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CDMA Technology Full Download Seminar Report and Paper Presentation
Post: #1

CDMA Technology

Abstract :

CDMA was developed by QUALCOMM Incorporated, a company in San Diego, California. QUALCOMM engineers decided to do something different and applied spread spectrum techniques to a multiple access system, which ultimately became CDMA.
In spread spectrum, instead of giving each person a channel, or each group of 3 or 8 people a time slot, CDMA puts everyone in the same channel at the same time.
At first thought, it would seem to be an impossible task to make work, but it does work. The reason it works is explained in the first two words of CDMA, Code Division.
Each user in the system is separated from every other user by a unique digital code. And, to make sure everyone could have one of these codes of their own, engineers designed 4.4 trillion of them into the system specification.
The fact is, each user is provided their own code for the reverse link. On the forward link, a group of codes is available for users of the system. There is a little more digital processing going on here that will be explained in more detail later. For now, once CDMA processing is complete, the information is converted to an RF signal and sent out over the air link.

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Post: #2
[attachment=3040]

An Introduction
To
CDMA Technology



Introduction
Short for Code Division Multiple Access
Developed by US company -QUALACOMM
Digital technology for delivering mobile telephone services
uses spread-spectrum techniques


IS-95 CDMA

is based on IS-95 Technology
Supports 95 million subscribers worldwide
Network operate in 800 & 1900 freq. band
Provides voice & data services having speed upto 64 kbits/sec
SMS services also


Benefits of CDMA

Increased Capacity
Improved Quality
Simplified System Planning
Enhanced Privacy
Improved Coverage
Increased Portable Talk Time
Bandwidth on Demand



CDMA-Applications

CDMA for Cellular
CDMA-Short Message Service
Over-the-Air Activation
CDMA Data and Fax
Subscriber Access Control
CDMA for Personal Communications Services


Conclusion


Technology of choice for 3G generation because of itâ„¢s
Greater total capacity
Outstanding voice quality
Fewer dropped calls

