When the cloud computing software was first introduced, the said issues became a hot debate. Therefore, to prove its capabilities, the technologists in the Information Technology industry tested the software. It’s no surprise that the system was proven to be reliable. The features allow the users to have that much-needed security which would protect their confidential details stored in the system.

One of the biggest benefits of using the said software is the powerful security system. It has a different approach when it comes to authorizing and verifying each and every system access attempts. All kinds of viruses and malicious wares will have a hard time penetrating the database. More so, hackers would also find it difficult to get the personal and classified details. The authorization system is just too firm to be infiltrated.

But that’s not all. By using the cloud computing software, you will also help optimize the performance of your computer as well. No matter how well your computer performs, the software will adapt itself to ensure that the operation will be better and faster. It would only take a few minutes before the program is fully installed in your system

-Gateway

-Gateway model of laptop

This is interesting…If you own a dell notebook battery and wanting to invest in a “genuine” Dell battery, and you go to DELL’s official web website only to discover that they offer you you non DELL brand batteries.What? How can this be? Funny uh? The story is, they don’t want you to invest in batteries, they want you to acquire a NEW mobile computer! That is why they have really limited support and supplies for individuals accessories, even though their speed of generating new laptop computer personal computer models out of the factory is super.
Now you know why.

Regardless of whether you have a HP Pavilion DV2000 Battery or a cool Apple Macbook Battery or a magsafe adapter, please, please, please, I beg of you, do not hesitate to use an aftermarket battery as long as the seller presents a fantastic return policy and quite excellent warranty on their Notebook Batteries and Adapters. Like a 1 year warranty. You will come across that you will pay 1/2 or 1/3 of the OEM costs, and get a fantastic Notebook battery or Adapter for as lengthy as the OEM counterparts, that’s excellent sufficient for me. Why pay far more for a high quality laptop battery for your HP Pavilion DV2000 battery#maintain# or other if you don’t will need to? one of

Laptop has become an inseparable part of your life. Be it a business executive, a student or even a house maker, they require computer and the Internet for information regarding so many things. And since laptop is used so often it is bound to show some side effects. It might go white screen while running and you cannot do absolutely anything about it. You would have to rush to your laptop service station or speak to the technical support group of your laptops brand. Only they can help you out and give a resolution through laptop screen repair service.

It is the problem of the connection on the mother board to the video controller if the laptop computer screen goes completely blank. The monitor is generally connected with pushes into a socket via a ribbon cable. See whether the ribbon cable is connected completely. Also the ribbon cable may be loosely connected to the monitor so you should check that also. If you didn’t find any problem in any of these then there might be the monitors’ internal problem and it should be replaced.

Prima facie, you need to check if laptop screen is broken physically, then you must replace it. It is just a matter of removing ribbon cable and set of screws to take out the screen. From a number of various resources you can find online the replacement screen. See that all the screws are kept back in the right locations and the ribbon cable is properly replaced. Above all if you feel uncomfortable with your own laptop screen or you may find that there is a big problem than just with the screen then you can consult a professional laptop screen repair company. It is always suggested to go for Repair Company rather than repairing it by your own as laptops are the fragile objects.

If the screen is physically damaged then it is better to replace generally or sell them for parts since the cost for repairing the old laptop may not be worth it. The hardware problems like the damage to the screen of laptop or malfunctioning of the screen are the general issues of the laptop owners. As they are very delicate pieces they should be handled by a well trained technical person. There are many laptop repairing companies that give you the best services. You can get your PC repaired in very less time. Choose a best repairing company by seeing in the Internet the appropriate one.

Laptops screens are very delicate. In order to avoid laptop screen repair expert visit, you just need to follow this – HANDLE WITH CARE.

Once you insert that new location, the GPS system is going to calculate and choose the best available route. At the end of this process, it is going to highlight the route you need to follow. Additionally, it will also show you the coordinates. While you drive your car, the system will dictate how you can arrive to the new destination. Even more, in some emergencies such as if your car is stolen, the GPS systems for cars are very useful as thanks to them the police can easily locate your car and recover it. Besides this, the GPS system can be set to notify the authorities about the location of the vehicle, in case that your car is part of an accident, stating that it is an emergency.

Additionally, the GPS systems for cars can notify the right persons, including your family members, when an accident occurs. This thing considerable increases the chance of survival of those implied in the accident. As well, some other devices work together with the GPS systems to lock and unlock the doors, to find the vehicle by using your flashlight if you forgot where you have parked it and diagnose different problems the vehicle might have such as system overheating, direction dysfunctions and others. Besides all these, the GPS systems are of great help in different business applications, which makes them almost indispensable for businesspersons; this is one more reason why the GPS systems are so popular.

Some of the business applications that can be taken care of by the GPS systems for cars are related to large transport companies which own numerous cars. By using the GPS systems, these companies can easily locate their cars, thing that ensures the updating of the delivery information and other important elements which are important for the control center. Besides this, the GPS systems help the drivers to follow specific routes without encountering any issues related to the route accuracy. Being connected to satellites, the systems provide the latest information about specific routes which is of great help whenever drivers encounter situations such as closed roads are. Currently, the GPS systems are the ones who can transfer different information related to cars and maps to the computer systems and it seems that this is only the beginning of a new era in high technology applications.

Inside World of a Computer Hardware
A puzzling collection of data cables and power cords would be visible inside the computer hardware, but you must be able to see some of the most important and widely known parts such as the following:
• System boards or the mother board consisting of the CPU and the accompanying microchip, a coprocessor, system clock, random access memory, power supply connections, jumpers and dip switches and ports. The system board is the most intricate part of the computer hardware where most of the activity takes place. It’s very much like the brain with which all the devices in the computer need to communicate somehow. A system board manages the performance of all other devices which are connected to it, either internally or externally.

Storage Devices
The storage devices inside a CPU are either primary storage devices or secondary storage devices. The primary storage devices help the CPU to process data or commands by holding the information provisionally. They are therefore, temporary storage devices and the memory they hold is known as volatile memory.

The most general type of primary storage devices are the memory chips which could hold either random access memory (RAM) or cache memory or both. If cache memory is stored on the system board, it’s known as COAST (cache on a stick).
In contrast to primary storage devices, the data which is stored in secondary storage devices is more permanent. It means it can hold the information even when the computer has been switched off and would remain so until some external agent or device physically removes the data. Another major difference is while the CPU could process the information stored in the primary storage devices directly, it cannot do so with the being stored in the secondary storage devices.

