Custom Search

Saturday, December 10, 2011

Frequency Division Multiple Access (FDMA)

Multiple Access Systems-Frequency Division Multiple Access (FDMA)
Frequency Division Multiple Access (FDMA)

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. It is particularly commonplace in satellite communication. FDMA, like other Multiple Access systems, coordinates access between multiple users.

Each FDMA subscriber is assigned a specific frequency channel. No one else in the same cell or a neighboring cell can use the frequency channel while it is assigned to a user. This reduces interference, but severely limits the number of users.

    Advantage of FDMA                         
* FDMA technique doesn't need any base-control station.
* Data that transfeered between each station to another during the transmission process will not be lost.
* After the transmission of data,the effect ot the delay distortion will be so small and it can be ignored.
* There is no need for network timing.
* The channel operations in FDMA are simple.
* In FDMA,the reduction of the information bit rate has a good effect on the capacity.
* No need for any equalization.
* Because of the transmission is continuous,there is almost no need for bits that are responsible for synchronization.
* Simplicity in FDMA algorithms.

    Disadvantages of FDMA                   

* In the FDMA technique,it is impossible for the stations to receive data from more than one transmission source.
* One of most important thing in communication systems is the maximum data rate which is small and fixed for every channel in FDMA.
* Because of the guard bands,the capacity of the FDMA will be decreased.
* Increasing the cost of FDMA,since the band filters are narrow that can't be recognized by VLSI.
* FDMA requires special filters to avoid any interference between the narrow channels.



    * Wikipedia
    * CDMA University
    * How Stuff Works   

" Frequency Division Multiple Access (FDMA) " !

Friday, December 9, 2011

Multiple Access Systems

    Why Multiple Access?  

Multiple Access systems coordinates access between multiple users.Wireless telecommunications has dramatically increased in popularity, resulting in the need for technologies that allow multiple users to share the same Bandwidth.
The following Multiple Access Systems have very different approaches to the bandwidth problem. 

Multiple Access Systems-Time Division Multiple Access (TDMA)
Time Division Multiple Access (TDMA)


Short for Time Division Multiple Access, a technology for delivering digital wireless service using time-division multiplexing (TDM). TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.
The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combat-net radio systems, and PON networks for upstream traffic from premises to the operator.
TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.

    Advantages of TDMA                       

The radio part of the mobile only needs to listen and broadcast for its own time slot. For the rest of the time, the mobile can carry out measurements on the network, detecting surrounding transmitters on different frequencies. This allows safe inter frequency handovers, something which is difficult in CDMA systems, not supported at all in IS-95 and supported through complex system additions in Universal Mobile Telecommunications System (UMTS). This in turn allows for co-existence of microcell layers with macrocell layers.

    Disadvantages of TDMA                 

TDMA systems create interference at a frequency which is directly connected to the time slot length. This is the buzz which can sometimes be heard if a TDMA phone is left next to a radio or speakers.Another disadvantage is that the "dead time" between time slots limits the potential bandwidth of a TDMA channel. These are implemented in part because of the difficulty in ensuring that different terminals transmit at exactly the times required. Handsets that are moving will need to constantly adjust their timings to ensure their transmission is received at precisely the right time, because as they move further from the base station, their signal will take longer to arrive. This also means that the major TDMA systems have hard limits on cell sizes in terms of range, though in practice the power levels required to receive and transmit over distances greater than the supported range would be mostly impractical anyway.


    * Wikipedia 
    * CDMA University
    * How Stuff Works

" Multiple Access Systems " !

Friday, November 18, 2011

Cell Phone Network Coverage

Network coverage

A key part of any mobile phone specification is its operating frequency bands. The supported frequency bands determine
whether a certain handset is compatible with a certain network carrier.

Cell Phone Network Coverage,GSM,2G,3G
Cell Phone Network Coverage
Beside the mobile phone specifications, GSM Arena is happy to also provide you with its own country-based frequency band directory. It's not operator-specific and it's helpful if you are choosing a handset to use in your home country or if you are making sure your phone will work in the country you are heading to.
You select the country you are interested in - as an example i selected Egypt - :


GSM 850     GSM 900     GSM 1800     GSM 1900     UMTS 850     UMTS 1900     UMTS 2100
  No               Yes               Yes                 No                  No                   No                    Yes   

Making calls, sending text messages and using GPRS/EDGE mobile data connection in the country of your choice requires a mobile phone that supports at least the frequency band filled as “Required” below.

2G capabilities

Required   GSM 900
Recommended   GSM 900 and GSM 1800

Making video calls and using a high-speed 3G data connection in the country of your choice, requires a mobile phone that supports at least the frequency band filled as “Required” below .

3G capabilities

Required   UMTS 2100

Make note that for complete accuracy you should always check with your home service provider or with the local service providers in the country you are staying at.

Check Network Coverage for your Country GSM Arena - Network Bands

                  * GSM Arena

" Cell Phone Network Coverage " !

