simulator.  This is fine when you know them, but often you do not, and users want a simulator that can run with partial or simple inputs.  Further, simple models can provide insight into the effects of various changes that complex models may hide.  Such features and capabilities seemed to find a favorable ear with the Navy.  Next quarter, we continue to build our simulator.  We are rapidly closing on the design, and coding will begin in earnest in a week or so.  If you have interests or stories regarding satellite or wireless performance simulations, we would love to hear from you.  Please post any comments and stories.

On September 17, 2009 we were awarded a Phase II SBIR contract for the development of a prototype of our Land-mobile Satellite Network Simulator. We kicked off the contract in early October and have been working on the software design. We are employing UML to define the structure and create a generic design that can be easilly carried into other software environments. We have been so busy or blogging has taken a back seat, but I hope the New Year will bring a reinvoration of my blogging.

Having completed most of the accounting system conversion, I had some time to return to the development of the Land-mobile Satellite Network Simulator (LMSNS). Specifically, I have manged to create a set of object classes that implement models for monofilar helical antennas operating in the first mode of the axial condition. Such antennas look much like that shown below.  The objective of this activity was to work out the object/class designs for the antenna portion of the software design, but helical antennas are common among satellite systems. The software can now create an antenna object whose subclass is a helix antenna. Based upon a design frequency and number of turns in the helix an object will be created along with all of the helix parameters. I have included methods to calculate the gain pattern for the helix and a sample result is plotted below. The plot shows the hemispherical gain pattern for a 17-turn and 4-turn helix each designed for 150 MHz operation. Gain patterns at 170 MHz are also shown. Measured patterns would likely show a drop in gain at 170 MHz, but this is a consequence of the models accuracy. The models were taken from “Antennas for All Applications”, by John Kraus and Ronald Marhefka. This develops the software basis for which other antenna classes may be developed for the LMSNS. One activity will be to implement the coordinate transformations that covert a direction to a earth terminal location to azimuth and elevation angles relative to the antenna main axis.

We are making progress on the development of Questiny’s Land-mobile Satellite Network Simulator (LMSNS). We have just completed its ability to download two-line elements from NORAD, propagate those elements to a common time, and predict the satellite locations. Below is a plot of the satellite orbits for 200 minutes. The four satellite planes are clearly visible.

In addition, our tool can now estimate the visibility of the satellite relative to a location on the earth. We have taken a location of 0.0 degrees N, 0.0 degrees E, and determined the elevation angle to each of the satellites. This location was chosen as the equator provides the most pronounced gaps for LEO constellations. The satellites are spaced the farthest apart along the equator, so we felt that it might be a most interesting case. The orbit locations were calculated every 2 mintues throughout the 200 minute simulation duration. Calculating these elevation angles that were above 5 degrees and summing the number of such satellite at each time period results in the number of visible satellites. We have plotted this in the graph below.

The interesting thing about this plot is that most of the time an earth terminal will have good visibility to the constellation, but it is not without gaps. We see that there is about a 2 minute gap around 82 minutes into the simulation, and a one minute gap around 19 minutes into the simulation. That means using Orbcomm for continuous back-haul communications is difficult in the current constellation. The reasons for this gap may be due to an incomplete constellation. If so, these gaps would disappear when the constellation is fully populated. In addition to the technical algorithms and software, wer are making progress on the GUI as well. We currently have a mock-up of the GUI, and are developing a working prototype within Matlab. We hope to have furhter progress on it this week.

Next week I will meet with EDX Wireless regarding the use of their products to assist us in the development of our UHF SATCOM Campaign Planner. The provide an engineering tool for the capacity estimation and planning of wireless networks. We will be reviewing their products looking for synergies. More of information can be seen in myBrain under the UHF SATCOM Campaign Planner/Other USCP Technology.

So I begin a blog for Questiny Engineering.  My intent for this blog is as a respository for my product ideas, design concepts, analysis results, and other thougths.  This is a new venture for me, and I must admit, I am a bit uncomfortable with this new media.  Be that as it may, I begin this blig with the hoping that others will find it useful.  So with out much ado, here I go “a blogging.”

This week’s activities included attending the MILCOM 2008 conference where I presented two of my papers (I will have these papers available on my web-site as I get begin to fill it out).  This was my first MILCOM conference so I cannot compare it to other MILCOM conferences.  Compared to other conferences, however, I found it outstanding.  Now my basis for evaluation includes two factors; 1) How often are there interesting technical topics to listen to, and 2) How often am I connecting wtih potential business contacts.  In both of those categories, I found my self constantly engaged.      The technical program had so many papers of interest to me that I could not cover them all.  Many that piqued my interest were presented at the same time.  I have not found that to be the case at past conferences.  As for business contacts, I found myself engaged all of the time.  At no time did I find myself wanting for someone to talk to of feeling disconnected from the conference.  That is unusual for me at these conferences.

As for the keynote speakers, most were ok.  Mike Mcconnel was the most interesting (Dir. National Intel.), but for me, one of the most interesting was byAdmiral James G. Stavridis Commander, United States Southern Command. In his talk he showed a picture of a semi-submersible boat (http://edition.cnn.com/2008/CRIME/03/20/drug.subs/index.html) developed by the South American drug cartels. These are half boats, half submarines built for the purpose of carryiing drugs from South America to the US Gulf Coast. What was interesting in his talk was that he had one of these placed at the entrance to USSOCOM. This was not placed as a trophy, but as a reminder that our foes are smart and innovative as well as dangerous. I thought this was a mark of a good leader.