Record-breaking optical fibers for global communications.
The 2,000 kilometers of fiber-optic cable stacked in Gabriel Charlet’s lab in the Alcatel-Lucent Bell research facility in Nozay, France, are a reminder of a record-breaking achievement: in 2009 Charlet smashed the world high-speed long-distance record for fiber-optic communications, reaching a transmission rate of 7.2 terabits per second over a single fiber 7,040 kilometers long. That’s around five times as fast as existing commercial systems–the equivalent of transmitting more than 6,000 movie-length DVDs in a minute.
Charlet reinvigorated a field. The data-carrying capacity of the cables that form the backbone of the global telecommunications network had improved little in recent years: as other researchers tried to boost transmission rates, microscopic imperfections in the cables introduced distortions that could not be compensated for. These researchers were encoding digital data by varying the intensity of a pulse of light. For example, high intensity would represent a 1 and low intensity would represent a 0. At high data rates over long distances, the imperfections blurred the distinction between intensity levels, meaning that at distances over 7,000 kilometers, around 1.2 terabits per second was the limit of reliable communication.
To solve the problem, Charlet perfected a system that uses the polarization and phase of a pulse of light, rather than its intensity, to encode data. Errors induced by imperfections are far less problematic thanks to the development of a new receiver that detects the whole electrical field of the signal, rather than just its intensity. As a bonus, each pulse of light can now encode four bits of data instead of just one, because different polarizations can be used to indicate different bit values.
Drawing on Charlet’s research, Alcatel-Lucent recently launched a new generation of commercial equipment that transmits data at 3.2 terabits per second over distances of up to 7,000 kilometers (the speeds are slower than Charlet’s record because of the limitations of current chip designs; the next generation will use specially made chips). The next time you watch a video on YouTube, it may have been piped to you with Charlet’s help.
Delivering high-speed wireless Internet connections over longer distances.
PROBLEM: Wi-Fi uses frequencies that can’t carry a signal more than a few tens of meters. TV stations, on the other hand, use a portion of the radio spectrum that lets signals travel long distances, and the end of analog television has opened up unused slices of the spectrum between stations. They could be used for wireless Internet service, but it has been difficult to take advantage of these so-called white spaces without causing interference, because the exact frequencies used by TV stations vary geographically.
SOLUTION: Ranveer Chandra made the Microsoft campus in Redmond, WA, his laboratory for the first large-scale network to demonstrate the potential of using white spaces to deliver broadband wireless. Links in the prototype network can span up to two kilometers. To avoid treading on the toes of TV broadcasters, his system uses GPS to determine its location; then it checks the Web to find out what stations are active in the area. Chandra’s devices can also listen for nearby transmissions from wireless microphones, which use the same bands. When a conflict is detected, they switch to a backup slice of unused spectrum on the fly.
If such a system gains currency, “all of us should be connected and better connected, and not just here in the U.S.,” says Chandra. Spectrum regulators from Singapore, India, Brazil, and China have all come to visit his prototype network to explore the potential for white-space signals to connect large rural areas with minimal infrastructure.
Amir Alexander Hasson
Using cell phones to supply rural shop owners.
Many shop owners in Indian villages are beyond the reach of major distributors. Some goods are sold to them by local producers, but owners “have to leave their shops four times a month to get 81 percent of the stuff that they sell,” says Amir Alexander Hasson. Having to travel to restock doesn’t just affect shop owners; villagers end up paying higher prices for a smaller selection of goods. Since founding United Villages in 2004, Hasson has been using wireless technologies to help solve this and other problems facing the rural poor in developing nations.
Hasson started out with a system that helped people in isolated communities send and receive e-mail and search for jobs. Wi-Fi routers were attached to buses; when a bus drove into a village, its router connected with computers set up at local kiosks. Now Hasson is taking advantage of the rapid expansion of cell-phone networks to set up a for-profit wholesale service called E-Shop. Shop owners with phones that run Java applications can browse an online catalogue and place orders; data is transferred between the phones and United Villages using SMS text messages. This method is cheap and doesn’t require powerful smart phones. In about 36 hours, the goods are delivered directly to the shop.
Hasson is planning to introduce another use of E-Shop, as a way for people to post advertisements through a local store owner. “For [50 cents], someone can post his motorbike for sale,” says Hasson, “It will be India’s first mobile-based classifieds.”