Questiny Group

Questiny has been awarded a new $100K  contract to supply software and modeling services to the US Army Space Command at Peterson Air Force Base.  This continues to update the Wireless Network Simulator (WiNS) supplied  over the past year, and continues to provide services in support of the Defense Information Systems Agency (DISA) Mix-of-Media study.  Delivery of the updated software will occur around July 1, 2014.

On a lark, I bought this audio distortion analyzer from eBay for $100 including shipping.  Similar working units on eBay run anywhere from $150 to $900, so this was a fair price for what I got.  Convenience really drove this purchase as to make FM receiver measurements (Signal plus noise and distortion, or SINAD) the distortion of the demodulated audio tone is measured at the speaker output.  Questiny has digital instruments that can do this in easy fashion, but the set-up can take some time, so I thought I would buy a used distortion analyzer and see how it worked.  This unit came last week, and was DOA; plus the feet had been damaged in shipping.  This is not altogether unexpected as the seller stated that the unit powered up, but had not been tested in any other fashion .

I confirmed that the unit did light up the power indicator light, but checking the service manual showed that the light is actually right across the input mains, so it is no indication of function.  In the end, three electrolytic capacitors had failed.  One on the positive rail of the power supply, and two in the meter circuit.  Upon replacing the capacitors, the unit sprang to life.  A few hours with the manual walking through the calibration procedure, and the unit seems to be functioning as expected.  The only issue remaining is that the frequency dial is off, but the set screws have been stripped.  That’s going to take some effort to figure how to get this off without further damage.  I may have to resort to buying a sacrificial unit on eBay.  The unit is also capable of AM detection up to 65 MHz, but that doesn’t seem to working either.  Likely just a diode failure.

In the end, I have to be impressed by HP’s design.  This unit is over 40 years old, and the construction used discrete transistors.  It has probably 30 electrolytic capacitors and only three of them failed after forty years.  Not bad.  Further, during the calibration procedure I was able to measure distortion down to .03%.  That’s about a 70 dB null from 40 year-old analog circuitry!  Not bad.  Even as a just voltmeter, it has a 10 MOhm input impedance and a frequency response of nearly 3 MHz.

The bottom-line is that this is a handy addition to the lab, and repairing it really gave me a chance to check out some of the other equipment in the lab such as the in-circuit ESR  (equivalent series resistance) meter, the LCR (inductance, capacitance, resistance) meter, the variable isolation transformer, the function generator, and the digital oscilloscope.  All of these units provided invaluable contributions to the troubleshooting and justified their procurement.  I have to make special note of the LCR meter.  Typically, electrolytic caps open as the dry out, but in this case, two of the capacitors actually shorted.  The ESR meter showed a small amount of resistance indicating a good cap, but a dc continuity test showed them as shorted.  One of the capacitors in the meter circuit was in between an open and a short.  Here is where the LCR meter really shined.  The capacitor was rated at 50 uF, but it measured at 800 uF!  Not shorted, and not open, but not operating as rated.  Without the meter, I would either have not replaced this one.  In the end, I will re-cap the whole unit.  If 10% of the caps have failed, it’s likely others will fail soon.  More to the Mouser order!

Over the past year Questiny has been compiling a set of equipment to allow us to develop a basic radio lab development and test capability.  Through many hours on eBay, we have constructed the following.  The top-end frequency is limited to about 3 GHz, but it is a start, and can be expanded when needs arise.  Our budget was about $25K which is new the low-end for a single new piece of Agilent equipment.  Through careful purchasing, all of the equipment was purchased within the budgeted amount.  We can now do basic design testing of analog radios, and through the use of the software defined radios, we can do testing of digital communications was well.

With this capability, Questiny can now start to prototype some of our ideas related to our wireless communications ideas.  Stay tuned.

Sometimes, a corporate value statement is just so well stated that I am compelled to share it through our corporate blog. It’s a implied working philosophy that we have embraced but never stated so elegantly to grow our company. But credit goes to Reed Hastings, the CEO of Netflix, who authored the presentation. I will forgive you for your past sins committed in devaluing your stock price from its high of approximately $300 per share to current $190 (it was down to $52.81 in 2012).