Saturday, November 12, 2011

GSM Architecture and Definitions (3)

    The Operation and Support System 

The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations.

GSM Operation and Support System (OSS)
GSM Operation and Support System (OSS)
OSS: The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS).
       Here are some of the OMC functions:
       * Administration and commercial operation (subscription, end terminals, charging and statistics).
       * Security Management.
       * Network configuration, Operation and Performance Management.

       * Maintenance Tasks.    

GSM Architecture and Definitions
GSM Architecture and Definitions

GPRS (General Packet Radio Services
GPRS (General Packet Radio Services)

GPRS General Packet Radio Services

GPRS is a data network that overlays a second-generation GSM network. This data overlay network provides packet data transport at rates from 9.6 to 171 kbps. Additionally, multiple users can share the same air-interface resources simultaneously.

GPRS attempts to reuse the existing GSM network elements as much as possible, but to effectively build a packet-based mobile cellular network, some new network elements, interfaces, and protocols for handling packet traffic are required.

GSM Architecture and Definitions
GSM Architecture and Definitions

External Networks
  PSTN: Public Switched Telephone Network
  ISDN: Integrated Services Digital Network
  PDN: Packet Data Network

   * Alcatel-Lucent
   * Private Line
   * Tutorials Point 
  * SS7 Training

" GSM Architecture and Definitions (3) " !

GSM Architecture and Definitions (2)

    The Network Switching System  

The Network switching system (NSS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units.

GSM Architecture and Definitions
GSM Architecture and Definitions
MSC: Mobile Switching Center a switching exchange whose main functions are:
       – Call Handling
       – Specific GSM functions such as:
         • Mobility Management: Communication with the Location Databases (VLR
           and HLR)
         • Handover execution when involved
       – Gateway Function for Terminating Call (TC)
    VLR: Visitor Location Register is associated with one or more MSC. It is a local database with the following
         – Copy of the HLR data for visiting subscribers
         – More precise location of the Mobile Station (an area of the network called
           “Location Area” which is a group of cells

         – Call re-direction data

GSM Architecture and Definitions
GSM Architecture and Definitions


                   * Alcatel-Lucent    
                   * Private Line    
                   * Tutorials Point    
                   * SS7 Training

" GSM Architecture and Definitions (2) " !

GSM Architecture and Definitions (1)

    What is GSM?           

GSM, which stands for Global System for Mobile communications, reigns as the world’s most widely used cell phone technology. Cell phones use a cell phone service carrier’s GSM network by searching for cell phone towers in the nearby area.

The origins of GSM can be traced back to 1982 when the Groupe Sp├ęcial Mobile (GSM) was created by the European Conference of Postal and Telecommunications Administrations (CEPT) for the purpose of designing a pan-European mobile technology.

It is approximated that 80 percent of the world uses GSM
GSM Architecture and Definitions
GSM Architecture and Definitions
technology when placing wireless calls, according to the GSM
Association (GSMA), which represents the interests of the worldwide mobile communications industry. This amounts to nearly 3 billion global people.

    GSM Network Structure   

The network is structured into a number of discrete sections:

   *  The Base Station Subsystem (the base stations and their controllers).
   *  The Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network.
   * The GPRS Core Network (the optional part which allows packet based Internet connections).
   *  The Operations support system (OSS) for maintenance of the network.

Now,We will explain the meaning of the GSM Network shortcuts.

PLMN: Public Land Mobile Network is area covered by one network operator. A PLMN can contain one or more MSCs.
GSM: Global System for Mobile communication
  MS: Mobile Station is used by the subscriber for calling another subscriber either in the fixed network or in the mobile network.A Mobile Station (MS) is composed of a Mobile Termination (MT) and a Subscriber Module Identity (SIM) card.
   MT: Mobile Termination.The MT performs the following functions:
       - radio transmission termination;
       - radio transmission channel management;
       - terminal capabilities, including presentation of a  man-machine interface to a user;
       - speech encoding/decoding;
       - error protection for all information sent across the radio path;
       - flow control of signalling and user data;
       - rate adaptation of user data between the radio channel rate and user rates;
       - multiple terminal support;
       - mobility management.

SIM: SIM card stores information concerning the subscriber such as subscriber identity,services subscribed, parameters for security procedures and information on the location of the subscriber (dynamically refreshed according to its movements).
  Um > The Radio Interface between MS and Base Station.
     UpLink: The Path of the Data from MS to Base Station.
     DownLink: The Path of the Data from Base Station to MS.

GSM Architecture and Definitions
GSM Architecture and Definitions

GSM Architecture and Definitions
GSM Architecture and Definitions

   * Alcatel-Lucent
   * Private Line
   * Tutorials Point 
  * SS7 Training

" GSM Architecture and Definitions (1) " !

Wednesday, October 19, 2011

Optical Fiber Communication

An optical fiber is a flexible, transparent fiber made of very pure glass (silica) not much wider than a human hair that acts as a waveguide, or "light pipe", to transmit light between the two ends of the fiber.The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.

