Back in the olden days, when WiFi and Bluetooth were just a glimmer in the eye of IEEE, another short-range wireless communications technology ruled supreme: Infrared Data Association, or IrDA for short. IrDA was awful; early versions were only capable of kilobit-per-second speeds, and only over a distance of a few feet. Trying to get my laptop and mobile phone to link up via IrDA was, to date, one of the worst tech experiences I’ve ever had.
There’s a lot to be said for light-based communications, though. For a start, visible (and invisible) light has a frequency of between 400 and 800THz (800 and 375nm), which is unlicensed spectrum worldwide. Second, in cases where you really don’t want radio interference, such as hospitals, airplanes, and other sensitive environments, visible light communication (VLC), or free-space optical communication, is really rather desirable. Because of the prevalence of light sources (one in every room!) VLC could also be the basis for ubiquitous networking. Just last year, Harald Haas demonstrated an LED light bulb that could transmit HD video using VLC.
Now, I think for the first time ever, researchers at the National Taipei University of Technology in Taiwan have transmitted data using lasers — not high-powered, laboratory-dwelling lasers; handheld, AAA-battery laser pointers. The setup is rather simple: The engineers took a red and green laser pointer, wired in a 500Mbps data stream into each, and simply pointed them at photodiode receptors. On the receiving end, the signals are amplified and then multiplexed to create a 1Gbps data stream. The complete setup, according to New Scientist, cost just $600.
Yes, that’s a 1Gbps wireless network (around 100MB/sec, or about 10 times the speed of your 802.11n WiFi router), over distances of up to 25 meters, for $600. Not too shabby, especially when you consider that a commercial installation would probably cost a fraction of that. The bit error rate (BER) is also incredibly low: At 10 meters, just one bit per billion was erroneous; WiFi, by comparison, is fairly content with a BER of 1 in 100,000, or a packet error rate of 10%.
Will laser-based VLC actually find its way to market, then? There’s no getting around the fact that laser links are highly directional (even more so than the shoddy IrDA networks of yore), and atmospheric conditions will play a big part in the BER, and thus the actual data rate. With WiGig making its way to market, laser pointer VLC will probably never be seen by consumers. Still, for quick bursts of data between mobile devices, or wireless communications in hospitals, or simply as a fun hobby for amateur radio (?) operators, cheap, laser pointer VLC could be very useful indeed.
2011年9月13日 星期二
Power line expansion needs scrutiny now more than ever
An Electric Reliability Project.” They claim the line is necessary for reliability of our grid, and that PJM Interconnection — the grid operator — deemed the expansion necessary.
PJM operates the grid in New Jersey and 14 other eastern states, and is supposed to be an independent company charged with maintaining the grid’s reliability. In reality, however, PJM is a conglomerate of transmission line owners and power companies — like PSE&G — that generate electricity, mostly from coal-fired power plants to the west of New Jersey. Naturally, PJM is going to try to promote projects and policies that will generate income for their member corporations.
Recent studies by independent research firms — including ERPI and Synapse — have determined that consumer energy demand is falling, and will likely continue to fall or remain flat over the next decade. This drop in demand is not simply due to the depressed state of our current economy, but is more attributable to the efficiency of newer appliances and gadgets being introduced. New refrigerators use only 25 percent of the energy that they did years ago. LCD flat-screen TVs — despite their larger size — use less energy than older TVs. And increasing numbers of people are switching over to compact fluorescent and LED light bulbs.
Perhaps the largest contribution to decreased energy demand — especially during peak use periods — comes from “Demand Response,” a procedure where large energy consumers are paid to curtail energy use during times of high demand, essentially selling the unused surplus energy at a profit and reducing overall peak demand. Since Demand Response is used when transmission lines have the greatest potential to be overloaded — on really hot days with high peak demand — it alleviates most if not all of the need to build costly new transmission lines to cover peak usage, as the proposed Susquehanna-Roseland project is intended to do.
PJM operates the grid in New Jersey and 14 other eastern states, and is supposed to be an independent company charged with maintaining the grid’s reliability. In reality, however, PJM is a conglomerate of transmission line owners and power companies — like PSE&G — that generate electricity, mostly from coal-fired power plants to the west of New Jersey. Naturally, PJM is going to try to promote projects and policies that will generate income for their member corporations.
Recent studies by independent research firms — including ERPI and Synapse — have determined that consumer energy demand is falling, and will likely continue to fall or remain flat over the next decade. This drop in demand is not simply due to the depressed state of our current economy, but is more attributable to the efficiency of newer appliances and gadgets being introduced. New refrigerators use only 25 percent of the energy that they did years ago. LCD flat-screen TVs — despite their larger size — use less energy than older TVs. And increasing numbers of people are switching over to compact fluorescent and LED light bulbs.
Perhaps the largest contribution to decreased energy demand — especially during peak use periods — comes from “Demand Response,” a procedure where large energy consumers are paid to curtail energy use during times of high demand, essentially selling the unused surplus energy at a profit and reducing overall peak demand. Since Demand Response is used when transmission lines have the greatest potential to be overloaded — on really hot days with high peak demand — it alleviates most if not all of the need to build costly new transmission lines to cover peak usage, as the proposed Susquehanna-Roseland project is intended to do.
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