On Wed, Sep 25, 2013 at 02:04:34PM -0700, Rich Jones wrote: > That kind of technology is already widely deployed in walkie talkies - I > think I remember at HOPE a speaker mentioning that the NYPD used this > technique until they abandoned it due to its inconvenience. > > http://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum
Here's a potentially disruptive technology for global communication that bypasses the fiber infrastructure, and hence more difficult to tap and almost impossible to disrupt by other means than total orbit denial weapons. http://www.extremetech.com/extreme/165194-nasa-prepares-to-launch-space-laser-system-that-can-transmit-data-at-600mbps-to-deep-space NASA prepares to launch 600Mbps space laser system to replace conventional radio links By Sebastian Anthony on August 29, 2013 at 10:05 am19 Comments NASA is preparing to launch the Lunar Laser Communications Demonstration (LLCD), a testbed that will use lasers to send and receive data between Earth and the Moon. This will be the first time that NASA uses lasers instead of conventional S-band radio waves to communicate with spacecraft, allowing for massive data rates of up to 600 megabits per second, while also consuming much less power and requiring much smaller antennae. Ultimately, shifting to laser-based communications will allow NASA to receive much more data from spacecraft, allowing them to be outfitted with high-res cameras and other modern sensors that generate more data than S-band links can support. Optical communications, as opposed to radio frequency (RF) communications (or simply “radio”), are desirable for three key reasons: Massive bandwidth, higher security, and lower output power requirements. All of these traits derive from the frequency of optical and radio waves. While S-band signals are in the 2-4GHz range (similar to your GSM, LTE, or WiFi link), the laser light used by the LLCD (near-infrared in this case) is measured in hundreds of terahertz. As a result, the wavelength of S-band signals is around 10cm, while near-infrared has a wavelength of just 1000nm — or about 100,000 times shorter. Not only can you cram a lot more data into into the same physical space, but there’s also terahertz (compared to megahertz in the S band) of free, unlicensed space that can be used. A diagram of the LLCD architecture Because the wavelength is smaller, the sending and receiving antennae can also be a lot smaller, allowing for smaller/lighter spacecraft and much easier reception here on Earth. By the time a conventional RF signal arrives at Earth from outer space, the beam can cover an area as wide as 100 miles, requiring very large dish antennae (such as the Deep Space Network) to pick those signals up. Receiving laser signals, which are 100,000 times shorter, requires a much smaller dish. As a corollary, due to these beams being much tighter, they’re much harder for an enemy to snoop on, thus increasing security. Transmitting data via laser also requires less power than RF. NASA's LLCD laser link diagram The LLCD will be deployed upon the Lunar Atmosphere Dust Environment Explorer (LADEE), which is scheduled for launch in September. LADEE (which could be pronounced lay-dee or lad-ee, we’re not sure) will orbit the Moon, seeking to confirm whether the mysterious glow observed by Apollo astronauts was caused by dust in the lunar atmosphere. Thanks to the LLCD, NASA will have a 20Mbps uplink to LADEE (apparently 4,800 times faster than existing S-band uplinks), and LADEE will have a 600Mbps downlink to NASA (five times faster than current state-of-the-art lunar-distance links). The mission will only last for 30 days, after which, if it’s a success, NASA will launch the long-duration Lunar Communications Relay Demonstration (LCRD), which will hitch a ride aboard a commercial Loral satellite. The LCRD will allow NASA to perform further testing of space laser communications, with the hope of eventually replacing RF links in future spacecraft. Moving forward, space laser communications will allow for the creation of spacecraft that are smaller, cheaper, and capable of more advanced functionality. With 600Mbps of downlink capacity, we’ll be able to outfit spacecraft with high-resolution cameras and other advanced sensors that generate vast amounts of data — and view that data in real time, rather than waiting for the data to slowly dribble over the airwaves.
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