RF planning and implementation is simplified by itâ„¢s
Capability of re-using single cell frequency
non-contiguous bandwidth requirement
Itâ„¢s use in satellite communication is of great importance
Post: #3
CDMA
The world is demanding more from wireless communication technologies than ever before as more people around the world are subscribing to wireless. Add in exciting Third-Generation (3G) wireless data services and applications - such as wireless email, web, digital picture taking/sending, assisted-GPS position location applications, video and audio streaming and TV broadcasting - and wireless networks are doing much more than just a few years ago.
This is where CDMA technology fits in. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.
Code-Division Multiple Access, a digital Cellular technology that uses spread-spectrum techniques. Unlike competing systems such as GSM, that use TDMA. CDMA does not assign a specific frequency to each user. Instead, every Channel uses the full available spectrum. Individual conversations are encoded with a pseudo random digital sequence, but give the right to use both to all users simultaneously. To do this, it uses a technique known as Spread Spectrum. In effect, each user is assigned a code which spreads its signal bandwidth in such a way that only the same code can recover it at the receiver end. This method has the property that the unwanted signals
with different codes get spread even more by the process, making them like noise to the receiver.
Spread Spectrum
Spread Spectrum is a mean of transmission where the data occupies a larger bandwidth than necessary. Bandwidth spreading is accomplished before the transmission through the use of a code, which is independent of the transmitted data. The same code is used to demodulate the data at the receiving end. The following figure illustrate the spreading done on the data signal x(t) by the spreading signal c(t) resulting in the message signal to be transmitted, m(t).
Originally for military use to avoid jamming (interference created on purpose to make a communication channel unusable), spread spectrum modulation is now used in personal communication systems for its superior performance in an interference-dominated environment.
Processing Gain
In spread spectrum, the data is modulated by a spreading signal, which uses more bandwidth than the data signal. Since multiplication in the time domain corresponds to convolution in the frequency domain, a narrow band signal multiplied by a wide band signal ends up being wide band. One way of doing this is to use a binary waveform as a spreading function, at a higher rate than the data signal.
Here the three signals corresponds to x(t), c(t) and m(t) discussed above. The first two signals are multiplied together to give the third waveform.
Bits of the spreading signal are called chips. On the above figure, Tb represents the period of one data bit and Tc represents the period of one chip. The chip rate, 1/Tc, is often used to characterize a spread spectrum transmission system.
The Processing Gain or sometimes called the Spreading Factor is defined as the ratio of the information bit duration over the chip duration:
PG = SF = Tb / Tc
Hence, it represents the number of chips contained in one data bit. Higher Processing Gain (PG) means more spreading. High PG also means that more codes can be allocated on the same frequency channel (more on that later).
Pseudo-Noise Sequences
So far we haven't discussed what properties we would want the spreading signal to have. This depends on the type of system we want to implement. Let's first consider a system where we want to use spread spectrum to avoid jamming or narrow band interference.
If we want the signal to overcome narrow band interference, the spreading function needs to behave like noise. Random binary sequences are such functions. They have the following important properties:
Balanced: they have an equal number of 1's and 0's
Single Peak auto “ correlation function
In fact, the auto-correlation function of a random binary sequence is a triangular waveform as in the following figure, where TC is the period of one chip:
Hence the spectral density of such a waveform is a sin function squared, with first zeros at ± 1/TC
PN sequences are periodic sequences that have a noise like behavior. They are generated using shift registers, modulo-2 adders (XOR gates) and feedback loops. The following diagram illustrates this:
The length of the register and the configuration of the feedback network determine the maximum length of a PN sequence. An N bits register can take up to 2N different combinations of zeros and ones. Since the feedback network performs linear operations, if all the inputs (i.e. the content of the flip-flops) are zero, the output of the feedback network will also be zero. Therefore, the all zero combination will always give zero output for all subsequent clock cycles, so we do not include it in the sequence. Thus, the maximum length of any PN sequence is 2N-1 and sequences of that length are called Maximum-Length Sequences or m-sequences. They are useful because longer sequences have better properties. PN sequences are therefore periodic noise like binary functions generated by a network of feedback loops, modulo-2 adders and flip-flops. Maximum length PN functions have a period of 2N-1.
Advantages of CDMA
The advantage of CDMA for personal communication services is its ability to accommodate many user on the same frequency at the same time. As we mentioned earlier, a specific code is assigned to each user and only that code can demodulate the transmitted signal.
There are two ways of separating users in CDMA:
Orthogonal Multiple Access
Non-orthogonal Multiple Access or Asynchronous CDMA
Orthogonal Multiple Access
Each user is assigned one or many orthogonal waveform derived from an orthogonal code. Since the waveforms are orthogonal, users with different codes do not interfere with each other. Orthogonal-CDMA or O-CDMA requires synchronization among the users, since the waveforms are orthogonal only if they are aligned in time.
Orthogonal Codes
An important set of orthogonal code is the Walsh set. Walsh functions are generated using an iterative process of constructing a Hadamard matrix. starting with H1 = [0]. The Hadamard matrix is built by:
For example, here are the Walsh-Hadamard codes of length 2 and 4 respectively:
From the corresponding matrix, the Walsh-Hadamard code words are given by the rows. Note that we usually map the binary data to polar form so we can use real numbers arithmetic when computing the correlations. So 0's are mapped to 1's and 1's are mapped to -1.
Walsh-Hadamard codes are important because they form the basis for orthogonal codes with different spreading factors. This property becomes useful when we want signals with different Spreading Factors to share the same frequency channel. The codes that posses this property are called Orthogonal Variable Spreading Factor (OVSF) codes. To construct such codes, it is better to use a different approach than matrix manipulation. Using a Tree “ Structure allows better visualization of the relation between different code length and orthogonality between them.
For example, let's see if the second codeword of W2 which we will denote W2.2 and the third codeword of W4, W4.3, are orthogonal. Since they are of different length, we repeat W2.2 to match the length of W4.3. Hence we get the following two code words, in polar form:
W2.2 => (1 -1 | 1 -1) and W4.3 => (1 1 -1 -1)
Computing the orthogonality, we get: (multiplying elements by elements)
(1 x 1) + (-1 x 1) + (1 x -1) + (-1 x -1) = 1 - 1 - 1 + 1 = 0
Hence, W2.2 and W4.3 are orthogonal.
However, the auto-correlation function of Walsh-Hadamard code words does not have good characteristics. It can have more than one peak and therefore, it is not possible for the receiver to detect the beginning of the codeword without an external synchronization scheme. The cross - correlation can also be non-zero for a number of time shifts and un-synchronized users can interfere with each other. This is why Walsh-Hadamard codes can only be used in synchronous CDMA.
Walsh-Hadamard codes do not have the best spreading behavior. They do not spread data as well as PN sequences does because there power spectral density is concentrated in a small number of discrete frequencies.
Non-Orthogonal CDMA
The concept behind this is to give up orthogonality among users and reduce the interference by using spread spectrum techniques. PN sequences are used to spread the spectrum. The family of PN sequences, called Gold sequences are in particular popular for non-orthogonal CDMA. Gold sequences have only three cross-correlation peaks, which tend to get less important as the length of the code increases. They also have a single auto-correlation peak at zero, just like ordinary PN sequences.
Gold sequences (codes) are constructed from the modulo-2 addition of two maximum length preferred PN sequences. By shifting one of the two PN sequence, we get a different Gold sequence. This property can be use to generate codes which will permit multiple access on the channel.
The use of Gold sequences permits the transmission to be asynchronous. The receiver can synchronize using the auto-correlation property of the Gold sequence.
THE CONCEPT OF MULTIMEDIA
Murali Krishna Manikyam
1/3 M.C.A II Semester
INTRODUCTION
As the name suggests, multimedia is a set of more than one media element used to produce a concrete and more structured way of communication. In other words multimedia is simultaneous use of data from different sources. These sources in multimedia are known as media elements. With growing and very fast changing information technology, Multimedia has become a crucial part of computer world. Its importance has realized in almost all walks of life, may it be education, cinema, advertising, fashion and what not.
Throughout the 1960s, 1970s and 1980s, computers have been restricted to dealing with two main types of data - words and numbers. But the cutting edge of information technology introduced faster system capable of handling graphics, audio, animation and video. And the entire world was taken aback by the power of multimedia.
OBJECTIVES
explain what is multimedia
understand the importance of individual media elements
identify different hardware components required to run a multimedia
appreciate the impact of audio in educational presentation
describe how visual images, graphics and audio can be added to a presentation
enhance the capability of multimedia through interactive video impact
WHAT IS MULTIMEDIA?
