Role of Visual in Web Communication

Visual aids are often used to help audiences of informative and persuasive speeches understand

the topic being presented. Visual aids can play a large role in how the audience understands and takes in information that is presented. There are many different types of visual aids that range from handouts to powerpoints. The type of visual aid a speaker uses depends on their preference and the information they are trying to present. Each type of visual aid has pros and cons that must be evaluated to ensure it will be beneficial to the overall presentation. Before incorporating visual aids into speeches, the speaker should understand that if used incorrectly, the visual will not be an aid, but a distraction. Planning ahead is important when using visual aids. It is necessary to choose a visual aid that is appropriate for the material and audience. The purpose of the visual aid is to enhance the presentation.

Types of Visual Aids

• Objects

    The use of objects as visual aids involves bringing the actual object to demonstrate on during the speech. For example, a speech about tying knots would be more effective by bringing in a rope.

    Pro: the use of the actual object is often necessary when demonstrating how to do something so that the audience can fully understand procedure.

    Con: some objects are too large or unavailable for a speaker to bring with them.

• Models

    Models are representations of another object that serve to demonstrate that object when use of the real object is ineffective for some reason. Examples include human skeletal systems, the solar system, or architecture.

    Pros: models can serve as substitutes that provide a better example of the real thing to the audience when the object being spoken about is of an awkward size or composure for use in the demonstration.

    Cons: sometimes a model may take away from the reality of what is being spoken about. For example, the vast size of the solar system cannot be seen from a model, and the actual composure of a human body cannot be seen from a dummy.

• Graphs

    Graphs are used to visualize relationships between different quantities. Various types are used as visual aids, including bar graphs, line graphs, pie graphs, and scatter plots.

    Pros: graphs help the audience to visualize statistics so that they make a greater impact than just listing them verbally would.

    Cons: graphs can easily become cluttered during use in a speech by including too much detail, overwhelming the audience and making the graph ineffective.

• Maps

Maps show geographic areas that are of interest to the speech. They often are used as aids when speaking of differences between geographical areas or showing the location of something.

    Pros: when maps are simple and clear, they can be used to effectively make points about certain areas. For example, a map showing the building site for a new hospital could show its close location to key neighborhoods, or a map could show the differences in distribution of AIDS victims in North American and African countries.

    Cons: inclusion of too much detail on a map can cause the audience to lose focus on the key point being made. Also, if the map is disproportional or unrealistic, it may prove ineffective for the point being made.

• Tables

    Tables are columns and rows that organize words, symbols, and/or data.

    Pros: Good tables are easy to understand. They are a good way to compare facts and to gain a better overall understanding of the topic being discussed. For example, a table is a good choice to use when comparing the amount of rainfall in 3 counties each month.

    Cons: Tables are not very interesting or pleasing to the eye. They can be overwhelming if too much information is in a small space or the information is not organized in a convenient way. A table is not a good choice to use if the person viewing it has to take a lot of time to be able to understand it. Tables can be visual distractions if it is hard to read because the font is too small or the writing is too close together. It can also be a visual distraction if the table is not drawn evenly.

• Photographs

    Pros:Photographs are good tools to make or emphasize a point or to explain a topic. For example, when explaining the shanty-towns in a third world country it would be beneficial to show a picture of one so the reader can have a better understanding of how those people live. A photograph is also good to use when the actual object cannot be viewed. For example, in a health class learning about cocaine, the teacher cannot bring in cocaine to show the class because that would be illegal, but the teacher could show a picture of cocaine to the class. Using local photos can also help emphasize how your topic is important in the audience's area.[8]

    Cons: If the photograph is too small it just becomes a distraction. Enlarging photographs can be expensive if not using a powerpoint or other viewing device.

• Drawings/Diagrams

    Pros: Drawings or diagrams can be used when photographs do not show exactly what the speaker wants to show or explain. It could also be used when a photograph is too detailed. For example, a drawing or diagram of the circulatory system throughout the body is a lot more effective than a picture of a cadaver showing the circulatory system.

    Cons:If not drawn correctly a drawing can look sloppy and be ineffective. This type of drawing will appear unprofessional.