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.

An NTIA Report leaked to Bloomberg Press stated that LighSquared’s basestations continue to disrupt GPS receivers.  The Bloomberg article specifically stated,  “The results from testing conducted Oct. 31 to
Nov. 4 show that “millions of fielded GPS units are not compatible” with  the planned nationwide wholesale service, according to the draft seen by Bloomberg News.   “LightSquared signals caused harmful interference  to majority of GPS receivers tested,” according to the draft prepared  for a meeting next week of U.S. officials reviewing the LightSquared  proposal. “No additional testing is required to confirm harmful
interference exists.””  The article went on to say that, “It [the Report] found that 69 of 92, or 75 percent, of receivers tested “experienced harmful interference” at the equivalent of 100 meters (109 yards) from a
LightSquared base station.”  Without a copy of the report and access to the test data, Questiny cannot comment on the validity of the claims.  However, our previous analysis shows that even the single carrier LightSquared spectrum plan would degrade the performance of GPS receivers that did not have sufficient attenuation at the LightSquared’s frequencies (1526-1536 MHz).  It appears that the NTIA’s direct testing has confirmed this situation — but this is not new news.

LightSquared stated at the conclusion of the FCC testing in June of 2011 that additional filtering would be needed, and contracted with the Javed corporation to construct external filters for such GPS units.  There has never been any dougt in our minds that such filters could be developed, and that they would provide sufficient filtering of the LightSquared signal to permit operation of the GPS units.  The issue has always been the conditions under which EXISTING GPS receivers would work WITHOUT MODIFICATION.  Thus it is also no surprise to to us that GPS users would frequently  find themselves in such conditions.  The report states taht 75% of the receivers would be impacted when within 100m (328 feet) of the base station.  This is fairly close to the basestation, and such close range only provides 76 dBm of attenuation (free-space) due to propagation leading to a received power at the GPS unit of (62 dBm-76 dB) -14 dBm — a strong signal level.  The GPS units must then filter that signal by more that 100 dB to minimize the effect of the LightSquared signal on its performance.  It is not surprising that standard commercial units have such filtering when they were likely designed assuming adjacent signal levels of -120 dBm not -14 dBm!

All of this is the backdrop to the FCC’s decision that it has to address the fact that even if LightSquared operates well within the technical limits of their license, such operation will still degrade the operation of existing GPS receivers not designed to accommodate such signals.  As for our prediction as to how this will turn out…as there are more voters with GPS units than voters with LightSquared units, Questiny has always believed that the FCC will eventually side with the GPS community, and revoke LightSquared’s license.  From there, LightSquared will likely sue the FCC for damages, and the FCC will find other spectrum for LightSquared.  All of this will likely be too late for LightSquared to achieve sufficient revenue to remain solvent, and once again, LightSquared will find itself at the brink of bankruptcy.

An article came out today announcing that LightSquared solves GPS interference with new device!  The article stated that  GPS device manufacturer Javad GNSS has come up with a device that “”The solution we’ve come up with dispels the myth that a product that eliminates  interference couldn’t be done,” Martin Harriman, executive vice president of  LightSquared’s Ecosystem Development and Satellite Business, said on a  conference call with reporters. “We did it. And it didn’t cost billions of  dollars or 10 years to do it. We did it.”  The article goes on to say, “Harriman said that through its partnership with Javad GNSS, which makes GPS  devices for such clients as the U.S. Geological Survey, has developed new  receivers that can be used to avoid interference between LTE and GPS.  Javad GNSS  has also completed designing and testing prototypes that can be adapted to work  with existing high-precision GPS devices, including those already being used in  the field.”