Multimedia is nothing but the processing and presentation of information in a more structured and understandable manner using more than one media such as text, graphics, animation, audio and video. Thus multimedia products can be an academic presentation, game or corporate presentation, information kiosk, fashion-designing etc. Multimedia systems are those computer platforms and software tools that support the interactive uses of text, graphics, animation, audio, or motion video. In other words, a computer capable of handling text, graphics, audio, animation and video is called multimedia computer. If the user can control the sequence and timing of these media elements, then one can name it as Interactive Multimedia.
DIFFERENT MEDIA ELEMENTS
(i) Text
Inclusion of textual information in multimedia is the basic step towards development of multimedia software. Text can be of any type, may be a word, a single line, or a paragraph. The textual data for multimedia can be developed using any text editor. However to give special effects, one needs graphics software which supports this kind of job. Even one can use any of the most popular word processing software to create textual data for inclusion in multimedia. The text can have different type, size, color and style to suit the professional requirement of the multimedia software.
(ii) Graphics
Another interesting element in multimedia is graphics. As a matter of fact, taking into consideration the human nature, a subject is more explained with some sort of pictorial/graphical representation, rather than as a large chunk of text. This also helps to develop a clean multimedia screen, whereas use of large amount of text in a screen make it dull in presentation.
Unlike text, which uses a universal ASCII format, graphics does not have a single agreed format. They have different format to suit different requirement. Most commonly used format for graphics is .BMP or bitmap pictures. The size of a graphics depends on the resolution it is using. A computer image uses pixel or dots on the screen to form itself. And these dots or pixel, when combined with number of colors and other aspects are called resolution. Resolution of an image or graphics is basically the pixel density and number of colors it uses. And the size of the image depends on its resolution. A standard VGA (Virtual Graphics Arrays) screen can display a screen resolution of 640 ´ 480 = 307200 pixel. And a Super VGA screen can display up-to 1024 ´ 768 = 786432 pixel on the screen. While developing multimedia graphics one should always keep in mind the image resolution and number of colors to be used, as this has a direct relation with the image size. If the image size is bigger, it takes more time to load and also requires higher memory for processing and larger disk-space for storage.
However, different graphics formats are available which take less space and are faster to load into the memory.
There are several graphics packages available to develop excellent images and also to compress them so that they take lesser disk-space but use higher resolution and more colours. Packages like Adobe Photo Shop, Adobe Illustrator, PaintShop Pro etc. are excellent graphics packages. There are Graphics gallery available in CDâ„¢s (Compact Disk) with readymade images to suit almost every requirement. These images can directly be incorporated into multimedia development.
(iii) Animation
Moving images have an overpowering effect on the human peripheral vision. Followings are few points for its popularity.
Showing continuity in transitions:
Animation is a set of static state, related to each other with transition. When something has two or more states, then changes between states will be much easier for users to understand if the transitions are animated instead of being instantaneous. An animated transition allows the user to track the mapping between different subparts through the perceptual system instead of having to involve the cognitive system to deduce the mappings.
Indicating dimensionality in transitions:
Sometimes opposite animated transitions can be used to indicate movement back and forth along some navigational dimension. One example used in several user interfaces is the use of zooming to indicate that a new object is grown from a previous one (e.g., a detailed view or property list opened by clicking on an icon) or that an object is closed or minimized to a smaller representation. Zooming out from the small object to the enlargement is a navigational dimension and zooming in again as the enlargement is closed down is the opposite direction along that dimension.
Illustrating change over time
Since animation is a time-varying display, it provides a one-to-one mapping to phenomena that change over time. For example, deforestation of the rain forest can be illustrated by showing a map with an animation of the covered area changing over time.
Multiplexing the display
Animation can be used to show multiple information objects in the same space. A typical example is client-side image maps with explanations that pop up as the user moves the cursor over the various hypertext anchors.
Enriching graphical representations
Some types of information are easier to visualize with movement than with still pictures. Consider, for example, how to visualize the tool used to remove pixels in a graphics application.
Visualizing three-dimensional structures
As you know the computer screen is two-dimensional. Hence users can never get a full understanding of a three-dimensional structure by a single illustration, no matter how well designed. Animation can be used to emphasize the three-dimensional nature of objects and make it easier for users to visualize their spatial structure. The animation need not necessarily spin the object in a full circle - just slowly turning it back and forth a little will often be sufficient. The movement should be slow to allow the user to focus on the structure of the object.
You can also move three-dimensional objects, but often it is better if you determine in advance how best to animate a movement that provides optimal understanding of the object. This pre-determined animation can then be activated by simply placing the cursor over the object. On the other hand, user-controlled movements require the user to understand how to manipulate the object (which is inherently difficult with a two-dimensional control device like the mouse used with most computers - to be honest, 3D is never going to make it big time in user interfaces until we get a true 3D control device).
Attracting attention
Finally, there are a few cases where the ability of animation to dominate the userâ„¢s visual awareness can be turned to an advantage in the interface. If the goal is to draw the userâ„¢s attention to a single element out of several or to alert the user to updated information then an animated headline will do the trick. Animated text should be drawn by a one-time animation (e.g., text sliding in from the right, growing from the first character, or smoothly becoming larger) and never by a continuous animation since moving text is more difficult to read than static text. The user should be drawn to the new text by the initial animation and then left in peace to read the text without further distraction.
One of the excellent software available to create animation is Animator Pro. This provides tools to create impressive animation for multimedia development.
Video
Beside animation there is one more media element, which is known as video. With latest technology it is possible to include video impact on clips of any type into any multimedia creation, be it corporate presentation, fashion design, entertainment games, etc.
The video clips may contain some dialogues or sound effects and moving pictures. These video clips can be combined with the audio, text and graphics for multimedia presentation. Incorporation of video in a multimedia package is more important and complicated than other media elements. One can procure video clips from various sources such as existing video films or even can go for an outdoor video shooting.
All the video available are in analog format. To make it usable by computer, the video clips are needed to be converted into computer understandable format, i.e., digital format. Both combinations of software and hardware make it possible to convert the analog video clips into digital format. This alone does not help, as the digitized video clips take lots of hard disk space to store, depending on the frame rate used for digitization. The computer reads a particular video clip as a series of still pictures called frames. Thus video clip is made of a series of separate frames where each frame is slightly different from the previous one. The computer reads each frame as a bitmap image. Generally there are 15 to 25 frames per second so that the movement is smooth. If we take less frames than this, the movement of the images will not be smooth.
To cut down the space there are several modern technologies in windows environment. Essentially these technologies compress the video image so that lesser space is required.
However, latest video compression software makes it possible to compress the digitised video clips to its maximum. In the process, it takes lesser storage space. One more advantage of using digital video is, the quality of video will not deteriorate from copy to copy as the digital video signal is made up of digital code and not electrical signal. Caution should be taken while digitizing the video from analog source to avoid frame droppings and distortion. A good quality video source should be used for digitization.
Currently, video is good for:
Promoting television shows, films, or other non-computer media that traditionally have used trailers in their advertising.
Giving users an impression of a speakerâ„¢s personality.
Showing things that move. For example a clip from a motion picture. Product demos of physical products are also well suited for video.
Audio:
Audio has a greater role to play in multimedia development. It gives life to the static state of multimedia. Incorporation of audio is one of the most important features of multimedia, which enhance the multimedia usability to its full potential. There are several types of sound, which can be used in multimedia. They are human voices, instrumental notes, natural sound and many more. All these can be used in any combination as long as they give some meaning to their inclusion in multimedia.
There are many ways in which these sounds can be incorporated into the computer. For example;
1. Using microphone, human voice can directly be recorded in a computer.
2. Pre-recorded cassettes can be used to record the sound into computer.
3. Instrumental sound can also be played directly from a musical instrument for recording into the computer.
The sound transmitted from these sources is of analog nature. To enable the computer to process this sound, they need to be digitized.