Optical fibers are widely used in fiber-optic communications, which
Optical Fiber Communication
Optical Fiber Communication
permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

    Optical Fiber Communication       

Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. Additionally, the per-channel light signals propagating in the fiber have been modulated at rates as high as 111 gigabits per second by NTT,although 10 or 40 Gbit/s is typical in deployed systems.

Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing (WDM)). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008[update]).

The current laboratory fiber optic data rate record, held by Bell Labs in Villarceaux, France, is multiplexing 155 channels, each carrying 100 Gbit/s over a 7000 km fiber. Nippon Telegraph and Telephone Corporation have also managed 69.1 Tbit/s over a single 240 km fiber (multiplexing 432 channels, equating to 171 Gbit/s per channel).Bell Labs also broke a 100 Petabit per second kilometer barrier (15.5 Tbit/s over a single 7000 km fiber).

For short distance applications, such as a network in an office building, fiber-optic cabling can save space in cable ducts. This is because a single fiber can carry much more data than electrical cables such as standard category 5 Ethernet cabling, which typically runs at 1 Gbit/s. Fiber is also immune to electrical interference; there is no cross-talk between signals in different cables, and no pickup of environmental noise.

Non-armored fiber cables do not conduct electricity, which makes fiber a good solution for protecting communications equipment in high voltage environments, such as power generation facilities, or metal communication structures prone to lightning strikes. They can also be used in environments where explosive fumes are present, without danger of ignition. Wiretapping (in this case, fiber tapping) is more difficult compared to electrical connections, and there are concentric dual core fibers that are said to be tap-proof.

    Real Project                                         

                    * Wikipedia  
                    * Youtube (Make Magazine Channel) 

" Optical Fiber Communication " !

Sunday, September 25, 2011

Which Screen Protector should i use?

Best Screen Protector
Screen Protector

A screen protector is used to protect the LCD screens of digital, electronic devices. The personal digital assistant (PDA) is, perhaps, the most commonly used gadget for which screen protectors are used since PDAs are operated via a stylus. If not used carefully, the tip of the stylus can potentially mar or scratch the sensitive LCD screen surface, and so screen protectors were brought to market.

The "first generation" of screen protectors were made from very thin films based on the concept that an extra layer between the two surfaces (screen and stylus) would provide the needed protection to prolong the life of the device. These screen protectors came (and still come) in packs of 10 to 20 protectors and are hand-cut by the end consumer to fit the specific device. Such screen protectors, while offering extra protection, did not completely fill the need in the marketplace. They peeled up easily and they scratched almost as easily as the screens, causing the protector to be replaced often.

The newest generation of screen protectors are made from a much more durable film and are designed to be a more permanent part of the gadget which they protect. The material is a urethane-based film which is a little thicker than traditional screen protectors (.008 inches compared to .005 or .003),[citation needed] but the film is hardly noticeable once installed. The film originated when the U.S. military was looking for a way to protect the leading edges of their military helicopter blades from abrasive airborne particles (sand) while traveling at hundreds of miles per hour. The negative is that it is hard to remove and leaves a sticky residue. It is also made in small sizes, not recommended for bigger than four inch diagonal screens. Since the film is clear, there are problems with UV rays emanating from the display to the eyes and bounce back from the sun. It also does not provide protection from glare and hard to read outdoors.

And for the usage of the cell phone screen, there are mainly 7 kinds of screen protector:

    Privacy Screen Protector                          
   As its name suggests, it is used to give users protection while they use their gadgets. When viewed from a particular angle, the privacy protector darkens your screen. It is also able to offer scratch protection if your device is touchscreen. It is the thickest screen protector available which is why it is considered to be the best type to give you protection and to keep your gadget from getting scratched. Privacy screen protectors comes in pair and can be quite expensive but if you are intent on using these, it will be worth buying.
     Mirror Screen Protector                              
   Mirror Screen Protector is a mirror that prevents your LCD screen from getting scratched. Mirror Screen Protector looks and works like a mirror when your phone's screen is shut off (locked). Once the screen is activated, screen contents appear like normal. Mirror Screen Protector measures 85 x 70 mm (3.35 x 2.76 in.) - cut to fit your screen. One sheet can cover more than one screen depending on size of your screens. Mirror Screen Protector does not interfere with stylus or touch screen operation. Easy to apply with no bubbles and easily removable without leaving residue.