Am I missing something?  I thought the issue was not the inability to build new receivers, but the willingnesss of existing manufacturers and GPS users to accept retrofits and modifications to units already in the field?  Afterall this is not really a “Eureka” moment considering that LightSquared has had to 1) reduce the generation of intermodulation products by dropping the upper carriers and 2)consolidate GPS augmentation signals in that same part of their spectrum.  This latest announcement seems to be simply  a new receiver with better filtering, and that only has an effect AFTER the other two changes have been made.

After my shock that this is presented as such a “revelation”, the factis that with better filtering, the precision GPS receivers can coexist wtih LightSquared using the lower 10 MHz.  But we always knew this.  The issue for LightSquared is that this still sacrifices half of their capacity, and add the cost of retrofitting existing GPS receivers.  If anyone reads this article and believes that this solves the two-carrier LightSquared problem, please comment and let me know.

In their latest proposal, LightSquared has offered some concessions to mitigate their impacts with GPS.  They have offered the following adjustments to their technical design:

1. Limit the received power within the region 50m to 500m to under -30 dBm
2. Limit the degradation due to LS signals to under a 1 dB degradation in C/N0
3. Move the satellite GPS augmentation signals to the upper portion of the MSS Spectrum (above 1,536 MHz), and offer filters with 40 dB rejection at 1,536 MHz

On the first item of their proposal, the analysis below shows that in free-space, the received power from a LightSquared tower will exceed -30 dB by as much as 21.5 dB (power received at 50m from a 62 dBW EIRP  base station at a 10m antenna height). However, if the average loss is more urban-like (loss exponent of 2.7), the the received power drops to more than 3 dB below the -30 dBm limit they have set.

The FCC dictates that free-space loss be used in all calculations.  However, urban environments are not free-space, actual attenuation is often larger than free-space.  Such facts indicate that LightSquared is betting that propagation loss in excess of free-space is more likely, and they will not have to reduce their transmit power and reduce their transmit power.  Although calculated, this is a risky bet.  Measurements on GPS receivers made by LightSquared indicate that many general purpose GPS receivers perform well when subjected to LightSquared interference below -30 dBm with the exception of the precision GPS receivers that use augmented GPS information.  This brings up the second and third aspects to their proposal.

It seems LightSquared has dropped their opposition to using a 1 dB drop in received GPS signal-to-noise ratio (or Carrier-to-noise density ratio, C/N0) as the bench mark for performance.  This is a positive step forward.  Many standards use a 1 dB criteria as the limit of harmful interference.  In fact, some satellite regulations require interference be limited to a C/N0 degradation of less than 0.25 dB, so 1 dB is quite gracious.  Furthermore, it is measurable.

The last point in their proposal is the effect of their carrier on the precision receivers.  This is a more difficult issue as the receivers are designed to receive augmented GPS signals transmitted over satellites using the LightSquared frequency band.  To solve this, LightSquared has proposed consolidating the GPS augmentation signals at the upper portion of their band, and supplying the precision GPS receivers with external filters that provide the needed rejection/attenuation of the LightSquared carrier in lower portion of the band.  The analysis they present in their FCC proposal indicates that the degradation to precision receivers is limited, but the question remains if manufacturers and system operators (such as John Deere, Inc.) would accept such additions. 

In short, LightSquared has indeed made concessions by taking on more risk relative to interference with GPS receivers, such concession will make their system roll-out and set-up much more difficult/expensive. Furthermore, while LightSquared may now have a technically workable proposal for their initial roll-out, it still does not provide access to the upper portions of their spectrum in the long-term.  If an agreement is not reached for that spectrum, LightSquared will have one-half the capacity their current business model assumes.  Not a pretty picture for investors.

Analysis of Received Power Limitation to Below -30 dBm

LightSquared has offered a maximum received power level of less than -30 dBm within a circle of 50m to 500m around its towers.  This level seems currently based upon their latest test results of GPS receivers to their current frequency plan of using only the lower 10MHz portion of their spectrum. 