As all of us know that sound is a repeated pattern of pressure in the air and a microphone converts a sound wave into an electrical wave. The clarity of sound, the final output depends entirely on the shape and frequency of the sound wave. When digitized (recording into computer), the error in sound can be drastically reduced. Audio need to be converted into digital format to produce digitized audio in order to use them in multimedia. And these digitized sounds again can be re-converted into analog form so that the user can hear them though the speakers.
Musical Instrument Digitization Interface or MIDI provides a protocol or a set of rules, using which the details of a musical note from an instrument is communicated to the computer. But MIDI data is not digitized sound. It is directly recorded into the computer from musical instruments, whereas digitized audio is created from the analog sound. The quality of MIDI data depends upon the quality of musical instrument and the sound system. A MIDI file is basically a list command to produce the sound. For example, pressing of a guitar key can be represented as a computer command. When the MIDI device processes this command, the result will be the sound from the guitar. MIDI files occupy lesser space as compared to the digitized audio and they are editable also.
The main benefit of audio is that it provides an exclusive channel that is separate from that of the display. Speech can be used to offer commentary or help without obscuring information on the screen. Audio can also be used to provide a sense of place or mood. Mood-setting audio should employ very quiet background sounds in order not to compete with the main information for the userâ„¢s attention. Music is probably the most obvious use of sound. Whenever you need to inform the user about a certain work of music, it makes much more sense to simply play it than to show the notes or to try to describe it in words.
MULTIMEDIA HARDWARE REQUIREMENTS
For producing multimedia you need hardware, software and creativity. In this section we will discuss the multimedia equipment required in a personal computer (PC) so that multimedia can be produced.
(a) Central Processing Unit
As you know, Central Processing Unit (CPU) is an essential part in any computer. It is considered as the brain of computer, where processing and synchronization of all activities takes place. The efficiency of a computer is judged by the speed of the CPU in processing of data. For a multimedia computer a Pentium processor is preferred because of higher efficiency. However, the CPU of multimedia computer should be at least 486 with math coprocessor. The Pentium processor is one step up the evolutionary chain from the 486 series processor and Pentium Pro is one step above the Pentium. And the speed of the processor is measured in megahertz. It defines the number of commands the computer can perform in a second. The faster the speed, the faster the CPU and the faster the computer will be able to perform. As the multimedia involves more than one medial element, including high-resolution graphics, high quality motion video, and one need a faster processor for better performance.
In todayâ„¢s scenario, a Pentium processor with MMX technology and a speed of 166 to 200 MHz (Megahertz) is an ideal processor for multimedia. In addition to the processor one will need a minimum 16 MB RAM to run WINDOWS to edit large images or video clips. But a 32 or 64 MB RAM enhances the capacity of multimedia computer.
(b) Monitor
As you know that monitor is used to see the computer output. Generally, it displays 25 rows and 80 columns of text. The text or graphics in a monitor is created as a result of an arrangement of tiny dots, called pixels. Resolution is the amount of details the monitor can render. Resolution is defined in terms of horizontal and vertical pixel (picture elements) displayed on the screen. The greater the number of pixels, better visualization of the image.
Like any other computer device, monitor requires a source of input. The signals that monitor gets from the processor are routed through a graphics card. But there are computers available where this card is in-built into the motherboard. This card is also called the graphics adapter or display adapter. This card controls the individual pixels or tiny points on a screen that make up image. There are several types of display adapter available. But the most popular one is Super Virtual Graphics Arrays (SVGA) card and it suits the multimedia requirement. The advantage of having a SVGA card is that the quality of graphics and pictures is better.
Now the PCs, which are coming to the market, are fitted with SVGA graphics card. That allows images of up to 1024 ´ 768 pixels to be displayed in up to 16 millions of colours. What determines the maximum resolution and color depth is the amount of memory on the display adapters. Often you can select the amount of memory required such as 512KB, 1MB, 2MB, 4MB, etc. However, standard multimedia requirement is a 2MB of display memory (or Video RAM). But one must keep in mind that this increases the speed of the computer, also it allows displaying more colours and more resolutions. One can easily calculate the minimum amount of memory required for display adapter as
(Max. Horizontal Resolution x Max. Vertical Resolution ´ Colour Depths. in Bits )/8192 = The minimum video (or display) memory required in KB.
For example, if SVGA resolution (800´600) with 65,536 colours (with colour depth of 16) you will need 937.5 KB, i.e., approximately 1 MB of display memory.
Another consideration should be the refresh rate, i.e., the number of times the images is painted on the screen per second. More the refresh rate, better the image formation. Often a minimum of 70-72Mhz is used to reduce eye fatigue. As a matter of fact higher resolution requires higher refresh rates to prevent screen flickers.
© Video Grabbing Card
As we have already discussed, we need to convert the analog video signal to digital signal for processing in a computer. Normal computer will not be able to do it alone. It requires special equipment called video grabbing card and software to this conversion process. This card translates the analog signal it receives from conventional sources such as a VCR or a video camera, and converts them into digital format. The software available with it will capture this digital signal and store them into computer file. It also helps to compress the digitized video so that it takes lesser disk space as compared to a non-compressed digitized video.
This card is fitted into a free slot on the motherboard inside the computer and gets connected to an outside source such as TV, VCR or a video camera with the help of a cable. This card receives both video and audio signal from the outside source and conversion from analog to digital signal takes place. This process of conversion is known as sampling. This process converts the analog signal to digital data streams so that this signal can be stored in binary data format of 0â„¢s and 1â„¢s. This digital data stream is then compressed using the video capturing software and stores them in the hard disk as a file. This file is then used for incorporation into multimedia. This digitized file can also be edited according to the requirements using various editing software such as Adobe Premiere.
A number of digitizer or video grabbing cards are available in the market. However, one from Intel called Intel Smart Video Recorder III does a very good job of capturing and compressing video.
(d) Sound Card
Todayâ„¢s computers are capable of creating the professional multimedia needs. Not only you can use computer to compose your own music, but it can also be used for recognition of speech and synthesis. It can even read back the entire document for you. But before all this happens, we need to convert the conventional sound signal to computer understandable digital signals. This is done using a special component added to the system called sound card. This is installed into a free slot on the computer motherboard. As in the case of video grabber card, sound card will take the sound input from outside source (such as human voice, pre-recorded sounds, natural sounds etc.) and convert them into digital sound signal of 0â„¢s and 1â„¢s. The recording software used along with the sound card will store this digitized sound stream in a file. This file can latter be used with multimedia software. One can even edit the digitized sound file and add special sound effects into it.
Most popular sound card is from Creative Systems such as Sound Blaster-16, AWE32, etc. AWE32 sound card supports 16 channel, 32 voice and 128 instruments and 10 drums sound reproduction. It also has CD-ROM interface.
(e) CD-ROM Drive
CD-ROM is a magnetic disk of 4.7 inches diameter and it can contain data up to 680 Megabytes. It has become a standard by itself basically for its massive storage capacity, faster data transfer rate. To access CD-ROM a very special drive is required and it is known as CD-ROM drive. Let us look into the term ROM that stands for ËœRead Only Memoryâ„¢. It means the material contained in it can be read (as many times, as you like) but the content cannot be changed.
As multimedia involves high resolution of graphics, high quality video and sound, it requires large amount of storage space and at the same time require a media, which can support faster data transfer. CD-ROM solves this problem by satisfying both requirements.
Similar to the hard disk drive, the CD-ROM drive has certain specification, which will help to decide which drive suit best to your multimedia requirement.
(i) Transfer Rate
Transfer rate is basically the amount of data the drive is capable of transferring at a sustained rate from the CD to the CPU. This is measured in KB per second. For example, 1x drive is capable of transferring 150KB of data from the CD to the CPU. In other terms 1x CD drive will sustain a transfer rate of 150KB/sec, where x stands for 150 KB. This is the base measurement and all higher rates are multiple of this number, x. Latest CD-ROM drive available is of 64x, that means it is capable of sustaining a data transfer rate of 64x150=9600 KB =9.38MB per second from the CD to the CPU.
(ii) Average Seek time
The amount of time lapses between request and its delivery is known as average seeks time. The lower the value betters the result and time is measured in milliseconds. A good access time is 150ms.
Recently computer technology has made tremendous progress. You can now have CDs which can Ëœwrite many, read manyâ„¢ times. This means you can write your files in to a blank CD through a laser beam. The written material can be read many times and they can even be erased and re-written again. Basically this re-writable CDâ„¢s can be used a simple floppy disk.

