N. Korea jams GPS signals to disrupt Korea-U.S. drills: sources

SEOUL, March 6 (Yonhap) -- North Korea recently jammed GPS signals in South Korea in an apparent bid to disrupt Seoul's annual military drills with U.S. forces, government sources said Sunday.

GPS signals in Seoul and nearby cities, including Incheon and Paju, were temporarily disrupted on Friday afternoon, causing mobile phones and certain military equipment in the area to malfunction, the sources said.

"My understanding is that errors were detected in a very few equipment within the telecom industry," a defense official said. "Some measurement equipment in artillery units was also affected but only very slightly."

The jamming signals are thought to have come from vehicle-mountable devices at military units north of the inter-Korean border. Former Defense Minister Kim Tae-young said in October that he had intelligence that the communist regime had imported from Russia such devices capable of jamming GPS signals.

"The jamming signals came sporadically every five to 10 minutes," an intelligence official said, adding that North Korea was likely testing its imported devices.

Defense and intelligence officials said they suspect the jamming was aimed at disrupting the annual Key Resolve military drills between South Korean and U.S. forces, which started four days before the malfunctioning incident.

It also came nearly a week after North Korean representatives at the inter-Korean border village of Panmunjom repeated their threat against the drills, saying their armed forces would launch "an all-out war of unprecedented scale" and turn Seoul into "a sea of fire" if provoked.

The real question is, did it really affect military systems, or do we just want them to think their shiny news toys worked?

I believe trying to jam GPS is worse than useless in many cases. A GPS guided bomb falls, well, nose first right? So the GPS antenna is on the tail, looking up at the satellites. A signal coming from a ground based jammer is on the wrong side of the bomb, and the antenna probably picks up little or nothing of the jamming. The jammers would make great targets for a wild weasel though...

I've never fooled with military GPS gear, but it seems to me you could make a nominally directional antenna, keep it pointed up, and thereby reject most/all ground-based jamming. Commercial GPS units have omnidirectional antennas on purpose as a convenience to us commercial users who want the thing to work tossed on the dash, in the console, stuck to the windshield, stuffed in a pack, dangling on a lanyard around our necks, etc.

GPS operates in two modes concurrently. The great unwashed get the C/A channel. It is not encrypted. It is subject to purposely injected "selective availability" distortion to make it less useful to an adversary. There is a constant transmission of almanac and ephemeris information on this channel to allow identification of the general location of the satellites in service and fine details of their orbits. That allows the receiver to determine which of the possible birds should be assigned to receivers. Most devices have 8 to 12 parallel receivers that are assigned the PN code of the probable satellites. Once a bird is acquired i.e. PN sequence synchronized between the GPS receiver and the bird, the receiver gets its timebase locked and calculates the signal delay from the known satellite position to the receiver. It takes 3 birds for a 2D fix. More birds, better accuracy. The WAAS birds add additional "differential" information to improve the fix accuracy.

The GPS signal level is below the noise. A receiver must generate the same PN sequence as the satellite and add it to the received signal to push the total signal above the noise. It is a trial and error exercise that requires slipping a bit time and attempt a match until the signal "locks". If you know roughly where you are, have the current time and a current almanac, the "warm start" to sync the first bird can be as little as 8 seconds. A cold start with no concept of time/location (cold start) can take upwards of 20 minutes of guess work by the receiver to match the first bird. Once that is done, an almanac is loaded, the time is set and a much better estimate of which birds to seek is possible.

The military gets access to the encrypted channel. That data rate is 10 times as fast as the C/A channel. The encryption PN pattern repeats every 2 weeks. If you have the decrypt key and a current C/A broadcast, you'll be able to zero in on the segment of the current PN sequence and use the faster data. It's obviously useful of stuff like ICBMs that need faster rates.

All of this information is available for anyone who wants to pony up around $70 for a good book on GPS implementation.

“NK is doing SK a favor.”

Agree on that. Sometimes you have to use a bit of imagination when designing things. Sure GPS is great for military ops...but maybe the enemy knows that also and develops means to counteract it...as the Norks are showing to the, no doubt, HIGHLY SURPRISED US and South Korean forces. Just because GPS works great in a car does not mean it should be the sole source of navigation for a tank, during a wartime situation (and I certainly hope it’s not).

In Mexico, when our drug were attacked last month, their ARMORED vehicle popped the door locks open for the bad guys, just after they were run off the road...they put their SUV in park, and POP all the door locks opened, just like my Honda.

Sometimes you do have to think a bit harder when you design for difficult situations.

Those GPS jammers might have some utility against Arty units that rely on them for an accurate fix. But I suspect that in the presence of a jamming signal that the battery commander is going to do things the old fashioned way.

I was driving by a US airbase recently and my vehicle GPS went haywire. My plot was all over the place, so I suspect that jamming is technically possible.

WOW! You cannot buy training and testing like that for money! They let us see their capabilities for free and give our troops training in how to recognize and counter jamming. This is insane! If we jammed our own GPS to achieve the same end, there would be a hew and a cry! And nothing we could do could as reliably simulate the geometry and fidelity of an actual Nork attack. Please, Brer Jong, don’t throw me in dat dare briar patch.

One principle of electronic warfare, is not to let them see it coming. Unleash a total attack and follow up with iron and lead while they’re still trying to recognize and handle it.

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