LightSquared Testing of General GPS Receivers to Lower 10 MHz LTE Carrier

In addition, a sectored antenna is assumed with a downtilt of 7 degrees.Below is an analysis that examines the received power levels at GPS receivers from three different height Light Squared

The plot below shows the region around the tower where LightSquared intends to limit the received power to less than -30 dBm.  The minor ticks are every 10m showing the resolution to which LightSquared will measure the power levels.

Power Controlled Region around LightSquared ATC Tower

Starting with the power limitation on the ground, we can write an equation for the received power, Pt=PrGv/FSL.  This is the transmit power times the antenna pattern divided by the spreading loss (aka, free-space loss).  The average propagation loss is a function of the distance from the transmit source, the frequency, and the average loss exponent.  Free-space loss has a loss exponent of 2.  The formula is shown below.

The distance from the transmit source may be determined from the Pythagorean theorem assuming the tower antenna height and the distance from the tower base.

Combining these two equations shows and plotting as a function of transmit antenna height (10, 20, and 30 meters), we have the following free-space propagation loss for the three tower antenna heights.  As shown, there is little difference between the tower heights.

Free-space Loss between GPS Receiver and Tower Antennas (Antenna Heights = 10m, 20m, 30m)

The plot shows that the loss across the area surrounding a tower varies from a minimum of 71 dB to over 90 dB.  However, if the loss exponent is increased to 2.7, representing a suburban envioronment (urban environments have even higher exponents), the loss increases to 98 dB to over 120 dB (top, green line).

Propagation Loss from 20m Antenna Height to GPS Receiver for Loss Exponents 2.0, 2.4, and 2.7

The maximum effective isotropic radiated transmit power (EIRP) for LightSquared is 62 dBm, and the following plot shows the maximum received power at a GPS receiver from a 20m tower along the 50m to 500m distance LightSquared has defined.  The top curve (blue) shows the power received assuming free-space loss.  Note that since the FSL nearly the same for the three tower heights, this is what typical interference calculations for GPS receivers would use.  This shows a received power level of -8.8 dBm, or 21.2 dB higher than the -30 dBm specified by LightSquared’s proposal.  However, if the environment is more like an suburban environment, the received power is -33.5 dBm, or 3.5 dB better than the -30 dBM in the proposal.

Power Received at GPS Receiver Assuming Free-space Loss and Transmit EIRP of 62 dBm

However, the situation is  better when including the effects of a sectored cellular antenna.  The antenna pattern will further attenuate the LS signal as the GPS receivers move closer to the tower. 

A cellular antenna such as the Kathrein 724222 or 742223 has a 20 degree half-power beam width (HPBW), and the cellular operators typically point the antennas down to the ground (called a down tilt angle).  Typical downtilt angles vary from 3 degrees to 8 degrees.  For this analysis, 7 degrees is used.  If we assume a parabolic elevation antenna pattern, then along the maximum azimuth pattern, the antenna directivity is shown below (Downtilted Base Station Antennas –A Simulation Model Proposal and Impact on HSPA and LTE Performance, Fredrik Gunnarsson, Martin N Johansson, Anders Furuskär, Magnus Lundevall, Arne Simonsson, Claes Tidestav, Mats Blomgren).

This antenna model assume a side-lobe level of -20 dB. 

The geometric angle to the mobile terminal from the base station transmit antenna may be determined from simple trigonometry resulting in the following plot.

As shown, the angle to the GPS user is  is below 32 degrees.

Angle from Tower Antenna to GPS Receiver

Combining the angle calculations into a antenna equation, and calculating the the received power to a GPS receiver results in the following equation( as a function of the distance from the tower).  Plotting the equation for the various tower heights, frequency and loss exponent.

Plotting the above equation for three antenna/tower heights (10m, 20m, and 30m) shows that the received power when the antenna pattern is included.  The worst case is for a 10m tower antenna height, 50m away with a received power of -8.5 dBm.  Next is the 20m tower height with a received power of -10.6 dBm, and finally the 30m tower with -14.1 dBm.  Notice, however, that the power levels increase above this within the 50m circle for the lower tower heights.  This is also where one might expect free-space loss (exponent=2) to be more prevalent.

