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I see that Cell phones help bridge the digital divide by providing internet access to less privileged teens. As with GPS , for a receiver the satellites are only visible for a part of their orbit, therefore multiple satellites are necessary to establish a permanent internet connection, with low Earth orbits needing more satellites than medium Earth orbits. Typically a completely clear line of sight between the dish and the satellite is required for the system to work optimally. What enables this transmission and reception in the payload transponders is a repeater subsystem RF radio frequency equipment used to change frequencies, filter, separate, amplify and group signals before routing them to their destination address on Earth. Other components of a satellite Internet system include a modem at the user end which links the user's network with the transceiver, and a centralized network operations center NOC for monitoring the entire system.

Table of Contents

Satellite Internet access

Each gateway provides a multiservice access network for subscriber terminal connections to the Internet. In the continental United States, because it is north of the equator, all gateway and subscriber dish antenna must have an unobstructed view of the southern sky.

Because of the satellite's geostationary orbit, the gateway antenna can stay pointed at a fixed position. For the customer-provided equipment i. PC and router to access the broadband satellite network, the customer must have additional physical components installed:.

At the far end of the outdoor unit is typically a small 2—3-foot diameter , reflective dish-type radio antenna. There are three physical characteristic settings used to ensure that the antenna is configured correctly at the satellite, which are: The combination of these settings gives the outdoor unit a L-O-S to the chosen satellite and makes data transmission possible.

These parameters are generally set at the time the equipment is installed, along with a beam assignment K a -band only ; these steps must all be taken prior to the actual activation of service. The main parts are:. The satellite modem serves as an interface between the outdoor unit and customer-provided equipment i. PC, router and controls satellite transmission and reception.

From the sending device computer, router, etc. It provides two types of connectivity:. Latency or 'ping time' as it is commonly referred to is the delay between requesting data and the receipt of a response, or in the case of one-way communication, between the actual moment of a signal's broadcast and the time it is received at its destination.

Typically, during perfect conditions, the physics involved in satellite communications account for approximately milliseconds of latency round trip time. The longer latency is the primary difference between a standard terrestrial-based network and a geostationary satellite-based network.

The round trip latency of a geostationary satellite communications network can be more than 12 times that of a terrestrial based network. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers.

Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay. If all other signaling delays could be eliminated, it still takes a radio signal about milliseconds ms , or about a quarter of a second, to travel to the satellite and back to the ground. For an Internet packet, that delay is doubled before a reply is received.

That is the theoretical minimum. Factoring in other normal delays from network sources gives a typical one-way connection latency of — ms from the user to the ISP, or about 1,—1, ms latency for the total round-trip time RTT back to the user. For geostationary satellites, there is no way to eliminate latency, but the problem can be somewhat mitigated in Internet communications with TCP acceleration features that shorten the apparent round trip time RTT per packet by splitting "spoofing" the feedback loop between the sender and the receiver.

Certain acceleration features are often present in recent technology developments embedded in satellite Internet equipment. Latency also impacts the initiation of secure Internet connections such as SSL which require the exchange of numerous pieces of data between web server and web client. Although these pieces of data are small, the multiple round trips involved in the handshake produce long delays compared to other forms of Internet connectivity, as documented by Stephen T.

Cobb in a report published by the Rural Mobile and Broadband Alliance. The functionality of live interactive access to a distant computer—such as virtual private networks should be thoroughly tested. Many TCP protocols were not designed to work in high latency environments. Unlike geostationary satellites, low and medium Earth orbit satellites do not stay in a fixed position in the sky. Consequently, ground based antennas cannot be easily locked into communication with any one specific satellite.

As with GPS , for a receiver the satellites are only visible for a part of their orbit, therefore multiple satellites are necessary to establish a permanent internet connection, with low Earth orbits needing more satellites than medium Earth orbits. The network has to switch data transfer between satellites to keep a connection to a customer.

A proposed alternative to relay satellites is a special-purpose solar-powered ultralight aircraft, which would fly along a circular path above a fixed ground location, operating under autonomous computer control at a height of approximately 20, meters.

One example of this was the United States Defense Advanced Research Projects Agency Vulture project, an ultralight aircraft which aimed to be capable of station-keeping over a fixed area for a period of up to five years, able to provide both continuous surveillance to ground assets as well as to provide extremely low latency communications networks. Onboard batteries would be charged during daylight hours by solar panels covering the wings, and would provide power to the plane during night.