Choosing Lytec medical billing software gives you many great options and features with the software. With Lytec you can choose to have up to 3 computers with multiple users if you have a larger practice. The medical billing software from Complete Medical Billing is great because it offers several different programs at affordable prices. Lytec has many great qualities about their software and once you choose to use it, you’ll never want to switch again. The quality of your practice will improve and you’ll notice that your office will run smoother and more efficiently too. Try it and see the difference it can make.

Great Coding Tools: Lytec

With the awesome Lytec medical billing software available from Complete Medical Billing, you can choose to have great features like the encoder pro. With this tool, you can bill insurances with the most up to date and correct codes available so you can have fewer rejections. Billing insurance companies is one of the most important parts of your office work and it is important that it is done as accurately as possible. When you use Lytec you can be sure that you are using the tools that will help your practice be as successful as it can be with the most ease possible!

Bundle a Package: Lytec

When you are choosing what medical billing software to use, Lytec is one of the best. It combines great software with awesome features and the best part is, is that you can get whatever you want put together in a bundle pack. Complete Medical Billing offers great packages at great prices and you can add additional features to your package if you like. You can add things like a hands on training seminar or a support package or an advanced reports option. When you choose to purchase these all at once in a bundle, you can get them at a slightly discounted rate.

Introduction

Advances in technology have significantly influenced in the blind and low vision individuals. Over the past 20th year improvement in computer has allowed for readily access to VI. Today a large percentage of students with VI spend over 80% of their school days in general educational classroom. Student with very severe visual impairment may need to learn read and write using different methods. Braille is a coded system of dots embossed on paper, so that individuals can feel a page of text. Braille is use for different type of reading such as Maths, and Music. Now seen fewer people are using Braille as a reading method today. First reason is that Braille method is slow. According to Tuttle and Ferrell (1995) reported that good Braille reader achieve a rate of only 100 words per minutes. Nolan (1967) found that average high school students who is blind reads even fewer words per minutes.

Can you think of some other reason, Why Braille is less popular today? The first reason is that the teachers don’t know how to use or teach the Braille and unavailability of the experts. Another reason is increasing availability of audio tape, immediate computerized print to voice translation difficulty of getting Braille version of books. Braille literacy has become focus of a great debate. Advanced technology is a reason for its unpopularity.

VIBUG (Visually Impaired Blind User Group), the Boston Computer Society are exchanging information to expand computer literacy among person with visual impairment. Gaining access of technology and the assistive device designed to minimize the effect of their disability. These exciting technological advances open up a new world for people with severe visual impairment. Technological aids categorized under three heads.

Technological Aids

Visual aids Audio aids Tactile aids

CCTV Talking books                                       Emboss material

Microcomputer                        Record player                                     Perkins Brailler

OHP                                         Compact disk                                        Braille Printer

Audio cassettes

Telephone

Mobile

Karzweil Reader

Audiodescreption

Community Radio

CCTV – It can be used to enlarge the print found in printed texts and books.

Microcomputer – Using special word processing program can produce large print display that allow person with low vision.

Kurzweil Reader – One of the first computerized systems designed for people with visual impairments that translate print into synthesized speech.

Audiodescription – A technique in which trained narrators describe visual and nonverbal information during the pause in the audio or scripted dialogue of plays, films and TV shows by using FM transmission or extra sound track available on stereo TV.

Talking Books – A books available in auditory format.

Braille – A system of reading and writing that uses dot codes that are embossed on paper, developed by Louis Braille in 1929.

Perkins Brailler – It is a compact and portable machine that uses keys that, when pressed down, emboss special paper with the Braille code.

Braille Printer – A special designed Braille printer is attached to a micro computer, standard text can be translated into Braille, allowing teacher who does not know how to use Braille to produce Braille copies of handouts, tests, maps, charts and other class materials

Community Radio – It is a recent development in the technology.( Sakal Newspaper Published news on 23 March 2010)  conducted  exam of VI students with the help of community Radio. It is a great contribution of Vidyavani section – Advanced Educational lab for Blind of University of Pune, in the area of special education and especially for VI

Assistive Educational divice

Punani and Rawal (2000) have classified assistive educational device into eight categories. These are as follow.–

Braille duplicators and writer
Writing device
Braille paper
Talking books and tape recorders
Reading machines
Braille computers
Mathematical devices
Geography and Science devices

In addition there are also devices for children with low vision. Some of these devices are:

Spectacles, microscopes, telescopes, hand and magnifiers, visors, good contrast, reading writing stands, black pens, exercise book with dark lines, use of bright colours where needed, large print books, magnifying glass, computer, etc.

Use of technology for VI

Students with very severe visually impaired may need to learn read and write.
Immediate computerized print to voice and voice to print translation of document.
Many low vision students they can read a specially adapted version of the text.
Greater and easier access to classroom material for student with severe visual impairment
Benefits from improving their listening skills.
Independent learning is possible.
Increase the confidence level and minimize the effect of disability.
Enhanced participation in recreational and leisure activities.

Availability of technology and assistive educational devices is important for VI person is no doubt, but now the question is raised in mind that, what is the duty of teacher? How they know about technology? Are they interested to get knowledge about technology? Will they are aware about technology or not?

To find out this curious view point the researcher took following study:

Title: – : Teacher’s awareness about the availability and use of technology  for visually impaired : a study.

Purpose of the study: - The present study explores the teacher awareness about the technology and its use for VI.
Objective of the study: – To find out the technology awareness among teacher of VI.
Delimitation of the study:-

1)      This study is limited to technology which is available for VI

2)      This study is limited to teachers who teach the VI students at primary and secondary level.

Significance of the study:-

1)      The present study may provide the information to teachers of VI regarding the     technological facility which is useful for VI.

2)      The study creates awareness in teacher of VI to know the available technology for VI. If teachers aware about technology they will try to get the knowledge. Many NGO’s can take part to arrange training program for teacher to give the knowledge of technology. The study may give great contribution to generate knowledge and useful for VI.

Research method

This is a descriptive research and a survey method was used.