Increasing the loss exponent to 2.7, the received power is -33.1 dBm, -35.4 dBm, and -40.1 dBm for tower heights of 10m, 20m, and 30m, respectively.

Subtracting the -30 dBm from the above plot indicates the level of additional attenuation required for LightSquared to meet their proposed power limit.  The plot below shows the maximum attenuation they would need to achieve (for free-space) is approximately 21.5 dB (10m antenna tower).  This is a substantial reduction in power levels.  However, if the loss exponent is increased from 2 (free-space) to 2.7, LightSquared actually has margin!

Note that this risk is mitigated by the probability that a GPS receiver will be within it 50 meter radius of the tower.  If we assume that GPS receivers are uniformly distributed around the tower, we can calcuate the probability that GPS receivers are within the a particular distance from the tower.  As shown, 99% of the users are further away than 50m, and 95% are more than 110m away from the tower.

THE BOTTOM LINE.  This is the key point of LightSquared’s proposal.  By shifting to received power, typcial interference analysis would indicate that LightSquared would have to reduce their power level by 21.5 dB to 40.5 dBm.  However, by taking the risk that most areas will be experiencing something greater than free-space loss, LightSquared has a greater opportunity to operate at their current power levels.  This is not incorrect reasoning, but it does involve a calculated risk.  Flat, open regions that experience nearly free-space loss will indeed have to operate at reduced power, and in those regions, LightSquared will require more towers to cover the same area, or have to accept less capacity.

Companion Receiver Analysis

It’s insightful to examine how the received power from a LightSquared tower compares to typical GPS receiver characteristics.  From this analysis, we can determine the internal attenuation that GPS receivers likely have to the lower LightSquared carrier.  A usefull resource for GPS calculations is from National Instruments (http://zone.ni.com/devzone/cda/tut/p/id/7189).  This states that a good value to use for the received power from GPS satellites is -136 dBm, and that typical receivers have a noise figure between 2 dB and 5 dB.

The GPS receiver sensitivity may be determined from the following equation. 

Calculating the receiver noise density for a 10 dB noise figure:

This is equal to a receiver C/N0 of:

For a 1 dB degradation in C/N0, the required interference noise density (-5.8 dB from the receiver noise density)

If the interfereing LightSquared signal is received at the specified -30 dBm, or a noise density of -100 dBm (-30 dBm-10Log(10MHz), then nearly 76 dB of added attenuation is needed to achieve a 28 dB CNR. Such attenuation is possible when there are no intermodulation products created in the receiver front-end, and the receiver tests performed by LightSquared appears to support this.  However, the situation requires even more receiver attenuation when we consider the expected maximum average received power calculated from above.

When the received power is incorporated with the required interference noise density produced by LightSquared’s carrier, the required receiver attenuation exceeds 90 dB when 50m from the tower. 

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).

This week we completed our first internal design review of our performance simulation product.  This product simulates the terminals, platforms, networks and servcies associated with wireless networks.  It generality has caused us to rename the product from a land-mobile SATCOM network simulator (LMSNS) to the Wireless Network Simulator (WiNS).  At the core of the product is a very gerneric multiport linear system link calculator.  This engine calculates the power spectral density at all of the terminal receivers across the wireless network taking into account the spatial, spectral , and temporal aspects of the system.  By addressing these aspects within the common framework of WiNS, users can determine the interference spectrum, link signal-to-noise/interference ratios, terminal power requirements, and examine the spectral characteristics of the system.  This flexible, generic framework means that WiNS can simulate satellite systems, wireless terrestrial systems, or hybrid systems.  It can simulator homogenous or heterogeneous networks, and determine their cross-system impacts.   This can be paticularly usefull for those interested in interference calcualtions, licensing studies, cross-system coordination studies, system performance and capacity studies (particularly with many mobile terminals or many basestations or satellites).  Soon we expect to have a version of this product ready for release, and we are excited to meet with those who have expressed interest in a tool with these capabilities.

