GPS

            "Standalone" or "Autonomous" GPS operation uses radio signals from satellites alone. A-GPS additionally uses network resources to locate and utilize the satellites in poor signal conditions. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or be weakened by passing through atmospheric conditions, walls or tree cover. When first turned on in these conditions, some standalone GPS navigation devices may not be able to work out a position due to the fragmentary signal, rendering them unable to function until a clear signal can be received continuously for up to 12.5 minutes (the time needed to download the GPS almanac and ephemeris).

An Assisted GPS system can address these problems by using data available from a network. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.

Assistance falls into two categories:

1). Information used to more quickly acquire satellites

·         It can supply obital data or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases.

·         The network can provide precise time.

2). Calculation of position by the server using information from the GPS receiver

·         The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position.

·         The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it

·         Accurate, surveyed coordinates for the cell site towers allow better knowledge of local ionospheric conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position. (See also Wide Area Augmetation System)

As an additional benefit, in some A-GPS device implementations, known as "MS-Assisted," the amount of CPU and programming required for a GPS receiver is reduced by offloading most of the work onto the assistance server.

A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on time to first fix, but does not depend on the network, and therefore can work beyond network range, and without incurring data usage fees.^[Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.

Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System and cell-site triangulation and sometimes a hybrid positioning system.

High Sensitivity GPS is an allied technology that addresses some of these issues in a way that does not require additional infrastructure. However, unlike some forms of A-GPS, high-sensitivity GPS cannot provide a fix instantaneously when the GPS receiver has been off for some time.

Basic concepts

Standalone GPS provides first position in approximately 30-40 seconds. A Standalone GPS system needs orbital information of the satellites to calculate the current position. The data rate of the satellite signal is only 50 b/s, so downloading orbital information like ephemeris and almanac directly from satellites typically takes a long time, and if the satellite signals are lost during the acquisition of this information, it is discarded and the standalone system has to start from scratch. In AGPS, the Network Operator deploys an AGPS server. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM,CDMA, WCDMA,LTE or even using other wireless radio bearers such as Wi-Fi. Usually the data rate of these bearers is high, hence downloading orbital information takes less time.

 Modes of operation

AGPS has two modes of operation:

1.       Mobile Station Assisted (MSA) - In MSA mode A-GPS operation, the A-GPS capable device receives acquisition assistance, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and sends the measurements to the A-GPS server. The A-GPS server calculates the position and sends it back to the A-GPS device.

2.       Mobile Station Based (MSB) - In MSB mode A-GPS operation, the A-GPS device receives ephemeris, reference location, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and calculates the position.

Standards

AGPS protocols are part of Positioning Protocol defined by two different standardization body,3gpp and Open Mobile Alliance(OMA).

1). Control Plane Protocol - It is defined by 3gpp for various generations of mobile phone system. These protocols are defined for Ciucuit Switched Networks. Following positioning protocol has been defined.

1. 1.       RRLP - 3gpp defined RRLP or Radio resource location protocol to support positioning protocol on GSM networks.
2. 2.       TIA 801 - CDMA 2000 family defined this protocol for CDMA 2000 networks.
3. 3.       RRC position protocol - 3gpp defined this protocol as part of the RRC standard for UMTS network.
4. 4.       LPP - 3gpp defined LPP or LTE positioning protocol for LTE Networks.

2). User Plane Protocol - It is defined by OMA to support positioning protocols in Packet Switched  Networks. Two generations of User plane Protocol have evolved.

1. 1.       SUPL V1.0
2. 2.       SUPL V2.0

Printers

                             A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.

Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer.

                     One of the chief characteristics of laser printers is their resolution -- how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, offset printing usually prints at 1,200 or 2,400 dpi. Some laser printers achieve higher resolutions with special techniques known generally as resolution enhancement.

                         In addition to the standard monochrome laser printer, which uses a single toner, there also exist color laser printers that use four toners to print in full color. Color laser printers tend to be about five to ten times as expensive as their monochrome siblings.

Laser printers produce very high-quality print and are capable of printing an almost unlimited variety of fonts. Most laser printers come with a basic set of fonts, called internal or resident fonts, but you can add additional fonts in one of two ways:

·         font cartidges : Laser printers have slots in which you can insert font cartridges, ROM boards on which fonts have been recorded. The advantage of font cartridges is that they use none of the printer's memory.

·         soft fonts : All laser printers come with a certain amount of  RAMmemory, and you can usually increase the amount of memory by adding memory boards in the printer's expansion slots. You can then copy fonts from a disk to the printer's RAM. This is called downloading fonts. A font that has been downloaded is often referred to as a soft font, to distinguish it from the hard fonts available on font cartridges. The more RAM a printer has, the more fonts that can be downloaded at one time.