Visual Aids Media: Simple to Advanced

• Chalkboard or Whiteboard

Chalkboards and whiteboards are very useful visual aids, particularly when more advanced types of media are unavailable. They are cheap and also allow for much flexibility. The use of chalkboards and whiteboards is convenient, but they are not a perfect visual aid. Often, using this medium as an aid can create confusion or boredom. Particularly if a student who is not familiar with how to properly use visual aids attempts to draw on a board while they are speaking, they detract time and attention from their actual speech.

• Poster Board

A poster is a very simple and easy visual aid. Posters can display charts, graphs, pictures, or illustrations. The biggest drawback of using a poster as a visual aid is that often a poster can appear unprofessional. Since a poster board paper is relatively flimsy, often the paper will bend or fall over. The best way to present a poster is to hang it up or tape it to a wall.

• Handouts

Handouts can also display charts, graphs, pictures, or illustrations. An important aspect of the use of a handout is that a person can keep a handout with them long after the presentation is over. This can help the person better remember what was discussed. Passing out handouts, however, can be extremely distracting. Once a handout is given out, it might potentially be difficult to bring back your audience’s attention. The person who receives the handout might be tempted to read what is on the paper, which will keep them from listening to what the speaker is saying. If using a handout, the speaker distributes the hand out right before you reference it. Distributing handouts is acceptable in a lecture that is an hour or two, but in a short lecture of five to ten minutes, a handout should not be used.

• Video Excerpts

A video can be a great visual aid and attention grabber, however, a video is not a replacement for an actual speech. There are several potential drawbacks to playing a video during a speech or lecture. First, if a video is playing that includes audio, the speaker will not be able to talk. Also, if the video is very exciting and interesting, it can make what the speaker is saying appear boring and uninteresting. The key to showing a video during a presentation is to make sure to transition smoothly into the video and to only show very short clips.

• Projection Equipment

There are several types of projectors. These include slide projectors, PowerPoint presentations, overhead projectors, and computer projectors. Slide projectors are the oldest form of projector, and are no longer used. PowerPoint presentations are very popular and are used often. Overhead projectors are still used but are somewhat inconvenient to use. In order to use an overhead projector, a transparency must be made of whatever is being projected onto the screen. This takes time and costs money. Computer projectors are the most technologically advanced projectors. When using a computer projector, pictures and slides are easily taken right from a computer either online or from a saved file and are blown up and shown on a large screen. Though computer projectors are technologically advanced, they are not always completely reliable because technological breakdowns are not uncommon of the computers of today.

• Computer-Assisted Presentations

PowerPoint presentations can be an extremely useful visual aid, especially for longer presentations. For five to ten minute presentations, it is probably not worth the time or effort to put together a PowerPoint. For longer presentations, however, PowerPoints can be a great way to keep the audience engaged and keep the speaker on track. A potential drawback of using a PowerPoint is that it usually takes a lot of time and energy to put together. There is also the possibility of a computer malfunction, which can mess up the flow of a presentation.

Understanding Visuals

Visual communication: Image analysis

Visual communication contains image aspects. The interpretation of images is subjective and to understand the depth of meaning, or multiple meanings, communicated in an image requires analysis. Images can be analysed through many perspectives, for example these six major perspectives presented by Paul Martin Lester:

• Personal perspective: When a viewer has an opinion about an image based on their personal thoughts. Personal response depends on the viewer’s thoughts and values individually. This might be sometimes in conflict with cultural values. Also when a viewer has viewed an image with a personal perspective, it is then hard to change the view of the image on the viewer, even the image also can be seen in other ways.

• Historical perspective: An image’s view can be arising from the history of the use media. Through times sort images have been changed, because the use of different (new) media. For example: The result of using the computer to edit images (e.g. Photoshop) is quite different when comparing images that are made and edited by craft.

• Technical perspective: When the view of an image is influenced by the use of lights, position and the presentation of the image. The right use of light, position and presentation of the image can improve the view of the image. It makes the image looks better than the reality.

