GPS Jamming Exercise

[goingnowherefast]

The redundancy is in the different systems, different frequencies, different satellite constellations and different receivers. You can blast "noise" on the GPS system frequencies, but Galileo and GLONASS will be unaffected.

Radio Direction Finding dates back to 1888 with experiments Heinrich Hertz was doing, and it was commercialized in the 1920s for naval and early aeronautical navigation. In the 1930s the concept was fully implemented for aviation use. The Automatic Direction Finder is from the 1940s, but that's just the Automatic part of the receiver.

I never said VOR, ILS or DME technology was 100 years old, just NDB. NDBs also differ from ADF, as one is the transmitter station and the other being the receiver. The transmitter technology is really old, the receiver technology dates to the 20s and reached it's technological potential in the 40s as you stated.

NDB, VOR, ILS, and DME technology has already been fully exploited and there is very little left to gain. In the case of the NDB and VOR is actually being phased out slowly. Satellite navigation based has lots of development potential remaining.

Not sure what you're arguing about the ILS, I said "The ILS will take a while to die as it still allows more precision for CAT II and CAT III approaches." and your statement seems to agree.

As for procedure turns, GPS allows for straight in approaches. Pretend you are flying in from the south and want to land on runway 36. In the airline world, even with a STAR, the process is a mostly straight line. With a stand-alone NDB approach, you are still required to do a procedure turn.

What I was trying to imply (and apparently failed) was that in most of Canada, we are depending on NDBs as a backup to GPS.

[fish4life]

How would one get true heading without ndb? Assume your in cloud and can't use your sexton.

[AuxBatOn]

Because a signal is below the noise floor doesn't mean you can't pull it out of it. Integrating the signal, for one technique, will increase the signal to noise ratio. In fact, some systems purposely make the signal weaker than the noise.

[ahramin]

Sextant, it's a sextant . And a sextant gives position, not heading. You're talking about an astro compass.

[CID]

Because a signal is below the noise floor doesn't mean you can't pull it out of it. Integrating the signal, for one technique, will increase the signal to noise ratio. In fact, some systems purposely make the signal weaker than the noise.

Thats not the way receivers work. Receivers adjust their gain (automatically) based on the strength of the signal at the front end. As signals increase, gain decreases. That makes the threshold for readible signals (noise floor) so high the GPS intelligence dissppears from subsequent stages.

[CID]

The redundancy is in the different systems, different frequencies, different satellite constellations and different receivers. You can blast "noise" on the GPS system frequencies, but Galileo and GLONASS will be unaffected.

The differences aren't as vast as you imply. And even if they were, if one system can be jammed in an area 3 can be jammed.

[AuxBatOn]

Because a signal is below the noise floor doesn't mean you can't pull it out of it. Integrating the signal, for one technique, will increase the signal to noise ratio. In fact, some systems purposely make the signal weaker than the noise.

Thats not the way receivers work. Receivers adjust their gain (automatically) based on the strength of the signal at the front end. As signals increase, gain decreases. That makes the threshold for readible signals (noise floor) so high the GPS intelligence dissppears from subsequent stages.

ACG circuits are not part of all receivers. It's one type of technique to enhance a received signal. If you are purposefully transmitting a signal that is below the noise floor, a simple ACG is useless.

[goingnowherefast]

Independence from GPS was the whole point in developing Galileo. I'm sure it's the same case with GLONASS.

It would require a more powerful transmitter/jammer, but you could jam an ILS frequency too. Jam GPS, then jam the ILS and you'd render an airport useless in bad weather. Not a whole lot different than multiple independent satellite navigation systems.

I know GPS is complex and they are "magic boxes" to some. However utilizing the redundancy with the different systems now available, they are every bit as safe as VORs and NDBs. Perhaps safer.

Technological development takes time, and we're not there yet with in the aviation industry. Many cell phones utilize GPS and GLONASS for enhanced accuracy and availability.

[Posthumane]

Because a signal is below the noise floor doesn't mean you can't pull it out of it. Integrating the signal, for one technique, will increase the signal to noise ratio. In fact, some systems purposely make the signal weaker than the noise.

Thats not the way receivers work. Receivers adjust their gain (automatically) based on the strength of the signal at the front end. As signals increase, gain decreases. That makes the threshold for readible signals (noise floor) so high the GPS intelligence dissppears from subsequent stages.