     Matte Screen Protector                      
        ViewGuard Anti-Glare Matte Screen Protectors are composed of multiple layers of material, each of which helps to either reduce reflected light or provide additional impact protection for your screen. The anti-scratch coating layer protects your screen from fingerprints, smudges, and scratches. This layer also helps make the ViewGuard screen protector ideal for use with touch-screen tablet PCs and Ultra-Mobile PCs (UMPC). Honestly, who wants to clean fingerprints off a glossy screen all the time?
   One of the best features of the ViewGuard Anti-Glare Matte Screen Protectors is the easy on/off application. The protector is easily attached and removed time and time again without damage to your screen. The screen protector attaches directly to the surface of your display with a silicone adhesive. Since the entire multi-layer film is less than one millimeter thick it can stay attached to your screen and still allow your laptop lid to close.
     Ultra-Clear Screen Protector                                               
      More or less,the screen protector will reduce the clearance of the screen. In order to get the best visual effect, the ultra-clear screen protector come out. And high transparency up to 95%.
   1. Anti-scratch,anti-grease and dust and stain-proof.
   2. No-glue , static electricity self-adhesive.
   3. No bubble,washable and reusable.
   4. Long lasting protection and firmly on screen
   5. Leave with no residue and would not corrode the surface.
   6. Easy installation .Stability adhesion performance, excellent      high  or low temperature resistance
   7. Standard packing:Color card package,PE bag,cleaning cloth,soft card. Customer package available
     Grid Screen Protector                            
      If the use need the screen protector looks threads,the grid screen protetor is good choose.
   1. Anti-scratch,anti-grease and dust and stain-proof.
   2. No-glue , static electricity self-adhesive.
   3. No bubble,washable and reusable.
   4. Long lasting protection and firmly on screen
   5. Leave with no residue and would not corrode the surface.
   6. Easy installation .Stability adhesion performance, excellent high or low temperature resistance
   7. Standard packing:Color card package,PE bag,cleaning cloth,soft card. Customer package available
     Diamond Screen Protector                                        
         this kind of screen protector can show colorfull shine
   1. Anti-scratch,anti-grease and dust and stain-proof.
   2. No-glue , static electricity self-adhesive.
   3. No bubble,washable and reusable.
   4. Long lasting protection and firmly on screen
   5. Leave with no residue and would not corrode the surface.
   6. Easy installation .Stability adhesion performance, excellent high or low temperature resistance
   7. Standard packing:Color card package,PE bag,cleaning cloth,soft card. Customer package available
     3D Screen Protector                                             
     The HTC Evo 3D Screen Protector -As an example- is the clear choice for maximum scratch protection. The HTC Evo 3D Screen Protector goes beyond your traditional HTC Evo 3D screen protectors, skins, covers, and cases. TechSkin is made from the same film material used to protect luxury cars, military aircrafts, and NASA space shuttles. The HTC Evo 3D Screen Protector is custom made to specifically fit the HTC Evo 3D .
    * • Toughest clear protective film in the market
    * • Clear protection that is virtually invisible
    * • Preserves your HTC Evo 3D 's original design
    * • Protects your HTC Evo 3D from scratches, dents, and physical wear-and-tear
    * • Patented layer of UV protection for anti-yellowing
    * • Provides protection without affecting the functions of your HTC Evo 3D
    * • Non-sticky or restrictive outer surface

" Which Screen Protector should i use? " !

Friday, September 16, 2011

All About iPhone 4

iphone 4
iPhone 4

While everyone else was busy trying to keep up with iPhone, we were busy creating amazing new features that make iPhone more powerful, easier to use, and more indispensable than ever. The result is iPhone 4. The biggest thing to happen to iPhone since iPhone.

People have been dreaming about video calling for decades. iPhone 4 makes it a reality. With just a tap, you can wave hello to your kids, share a smile from across the globe, or watch your best friend laugh at your stories — iPhone 4 to iPhone 4 or to the new iPod touch over Wi-Fi. And it works right out of the box. No other phone makes staying in touch this much fun.

Two cameras,two views.
iPhone 4 has two cameras: One on the front, which focuses on you. And one on the back, which focuses on everything else. FaceTime lets you switch back and forth between them at any time during a video call. All you have to do is tap a button.

Retina Display
The Retina display on iPhone 4 is the sharpest, most vibrant, highest-resolution phone screen ever, with four times the pixel count of previous iPhone models. In fact, the pixel density is so high that the human eye is unable to distinguish individual pixels. Which makes text amazingly crisp and images stunningly sharp.

iPhone 4 introduces a whole new way of multitasking. Now you can run your favorite third-party apps — and switch between them instantly — without slowing down the performance of the foreground app or draining the battery unnecessarily.1 This smarter approach to multitasking is available only in iOS 4.

HD Video Recording and Editing
Shoot your own movies in high definition. Capture impressive video even in low-light settings, thanks to the advanced backside illumination sensor and built-in LED light. Then edit and create your own mini-masterpiece right on iPhone 4 using the iMovie app — with Apple-designed themes, titles, and transitions. It’s available on the App Store for $4.99.

5-Megapixel Camera with LED Flash
Take beautiful, detailed photos using the 5-megapixel camera with built-in LED flash. The advanced backside illumination sensor captures great pictures even in low light. And the front-facing camera makes it easy to take self-portraits.

