You can see such symmetry breaking in a once-common 20th century technology: the two-wire ribbons used during television’s first few decades to send RF signals from rooftop VHF antennas to television sets without any loss. The electric RF current in the two conductors flow in opposite directions and have opposite phase. Because of the translational symmetry (the two conductors are parallel) the radiation fields cancel each other out, so there is no net radiation into space. But if you would flare the ends of the two conductors at one end of the ribbon, they aren’t parallel anymore and you break the translational symmetry. The two electric fields are no longer aligned and don’t cancel each other out, causing the RF signal to be converted into electromagnetic radiation.
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Perlman says pCell takes a different approach: it embraces signal interference. In his vision, base stations smaller than your typical satellite TV antenna are placed wherever it’s convenient (such as on the roof or the side of a building), and their signals purposely overlap. Those overlapping signals, Perlman says, combine constructively to create a sort of personal cell, a centimeter in diameter, that moves with you as you move around the network. The signal doesn’t diminish as each additional user joins the network. Overall capacity can grow by adding more access points.
Through a series of microwave towers, the dish beams market data 734 miles to the Chicago Mercantile Exchange’s computer warehouse in Aurora, Ill., in 4.13 milliseconds, or about 95% of the theoretical speed of light, according to the company.
Fiber-optic cables, which are made up of long strands of glass, carry data at roughly 65% of light speed.
I found this paper very useful.
Wireless sensor networks promise fine-grain monitoring in a wide variety of environments. Many of these environments (e.g., indoor environments or habitats) can be harsh for wireless communication. From a networking perspective, the most basic aspect of wireless communication is the packet delivery performance: the spatio-temporal characteristics of packet loss, and its environmental dependence.
These factors will deeply impact the performance of data acquisition from these networks.
In this paper, we report on a systematic medium-scale (up to sixty nodes) measurement of packet delivery in three different environments: an indoor office building, a habitat with moderate foliage, and an open parking lot. Our findings have interesting implications for the design and evaluation of routing and medium-access protocols for sensor networks.
Patch antennas focus the radio beam within a specific area. (A couple of vendors, Ruckus Wireless and Xirrus, have developed their own built-in “smart” antennas that adjust and focus Wi-Fi signals on clients.) Depending on the beamwidth, the effect can be that of a floodlight or a spotlight, says Jeff Lime, Ventev’s vice president. Ventev’s newest TerraWave High-Density products focus the radio beam within narrower ranges than some competing products, and offer higher gain (in effect putting more oomph into the signal to drive it further), he says.
At Georgia Tech, each antenna focused the Wi-Fi signal from a specific overhead access point to cover a section of seats below it. Fewer users associate with each access point. The result is a kind of virtuous circle. “It gives more capacity per user, so more bandwidth, so a better user experience,” says Lime.
“In that demonstration, the LEDs, touch sensors, microcontrollers, and the wireless communication are all powered by those ambient TV signals,” says Gollakota.
There are a lot more channels on OTA ever since they went digital and added all sorts of sub-channels.
Current phones generally use only one antenna taking one stream of data at a time. LTE Advanced devices will also need more energy storage to do the necessary onboard computation. Without new breakthroughs in batteries or reductions in power consumption by other means (see “Efficiency Breakthrough Promises Smartphones that use Half the Power”), phones will simply get larger.
via For superfast 4G LTE Advanced smartphone and tablet connections, AT&T, Verizon, Sprint, T-Mobile plan new network tests, and rollouts use chipsets from Qualcomm and others | MIT Technology Review.
Will ubiquitous mobile data bring down its cost for low bandwidth users? We shall see.
The only thing my boss said to me was, ‘Chip, the only thing that has to work is the cell phones.’”
That’s why stadiums across the country are partnering with cellular carriers to build Distributed Antenna Systems, or DAS. These are essentially a bunch of antennas spread throughout a building to make sure phones don’t lose their connections to the cellular network when fans walk in the door. But it’s not just phone calls and text messages filling up wireless networks during games. Fans are streaming video, whether from third-party sources or apps created by the home teams to provide replays, different camera angles, or action happening in other cities. Teams are concluding that cellular just isn’t enough, and are thus building WiFi networks to offload traffic from cellular and provide connections to devices that are WiFi-only.
Distributed Antenna Systems connect to the service provider’s network either with a bi-directional amplifier, which uses an outdoor antenna to bring the cellular signal into the building, or a base transceiver station, which is installed inside and is the same type of radio used at cell sites, as explained by the Steel In The Air cellular consultancy. Signals are then distributed throughout the facility with a series of hubs, cables, and antennas.