Ground-based satellite dishes would relay signals to and from the aircraft, resulting in a greatly reduced round-trip signal latency of only 0.

The planes could potentially run for long periods without refueling. Several such schemes involving various types of aircraft have been proposed in the past.

Satellite communications are affected by moisture and various forms of precipitation such as rain or snow in the signal path between end users or ground stations and the satellite being utilized.

This interference with the signal is known as rain fade. The effects are less pronounced on the lower frequency 'L' and 'C' bands, but can become quite severe on the higher frequency 'Ku' and 'Ka' band.

The amount of time during which service is lost can be reduced by increasing the size of the satellite communication dish so as to gather more of the satellite signal on the downlink and also to provide a stronger signal on the uplink. Modern consumer-grade dish antennas tend to be fairly small, which reduces the rain margin or increases the required satellite downlink power and cost.

However, it is often more economical to build a more expensive satellite and smaller, less expensive consumer antennas than to increase the consumer antenna size to reduce the satellite cost.

Large commercial dishes of 3. Alternately, larger aperture antennae can require less power from the satellite to achieve acceptable performance. Satellites typically use photovoltaic solar power, so there is no expense for the energy itself, but a more powerful satellite will require larger, more powerful solar panels and electronics, often including a larger transmitting antenna.

The larger satellite components not only increase materials costs but also increase the weight of the satellite, and in general, the cost to launch a satellite into an orbit is directly proportional to its weight. In addition, since satellite launch vehicles [i.

Modulated carriers can be dynamically altered in response to rain problems or other link impairments using a process called adaptive coding and modulation, or "ACM". ACM allows the bit rates to be increased substantially during normal clear sky conditions, increasing the number of bits per Hz transmitted, and thus reducing overall cost per bit. Adaptive coding requires some sort of a return or feedback channel which can be via any available means, satellite or terrestrial.

An object is in your line of sight if you can draw a straight line between yourself and the object without any interference, such as a mountain or a bend in a road. An object beyond the horizon is below the line of sight and, therefore, can be difficult to communicate with. Typically a completely clear line of sight between the dish and the satellite is required for the system to work optimally.

In addition to the signal being susceptible to absorption and scattering by moisture, the signal is similarly impacted by the presence of trees and other vegetation in the path of the signal. A dish installation in the winter must factor in plant foliage growth that will appear in the spring and summer. Even if there is a direct line of sight between the transmitting and receiving antenna, reflections from objects near the path of the signal can decrease apparent signal power through phase cancellations.

Whether and how much signal is lost from a reflection is determined by the location of the object in the Fresnel zone of the antennas. Home or consumer grade two-way satellite Internet service involves both sending and receiving data from a remote very-small-aperture terminal VSAT via satellite to a hub telecommunications port teleport , which then relays data via the terrestrial Internet. The satellite dish at each location must be precisely pointed to avoid interference with other satellites.

At each VSAT site the uplink frequency, bit rate and power must be accurately set, under control of the service provider hub. Such systems are frequently marketed as "satellite broadband" and can cost two to three times as much per month as land-based systems such as ADSL. The modems required for this service are often proprietary, but some are compatible with several different providers.

These types of system are generally unsuitable for use on moving vehicles, although some dishes may be fitted to an automatic pan and tilt mechanism to continuously re-align the dish—but these are more expensive. Consumer satellite Internet customers range from individual home users with one PC to large remote business sites with several hundred PCs.

Home users tend to use shared satellite capacity to reduce the cost, while still allowing high peak bit rates when congestion is absent. There are usually restrictive time-based bandwidth allowances so that each user gets their fair share, according to their payment.

When a user exceeds their allowance, the company may slow down their access, deprioritise their traffic or charge for the excess bandwidth used. The uplink direction for shared user customers is normally time division multiple access TDMA , which involves transmitting occasional short packet bursts in between other users similar to how a cellular phone shares a cell tower.

Each remote location may also be equipped with a telephone modem; the connections for this are as with a conventional dial-up ISP. Two-way satellite systems may sometimes use the modem channel in both directions for data where latency is more important than bandwidth, reserving the satellite channel for download data where bandwidth is more important than latency, such as for file transfers.