Reference: Apple

" All About iPhone 4 " !

Wednesday, September 14, 2011

Luxury retailer introduces solid gold phone with a $60,000 price tag

Gold Phone
Gold Phone

Feature-rich smartphones aren't cheap, and critics of pricey mobile devices often claim that they are too expensive, despite their wide-ranging capabilities. Those people will want to look away now, as the newest device from Danish luxury retailer Aesir is sure to make their blood boil. Introducing the limited edition AE+Y phone — an 18-carat solid gold handset that can't use apps, email, or mobile internet, but still carries a ridiculous price of 42,000 euros (roughly $60,000).
The lavish device boasts groundbreaking features such as speed dial, call forwarding, and even a built-in calculator.

Its LCD screen measures a modest 2", and its battery can handle a measly 5 hours of talk time — compared to the Droid Bionic's 11-hour, and iPhone 4's 14-hour limits. But Aesir is focusing more on form than function, and the manufacturer is quick to point out that the edge-to-edge key design is a first in mobile handsets.

The AE+Y's barebones user interface was shaped by renowned designer Tom Hingston, and the phone's unorthodox keypad is laser-engraved and features "advanced LED backlighting." We're not quite sure how that varies from regular LED backlighting, but I guess we have to take Aesir's word on that.

Aesir's target market is clearly the super rich, but do the wealthy not also desire useful gadgets? Then again, if you're affluent enough to drop $60,000 on a solid gold phone, you're probably too busy playing polo and ordering around your servants to care about apps or email anyway.

For those of you who are only rich — as opposed to super rich — Aesir is also making a stainless steel version which will retail for a slightly less mind boggling $10,000. Both devices will debut this fall in Europe, and shortly thereafter in the U.S.

Source: Yahoo 

" Luxury retailer introduces solid gold phone with a $60,000 price tag " !

Tuesday, August 30, 2011

All about ipad 2

There‘s more to it. And even less of it. 
Two cameras for FaceTime and HD video recording. The dual-core A5 chip. The same 10-hour battery life.1 All in a thinner, lighter design. Now iPad is even more amazing. And even less like anything else.
Thinner, lighter, and
full of great ideas.

Once you pick up iPad 2, it’ll be hard to put down.
That’s the idea behind the all-new design. It’s 33 percent thinner and up to 15 percent lighter, so it feels even more comfortable in your hands.2 And it makes surfing the web, checking email, watching movies, and reading books so natural, you might forget there’s incredible technology under your fingers.

Dual-core A5 chip.It’s fast, times two.
Two powerful cores in one A5 chip mean iPad can do twice the work at once. You’ll notice the difference when you’re surfing the web, watching movies, making FaceTime video calls, gaming, and going from app to app to app. Multitasking is smoother, apps load faster, and everything just works better.

Superfast graphics.Go, gamers, go.
With up to nine times the graphics performance, gameplay on iPad is even smoother and more realistic. And faster graphics help apps perform better — especially those with video. You’ll see it when you’re scrolling through your photo library, editing video with iMovie, and viewing animations in Keynote.

Battery life keeps on going. So you can, too.
Even with the new thinner and lighter design, iPad has the same amazing 10-hour battery life.1 That’s enough juice for one flight across the ocean, or one movie-watching all-nighter, or a week’s commute across town. The power-efficient A5 chip and iOS keep battery life from fading away, so you can get carried away.

Two cameras. And a big hello to FaceTime for iPad.
You’ll see two cameras on iPad — one on the front and one on the back. They may be tiny, but they’re a big deal. They’re designed for FaceTime video calling, and they work together so you can talk to your favorite people and see them smile and laugh back at you.3 The front camera puts you and your friend face-to-face. Switch to the back camera during your video call to share where you are, who you’re with, or what’s going on around you. When you’re not using FaceTime, let the back camera roll if you see something movie-worthy. It’s HD, so whatever you shoot is a mini-masterpiece. And you can take wacky snapshots in Photo Booth. It’s the most fun a face can have.

iPad Smart Cover. Designed for iPad. And vice versa.

LED-backlit display.The view is amazing.

Multi-Touch.Everything’s at your fingertips.

iOS 4.The world’s most advanced mobile operating system.

Wi-Fi and 3G.Two great ways to stay connected.

Gyro, accelerometer, and compass.
iPad knows your every move.

AirPlay.Your movie-photo-music stream.

Video mirroring.What you do is what they see.

AirPrint. Print everything wirelessly.

" All about ipad 2 " !

Sunday, August 28, 2011

Computing Future

The history of computers and computer technology thus far has been a long and a fascinating one, stretching back more than half a century to the first primitive computing machines. These machines were huge and complicated affairs, consisting of row upon row of vacuum tubes and wires, often encompassing several rooms to fit it all in.
As anyone who has looked at the world of computers lately can attest, the size of computers has been reduced sharply, even as the power of these machines has increased at an exponential rate. In fact, the cost of computers has come down so much that many households now own not only one, but two, three or even more, PCs.