                          In addition to text, laser printers are very adept at printing graphics. However, you need significant amounts of memory in the printer to print high-resolution graphics. To print a full-page graphic at 300 dpi, for example, you need at least 1 MB  of printer RAM. For a 600-dpi graphic, you need at least 4 MB RAM.

Because laser printers are nonimpact printers, they are much quieter than dot-matrix or daisy-wheel printes. They are also relatively fast, although not as fast as some dot-matrix printers. The speed of laser printers ranges from about 4 to 20 pages of text per minute   (ppm). A typical rate of 6 ppm is equivalent to about 40 characters per second (cps).

Laser printers are controlled through page description languages(PDLs). There are two de facto standards for PDLs:

·         PCL : Hewlett-Packard (HP) was one of the pioneers of laser printers and has developed a Printer Control Language (PCL) to control output. There are several versions of PCL, so a printer may be compatible with one but not another. In addition, many printers that claim compatibility cannot accept HP font cartridges.

·         PostScript : This is the de facto standard for Apple Macintosh printers and for all  desktop publishing systems.

RAM

              RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM. However, the data in RAM stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. When you turn your computer on again, your operating system and other files are once again loaded into RAM, usually from your hard disk.

            RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time. If short-term memory fills up, your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won't accept any more, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.

Mail Server

                           A mail server is an application that receives incoming e-mail from local users (people within the same domain) and remote senders and forwards outgoing e-mail for delivery. A computer dedicated to running such applications is also called a mail server. Microsoft Exchange, gmail, Exim and sendmail are among the more common mail server programs.The mail server works in conjunction with other programs to make up what is sometimes referred to as a messaging system. A messaging system includes all the applications necessary to keep e-mail moving as it should. When you send an e-mail message, your e-mail program, such as Outlook or Eudora, forwards the message to your mail server, which in turn forwards it either to another mail server or to a holding area on the same server called a message store to be forwarded later. As a rule, the system uses SMTP (Simple Mail Transfer Protocol) or ESMTP (extended SMTP) for sending e-mail, and either POP3 (Post Office Protocol 3) or IMP (Internet Message Access Protocol) for receiving e-mail.

Artificial intelligence

            The branch of computer science concerned with making computers  behave like humans. The term was coined in 1956 by John McCarthy at the Massachusetts Institute of Technology. Artificial intelligence includes

·  games playing: programming  computers to play games such as chess and checkers

·  expert systems : programming computers to make decisions in real-life situations (for example, some expert systems help doctors diagnose diseases based on symptoms)

·  natural language:: programming computers to understand natural human  languages

  neural networks : Systems that simulate intelligence by attempting to reproduce the types of physical connections that occur in animal brains

·  robotics : programming computers to see and hear and react to other sensory stimuli

             Currently, no computers exhibit full artificial intelligence (that is, are able to simulate human behavior). The greatest advances have occurred in the field of games playing. The best computer chess programs are now capable of beating humans. In May, 1997, an IBM super-computer called Deep Bluedefeated world chess champion Gary Kasparov in a chess match.

In the area of robotics, computers are now widely used in assembly plants, but they are capable only of very limited tasks. Robots have great difficulty identifying objects based on appearance or feel, and they still move and handle objects clumsily.

                Natural-language processing offers the greatest potential rewards because it would allow people to interact with computers without needing any specialized knowledge. You could simply walk up to a computer and talk to it. Unfortunately, programming computers to understand natural languages has proved to be more difficult than originally thought. Some rudimentary translation systems that translate from one human language to another are in existence, but they are not nearly as good as human translators. There are also voice recognition systems that can convert spoken sounds into written words, but they do not understand what they are writing; they simply take dictation. Even these systems are quite limited -- you must speak slowly and distinctly.

               In the early 1980s, expert systems were believed to represent the future of artificial intelligence and of computers in general. To date, however, they have not lived up to expectations. Many expert systems help human experts in such fields as medicine and engineering, but they are very expensive to produce and are helpful only in special situations.

               Today, the hottest area of artificial intelligence is neural networks, which are proving successful in a number of disciplines such as voice recognition and natural-language processing.

There are several programming languages that are known as AI languages because they are used almost exclusively for AI applications. The two most common are LISP and Prolog.

OSI 7 Layers Reference Model For Network Communication

                Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and internetworking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.  

              The OSI 7 layers model has clear characteristics. Layers 7 through 4 deal with end to end communications between data source and destinations. Layers 3 to 1 deal with communications between network devices. 