In , the European Commission sponsored the UNIC project which aims at developing an end-to-end scientific test bed for the distribution of new broadband interactive TV-centric services delivered over low-cost two-way satellite to actual end-users in the home. Normal VSAT dishes 1. A voice call is sent by means of packets via the satellite and Internet. Using coding and compression techniques the bit rate needed per call is only These usually come in the shape of a self-contained flat rectangular box that needs to be pointed in the general direction of the satellite—unlike VSAT the alignment need not be very precise and the modems have built in signal strength meters to help the user align the device properly.

Some also have an integrated Bluetooth transceiver and double as a satellite phone. The modems also tend to have their own batteries so they can be connected to a laptop without draining its battery. For many years [ when? Due to the low bandwidths involved it is extremely slow to browse the web with such a connection, but useful for sending email, Secure Shell data and using other low-bandwidth protocols.

Since satellite phones tend to have omnidirectional antennas no alignment is required as long as there is a line of sight between the phone and the satellite. One-way terrestrial return satellite Internet systems are used with conventional dial-up Internet access , with outbound upstream data traveling through a telephone modem , but downstream data sent via satellite at a higher rate. The transmitting station has two components, consisting of a high speed Internet connection to serve many customers at once, and the satellite uplink to broadcast requested data to the customers.

The ISP's routers connect to proxy servers which can enforce quality of service QoS bandwidth limits and guarantees for each customer's traffic. Often, nonstandard IP stacks are used to address the latency and asymmetry problems of the satellite connection.

As with one-way receive systems, data sent over the satellite link is generally also encrypted, as otherwise it would be accessible to anyone with a satellite receiver. Many IP-over-satellite implementations use paired proxy servers at both endpoints so that certain communications between clients and servers [32] need not to accept the latency inherent in a satellite connection.

For similar reasons, there exist special Virtual private network VPN implementations designed for use over satellite links because standard VPN software cannot handle the long packet travel times. Upload speeds are limited by the user's dial-up modem, while download speeds can be very fast compared to dial-up, using the modem only as the control channel for packet acknowledgement. Latency is still high, although lower than full two-way geostationary satellite Internet, since only half of the data path is via satellite, the other half being via the terrestrial channel.

One-way broadcast satellite Internet systems are used for Internet Protocol IP broadcast -based data, audio and video distribution. Those with unlimited voice and texting plans are more likely to call others daily or more often for almost every reason we queried — to call and check in with someone, to coordinate meeting, to talk about school work or have long personal conversations. Teens with unlimited texting typically send and receive 70 texts per day, compared with 10 texts a day for teens on limited plans and 5 texts a day for teens who pay per message.

A relatively small number of teens have sent and received sexually suggestive images by text:. More details about cell phone use among teens and distracted driving maybe found in our earlier report Teens and Distracted Driving. Forthcoming from the Pew Hispanic Center, a sister project to the Pew Internet Project, is a new report about the ways young Latinos, ages 16 to 25, communicate with each other.

This report will contain results based on a national survey of Hispanics conducted in the fall of Over 1, young Latinos were asked about the ways they communicate with each other, whether through text messaging, face-to-face contact, email or social network sites.

About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world.

It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts. Text messaging explodes as teens embrace it as the centerpiece of their communication strategies with friends. Half of teens send 50 or more text messages a day, or 1, texts a month, and one in three send more than texts a day, or more than 3, texts a month.

Boys typically send and receive 30 texts a day; girls typically send and receive 80 messages per day. Teen texters ages typically send and receive 20 texts a day.

Older girls who text are the most active, with year-old girls typically sending or more messages a day or more than 3, texts a month. However, while many teens are avid texters, a substantial minority are not.

Girls more fully embrace most aspects of cell phone-based communication. Girls typically send and receive 80 texts a day; boys send and receive Teens whose parents limit their texting are also less likely to report being passengers in cars where the driver texted behind the wheel or used the phone in a dangerous manner while driving.

The most popular are taking and sharing pictures and playing music: The majority of teens are on family plans where someone else foots the bill. The difference lies in the question wording. For this question, we asked about teens texting friends, but we did not specify the platform computer, cell phone on which the texting was taking place. Please see K9c and K20a in our questionnaire for exact question wording. Table of Contents Overview Text messaging explodes as teens embrace it as the centerpiece of their communication strategies with friends.

Why study mobile phones? The basics of how teens acquire and use mobile phones Chapter Two: How phones are used with friends - What they can do and how teens use them Chapter Three: Attitudes towards cell phones Chapter Four: Related Uncategorized Mar 19, Uncategorized Sep 2, Uncategorized May 3, Uncategorized Dec 15, Uncategorized Nov 16,

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