As the world of computers and computer technology continues to evolve and change, many people, from science fiction writers and futurists to computer workers and ordinary users, have wondered what the future holds for the computer and related technologies. Many things have been pictured, from robots in the form of household servants to computers so small they can fit in a pocket. Indeed, some of these predicted inventions have already come to pass, with the introduction of PDA's and robotic vacuum cleaners.
Beyond these innovations, however, there are likely to be many, many more. One of the most important areas of research in the world of computers is that of artificial intelligence. When many people think of artificial intelligence, they may picture fully aware machines, complete with emotions, and the problems that can arise from them. Even though this remains the goal of many artificial intelligence researchers, in fact artificial intelligence technology is already in place and already serving the needs of humans everywhere.
By a Poll created by HotHardWare about Computing Tool in the next 10 Years Handsets had 34% of 6928 Votes .

Computing Future

" Computing Future " !

Your Choice for Social Network Dominance

A social network is a social structure made up of individuals (or organizations) called "nodes", which are tied (connected) by one or more specific types of interdependency, such as friendship, kinship, common interest, financial exchange, dislike, or relationships of beliefs, knowledge or prestige.

Social network analysis views social relationships in terms of network theory consisting of nodes and ties (also called edges, links, or connections). Nodes are the individual actors within the networks, and ties are the relationships between the actors.

The resulting graph-based structures are often very complex. There can be many kinds of ties between the nodes. Research in a number of academic fields has shown that social networks operate on many levels, from families up to the level of nations, and play a critical role in determining the way problems are solved, organizations are run, and the degree to which individuals succeed in achieving their goals.

In its simplest form, a social network is a map of specified ties, such as friendship, between the nodes being studied. The nodes to which an individual is thus connected are the social contacts of that individual. The network can also be used to measure social capital – the value that an individual gets from the social network. These concepts are often displayed in a social network diagram, where nodes are the points and ties are the lines.
By a Poll created by HotHardWare about Social Network Dominance Google+ had 41% of 1170 Votes .

Social Network
" Your Choice for Social Network Dominance " !

Friday, August 19, 2011

Cell Phones (6)

Along Comes Digital

Digital Cell Phone
Digital cell phones are the second generation (2G) of cellular technology. They use the same radio technology as analog phones, but they use it in a different way. Analog systems do not fully utilize the signal between the phone and the cellular network -- analog signals cannot be compressed and manipulated as easily as a true digital signal.

This is the reason why many cable companies are switching to digital -- so they can fit more channels within a given bandwidth. It is amazing how much more efficient digital systems can be.

Digital phones convert your voice into binary information (1s and 0s) and then compress it (see How Analog-Digital Recording Works for details on the conversion process). This compression allows between three and 10 digital cell-phone calls to occupy the space of a single analog call.

Many digital cellular systems rely on frequency-shift keying (FSK) to send data back and forth over AMPS. FSK uses two frequencies, one for 1s and the other for 0s, alternating rapidly between the two to send digital information between the cell tower and the phone. Clever modulation and encoding schemes are required to convert the analog information to digital, compress it and convert it back again while maintaining an acceptable level of voice quality. All of this means that digital cell phones have to contain a lot of processing power.

Source: How Stuff Works

" Cell Phones (6) " !

Five things you probably didn’t know could be hacked


Hackers are making headlines these days like never before. From video game systems to voice mail accounts, it seems like almost every type of electronic device or information storage medium can be hacked to either give up information or perform actions it wasn't initially designed to do.

We've gathered a handful of the weirdest hacks out there, and the vulnerability of some of your everyday devices might surprise you.

1. Medical implants

High-tech medical devices like pacemakers and insulin pumps can save lives, but hackers can actually utilize their built-in wireless features for less helpful purposes. Researchers have demonstrated that certain pacemakers that use a wireless signal for easy tweaking are vulnerable to anyone with the correct reprogramming hardware.

Doctors use these wireless programming devices to make subtle adjustments to the heart helpers without the need for further surgeries. Unfortunately, the signal they use is unencrypted, meaning that anyone who finds a way to obtain such a device could literally manipulate the heart of a patient, causing cardiac arrest, or even death.

Insulin pumps are apparently even more susceptible to outside interference, and at the recent Black Hat hacker conference in Las Vegas, the life-saving pumps were shown to be vulnerable from distances of up to a half mile. Using power radio antennas, hackers can hijack a pump's wireless signal and cause it to give a blast of insulin to a wearer, with potentially deadly results.

2. Baby monitors

Having a constant ear and eye on your baby's crib is something that most parents take for granted. Baby monitors have been around for a long time, and in recent years, video-equipped versions have become very popular with new parents.

What most users probably don't realize, is that the dozen or so wireless channels that these helpful devices use can often be picked up outside the home — giving anyone with a similar device or wireless receiver an undetectable window into your home.