Population

All teachers who teach in special school and integrated school set up in Pune district.

Sample

23 teachers who teach at primary and secondary level from special school and integrated school were selected.

A purposive sample method was used.

Data gathering tool and technique

To understand the awareness about technology, the researcher constructed the questionnaire. The researcher used open and close ended question to get maximum information from teacher.

Analysis of Data

Table no: 01

Technology available in school

Braille Printer

Screen reader

Graphical Embosser

Instant book reader

Karzweil Reader

CCTV TTI

Others

Responses

Yes

Yes

Yes

No

No

Yes

—-

Observation & Interpretation Table No.1 revealed that Braille Printer, Screen reader, CCTV TTI, Graphical Embosser are available in school but Karzweil Reader, Instant book reader are not available in school. Out of these technological aids, no others aids are available in school. Teachers have not responded the others.

Table no: 02

Knowledge about Technology

Response

Braille Printer

Screen reader

Graphical Embosser

Instant book reader

Karzweil Reader

CCTV TTI

Yes

21

18

13

6

9

14

PERCENT

91%

78%

57%

26%

39%

61%

No

2

5

10

17

14

9

PERCENT

9%

22%

43%

74%

61%

39%

Observation & Interpretation

Table No.-2 shows that the teachers have very well knowledge about technology. As compare to others aids teachers have minimum knowledge aboutInstant book reader andKarzweil Reader because of unavailability of aids in school

. Table no: 03

Technology use in teaching

Response

Braille Printer

Screen reader

Graphical Embosser

Instant book reader

Karzweil Reader

CCTV TTI

Yes

11

07

4

00

00

2

PERCENT

48%

30%

17%

00%

00%

9%

No

12

16

19

23

23

21

PERCENT

52%

70%

83%

100%

!00%

91%

Observation & Interpretation

Table No.-3 indicates that a few teachers are use technology in their teaching. Only 9% teachers use CCTV for VI because the electricity problem and inconvenience about use.

Table no: 04

Provide training program aboutTechnology

Response

Frequency

Percent

Yes

5

22%

No

18%

78%

Total

23

100%

Observation & Interpretation

Table No.4 highlighted very high percent (78%) teachers said that no any training program arrange about the technology for them.

Table No. 5

Need of training Program

Response

Frequency

Percent

Yes

23

100%

No

00

00%

Total

23

100

Observation & Interpretation

Table No.5 indicates that (100%) all teacher have need a training program about technology and how its use. The program should organize for VI students.

Table no: 06

Need of training Program from which level

Response

Frequency

Percent

primary

22

96%

Secondary

1

4%

Higher secondary

00

00%

Total

23

100

Observation & Interpretation

Table No.6 indicates that (96%) teachers are said that the training program should be arranged from the primary level.

Statement: – What is your opinion about the technology? It is really useful for VI students or not?

Responses:-

Technology is really good and it is very useful for person who can not see.
Because of technology, student can learn independently without any supporter
For the easy interaction with normal children
Increase their reading, and listening skills
It is a powerful learning resource for them through which they can progress and fight in today’s world.

Statement: – Why you are not use technology?

Responses

Technology is not available in school
It is available but we do not have knowledge about technology.
Financially it is not affordable for school.

CONCLUSION

Technology is available in school. Karzweil Reader and instant book reader is not available in school. Most of the teachers have the knowledge about technology.
In case of the awareness about technology the study found that the teachers are better aware about the technology.
All (100%) teachers wanted a special training program about technology, through which they will get sufficient knowledge

REFERANCES

Encyclopedia of Indian Education, Volume I ( A-K ), J. S. Rajput, NCERT.
Encyclopedia of Indian Education, Volume II ( A-K ), J. S. Rajput, NCERT. 1st edition April, 2004.
The international encyclopedia of Education ,Research and Studies, Torsten, Husen, T Neville Postle thwattb, Volume IX T.2, Pergaman press, Oxford New york. Toronto 1985.
Doing Research in the Real world, second edi . David Gray. Sage Publication.2009
Educational research, eigth edi,Gay, Mills,Airasian. Pearson Merill Prentice hall ,2006

The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed/direction, and time.

Developed by the United States Department of Defense, it is officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by Mr. John Walsh, a key decision maker when it came to the budget for the GPS program[1]). The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year,[2] including the replacement of aging satellites, and research and development. Despite these costs, GPS is free for civilian use as a public good.

GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.

Simplified method of operation

A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS microwave signal gives the distance to each satellite, since the signal travels at a known speed – the speed of light. These signals also carry information about the satellites’ location and general system health (known as almanac and ephemeris data). By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration.[3] Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites, using their atomic clocks to correct the receiver’s own clock error.

[edit] Technical description

Unlaunched GPS satellite on display at the San Diego Aerospace museum

Unlaunched GPS satellite on display at the San Diego Aerospace museum

[edit] System segmentation

The current GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US).[4]

[edit] Space segment

The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS design calls for 24 SVs to be distributed equally among six circular orbital planes.[5] The orbital planes are centered on the Earth, not rotating with respect to the distant stars.[6] The six planes have approximately 55° inclination (tilt relative to Earth’s equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit’s intersection).[2]

Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day, so it passes over the same location on Earth once each day. The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth’s surface.[7]

As of September 2007, there are 31 actively broadcasting satellites in the GPS constellation. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.[8]

[edit] Control segment

The flight paths of the satellites are tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA).[9] The tracking information is sent to the Air Force Space Command’s master control station at Schriever Air Force Base in Colorado Springs, which is operated by the 2d Space Operations Squadron (2 SOPS) of the United States Air Force (USAF). 2 SOPS contacts each GPS satellite regularly with a navigational update (using the ground antennas at Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs). These updates synchronize the atomic clocks on board the satellites to within one microsecond and adjust the ephemeris of each satellite’s internal orbital model. The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.[10]

GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).

GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).

[edit] User segment

The user’s GPS receiver is the user segment (US) of the GPS system. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2006, receivers typically have between twelve and twenty channels.

A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.

A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.

GPS receivers may include an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of a RS-232 port at 4,800 bit/s speed. Data are actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data. As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers.

Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol. NMEA 2000[11] is a newer and less widely adopted protocol. Both are proprietary and controlled by the US-based National Marine Electronics Association. References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws. Other proprietary protocols exist as well, such as the SiRF and MTK protocols. Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth.

[edit] Navigation signals

Main article: GPS signals

GPS broadcast signal

GPS broadcast signal

Each GPS satellite continuously broadcasts a Navigation Message at 50 bit/s giving the time-of-day, GPS week number and satellite health information (all transmitted in the first part of the message), an ephemeris (transmitted in the second part of the message) and an almanac (later part of the message). The ephemeris data gives the satellite’s own precise orbit and is output over 18 seconds, repeating every 30 seconds. The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for 6 hour time-outs. The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate. The almanac consists of coarse orbit and status information for each satellite in the constellation and takes 12 seconds for each satellite present, with information for a new satellite being transmitted every 30 seconds (15.5 minutes for 31 satellites). The purpose of the data is to assist in the acquisition of satellites at power-up by allowing the receiver to generate a list of visible satellites based on stored position and time, while an ephemeris from each satellite is needed to compute position fixes using that satellite. In older hardware, lack of an almanac in a new receiver would cause long delays before providing a valid position, because the search for each satellite was a slow process. Advances in hardware have made the acquisition process much faster, so not having an almanac is no longer an issue. An important thing to note about navigation data is that each satellite transmits only its own ephemeris, but transmits an almanac for all satellites.

Each satellite transmits its navigation message with at least two distinct spread spectrum codes: the Coarse / Acquisition (C/A) code, which is freely available to the public, and the Precise (P) code, which is usually encrypted and reserved for military applications. The C/A code is a 1,023 chip pseudo-random (PRN) code at 1.023 million chips/sec so that it repeats every millisecond. Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency. The P-code is a 10.23 megachip/sec PRN code that repeats only every week. When the “anti-spoofing” mode is on, as it is in normal operation, the P code is encrypted by the Y-code to produce the P(Y) code, which can only be decrypted by units with a valid decryption key. Both the C/A and P(Y) codes impart the precise time-of-day to the user. Frequencies used by GPS include

* L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites.

* L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites.

* L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events. Used to enforce nuclear test ban treaties.

* L4 (1379.913 MHz): Being studied for additional ionospheric correction.

* L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization). This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. The first Block IIF satellite that would provide this signal is set to be launched in 2008.

[edit] Calculating positions

[edit] Using the C/A code

To start off, the receiver picks which C/A codes to listen for by PRN number, based on the almanac information it has previously acquired. As it detects each satellite’s signal, it identifies it by its distinct C/A code pattern, then measures the time delay for each satellite. To do this, the receiver produces an identical C/A sequence using the same seed number as the satellite. By lining up the two sequences, the receiver can measure the delay and calculate the distance to the satellite, called the pseudorange[12].

Overlapping pseudoranges, represented as curves, are modified to yield the probable position

Overlapping pseudoranges, represented as curves, are modified to yield the probable position

Next, the orbital position data, or ephemeris, from the Navigation Message is then downloaded to calculate the satellite’s precise position. A more-sensitive receiver will potentially acquire the ephemeris data quicker than a less-sensitive receiver, especially in a noisy environment.[13] Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it. Receivers can substitute altitude for one satellite, which the GPS receiver translates to a pseudorange measured from the center of the earth.

Locations are calculated not in three-dimensional space, but in four-dimensional spacetime, meaning a measure of the precise time-of-day is very important. The measured pseudoranges from four satellites have already been determined with the receiver’s internal clock, and thus have an unknown amount of clock error. (The clock error or actual time does not matter in the initial pseudorange calculation, because that is based on how much time has passed between reception of each of the signals.[clarify][citation needed]) The four-dimensional point that is equidistant from the pseudoranges is calculated as a guess as to the receiver’s location, and the factor used to adjust those pseudoranges to intersect at that four-dimensional point gives a guess as to the receiver’s clock offset. With each guess, a geometric dilution of precision (GDOP) vector is calculated, based on the relative sky positions of the satellites used. As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more guesses to the location and clock offset. The receiver then determines which combinations to use and how to calculate the estimated position by determining the weighted average of these positions and clock offsets. After the final location and time are calculated, the location is expressed in a specific coordinate system, e.g. latitude/longitude, using the WGS 84 geodetic datum or a local system specific to a country.

[edit] Using the P(Y) code

Calculating a position with the P(Y) signal is generally similar in concept, assuming one can decrypt it. The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite.[citation needed] In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators. RAIM features do not protect against spoofing, since RAIM only checks the signals from a navigational perspective.

[edit] Accuracy and error sources

The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal. The position accuracy is primarily dependent on the satellite position and signal delay.

To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version. By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about 1% of a bit time, or approximately 10 nanoseconds for the C/A code. Since GPS signals propagate nearly at the speed of light, this represents an error of about 3 meters. This is the minimum error possible using only the GPS C/A signal.

Position accuracy can be improved by using the higher-chiprate P(Y) signal. Assuming the same 1% bit time accuracy, the high frequency P(Y) signal results in an accuracy of about 30 centimeters.

Electronics errors are one of several accuracy-degrading effects outlined in the table below. When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft). These effects also reduce the more precise P(Y) code’s accuracy.

Sources of User Equivalent Range Errors (UERE) Source Effect

Ionospheric effects ± 5 meter

Ephemeris errors ± 2.5 meter

Satellite clock errors ± 2 meter

Multipath distortion ± 1 meter

Tropospheric effects ± 0.5 meter

Numerical errors ± 1 meter

[edit] Atmospheric effects

Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth’s atmosphere and ionosphere. Correcting these errors is a significant challenge to improving GPS position accuracy. These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the signal is affected for a longer time. Once the receiver’s approximate location is known, a mathematical model can be used to estimate and compensate for these errors.

Because ionospheric delay affects the speed of microwave signals differently based on frequency—a characteristic known as dispersion—both frequency bands can be used to help reduce this error. Some military and expensive survey-grade civilian receivers compare the different delays in the L1 and L2 frequencies to measure atmospheric dispersion, and apply a more precise correction. This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code. To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2C, was added to the Block IIR-M satellites, which was first launched in 2005. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.

The effects of the ionosphere generally change slowly, and can be averaged over time. The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1 only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random number (PRN), so only one antenna and receiver are required.

Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere. This effect is both more localized and changes more quickly than ionospheric effects and is not frequency dependent. These traits making precise measurement and compensation of humidity errors more difficult than ionospheric effects.

Changes in altitude also change the amount of delay due to the signal passing through less of the atmosphere at higher elevations. Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct.

[edit] Multipath effects

GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc. These delayed signals can cause inaccuracy. A variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. For long delay multipath, the receiver itself can recognize the wayward signal and discard it. To address shorter delay multipath from the signal reflecting off the ground, specialized antennas may be used to reduce the signal power as received by the antenna. Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay.

Multipath effects are much less severe in moving vehicles. When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions.

[edit] Ephemeris and clock errors

The navigation message from a satellite is sent out only every 30 seconds. In reality, the data contained in these messages tend to be “out of date” by an even larger amount. Consider the case when a GPS satellite is boosted back into a proper orbit; for some time following the maneuver, the receiver’s calculation of the satellite’s position will be incorrect until it receives another ephemeris update. The onboard clocks are extremely accurate, but they do suffer from some clock drift. This problem tends to be very small, but may add up to 2 meters (6 ft) of inaccuracy.

This class of error is more “stable” than ionospheric problems and tends to change over days or weeks rather than minutes. This makes correction fairly simple by sending out a more accurate almanac on a separate channel.

[edit] Selective availability

The GPS includes a feature called Selective Availability (SA) that introduces intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals to confound, for example, guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.

SA typically added signal errors of up to about 10 meters (32 ft) horizontally and 30 meters (98 ft) vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern U.S. area might read 30 m off, but 30 m off everywhere and in the same direction. To improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy.

During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in a decision to disable Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy. But since SA was also denying the same accuracy to thousands of friendly troops, turning it off or setting it to an error of zero meters (effectively the same thing) presented a clear benefit.

In the 1990s, the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems. The military resisted for most of the 1990s, and it ultimately took an executive order to have SA removed from the GPS signal. The amount of error added was “set to zero”[14] at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton, allowing users access to the error-free L1 signal. Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). Selective Availability is still a system capability of GPS, and error could, in theory, be reintroduced at any time. In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA,[15] have stated that it is not intended to be reintroduced.

The US military has developed the ability to locally deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.[14]

One interesting side effect of the Selective Availability hardware is the capability to correct the frequency of the GPS caesium and rubidium atomic clocks to an accuracy of approximately 2 × 10-13 (one in five trillion). This represented a significant improvement over the raw accuracy of the clocks.[citation needed]

On 19 September 2007, the United States Department of Defense announced that they would not procure any more satellites capable of implementing SA. [16]

[edit] Relativity

According to the theory of relativity, due to their constant movement and height relative to the Earth-centered inertial reference frame, the clocks on the satellites are affected by their speed (special relativity) as well as their gravitational potential (general relativity). For the GPS satellites, general relativity predicts that the atomic clocks at GPS orbital altitudes will tick more rapidly, by about 45,900 nanoseconds (ns) per day, because they are in a weaker gravitational field than atomic clocks on Earth’s surface. Special relativity predicts that atomic clocks moving at GPS orbital speeds will tick more slowly than stationary ground clocks by about 7,200 ns per day. When combined, the discrepancy is 38 microseconds per day; a difference of 4.465 parts in 1010.[17]. To account for this, the frequency standard onboard each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.[18]

GPS observation processing must also compensate for another relativistic effect, the Sagnac effect. The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined. The Lorentz transformation between the two systems modifies the signal run time, a correction having opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.[19]

The atomic clocks on board the GPS satellites are precisely tuned, making the system a practical engineering application of the scientific theory of relativity in a real-world environment.

[edit] GPS interference and jamming

Since GPS signals at terrestrial receivers tend to be relatively weak, it is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible.

Solar flares are one such naturally occurring emission with the potential to degrade GPS reception, and their impact can affect reception over the half of the Earth facing the sun. GPS signals can also be interfered with by naturally occurring geomagnetic storms, predominantly found near the poles of the Earth’s magnetic field.[20] Another source of problems is the metal embedded in some car windscreens to prevent icing, degrading reception just inside the car.

Man-made interference can also disrupt, or jam, GPS signals. In one well documented case, an entire harbor was unable to receive GPS signals due to unintentional jamming caused by a malfunctioning TV antenna preamplifier.[21] Intentional jamming is also possible. Generally, stronger signals can interfere with GPS receivers when they are within radio range, or line of sight. In 2002, a detailed description of how to build a short range GPS L1 C/A jammer was published in the online magazine Phrack.[22]

The U.S. government believes that such jammers were used occasionally during the 2001 war in Afghanistan and the U.S. military claimed to destroy a GPS jammer with a GPS-guided bomb during the Iraq War.[23] Such a jammer is relatively easy to detect and locate, making it an attractive target for anti-radiation missiles. The UK Ministry of Defence tested a jamming system in the UK’s West Country on 7 and 8 June 2007. [24]

Some countries allow the use of GPS repeaters to allow for the reception of GPS signals indoors and in obscured locations, however, under EU and UK laws, the use of these is prohibited as the signals can cause interference to other GPS receivers that may receive data from both GPS satellites and the repeater.

Due to the potential for both natural and man-made noise, numerous techniques continue to be developed to deal with the interference. The first is to not rely on GPS as a sole source. According to John Ruley, “IFR pilots should have a fallback plan in case of a GPS malfunction”.[25] Receiver Autonomous Integrity Monitoring (RAIM) is a feature now included in some receivers, which is designed to provide a warning to the user if jamming or another problem is detected. The U.S. military has also deployed their Selective Availability / Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). In demonstration videos, the DAGR is able to detect jamming and maintain its lock on the encrypted GPS signals during interference which causes civilian receivers to lose lock.[26]

[edit] Techniques to improve accuracy

[edit] Augmentation

Main article: GNSS Augmentation

Augmentation methods of improving accuracy rely on external information being integrated into the calculation process. There are many such systems in place and they are generally named or described based on how the GPS sensor receives the information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional navigational or vehicle information to be integrated in the calculation process.

Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.

[edit] Precise monitoring

The accuracy of a calculation can also be improved through precise monitoring and measuring of the existing GPS signals in additional or alternate ways.