(f) Scanner
Multimedia requires high quality of images, graphics to be used. And it takes lot of time creating them. However there are ready-made sources such as real life photographs, books, arts, etc. available from where one easily digitized the required pictures. To convert these photographs to digital format, one need a small piece of equipment called scanner attached to the computer. A scanner is a piece of computer hardware that sends a beam of light across a picture or document and records it. It captures images from various sources such as photograph, poster, magazine, book, and similar sources. These pictures then can be displayed and edited on a computer. The captured or scanned pictures can be stored in various formats like;
File Format Explanation
PICT
A widely used format compatible with most Macintosh.
JPEG
Joint Photographic Experts Group - a format that compresses files and lets you choose compression versus quality
TIFF
Tagged Image File Format - a widely used format compatible with both Macintosh and Windows systems
Windows BMP
A format commonly used on MS-DOS and MS-Windows computers
GIF
Graphics Interchange Format - a format used on the Internet, GIF supports only 256 colors or grays. Scanners are available in various shapes and sizes like hand-held, feed-in, and flatbed types. They are also for scanning black-and-white only or color. Some of the reputed vendors of scanner are Epson, Hewlett-Packard, Microtek and Relisys.
(g) Touch screen
As the name suggests, touch screen is used where the user is required to touch the surface of the screen or monitor. It is basically a monitor that allows user to interact with computer by touching the display screen. This uses beams of infrared light that are projected across the screen surface. Interrupting the beams generates an electronic signal identifying the location of the screen. And the associated software interprets the signal and performs the required action. For example, touching the screen twice in quick succession works as double clicking of the mouse. Imagine how useful this will be for visually handicapped people who can identify things by touching a surface. Touch screen is normally not used for development of multimedia, it is rather used for multimedia presentation arena like trade show, information kiosk, etc.
Uses of Multimedia
Placing the media in a perspective within the instructional process is an important role of the teacher and library professional. Following are the possible areas of application of multimedia:
l Can be used as reinforcement
l Can be used to clarify or symbolize a concept
l Creates the positive attitude of individuals toward what they are learning and the learning process itself can be enhanced.
l The content of a topic can be more carefully selected and organized
l The teaching and learning can be more interesting and interactive
l The delivery of instruction can be more standardized.
l The length of time needed for instruction can be reduce
Post: #4
[attachment=3190]