The vulnerability of such monitor systems was highlighted in 2009 when an Illinois family sued the manufacturer of a baby monitor system they purchased at Toys R Us.

After using the system for months, a neighbor — who had recently purchased a similar system — alerted them that their monitor's camera was broadcasting its signal strong enough to be picked up in the neighboring house. The camera's microphone was so sensitive that the unsuspecting neighbors were able to hear entire conversations happening outside of the nursery where it was placed.

Newer baby monitor models feature "frequency hopping" technology that changes channels randomly to ensure privacy, but older, less-secure versions can still be found on store shelves. Check the features list on the side of the box when considering a monitor system to verify this very the device you're purchasing includes this new technology.

3. Automobiles

Breaking into cars by smashing a window or picking a lock is so 90's. These days, security experts are worried about much more tech-savvy car thieves who can unlock your car, or even start it, simply by shooting it a text message or two. Many automotive systems — such as OnStar — utilize the same type of cellular technology as a common cell phone.

Demonstrating the hack at the Black Hat convention, security experts Don Bailey and Mathew Solnik explained how vulnerable new vehicles are to such manipulation.

Leaving out the details as to how the hack works — he is a security consultant after all — Bailey noted that the same hack could potentially affect infrastructure like power grids and traffic systems. But all it not lost — with just a few changes, car makers could close the door on hackers, though it won't be cheap.

Only vehicles with systems like OnStar are vulnerable in this way, and older, less feature-rich cars are immune to these advanced hacking techniques. Consider the risks when purchasing a vehicle with advanced connectivity and know that you can opt to have these features disabled if you think you may be vulnerable to theft.

4. Garage door openers

A garage door opener is an extremely convenient device, but relying on a handheld gadget to be the gatekeeper of some of your most precious possessions can sometimes backfire. If you've ever taken a look inside your garage door opener to replace its batteries, or perhaps because you dropped it on the ground, you may have noticed a plethora of tiny wires and contact points.

Hackers can easily modify a standard door opener to accept a USB port, and software is readily available on the web to modify how it operates. A number of tutorials can be found online to walk an amateur hacker through the process of hacking your garage door in just minutes.

Thankfully, this vulnerability is typically only an issue for older garage door systems, and newer, more sophisticated openers use a rolling code that changes each time it is used. However, if your opener was made more than 5 years ago, there's a good chance it can easily be hacked, so consider upgrading if you can.

5. The human brain

Of all the storage mediums you use to keep information that is most important to you, your brain is by far the most complex. Because of the immense amount of data that the human brain can hold, scientists have been attempting to crack our internal hard drives for quite some time. The scary part? They're actually getting close.

By building complex models of other brains in the animal kingdom — such as those of mice, cats, and primates — and then moving on to humans, researchers have begun to translate the trillions of impulses that go on in our heads into readable data. In fact, the Defense Advanced Research Projects Agency (DARPA) is funding a $4.9 million program to reverse-engineer the human brain in an effort to mine its computational abilities.

Some scientists, including Ray Kurzweil of Kurzweil Technologies, see a future where microscopic robots will be injected into a person's blood stream, head straight for the brain, and monitor activity. Of course, with the vulnerabilities of other medical implants already well documented, we'd hate to know the consequences of someone taking control of our brain's bots.

Source: Yahoo

" Five things you probably didn’t know could be hacked " !

Tuesday, August 16, 2011

Cell Phones (5)

Analog Cell Phones

Cell Phones
Analog Cell Phones
In 1983, the analog cell-phone standard called AMPS (Advanced Mobile Phone System) was approved by the FCC and first used in Chicago. AMPS uses a range of frequencies between 824 megahertz (MHz) and 894 MHz for analog cell phones. In order to encourage competition and keep prices low, the U. S. government required the presence of two carriers in every market, known as A and B carriers. One of the carriers was normally the local-exchange carrier (LEC), a fancy way of saying the local phone company.

Carriers A and B are each assigned 832 frequencies: 790 for voice and 42 for data. A pair of frequencies (one for transmit and one for receive) is used to create one channel. The frequencies used in analog voice channels are typically 30 kHz wide -- 30 kHz was chosen as the standard size because it gives you voice quality comparable to a wired telephone.

The transmit and receive frequencies of each voice channel are separated by 45 MHz to keep them from interfering with each other. Each carrier has 395 voice channels, as well as 21 data channels to use for housekeeping activities like registration and paging.
A version of AMPS known as Narrowband Advanced Mobile Phone Service (NAMPS) incorporates some digital technology to allow the system to carry about three times as many calls as the original version. Even though it uses digital technology, it is still considered analog. AMPS and NAMPS only operate in the 800-MHz band and do not offer many of the features common in digital cellular service, such as e-mail and Web browsing.

Source: How Stuff Works

" Cell Phones (5) " !