This week we hired Nathan Saichek to help with the development of our Land-mobile SATCOM Network Simulator (LMSNS). We are delighted to have Nathan on board and look forward to kicking the development into high gear. Furthermore, we have added some of our perspective on modeling to our web-site.  Please check out the Satellite Simulation page.

A new year for us hear at Questiny. 2009 was a tough year for everyone in small businesses, but we survived with the help of our clients and we managed to close on the Phase II SBIR contract with the Navy to develop our Land-mobile SATCOM Network Simulator (LMSNS). As we enter 2010, we look forward to an improved economic climate, and the expansion of our business.

We have added Robert Hu to our ranks as the VP of Marketing and Business Development. Robert and I share many common interests, but he will bring new focus and energy to Questiny, and we are delighted to have him on board. Along with the addition of Robert Hu, Questiny will be developing a new Information Practice. This practice will apply some new tools to assist enterprises develop navigable knowledge networks. We are very excited about this new development as it goes beyond the Google and Bing search engines. All of us are dealing with the onslaught of vast quantities of information, and struggle to derive understanding from that information. Questiny has developed ways to help with that, and we are looking forward to introducing them to our clients this year. If you have particular issues managing information, please let us know. Perhaps you can be part of our beta tests to create a new way of understanding the information you see everyday.

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.

Questiny is nearing the completion of a DCAA audit in anticipation of the Phase II SBIR award. Over the past few weeks, we have had to updgrade our accounting system to a cost accounting system. Other than the cost of the consultants to do the conversion and the cost of the software, this did not change any of our costs. The upgrade will allow us to bid on Government cost-type contracts.

Questiny’s offices at 161 W. 25th Ave. in San Mateo are now operational. We have managed to consolidate all of our files and communications at one location. Finally! We have a two office suite located on the second foor of a professional office building. This move completes a consolidation plan where we can now perform on the anticipated development of the Land-mobile Satellite Network Simulator/Planner.

Located on the 2nd Floor, 161 W. 25th Ave., San Mateo, CA

On April 10th, Questiny completed the final report for the Phase I SBIR Option. The final report titled, Land-mobile Satellite Communications-Improved Mathematical Methods for Stressed Environments: Phase I Option Final Technical Report, outlined the software design for a new satellite network performance simulator. This performance simulator has been designed to simulate the performance of mobile terminals operating over satellites. While mobile terminals have been used over satellites before, the size of the networks along wtih the diversity of channel environments creates scenarios that exceed the current capabilities of satellite performance simulators. We have designed a new simulator that can model both commercial and military mobile communications networks and environments. The SBIR program will develop the underlying technology for this simulator. One of the first applications for this simulator will be the Navy’s MUOS Program for mission planning. SPAWAR has expressed interest in customizin the application for this program.

After five years of working out of my house, Questiny has moved to new spaces at 161 W. 25th Ave. Suite 201A in San Mateo. We are currently in the process of moving this week, and hope to complete our move by the end of the week. We apologize to those who might have tried to reach us during the past few weeks as the communications has taken some time to transition. In spite of the difficulties, we now have our phones and network operational again. After we complete the move, we will post pictures of our new spaces.

I was wondering if anyone thought Microsoft was poised for a big fall?  What has Microsoft done in the past few years that one would call successful?  The last I can remember was MS won the browser war over Netscape.  After that, what did the do?  Let’s see.  AOL vs. MSN.  No contest, who uses MSN?  Digital TV?  No one came near to using Microsoft TV.  MS-Office?  Prior win, and they bought Excel rather than develop it.  Search engines?  Google, google, … gurgle, gurgle, bye bye MS (down the drain).  How about Operating Systems, MS’s been pretty good at that, right?  Vista versus Mac OSX.  Well, that went so well for MS, they had to change it’s name and release it as Windows 7, which nobody wants.  After that, I think we’re into fringe markets.  So is this why Bill Gates decided to concentrate on philanthropy?