CDMA Technology Overview

CDMA Basics
Course Objectives
Upon completion of this course, you will have an understanding of the following concepts:
CDMA and other access technologies
CDMA coding, forward, and reverse channels
Vocoding, multiplexing, and power control
Components that comprise a CDMA system
CDMA messaging and call flow

Why CDMA?

CDMA is the technology of choice for both 800 MHz Cellular and 1900 MHz PCS service providers
CDMA satisfies CTIA Usersâ„¢ Performance Requirements
CDMA provides high capacity (many times the capacity of AMPS)
CDMA provides privacy through its coding scheme
What is Multiple Access?
Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit
Types of Media
Twisted pair - copper
Coaxial cable
Fiber optic cable
Air interface (radio signals)
Advantages of Multiple Access
Increased capacity: serve more users
Reduced capital requirements since fewer media can carry the traffic
Decreased per-user expense
Easier to manage and administer
Multiple Access Technologies
The physical transmission medium is a resource that can be subdivided into individual channels according to different criteria depending on the technology used:
Hereâ„¢s how the three most popular technologies establish channels:
FDMA (Frequency Division Multiplex Access)
each user on a different frequency
a channel is a frequency
TDMA (Time Division Multiplex Access)

each user on a different window period in time (time slot)
a channel is a specific time slot on a specific frequency
CDMA (Code Division Multiplex Access)
each user uses the same frequency all the time, but mixed with different distinguishing code patterns
a channel is a unique set of code patterns
Defining Our Terms
CDMA Channel or CDMA Carrier or CDMA Frequency

Duplex channel made of two 1.25 MHz-wide bands of electromagnetic spectrum, one for Base Station to Mobile Station communication (called the FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base Station communication (called the REVERSE LINK or the UPLINK)
In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart
In 1900 MHz PCS they are 80 MHz apart
CDMA Forward Channel

1.25 MHz Forward Link
CDMA Reverse Channel
1.25 MHz Reverse Link
CDMA Code Channel
Each individual stream of 0â„¢s and 1â„¢s contained in either the CDMA Forward Channel or in the CDMA Reverse Channel
Code Channels are characterized (made unique) by mathematical codes
Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic channels
Code channels in the reverse link: Access and Reverse Traffic channels
CDMA Is a Spread-Spectrum System
Traditional technologies try to squeeze the signal into the minimum required bandwidth
Direct-Sequence Spread spectrum systems mix their input data with a fast spreading sequence and transmit a wideband signal
The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data
The de-spreading gives substantial gain proportional to the bandwidth of the spreading signal
CDMA uses a larger bandwidth but then uses resulting processing gain to increase capacity
Spread Spectrum Principles
Spread Spectrum Principles
Spread Spectrum Principles
Anything We Can Do, We Can Undo
Any data bit stream can be combined with a spreading sequence
The resulting signal can be de-spread and the data stream recovered if the original spreading sequence is available and properly synchronized
After de-spreading, the original data stream is recovered intact
Shipping and Receiving via CDMA
Whether in shipping and receiving, or in CDMA, packaging is extremely important!
Cargo is placed inside nested containers for protection and to allow addressing
The shipper packs in a certain order, and the receiver unpacks in the reverse order
CDMA containers are spreading codes
CDMAâ„¢s Nested Spreading Sequences
CDMA combines three different spreading sequences to create unique, robust channels
The sequences are easy to generate on both sending and receiving ends of each link
The sequences are applied in succession at the sending end and then reapplied in opposite order to recover the original data stream at the receiving end
Walsh Codes
64 Sequences, each 64 chips long
a chip is a binary digit (0 or 1)
Each Walsh Code is Orthogonal to all other Walsh Codes
It is possible to recognize, and therefore extract, a particular Walsh code from a mixture of other Walsh codes that are filtered out in the process
Two same-length binary strings are orthogonal if the result of XORing them has the same number of 0s as 1s
Correlation and Orthogonality
The Short PN Sequences
The two Short PN Sequences, I and Q, are 32,768 chips long
Together they can be considered a two-dimensional binary vector with distinct I and Q component sequences, each 32,768 chips long
Each Short PN Sequence (and, as a matter of fact, any sequence) correlates with itself perfectly if compared at a timing offset of 0 chips
Each Short PN Sequence is special: Orthogonal to a copy of itself that has been offset by any number of chips (other than 0)
The Long PN Sequence
Each mobile station uses a unique User Long Code Sequence generated by applying a mask, based on its 32-bit ESN, to the 42-bit Long Code Generator which was synchronized with the CDMA system during the mobile station initialization
Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete
Portions of the Users Long Codes generated by different mobile stations for the duration of a call are not exactly orthogonal but are sufficiently different to permit reliable decoding on the reverse link
How Many Spreading Codes Do We Need?
(Discriminating Among Forward Code Channels)
A Mobile Station tuned to a particular CDMA frequency receives a Forward CDMA Channel from a sector in a Base Station.
This Forward CDMA Channel carries a composite signal made of up to 64 forward code channels
Some of these code channels are traffic channels while other are overhead channels needed by the CDMA system to operate properly.
A set of 64 mathematical codes is needed to differentiate the 64 possible forward code channels that can be contained in a Forward CDMA Channel.
The codes in this set are called Walsh Codes
How Many Spreading Codes Do We Need?
(Discriminating Among Base Stations)
A mobile Station is surrounded by Base Stations, all of them transmitting on the same CDMA Frequency
Each Sector in each Base Station is transmitting a CDMA Forward Traffic Channel containing up to 64 distinct forward code channels
A Mobile Station must be able to discriminate between different Sectors of different Base Stations and listen to only one set of code channels
Two binary digit sequences called the I and Q Short PN Sequences (or Short PN Codes) are defined for the purpose of identifying sectors of different base stations
These Short PN Sequences can be used in 512 different ways in a CDMA system. Each one of them constitutes a mathematical code which can be used to identify a particular sector of a particular base station
How Many Spreading Codes Do We Need?
(Discriminating Among Reverse Code Channels)
The CDMA system must be able to uniquely identify each Mobile Station that may attempt to communicate with a Base Station
A very large number of Mobile Stations will be in the market
One binary digit sequence called the Long PN Sequence (or Long PN Code) is defined for the purpose of uniquely identifying each possible reverse code channel
This sequence is extremely long and can be used in trillions of different ways. Each one of them constitutes a mathematical code which can be used to identify a particular user (and is then called a User Long Code) or a particular access channel (explained later in this course)
Summary of Characteristics & Functions
Lesson Review
If a signal is deliberately transmitted using more RF bandwidth than required, it is easier to detect at the receiver. This waste is formally defined as what?
Processing gain
What vocoder function stores a collection of arbitrary waveform segments?
Code book
Are all CDMA Walsh Codes orthogonal?