Sunday, August 7, 2011

Cell Phones (4)

Cell-phone Codes

All cell phones have special codes associated with them. These codes are used to identify the phone, the phone's owner and the service provider.
Let's say you have a cell phone, you turn it on and someone tries to call you. Here is what happens to the call:
  • When you first power up the phone, it listens for an SID (see sidebar) on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a "no service" message.
  • When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.
  • Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO knows which cell you are in when it wants to ring your phone.
  • The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.
  • The MTSO picks a frequency pair that your phone will use in that cell to take the call.
  • The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. Now, you are talking by two-way radio to a friend.
  • As you move toward the edge of your cell, your cell's base station notes that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone's signal strength increasing. The two base stations coordinate with each other through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.

Cell-to-Cell Travel:Hand off switches your phone to the new cell
Hand off switches your phone to the new cell

Let's say you're on the phone and you move from one cell to another -- but the cell you move into is covered by another service provider, not yours. Instead of dropping the call, it'll actually be handed off to the other service provider.
If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells. And the amazing thing is that all of this happens within seconds.
The less amazing thing is that you may be charged insane rates for your roaming call. On most phones, the word "roam" will come up on your phone's screen when you leave your provider's coverage area and enter another's. If not, you'd better study your coverage maps carefully -- more than one person has been unpleasantly surprised by the cost of roaming. Check your service contract carefully to find out how much you're paying when you roam.
Note that if you want to roam internationally, you'll need a phone that will work both at home and abroad. Different countries use different cellular access technologies. More on those technologies later. First, let's get some background on analog cell-phone technology so we can understand how the industry has developed.

Cell Phone Codes
Electronic Serial Number (ESN) - a unique 32-bit number programmed into the phone when it is manufactured
Mobile Identification Number (MIN) - a 10-digit number derived from your phone's number
System Identification Code (SID) - a unique 5-digit number that is assigned to each carrier by the FCC
While the ESN is considered a permanent part of the phone, both the MIN and SID codes are programmed into the phone when you purchase a service plan and have the phone activated.

" Cell Phones (4) " !

Thursday, July 28, 2011

Cell Phones (3)

Cell-phone Channels
A single cell in an analog cell-phone system uses one-seventh of the available duplex voice channels. That is, each cell (of the seven on a hexagonal grid) is using one-seventh of the available channels so it has a unique set of frequencies and there are no collisions:
  • A cell-phone carrier typically gets 832 radio frequencies to use in a city.
  • Each cell phone uses two frequencies per call -- a duplex channel -- so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels -- more on this later.)

­Therefore, each cell has about 56 voice channels available. In other words, in any cell, 56 people can be talking on their cell phone at one time. Analog cellular systems are considered first-generation mobile technology, or 1G. With digital transmission methods (2G), the number of available channels increases. For example, a TDMA-based digital system (more on TDMA later) can carry three times as many calls as an analog system, so each cell has about 168 channels available. ­
Cell phones have low-power transmitters in them. Many cell phones have two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts). The base station is also transmitting at low power. Low-power transmitters have two advantages:
  • The transmissions of a base station and the phones within its cell do not make it very far outside that cell. Therefore, in the figure above, both of the purple cells can reuse the same 56 frequencies. The same frequencies can be reused extensively across the city.
  • The power consumption of the cell phone, which is normally battery-operated, is relatively low. Low power means small batteries, and this is what has made handheld cellular phones possible.
The cellular approach requires a large number of base stations in a city of any size. A typical large city can have hundreds of towers. But because so many people are using cell phones, costs remain low per user. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.

" Cell Phones (3) " !

Monday, July 18, 2011

Cell Phones (2)

Cell-phone Frequencies

In the dark ages before cell phones, people who really needed mobile-communications ability installed radio telephones in their cars. In the radio-telephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. This central antenna meant that the phone in your car needed a powerful transmitter -- big enough to transmit 40 or 50 miles (about 70 km). It also meant that not many people could use radio telephones -- there just were not enough channels.
The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously.
A good way to understand the sophistication of a cell phone is to compare it to a CB radio or a walkie-talkie.

  • Full-duplex vs. half-duplex - Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.
  • Channels - A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical cell phone can communicate on 1,664 channels or more!
  • Range - A walkie-talkie can transmit about 1 mile (1.6 km) using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about 5 miles (8 km) using a 5-watt transmitter. Cell phones operate within cells, and they can switch cells as they move around. Cells give cell phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.

In half-duplex radio, both transmitters use the same frequency. Only one party can talk at a time.

In full-duplex radio, the two transmitters use different frequencies, so both parties can talk at the same time.
Cell phones are full-duplex.

In a typical analog cell-phone system in the United States, the cell-phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). Cells are normally thought of as hexagons on a big hexagonal grid, like this:

Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells. The two purple cells can reuse the same frequencies.

Each cell has a base station that consists of a tower and a small building containing the radio equipment. We'll get into base stations later. First, let's examine the "cells" that make up a cellular system.

Source: How Stuff Works

" Cell Phones (2) " !