• Ethical perspective: From this perspective, the maker of the image, the viewer and the image itself must be responsible morally and ethically to the image. This perspective is also categorized in six categories: categorical imperative, utilitarianism, hedonism, golden mean, golden rule and veil of ignorance.

• Cultural perspective: Symbolization is an important definition for this perspective. Cultural perspective involves identity of symbols. The uses of words that are related with the image, the use of heroes in the image, etc. are the symbolization of the image. The cultural perspective can also be seen as the semiotic perspective.

• Critical perspective: The view of images in the critical perspective is when the viewers criticise the images, but the critics have been made in interests of the society, although an individual makes the critics. This way this perspective differs from the personal perspective.

Visual Communication: Introduction, Definition, Significance

Visual communication as the name suggests is communication through visual aid and is described as the conveyance of ideas and information in forms that can be read or looked upon. Visual communication in part or whole relies on vision, and is primarily represented or expressed with two dimensional images, it includes: signs, typography, drawing, graphic design, illustration, colour and electronic resources. It also explores the idea that a visual message accompanying text has a greater power to inform, educate, or persuade a person or audience.

The evaluation of a good visual communication design is mainly based on measuring comprehension by the audience, not on personal aesthetic and/or artistic preference as there are no universally agreed-upon principles of beauty and ugliness. Excluding two dimensional images, there are other ways to express information visually - gestures and body language, animation (digital or analogue), and film. Visual communication by e-mail, a textual medium, is commonly expressed with ASCII art, emoticons, and embedded digital images.

The term 'visual presentation' is used to refer to the actual presentation of information through a visible medium such as text or images. Recent research in the field has focused on web design and graphically-oriented usability. Graphic designers also use methods of visual communication in their professional practice. Visual communication on the World Wide Web is perhaps the most important form of communication that takes place while users are surfing the Internet. When experiencing the web, one uses the eyes as the primary sense, and therefore the visual presentation of a website is very important for users to understand the message or of the communication taking place.

The Eye of Horus is often referred to as the symbol of visual communication.[citation needed] It is said to be a representation of an eclipse, as the corona around the pupil is like the corona around the sun during a solar eclipse.

Definition of visual communication

Visual Communication is the conveyance of ideas and information in forms that can be read or viewed. The subject includes Graphic Design, Illustration and Animation for; books, print, magazines, screen-based media, interactive web design, short film, design for advertising, promotion, corporate identity, packaging design,etc.

Significance of visual communication

Immediacy

One of the primary benefits from visual communication over verbal is immediacy. Think back to the last time you tried to explain something complex to a friend, coworker, family member, more often than not in these situations you spend long periods of time making sure your audience understands what it is you’re explaining. Now, contrast that experience with looking at a chart explaining the sales for a specific product, you can show that information almost instantaneously. Visual Communication can bring a thing, location and even and idea to life in dynamic ways.

Simplicity

Another advantage is simplicity. Often visual communication can simplify the information of ideas that you are seeking to pass on to others. For example, architects use visual diagrams and schematics to pass on valuable information to contractors in a quick, easy to understand manner. Visual communication can also demonstrate the relationship between two entities or ideas in accessible ways.

Flexibility

Visual communication can also be more flexible in many ways than verbal communication. Visual communication not only bridges geographic distances, it can span cultural references. If you are looking to appeal to a broad demographic audience, such as a television or cable audience, visual images may allow you to reach more people with your message. Appealing visual images will often be more persuasive than verbal pitches.

Multimedia communication

Multimedia communication deals with the transfer, the protocols, services and mechanisms of discrete media data (such as text and graphics) and continuous media data (like audio and video) in/over digital networks.

Such a communication requires all involved components to be capable of handling a well-defined quality of service. The most important quality of service parameters are used to request (1) the required capacities of the involved resources, (2) compliance to end-to-end delay and jitter as timing restrictions, and (3) restriction of the loss characteristics.

Multimedia systems have attracted much attention during the last few years in the society as a whole and in the information technology field in particular. Multimedia communication comprises the techniques needed for distributed multimedia systems. To enable the access to information such as audio and video data, techniques must be developed which allow for the handling of audiovisual information in computer and communication systems.