After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere. The spacecraft broadcast ionospheric model parameters, but errors remain. This is one reason the GPS spacecraft transmit on at least two frequencies, L1 and L2. Ionospheric delay is a well-defined function of frequency and the total electron content (TEC) along the path, so measuring the arrival time difference between the frequencies determines TEC and thus the precise ionospheric delay at each frequency.

Receivers with decryption keys can decode the P(Y)-code transmitted on both L1 and L2. However, these keys are reserved for the military and “authorized” agencies and are not available to the public. Without keys, it is still possible to use a codeless technique to compare the P(Y) codes on L1 and L2 to gain much of the same error information. However, this technique is slow, so it is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies (see GPS modernization, below). Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.

A second form of precise monitoring is called Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a period 1000 times smaller than that of the C/A bit period, to act as an additional clock signal and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy.

Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to an accuracy of less than 10 centimeters (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).

[edit] GPS time and date

While most clocks are synchronized to Coordinated Universal Time (UTC), the Atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC. GPS time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset (19 seconds) with International Atomic Time (TAI). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks.

The GPS navigation message includes the difference between GPS time and UTC, which as of 2006 is 14 seconds. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits) which, at the current rate of change of the Earth’s rotation, is sufficient to last until the year 2330.

As opposed to the year, month, and day format of the Julian calendar, the GPS date is expressed as a week number and a day-of-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980 and the week number became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.

[edit] GPS modernization

Main article: GPS modernization

Having reached the program’s requirements for Full Operational Capability (FOC) on July 17, 1995,[27] the GPS completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to modernize the GPS system. Announcements from the Vice President and the White House in 1998 initiated these changes, and in 2000 the U.S. Congress authorized the effort, referring to it as GPS III.

The project aims to improve the accuracy and availability for all users and involves new ground stations, new satellites, and four additional navigation signals. New civilian signals are called L2C, L5 and L1C; the new military code is called M-Code. Initial Operational Capability (IOC) of the L2C code is expected in 2008.[28] A goal of 2013 has been established for the entire program, with incentives offered to the contractors if they can complete it by 2011.

[edit] Applications

The Global Positioning System, while originally a military project, is considered a dual-use technology, meaning it has significant applications for both the military and the civilian industry.

[edit] Military

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The military use GPS for the following purposes:

[edit] Navigation

GPS allows soldiers to find objectives in the dark or in unfamiliar territory, and to coordinate the movement of troops and supplies.

[edit] Target tracking

Various military weapons systems use GPS to track potential ground and air targets before they are flagged as hostile. These weapons systems pass GPS co-ordinates of targets to precision-guided munitions to allow them to engage the targets accurately.

Military aircraft, particularly those used in air-to-ground roles use GPS to find targets (for example, gun camera video from AH-1 Cobras in Iraq show GPS co-ordinates that can be looked up in Google Earth).

[edit] Missile and projectile guidance

GPS allows accurate targeting of various military weapons including ICBMs, cruise missiles and precision-guided munitions.

Artillery projectiles with embedded GPS receivers able to withstand forces of 12,000G have been developed for use in 155 mm howitzers.[29]

[edit] Search and Rescue

Downed pilots can be located faster if they have a GPS receiver.

[edit] Reconnaissance and Map Creation

The military use GPS extensively to aid mapping and reconnaissance.

[edit] Other

The GPS satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation Detection System.[30]

[edit] Civilian

See also: GPS applications

This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.

This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.

Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS; absolute location, relative movement, time transfer.

The ability to determine the receiver’s absolute location allows GPS receivers to perform as a surveying tool or as an aid to navigation. The capacity to determine relative movement enables a receiver to calculate local velocity and orientation, useful in vessels or observations of the Earth. Being able to synchronize clocks to exacting standards enables time transfer, which is critical in large communication and observation systems. An example is CDMA digital cellular. Each base station has a GPS timing receiver to synchronize its spreading codes with other base stations to facilitate inter-cell hand off and support hybrid GPS/CDMA positioning of mobiles for emergency calls and other applications.

Finally, GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere and gravity field. GPS survey equipment has revolutionized tectonics by directly measuring the motion of faults in earthquakes.

To help prevent civilian GPS guidance from being used in an enemy’s military or improvised weaponry, the US Government controls the export of civilian receivers. A US-based manufacturer cannot generally export a GPS receiver unless the receiver contains limits restricting it from functioning when it is simultaneously (1) at an altitude above 18 kilometers (60,000 ft) and (2) traveling at over 515 m/s (1,000 knots).[31]

[edit] History

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The design of GPS is based partly on the similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS system came when the Soviet Union launched the first Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik’s radio transmissions. They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.

The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS system relies upon. In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first world-wide radio navigation system.

The first experimental Block-I GPS satellite was launched in February 1978.[28] The GPS satellites were initially manufactured by Rockwell International and are now manufactured by Lockheed Martin.

[edit] Timeline

* In 1972, the US Air Force Central Inertial Guidance Test Facility (Holloman AFB) conducted developmental fight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.

* In 1978 the first experimental Block-I GPS satellite was launched.

* In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 in restricted Soviet airspace, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS system would be made available for civilian uses once it was completed.

* By 1985, ten more experimental Block-I satellites had been launched to validate the concept.

* On February 14, 1989, the first modern Block-II satellite was launched.

* In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.

* By December 1993 the GPS system achieved initial operational capability[32]

* By January 17, 1994 a complete constellation of 24 satellites was in orbit.

* Full Operational Capability was declared by NAVSTAR in April 1995.

* In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[33] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.

* In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.

* On May 2, 2000 “Selective Availability” was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.

* In 2004, the United States Government signed a historic agreement with the European Community establishing cooperation related to GPS and Europe’s planned Galileo system.

* In 2004, U.S. President George W. Bush updated the national policy, replacing the executive board with the National Space-Based Positioning, Navigation, and Timing Executive Committee.

* November 2004, QUALCOMM announced successful tests of Assisted-GPS system for mobile phones.[3]

* In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.

* The most recent launch was on 17 November 2006. The oldest GPS satellite still in operation was launched in August 1991.