Yes
What sequence best describes this conversion relationship in CDMA:
chips à symbols à bits
List the four overhead (support) channels.
Paging, sync, access, pilot
Post: #5
[attachment=3890]


CDMA Technology
Presented By:

- Gudimetla Sri Latha
1/3 M.C.A II Semester

CDMA

The world is demanding more from wireless communication technologies than ever before as more people around the world are subscribing to wireless. Add in exciting Third-Generation (3G) wireless data services and applications - such as wireless email, web, digital picture taking/sending, assisted-GPS position location applications, video and audio streaming and TV broadcasting - and wireless networks are doing much more than just a few years ago.
This is where CDMA technology fits in. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

Code-Division Multiple Access, a digital Cellular technology that uses spread-spectrum techniques. Unlike competing systems such as GSM, that use TDMA. CDMA does not assign a specific frequency to each user. Instead, every Channel uses the full available spectrum. Individual conversations are encoded with a pseudo random digital sequence, but give the right to use both to all users simultaneously. To do this, it uses a technique known as Spread Spectrum. In effect, each user is assigned a code which spreads its signal bandwidth in such a way that only the same code can recover it at the receiver end. This method has the property that the unwanted signals
with different codes get spread even more by the process, making them like noise to the receiver.
Spread Spectrum
Spread Spectrum is a mean of transmission where the data occupies a larger bandwidth than necessary. Bandwidth spreading is accomplished before the transmission through the use of a code, which is independent of the transmitted data. The same code is used to demodulate the data at the receiving end. The following figure illustrate the spreading done on the data signal x(t) by the spreading signal c(t) resulting in the message signal to be transmitted, m(t).

Originally for military use to avoid jamming (interference created on purpose to make a communication channel unusable), spread spectrum modulation is now used in personal communication systems for its superior performance in an interference-dominated environment.

Processing Gain

In spread spectrum, the data is modulated by a spreading signal, which uses more bandwidth than the data signal. Since multiplication in the time domain corresponds to convolution in the frequency domain, a narrow band signal multiplied by a wide band signal ends up being wide band. One way of doing this is to use a binary waveform as a spreading function, at a higher rate than the data signal.

Here the three signals corresponds to x(t), c(t) and m(t) discussed above. The first two signals are multiplied together to give the third waveform.
Bits of the spreading signal are called chips. On the above figure, Tb represents the period of one data bit and Tc represents the period of one chip. The chip rate, 1/Tc, is often used to characterize a spread spectrum transmission system.
The Processing Gain or sometimes called the Spreading Factor is defined as the ratio of the information bit duration over the chip duration:
PG = SF = Tb / Tc
Hence, it represents the number of chips contained in one data bit. Higher Processing Gain (PG) means more spreading. High PG also means that more codes can be allocated on the same frequency channel (more on that later).
Pseudo-Noise Sequences

So far we haven't discussed what properties we would want the spreading signal to have. This depends on the type of system we want to implement. Let's first consider a system where we want to use spread spectrum to avoid jamming or narrow band interference.
If we want the signal to overcome narrow band interference, the spreading function needs to behave like noise. Random binary sequences are such functions. They have the following important properties:
Balanced: they have an equal number of 1's and 0's
Single Peak auto “ correlation function
In fact, the auto-correlation function of a random binary sequence is a triangular waveform as in the following figure, where TC is the period of one chip:

Hence the spectral density of such a waveform is a sin function squared, with first zeros at ± 1/TC
PN sequences are periodic sequences that have a noise like behavior. They are generated using shift registers, modulo-2 adders (XOR gates) and feedback loops. The following diagram illustrates this:

The length of the register and the configuration of the feedback network determine the maximum length of a PN sequence. An N bits register can take up to 2N different combinations of zeros and ones. Since the feedback network performs linear operations, if all the inputs (i.e. the content of the flip-flops) are zero, the output of the feedback network will also be zero. Therefore, the all zero combination will always give zero output for all subsequent clock cycles, so we do not include it in the sequence. Thus, the maximum length of any PN sequence is 2N-1 and sequences of that length are called Maximum-Length Sequences or m-sequences. They are useful because longer sequences have better properties. PN sequences are therefore periodic noise like binary functions generated by a network of feedback loops, modulo-2 adders and flip-flops. Maximum length PN functions have a period of 2N-1.