On January 10th, Questiny received notification from SPAWAR that they would exercise the option on our Phase I SBIR on Land-mobile Satellite Communications: Improved Mathematical Methods for Stressed Users. In addition, on January 25, 2009 we submitted our Phase II proposal to SPAWAR for consideration. Together, the Phase I Option and the Phase II effort will prototype an advanced discrete event satellite communications simulator for US military UHF satellite communications. This simulator employs our advances in land-mobile satellite channel models, and our advanced design in discrete-event radio propagation modeling. When completed, this tool will provide a comprehensive US military communications planning tool.

In this photo released by the U.S. Coast Guard, members of Coast Guard law enforcement detachment 404 survey the deck of the self-propelled, semi-submersible craft they seized on Saturday, Sept. 13, 2008. The LEDET, embarked aboard the USS McInerney (seen to the left of the SPSS), seized seven tons of cocaine from the vessel. The estimated street value of the cocaine is more than $187 million. The seized vessel has the capability to travel from Ecuador to San Diego, Calif., without having to stop for replenishment. (U.S. Navy photo/Petty Officer 1st Class Nico Figueroa)

I recently asked Uniden if they had a blog set up for product suggestions from their customers. They responded that they did not have a blog and did not intend to set up one. They went on to say if I sent them an email, they would ensure that it got to the right department. I found this very short-sighted on their part, but complied with their request. Below is the response I sent them.

Ok. Let me begin by suggesting you start a Blog for your customers. Without one you are behind the times and out of touch with your customers. I may not be a typical Uniden customer, but I currently own seven Uniden products (3 scanners, 1 Marine Radio, 2 WHAM mics, 1 cordless phone), but I would think you would want to keep me happy and create a forum where you can listen to me and others like me. I suggest your Management read the book “groundswell” by C. Li. here are a few suggestions/comments:

WhamX4 mics

1) Volume Power button. This is wrong. When I am in the cockpit of the boat and want to turn up the volume, but I press the button too long, I turn off the Wham mic! This can be at a critical point in communications, and I just lost my ability to talk. This design decision was made by someone who does not sail and has not been on the ocean when a lot of things are happening at once.

2) DSC menus. The menus are different from the main radio meaning that I have relearn how to make a DSC call al over again depending if I am at the radio or at the wireless mic. This is bad. Also, the DSC calls take too many steps. It should be more like a cell phone and offer speed DSC. That is one button DSC calling.

3) Battery life. The batteries completely died after one year of operation requiring 20% of the cost of the mics to replace. This is too expensive to maintain. Also, the battery life is about 2 hours. We might get 3 hours if the batteries are new, but 3 hours is too short of a battery life. Luckily we run 2-3 hour watches, so we just change them out when we go off watch. However, they need more than 3 hours of charging time so the batteries never reach full charge. (Note we run two mics, if we had only one, it would likely have been tossed overboard in frustration long ago.)

4) Setting up and using the intercom is too complicated. This took us quite a bit of time and the manual was particularly unclear.

5) [Added, not sent to Uniden] The one second delay between keying the WhamX4 and the initiation of transmission is too long. Emergency communications is often fast with short transmissions. One second often means the start of the speech is cut off.

UM525 Radio

1) The UM525 needs better image rejection and selectivity. We sail in the SF Bay area where there are many public safety and paging repeaters. They constantly bleed over into the radio making the squelch break. This is no untypical of recreational boating areas, and I have had many colleagues and friends disparage Uniden products due to this selectivity problem.  If you compare the specifications of your competitor ICOM, their image rejection is nearly 20 dB better. Again, you don’t have to make me happy, but as a radio engineer, I recommend the ICOM rather than Uniden radios.

2) We connected a GPS unit to the radio, but it sure took a while to figure out the pin connections. You should have a web-site with pictures and configurations for all of the major GPS manufacturers.