ACG circuits are not part of all receivers. It's one type of technique to enhance a received signal. If you are purposefully transmitting a signal that is below the noise floor, a simple ACG is useless.

AuxBatOn is right that there are techniques that are used to pull usable signals from below what would normally be considered the noise floor.* In a sense, GPS receivers already have to do that just to get a signal in normal operation. They have their limits though - slightly below the current noise floor is one thing, but trying to receive a signal that is jammed by a carrier several orders of magnitued higher in power is pretty much impossible. Whether a GPS signal is easy or difficult to jam is a relative term. I would say it is "easy" if you have a decent transmitter capable of transmitting on the appropriate bands and are in relatively close proximity to the receiver you're trying to jam.


* Side note: "Noise floor" is a relative term as well. You have a local noise floor which is a result of various intentional and spurious emissions from various devices, you have a thermal noise floor which is a result of heat and varies with bandwidth, and you have an instrument noise floor which is a property of the receiver you are using and how well isolated it is. Any one of these can be a limiting factor, depending on what you're trying to do.

[light chop]

DOC-304575A1.pdf

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I hope people that sell, purchase and use jamming devices realize it's a federal offense (in the US and Canada).

And this is why we can't have nice things...

[photofly]

AuxBatOn is right that there are techniques that are used to pull usable signals from below what would normally be considered the noise floor.* In a sense, GPS receivers already have to do that just to get a signal in normal operation. They have their limits though - slightly below the current noise floor is one thing, but trying to receive a signal that is jammed by a carrier several orders of magnitued higher in power is pretty much impossible..

GPS signals are already 20dB below the thermal noise floor. Thats why they use Gold codes.

[cgzro]

Minor quibble .. Spreading the low bit rate signal evenly into a much wider bandwidth signal is what makes it possible. Any sequence that spreads it out will work. Pseudo random sequences are needed when there are multiple transmitters and you dont want them to collide. Gold codes are just a set of sequences with low likelihood of correlation. There are other techniques too like OFDM which uses Fourier to spread and recover signals and it is the basis of all 4G, and soon to be 5G.

[CID]

Let's begin with the simple definition of "noise floor":

In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where noise is defined as any signal other than the one being monitored.

Typical sources of "noise" are typical naturally occurring phenomena like "thermal noise" as mentioned earlier. In the case of a jamming device, the "noise" source includes the "unwanted" jamming signal. So the noise floor is established by all the typical sources of radio noise PLUS the jamming signal.

You can spew all the radio signal theory and GNSS signal theory you want but if I have a high power transmitter operating on the proper frequency or frequencies or wide band in your vicinity, the GNSS signals will be completely obliterated well beneath the noise floor which is now composed primarily of the jamming signal.

[AuxBatOn]

Sure but that's going to be a very local phenomenon maybe even a very directed one. Effectively jamming a GPS signal over a wide area affecting many users is actually difficult.

[complexintentions]

I realize this topic has become mostly about desperately trying to appear smarter than the last guy, but if I can interject to suggest the operational impacts of GPS signal loss are quite a bit more important to me as a pilot than arguing the arcane technical points of the tech. Although gold codes sound cool.

Most modern airliners are operating with increasingly sophisticated inertial systems for primary navigation, with corrective updating from whatever external source is available, land or space-based. The external signals are not, technically speaking, the primary source of navigation. A temporary loss of GPS signal is usually a non-event, unless of course you are on a GPS-based approach, particularly a RNP-AR approach. But the same could be said for loss/degradation of an ILS signal. There are procedures to deal with both.

Enroute navigation is even less critical. In my former operation we would routinely lose GPS temporarily when operating in such places as close to the Ukraine due to jamming (and no, it wasn't an exercise) or over the pole when there was increased solar activity. It was completely anti-climactic, the a/c navigates at a reduced level of precision and life goes on. Eventually GPS and/or radio updating is restored.

I find it amusing that a NOTAM'ed temp outage seems to be cause for such drama. The airplane WILL keep flying without GPS or NDB, promise.

[cgzro]

Spread spectrum signals are hard to jam or spoof only if you dont know the sequence of shifts.
Since the sequences for each satellite are kown for the civil frequency band it would not be difficult to spoof or jam them by just using the exact same sequences and you could go further and create arbitrary position errors. A lot of power to saturate thd entire band would not be necessary, just more than each satellite is delivering to your antenna.

Military would be harder of course by an order of magnitude in power.