* On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan. [4]

[edit] Satellite numbers

Name Launch Period No of satellites launched, inc. launch failures Currently in service

Block I 1978-1985 11 0

Block II 1985-1990 9 0

Block IIA 1990-1997 19 15+11

Block IIR 1997-2004 12 12

Block IIR-M 2005- 3 3

Total 54 (plus one not launched) 30+1

1One test satellite

[edit] Awards

Two GPS developers have received the National Academy of Engineering Charles Stark Draper prize year 2003:

* Ivan Getting, emeritus president of The Aerospace Corporation and engineer at the Massachusetts Institute of Technology, established the basis for GPS, improving on the World War II land-based radio system called LORAN (Long-range Radio Aid to Navigation).

* Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.

One GPS developer, Roger L. Easton, received the National Medal of Technology on February 13, 2006 at the White House.[34]

On February 10, 1993, the National Aeronautic Association selected the Global Positioning System Team as winners of the 1992 Robert J. Collier Trophy, the most prestigious aviation award in the United States. This team consists of researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation, Rockwell International Corporation, and IBM Federal Systems Company. The citation accompanying the presentation of the trophy honors the GPS Team “for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago.”

[edit] Other systems

Main article: Global Navigation Satellite System

Other satellite navigation systems in use or various states of development include:

* Beidou — China’s regional system that China has proposed to expand into a global system named COMPASS.

* Galileo — a proposed global system being developed by the European Union, joined by China, Israel, India, Morocco, Saudi Arabia and South Korea, Ukraine planned to be operational by 2011–12.

* GLONASS — Russia’s global system which is being restored to full availability in partnership with India.

* Indian Regional Navigational Satellite System (IRNSS) — India’s proposed regional system.

* QZSS – Japanese proposed regional system, adding better coverage to the Japanese islands.

[edit] See also

Satellite navigation systems Portal

Nautical Portal

* RAIM

* SIGI

* radio navigation

* High Sensitivity GPS

* Degree Confluence Project Use GPS to visit integral degrees of latitude and longitude.

* Exif, GPS data transfer.

* Geotagging

* Geocaching

* NaviTraveler.com, – a GPS point sharing community.

* GPS Drawing Digital mapping and drawing with GPS tracks.

* GPS tracking

* GPS/INS

* Assisted GPS

* GPX (XML schema for interchange of waypoints)

* ID Sniper rifle

* OpenStreetMap, free content maps and street pictures (GFDL)

* Telematics: Many telematics devices use GPS to determine the location of mobile equipment.

* The American Practical Navigator—Chapter 11 “Satellite Navigation”

* Point of Interest

* Automotive navigation system

* NextGen

[edit] Notes

1. ^ Parkinson, B.W. (1996), Global Positioning System: Theory and Applications, chap. 1: Introduction and Heritage of NAVSTAR, the Global Positioning System. pp. 3-28, American Institute of Aeronautics and Astronautics, Washington, D.C.

2. ^ a b GPS Overview from the NAVSTAR Joint Program Office. Accessed December 15, 2006.

3. ^ HowStuffWorks. How GPS Receivers Work. Accessed May 14, 2006.

4. ^ globalsecurity.org [1].

5. ^ Dana, Peter H. GPS Orbital Planes. August 8, 1996.

6. ^ What the Global Positioning System Tells Us about Relativity. Accessed January 2, 2007.

7. ^ USCG Navcen: GPS Frequently Asked Questions. Accessed January 3, 2007.

8. ^ Massatt, Paul and Brady, Wayne. “Optimizing performance through constellation management”, Crosslink, Summer 2002, pages 17-21.

9. ^ US Coast Guard General GPS News 9-9-05

10. ^ USNO. NAVSTAR Global Positioning System. Accessed May 14, 2006.

11. ^ NMEA NMEA 2000

12. ^ http://gge.unb.ca/Resources/HowDoesGPSWork.html

13. ^ AN02 Network Assistance (HTML). Retrieved on 2007-09-10.

14. ^ a b Office of Science and Technology Policy. Presidential statement to stop degrading GPS. May 1, 2000.

15. ^ FAA, Selective Availability. Retrieved Jan. 6, 2007.

16. ^ http://www.defenselink.mil/releases/release.aspx?releaseid=11335

17. ^ Rizos, Chris. University of New South Wales. GPS Satellite Signals. 1999.

18. ^ The Global Positioning System by Robert A. Nelson Via Satellite, November 1999

19. ^ Ashby, Neil Relativity and GPS. Physics Today, May 2002.

20. ^ Space Environment Center. SEC Navigation Systems GPS Page. August 26, 1996.

21. ^ The hunt for an unintentional GPS jammer. GPS World. January 1, 2003.

22. ^ Low Cost and Portable GPS Jammer. Phrack issue 0x3c (60), article 13]. Published December 28, 2002.

23. ^ American Forces Press Service. CENTCOM charts progress. March 25, 2003.

24. ^ [2]

25. ^ Ruley, John. AVweb. GPS jamming. February 12, 2003.

26. ^ Commercial GPS Receivers: Facts for the Warfighter. Hosted at the Joint Chiefs website, linked by the USAF’s GPS Wing DAGR program website. Accessed on 10 April, 2007

27. ^ US Coast Guard news release. Global Positioning System Fully Operational

28. ^ a b Hydrographic Society Journal. Developments in Global Navigation Satellite Systems. Issue #104, April 2002. Accessed April 5, 2007.

29. ^ XM982 Excalibur Precision Guided Extended Range Artillery Projectile. GlobalSecurity.org (2007-05-29). Retrieved on 2007-09-26.

30. ^ Sandia National Laboratory’s Nonproliferation programs and arms control technology.

31. ^ Arms Control Association. Missile Technology Control Regime. Accessed May 17, 2006.

32. ^ United States Department of Defense. Announcement of Initial Operational Capability. December 8, 1993.

33. ^ National Archives and Records Administration. U.S. GLOBAL POSITIONING SYSTEM POLICY. March 29, 1996.

34. ^ United States Naval Research Laboratory. National Medal of Technology for GPS. November 21, 2005

[edit] External links

Wikimedia Commons has media related to:

Global Positioning System

Government links

* GPS.gov—General public education website created by the U.S. Government

* National Space-Based PNT Executive Committee—Established in 2004 to oversee management of GPS and GPS augmentations at a national level.