                 On the other hand, the seven layers of the OSI model can be divided into two groups: upper layers (layers 7, 6 & 5) and lower layers (layers 4, 3, 2, 1). The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end user. The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the wires, for example) and is responsible for placing data on the medium.

Application (Layer 7)

                This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail , and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Presentation (Layer 6)

             This layer provides independence from differences in data representation (e.g.,encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Session (Layer 5)

           This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Transport (Layer 4)

              This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network (Layer 3)

            This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Data Link (Layer 2)

               At this layer, data packets are and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control  (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Physical (Layer 1)

                  This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Output Devices

                     Output devices translate information processed by the computer into a from that either humans or other machines can understand.There are a variety of output devices,which can be connected to a computer.Some of the common output devices are explained in the following sections.

Monitor

                The most common from of output is the computer screen.It is more correctly called the ‘monitor’ and sometime referred to as the visual display unit or VDU.

The quality of computer monitor is based on the following properties:

·         Resolution: Resolution is the number of pixels,which the sceen can display.A’pixel’ is the ‘pictuer element’ and refers to the smallest area of the screen that the computer can change.

·         The number of colours it can display (dependent on the computer as well)

·         Radiation output.

Different types of display sceens

CRT monitor  –  A cathode-ray tube and associated electronics connected to the video output of computer.These have higher resolution than TVs.Larger monitors with high resolution are used for specialized application such as desktop publishing and CAD.

Liquid crystal display (LCD)  –  LCDs are screens made from two glass/plastic plates with liquid in between.LCDs are commonly used for calculators and laptop computers,as they are far flatter than is possible with cathode ray screens used in TVs and standard computer monitors.

Main differences of LCDs as compared with CRT monitors are :

·         Take s very little space

·         Small energy consumption

·         Sharp pictures

·         No flicker or geometric distortion

·         Fairly expencive

·         Limited viewing angle

·         Slower response time

Printers


             Many different types of printer are in use today.Two primary technologies used for printing are impact printing and non-impact Printers use a print head containing a number of metal pins which strike an inked ribbon placed between the print head and the paper.The non-impact printers are much quieter than impact printers as their printing head do not strike the paper.

Three most common printer types are :

EX:- Dot matrix printers,Inkjet printers and Laser printers.


Dot matrix Printers

         These printers work by firing of tiny pins(which are located in the print head),through a ribbon similar to that found on a typewriter.Such printers are cheap and have the lowest running cost compared to any other type of printer.As the head moves across the head moves across the paper the correct pins are fired out to hit an inked ribbon and from the shape of the number of pins,the higher the quality of the print.Dot matrix printers are impact printers and are used to print multipart stationary.So to print several copies of a document at the same time you will need to use a dot matrix printer.

Inkjet Printers
         Inkjet printers can produce high quality text and graphics.They are quieter than dot matrix printers.The technology involves ink flowing through the appropriate nozzles (usually in an array of 64) where it is then heated and a bubble is formed.This expands to release a tiny droplet of ink onto the paper.

Laser Printer

            These non-impact printers offer high-speed printing and an excellent quality of text and graphics.A laser beam is used to from an image on a rotating, charge metal drum.This then picks up toner cartridge and transfers it onto paper.Very soon afterwards heat and pressure are applied so the toner sticks to the paper.Slince they are page printers they are very fast.Color laser printers are now available and are mainly used for desktop publishing.Although they are expensive,they are likely eventually to come into widespread use.

Speakers / Headphones
                   Speakers or headphones may be used to get sound output from a computer.There are different types of speakers ranging from simple speakers, which provide simple sound to speakers, which can provide theater-like surround sound.

4G technology

                  4G technology, the Fourth Generation Technology, is the very latest and ultra fast technology and it is getting more attention day by day even though this technology is still at its initial stages. 4G technology aims to provide fastest speed to all the users, to the users of mobile or smartphones it intends to provide data transfer rate up to 100 mbps while for its stationary users, it aims to the highest speed of 1 Gbps.

WiMAX and LTE

              These are two 4G cellular broadband networks. The WiMAX provides speed up to 128mbps of downloading and for uploading it provides 56mbps, whereas LTE showed in an early implementation speed up to 100mbps downloading and 50 mbps uploading. ITU considers the LTE (Long-Term Evolution) as a standard technology because LTE aims to exceed the specifications of ITU. While WiMAX on the other hand is an IEEE standard, also ITU doesn’t considered WiMAX a true 4G technology because it is not up to the specifications that ITU put forth.