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See also: "laser communication in space
The massive advantages of laser communication in space have multiple space agencies racing to develop a stable space communication platform, with many significant demonstrations and achievements. As of 18 December 2014no laser communication system is in use in space.
Demonstrations in space:
The first gigabit laser-based communication was achieved by the European Space Agency and called the "European Data Relay System (EDRS) on November 28, 2014. The initial images have just been demonstrated, and a working system is expected to be in place in the 2015–2016 time frame.
NASA's "OPALS announced a breakthrough in space-to-ground communication December 9, 2014, uploading 175 megabytes in 3.5 seconds. Their system is also able to re-acquire tracking after the signal was lost due to cloud cover.
In January 2013, NASA used lasers to beam an image of the Mona Lisa to the Lunar Reconnaissance Orbiter roughly 390,000 km (240,000 mi) away. To compensate for atmospheric interference, an error correction code algorithm similar to that used in CDs was implemented.
A two-way distance record for communication was set by the Mercury laser altimeter instrument aboard the "MESSENGER spacecraft, and was able to communicate across a distance of 24 million km (15 million miles), as the craft neared Earth on a fly-by in May, 2005. The previous record had been set with a one-way detection of laser light from Earth, by the Galileo probe, of 6 million km in 1992. "Quote from Laser Communication in Space Demonstrations (EDRS)
is a "free
implementation of FSO using high-intensity "LEDs
In 2001, Twibright Labs released Ronja Metropolis, an open source DIY 10 Mbit/s full duplex LED FSO over 1.4 km In 2004, a Visible Light Communication Consortium was formed in "Japan. This was based on work from researchers that used a white LED-based space lighting system for indoor "local area network (LAN) communications. These systems present advantages over traditional "UHF RF-based systems from improved isolation between systems, the size and cost of receivers/transmitters, RF licensing laws and by combining space lighting and communication into the same system. In January 2009, a task force for visible light communication was formed by the "Institute of Electrical and Electronics Engineers working group for wireless "personal area network standards known as "IEEE 802.15.7. A trial was announced in 2010, in "St. Cloud, Minnesota.
"Amateur radio operators have achieved significantly farther distances using incoherent sources of light from high-intensity LEDs. One reported 173 miles (278 km) in 2007. However, physical limitations of the equipment used limited "bandwidths to about 4 "kHz. The high sensitivities required of the detector to cover such distances made the internal capacitance of the photodiode used a dominant factor in the high-impedance amplifier which followed it, thus naturally forming a low-pass filter with a cut-off frequency in the 4 kHz range. From the other side use of lasers radiation source allows to reach very high data rates which are comparable to fiber communications.
Projected data rates and future data rate claims vary. A low-cost "white LED (GaN-phosphor) which could be used for space lighting can typically be modulated up to 20 MHz. Data rates of over 100 "Mbit/s can be easily achieved using efficient "modulation schemes and "Siemens claimed to have achieved over 500 Mbit/s in 2010. Research published in 2009, used a similar system for traffic control of automated vehicles with LED traffic lights.
In September 2013, pureLiFi, the Edinburgh start-up working on "Li-Fi, also demonstrated high speed point-to-point connectivity using any off-the-shelf LED light bulb. In previous work, high bandwidth specialist LEDs have been used to achieve the high data rates. The new system, the Li-1st, maximizes the available optical bandwidth for any LED device, thereby reducing the cost and improving the performance of deploying indoor FSO systems.
Typically, best use scenarios for this technology are:
- LAN-to-LAN connections on "campuses at "Fast Ethernet or "Gigabit Ethernet speeds
- LAN-to-LAN connections in a "city, a "metropolitan area network
- To cross a public road or other barriers which the sender and receiver do not own
- Speedy service delivery of high-bandwidth access to "optical fiber networks
- Converged Voice-Data-Connection
- Temporary network installation (for events or other purposes)
- Reestablish high-speed connection quickly ("disaster recovery)
- As an alternative or upgrade add-on to existing wireless technologies
- Especially powerful in combination with auto aiming systems, this way you could power moving cars or you can power your laptop while you move or use auto-aiming nodes to create a network with other nodes.
- As a safety add-on for important fiber connections (redundancy)
- For communications between "spacecraft, including elements of a "satellite constellation
- For inter- and intra-chip communication
The light beam can be very narrow, which makes FSO hard to intercept, improving security. In any case, it is comparatively easy to "encrypt any data traveling across the FSO connection for additional security. FSO provides vastly improved "electromagnetic interference (EMI) behavior compared to using "microwaves.
Range limiting factors
For terrestrial applications, the principal limiting factors are:
These factors cause an attenuated receiver signal and lead to higher "bit error ratio (BER). To overcome these issues, vendors found some solutions, like multi-beam or multi-path architectures, which use more than one sender and more than one receiver. Some state-of-the-art devices also have larger "fade margin (extra power, reserved for rain, smog, fog). To keep an eye-safe environment, good FSO systems have a limited laser power density and support "laser classes 1 or 1M. Atmospheric and fog attenuation, which are exponential in nature, limit practical range of FSO devices to several kilometres.
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