* USCG Navigation Center—Status of the GPS constellation, government policy, and links to other references. Also includes satellite almanac data.

* The GPS Joint Program Office (GPS JPO)—Responsible for designing and acquiring the system on behalf of the US Government.

* U.S. Naval Observatory’s GPS constellation status

* U.S. Army Corps of Engineers manual: NAVSTAR HTML and PDF (22.6 MB, 328 pages)

* PNT Selective Availability Announcements

* GPS SPS Signal Specification, 2nd Edition—The official Standard Positioning Signal specification.

* Federal Aviation Administration’s GPS FAQ

Introductory / tutorial links

* How does GPS work? TomTom explains GPS, navigation, and digital maps

* GPS Academy Garmin interactive video web site explaing what exactly GPS is and what it can do for you

* HowStuffWorks’ Simplified explanation of GPS and video about how GPS works.

* Trimble’s Online GPS Tutorial Tutorial designed to introduce you to the principles behind GPS

* GPS and GLONASS Simulation(Java applet) Simulation and graphical depiction of space vehicle motion including computation of dilution of precision (DOP)

Technical, historical, and ancillary topics links

* Dana, Peter H. “Global Positioning System Overview”

* Satellite Navigation: GPS & Galileo (PDF)—16-page paper about the history and working of GPS, touching on the upcoming Galileo

* History of GPS, including information about each satellite’s configuration and launch.

* Chadha, Kanwar. “The Global Positioning System: Challenges in Bringing GPS to Mainstream Consumers” Technical Article (1998)

* GPS Weapon Guidance Techniques

* RAND history of the GPS system (PDF)

* GPS Anti-Jam Protection Techniques

* Crosslink Summer 2002 issue by The Aerospace Corporation on satellite navigation.

* Improved weather predictions from COSMIC GPS satellite signal occultation data.

* David L. Wilson’s GPS Accuracy Web Page A thorough analysis of the accuracy of GPS.

* Innovation: Spacecraft Navigator, Autonomous GPS Positioning at High Earth Orbits Example of GPS receiver designed for high altitude spaceflight.

* The Navigator GPS Receiver GSFC’s Navigator spaceflight receiver.

* Neil Ashby’s Relativity in the Global Positioning System

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v • d • e

Satellite navigation systems

Historical Flag of the United States Transit

Operational Flag of the Soviet Union / Flag of Russia GLONASS · Flag of the United States GPS

Developmental Flag of the People’s Republic of China Beidou/COMPASS · Flag of Europe Galileo · Flag of India IRNSS · Flag of Japan QZSS

Related topics EGNOS · GAGAN · GPS·C · LAAS · MSAS · WAAS

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Time signal stations

Longwave DCF77 · HBG · JJY · MSF · TDF · WWVB

Shortwave BPM · CHU · RWM · WWV · WWVH · YVTO

GNSS time transfer Beidou · Galileo · GLONASS · GPS · IRNSS

Defunct time stations OMA · VNG

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Global structure in Systems, Systems sciences and Systems scientists

Categories Category:Conceptual systems · Category:Physical systems · Category:Social systems · Category:Systems · Category:Systems science · Category:Systems scientists · Category:Systems theory

Systems Biological system · Complex system · Complex adaptive system · Conceptual system · Cultural system · Dynamical system · Economic system · Ecosystem · Formal system · Global Positioning System · Human organ systems · Information systems · Legal system · Metric system · Nervous system · Non-linear system · Operating system · Physical system · Political system · Sensory system · Social system · Solar System · System · Systems of measurement

Fields of theory Chaos theory · Complex systems · Control theory · Cybernetics · Holism in science · Sociotechnical systems theory · Systems biology · System dynamics · Systems ecology · Systems engineering · Systems theory · Systems science

Systems scientists Russell L. Ackoff · William Ross Ashby · Gregory Bateson · Ludwig von Bertalanffy · Kenneth E. Boulding · Peter Checkland · C. West Churchman · Heinz von Foerster · Charles François · Jay Wright Forrester · Ralph W. Gerard · Debora Hammond · George Klir · Niklas Luhmann · Humberto Maturana · Donella Meadows · Mihajlo D. Mesarovic · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Francisco Varela · John N. Warfield · Norbert Wiener

Retrieved from “http://en.wikipedia.org/wiki/Global_Positioning_System”

Details about PC Hardware can be easily accessed in Device Manager of a personal computer. All the PC Hardware devices are listed on the device manager installed of the computer. The device manager, in a computer, can be used to change the properties of any device. Each device is listed under the hardware to which it is connected. The hardware devices, which are installed in the computer and are connected, are grouped as type of resources- Direct Memory Access (DMA), Input/output (I/O), Interrupt Request (IRQ) and Memory.

The Hardware in the device manager can be seen as how they are connected to the computer. PC Hardware profiles provide a way to set up and store different hardware configurations. Hardware Profiles suggest which driver to load when the available PC Hardware changes. PC hardware requires resources to properly operate with the computer and the software installed in the computer. Hardware compatibility tests implement the combination of a device, a software driver, and an operating system under controlled conditions to verify that all components operate properly.

Drivers are the group of files, which make possible for the PC Hardware device to communicate with the operating system of the computer. Every PC Hardware devices have particular driver files, with particular version and made for a particular Hardware model, without which the Hardware devices can not work with the computer. The drivers are required to be updated, which enable PC Hardware to function properly. New or different operating systems always ask for new versions of Hardware drivers. Updating the driver version not only makes the PC Hardware compatible with the latest operating systems, it also advances the stability of the computer and increases reliability of the PC Hardware.

PC support services are necessary for PC Hardware to work properly and efficiently. Sometimes, PC system may have incompatibilities with hardware that is already installed in the computer. The need of PC Support is hence very vital in the world of computers. Basically, PC supports are provided by Manufacturers & Hardware and Software Professionals. PC Support services depend on the kind of issues a computer is having. PC support works around PC hardware issues and software issues and it may exist with the hardware device or the software component. On location care is taken by the service providers in case of complicated PC hardware issues.

Today, PC Hardware maintenance has become more cost effective and with coming up of remote PC Support services, it has become more convenient and cogitative, since these services are free policies. Customers do not have to pay if the issue is not resolved.