We first describe in a more precise way what we mean by the term “multimedia”. Unfortunately,

“multimedia” has become a buzzword used to denote any kind of “new digital media” being manipulated or displayed by machines. This very imprecise (and very often employed) notion leads to a labelling of all types of media data computation, transmission, storage, manipulation and presentation with the term “multimedia”. Since the mid eighties we have proposed (and even from time to time we imposed) a much more crisp and restricted specification.

Multimedia itself denotes the integrated manipulation of at least some information represented

as continuous media data as well as some information encoded as discrete media data (such as text and graphics). The “manipulation” refers to the act of capturing, processing, communication, presentation and/or storage.

Hence “multimedia communications” deals with the transfer, the protocols, the services and the mechanisms of/for discrete and continuous media in/over digital networks. The transmission of digital video data over a dedicated TV distribution network is not multimedia as long as it does not allow the transfer of some type of discrete media data as well. A protocol designed to reserve capacity for continuous media data transmitted in conjunction with discrete media data over, e.g., an ATM-LAN, is certainly a multimedia communication issue.

Information processing in a time-sharing environment is performed without any hard time constraints. The system responds to a user interaction as soon as possible but often lacks support for realtime data. The use of discrete media still governs traditional computing, while the integration of continuous media into existing computer environments creates the new complexity of time-dependent data processing. ‘Correctness’ in multimedia communications is – in addition to the traditional computer communications error handling – determined by whether deadlines are met or not.

In networked multimedia applications various entities typically cooperate in order to provide the

mentioned real-time guarantees to allow data to be presented at the user interface. These requirements are most often defined in terms of Quality of Service (QoS). QoS is defined as the set of parameters which defines the properties of media streams. In accordance with [StNa95] we distinguish four layers of QoS: User QoS, Application QoS, System QoS and Network QoS. The user QoS parameters describe requirements for the perception of multimedia data at the user interface. The application QoS parameters describe requirements for the application services possibly specified in terms of media quality (like end-to-end delay) and media relations (like inter/intra-stream synchronization). The system QoS parameters describe requirements on the communication services resulting from the application QoS. These may be specified in terms of both quantitative (like bits per second or task processing time) and qualitative (like multicast, interstream synchronization, error recovery or ordered delivery of data) criteria. The network QoS parameters describe requirements on network services (like network load or network performance).

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries a vast range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support electronic mail.

Most traditional communications media including telephone, music, film, and television are reshaped or redefined by the Internet, giving birth to new services such as Voice over Internet Protocol (VoIP) and IPTV. Newspaper, book and other print publishing are adapting to Web site technology, or are reshaped into blogging and web feeds. The Internet has enabled or accelerated new forms of human interactions through instant messaging, Internet forums, and social networking. Online shopping has boomed both for major retail outlets and small artisans and traders. Business-to-business and financial services on the Internet affect supply chains across entire industries.

The origins of the Internet reach back to research of the 1960s, commissioned by the United States government in collaboration with private commercial interests to build robust, fault-tolerant, and distributed computer networks. The funding of a new U.S. backbone by the National Science Foundation in the 1980s, as well as private funding for other commercial backbones, led to worldwide participation in the development of new networking technologies, and the merger of many networks. The commercialization of what was by the 1990s an international network resulted in its popularization and incorporation into virtually every aspect of modern human life. As of 2009, an estimated quarter of Earth's population used the services of the Internet.

The Internet has no centralized governance in either technological implementation or policies for access and usage; each constituent network sets its own standards. Only the overreaching definitions of the two principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System, are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The technical underpinning and standardization of the core protocols (IPv4 and IPv6) is an activity of the Internet Engineering Task Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise.

Types of Internet Communication

The Internet provides users with multiple means of communicating. Users may communicate with friends, colleagues, news reporters, editors and even strangers. Today there are more ways to reach out to people who were traditionally difficult to contact. As technology advances, the means of Internet communications becomes increasingly convenient and varied.

Social Networking

Members of social networking sites are able to send messages, comments, links, articles and pictures to other members of the site. Communication is not just between the sender and receiver, it is also available to other members who have access to browse your site. These other members may also make comments. This type of relationship is known as an Internet community.