BC296 and BC796 Scanners

1) Generally I have been happy with you scanners, but the interface is getting harder and harder to operate. I have not had a chance to view your new products, but these clearly had some problems. The digital audio codecs sound worse than the GRE/Radioshack models. Also, there is a manual voice optimization that your competitors do not require.

2) Memory management. None of the scanner manufacturers seem to understand memory management. The memories need to be flexible. Memory banks are a thing of the past, and they do not work with they way we listen to trunking systems. When we listen to scanners, we listen within the context of scenarios. Casual background listening, emergency fire, emergency police, etc. Memories need to be programmed, but then scanning them needs to be governed by a scanning scenario.

For example, I may want to only listen to a few local channels in the background, but then when I hear something happen, I want to change the channel list (with a single button) to bring in the other channels (along with a priority order of scanning) that allows me to monitor the situation. For example, I may hear of a fire over the police channel (the only one I was monitoring), I hear that this is a traffic accident, so I want (with one button) to switch to a scanning list that scans the HWY patrol, fire for that location, ambulance (for that location), and Lifeflight. And this has to work seamlessly with the trunking systems. Can I do this with a computer connected to the scanner? Yes, but why do I want to? I have three portable scanners so I can take them with me! This is not a hard engineering problem.

3) Quality. Take a look at the AOR form factor and case design. It is much more rugged and ergonomic than the BC296. Spending this much money on a portable scanner means it has to be ruggedized for harsh environments. If AOR can do it, so can Uniden. Like I said, you don’t have to listen to me, but think about how much product intelligence you might get if you started an online forum for your customers. Don’t worry about me, but I will ask this same question of GRE and AOR.

Kindest Regards,

Keith

I will be interested to see their repsonse-if there is any.

A 2003 article written by George Hockney, et. al, for NASA titled, Multiresolution Global Coverage Analysis Using A Point Quad Tree Implementation Of Visual Calculus, began me thinking about more efficient ways to calculate satellite coverage. This article lays out the basic concept, but is very light on details as to where the efficiencies actually come from. The basic idea is to use a quad-tree to compress the storage requirements for maps that define the coverage areas of satellites. In addition, the operations (the computational geometry portion of this treatise) deal with the ability to manipulate these maps in an efficient manner. What I was missing in their article was the efficiency at examining the satellite-earth geometry. The idea behind a quad tree is that each node of the tree represents a large square area of the map subdivided into four equal square. If all of the points (characteristics, etc.) within a sub-area share the same characteristics, then this area need not be further examined and subdivided. If it does contain the characteristics desired, then the area is further subdivided into four smaller squares. The same evaluation process takes place. This creates a situation such as shown below:

The image shows how the squares are more frequent around the circle boundary. This shows that much of the area has no change, but the boundaries have increasing resolution to describe the change from the white area to the circle. In a similar manner, the circle can represent a satellite coverage area. While this does save on storing information about the location of a boundary between satellite coverage and no satellite coverage, it does not resolve how to determine the coverage area without having to check all of the points. At this time, I have not exactly figured out an efficient way to perform this, but here is an outline of my attack. The satellite nadir, or sub-point, is the center of its coverage area. The coverage radius indicates the distance to the satellite “edge of coverage”. Each square (assuming they are square for the moment) has a center point and a coverage radius. If the distance between the square center point and the coverage center point minus the coverage radius, is less than the radius of the square, then the satellite covers the square for this node of the tree. If so, this node is tagged for further sub-division, otherwise the satellite does not cover this subsquare, and no further examination of this region is needed. This means that the algorithm will calculate more points around the edge of coverage just as shown in the circle diagram. Furthermore, for many satellites this coverage area is constant across a sphere and a simple translation of the quad tree may be used to define the coverage region when the satellite moves to another location. This translated tree combined (i.e., using computational geometry) can use boolean operations to define overall coverage regions. If this works, it is a neat trick! This promises to be a very fast efficient way to calculate the coverage of LEO satellite constellations that involve large numbers of satellites. I have already tried a brute force method for this in Matlab, and it is intensly slow. As I develop the algorithm, I will post more about the results.