Advantages of CDMA

The advantage of CDMA for personal communication services is its ability to accommodate many user on the same frequency at the same time. As we mentioned earlier, a specific code is assigned to each user and only that code can demodulate the transmitted signal.
There are two ways of separating users in CDMA:
¢ Orthogonal Multiple Access
¢ Non-orthogonal Multiple Access or Asynchronous CDMA
Orthogonal Multiple Access
Each user is assigned one or many orthogonal waveform derived from an orthogonal code. Since the waveforms are orthogonal, users with different codes do not interfere with each other. Orthogonal-CDMA or O-CDMA requires synchronization among the users, since the waveforms are orthogonal only if they are aligned in time.
Orthogonal Codes
An important set of orthogonal code is the Walsh set. Walsh functions are generated using an iterative process of constructing a Hadamard matrix. starting with H1 = [0]. The Hadamard matrix is built by:

For example, here are the Walsh-Hadamard codes of length 2 and 4 respectively:

From the corresponding matrix, the Walsh-Hadamard code words are given by the rows. Note that we usually map the binary data to polar form so we can use real numbers arithmetic when computing the correlations. So 0's are mapped to 1's and 1's are mapped to -1.
Walsh-Hadamard codes are important because they form the basis for orthogonal codes with different spreading factors. This property becomes useful when we want signals with different Spreading Factors to share the same frequency channel. The codes that posses this property are called Orthogonal Variable Spreading Factor (OVSF) codes. To construct such codes, it is better to use a different approach than matrix manipulation. Using a Tree “ Structure allows better visualization of the relation between different code length and orthogonality between them.
For example, let's see if the second codeword of W2 which we will denote W2.2 and the third codeword of W4, W4.3, are orthogonal. Since they are of different length, we repeat W2.2 to match the length of W4.3. Hence we get the following two code words, in polar form:
W2.2 => (1 -1 | 1 -1) and W4.3 => (1 1 -1 -1)
Computing the orthogonality, we get: (multiplying elements by elements)
(1 x 1) + (-1 x 1) + (1 x -1) + (-1 x -1) = 1 - 1 - 1 + 1 = 0
Hence, W2.2 and W4.3 are orthogonal.
However, the auto-correlation function of Walsh-Hadamard code words does not have good characteristics. It can have more than one peak and therefore, it is not possible for the receiver to detect the beginning of the codeword without an external synchronization scheme. The cross - correlation can also be non-zero for a number of time shifts and un-synchronized users can interfere with each other. This is why Walsh-Hadamard codes can only be used in synchronous CDMA.
Walsh-Hadamard codes do not have the best spreading behavior. They do not spread data as well as PN sequences does because there power spectral density is concentrated in a small number of discrete frequencies.
Non-Orthogonal CDMA

The concept behind this is to give up orthogonality among users and reduce the interference by using spread spectrum techniques. PN sequences are used to spread the spectrum. The family of PN sequences, called Gold sequences are in particular popular for non-orthogonal CDMA. Gold sequences have only three cross-correlation peaks, which tend to get less important as the length of the code increases. They also have a single auto-correlation peak at zero, just like ordinary PN sequences.
Gold sequences (codes) are constructed from the modulo-2 addition of two maximum length preferred PN sequences. By shifting one of the two PN sequence, we get a different Gold sequence. This property can be use to generate codes which will permit multiple access on the channel.
The use of Gold sequences permits the transmission to be asynchronous. The receiver can synchronize using the auto-correlation property of the Gold sequence.
Post: #6
Prepared By
Shashank arora,

[attachment=10913]
Type of Multiplexing:
Frequency-Division Multiple Access (FDMA)
Time-Division Multiple Access (TDMA).
Code-division Multiple-Access (CDMA)
Frequency-Division Multiple Access (FDMA)
It is a communications technique that divides a communications channel into a number of equally spaced frequency bands
Time-Division Multiple Access (TDMA)
It is a digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel.
Code Division Multiple Access (CDMA)
is a wireless communications technology that uses the principle of spread spectrum communication.
There are three ways to spread the bandwidth of the signal:
 Frequency hopping
 Time hopping
 Direct sequence
 CDMA is a Direct Sequence Spread Spectrum system
CDMA Features:
o All users use same frequency and may transmit simultaneously
o Narrowband message signal multiplied by wideband spreading signal, or codeword
o Each user has its own pseudo-codeword (orthogonal to others).
o Receivers detect only the desired codeword. All others appear
as noise.
o Receivers must know transmitter’s codeword.
Advantages:
o Increased capacity
o Improved voice quality
o Eliminating the audible effects of multipath fading
o Enhanced privacy and security
o Reduced average transmitted power
o Reduced interference to other electronic devices
Disadvantages:
o Wide bandwidth per user required
o Precision code synchronization needed
o The Future Planning For Next Semester
o Study the capacity of CDMA
 Study the interference rises from the increasing of capacity and how to reduce its effect
 We will evaluate interference and capacity in CDMA system and analysize them using MatLab simulator
Post: #7
eqWIOJF;QEFH AEUDFHA ARQulwem ncwerhban dcb
Post: #8
you can refer these page details of "CDMA Technology Full Download Seminar Report and Paper Presentation"link bellow
http://seminarprojectst-cdma-technology-full-download-seminars-report-and-paper-presentation
Post: #9
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Post: #10
to get the information about the topic"CDMA Technology Full Download Seminar Report and Paper Presentation" refer the link bellow

http://seminarprojectst-cdma-technology-full-download-seminars-report-and-paper-presentation
 

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