Online Phone Calls

Skype.com is a website dedicated to providing online phone calls to other Skype members. This type of communication is known as Skype-to-Skype calling. Users communicate once they have downloaded the Skype software program from the Skype website. Skype also allows users to make video calls, through which users can see each other as they talk. Skype allows members to make low, per-minute Skype calls to landlines and cell phones.

Emails

Email, also known as electronic mail, not only allows you to communicate with other email users, but it also is a way to receive, for example, newsletters, coupons, daily inspirational quotes and job postings. Registered users have the ability to save drafts and past important emails for future reference.

Blog and Vlog

Blogging is a writer's way of expressing his thoughts, ideas, and social and political views online. Bloggers communicate to readers, who in turn make comments and send their links to other readers. Some bloggers gain notoriety through building a devout group of readers. Once bloggers have a following, they may be contacted by sponsors or they may propose sponsorship to interested companies. For instance, a food and wine blogger may obtain sponsorship from restaurants, food and wine magazines or online publications.

Vlogs are the same concept as blogs, except vlogs are digitally recorded. You can create a vlog on a digital video camera, digital camera, or cell phone. Video can then be uploaded onto your computer and shared with viewers.

Speak Out Loud

Online forums or message boards are an interesting way for participants to express their knowledge or views of a particular subject. Participants may speak, for example, on issues like new political agendas, their favorite sports teams or discuss their concerns about new technology. Message boards range from home improvement to medical experiences and procedures.

Your Opinion Matters

Online retail stores now allow prospective customers the opportunity to read buyer reviews before purchasing an item. This is an excellent tool for people who are skeptical about making a purchase. Reviewers describe their shopping experience and also rate purchased item according to various scales.

Readers of news articles are able to communicate with the public, news reporters and editors by expressing their views of online articles. Other readers may make comments about the article or the previous comments about the article. Comments about comments comprise what is known as a thread.

Satellite communication

What is Satellite Communication?

In satellite communication, signal transferring between the sender and receiver is done with the help of satellite. In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface. So, all the signal transferring is happening in space. Thus this type of communication is known as space communication.

Two satellites which are commonly used in satellite communication are Active and passive satellites.

1. Passive satellites: It is just a plastic balloon having a metal coated over it. This sphere reflects the coming microwave signals coming from one part of the earth to other part. This is also known as passive sphere. Our earth also has a passive satellite i.e. moon.

Active satellites: It basically does the work of amplifying the microwave signals coming. In active satellites an antenna system, transmitter, power supply and a receiver is used. These satellites are also called as transponders. The transmitters fitted on the earth generate the microwaves. These rays are received by the transponders attached to the satellite. Then after amplifying, these signals are transmitted back to earth. This sending can be done at the same time or after some delay. These amplified signals are stored in the memory of the satellites, when earth properly faces the satellite. Then the satellite starts sending the signals to earth. Some active satellites also have programming and recording features. Then these recording can be easily played and watched. The first active satellite was launched by Russia in 1957. The signals coming from the satellite when reach the earth, are of very low intensity. Their amplification is done by the receivers themselves. After amplification these become available for further use.

Microwave communication is possible only if the position of satellite becomes stationary with respect to the position of earth. So, these types of satellites are known as geostationary satellites.

What are the requirements for a satellite to be geostationary?

1. Its revolutionary direction must be same as that of the earth, i.e. from west to east.

2. The time period of satellite’s revolution must be same to the time period of the rotation of earth along its polar axis, which is equal to 24 hours.

3. The equatorial plane of earth must be coplanar with the orbital plane of the satellites revolution.

The name given to the orbit of the geostationary satellites is synchronous orbit. Due to this geostationary satellites are also called as geosynchronous satellites. Geosynchronous orbit is at a height of nearly 36000 km from the surface of earth.

These orbits are capable of giving a successful communication link between two stations present on the earth. These satellites can handle communication up to large distances. But it is impossible for a single geostationary satellite to cover the whole earth and provide a communication link. Due to curvature of earth the stations will be out of sight after covering some distance. If we want to cover the whole earth then we have to put three satellites onto the geosynchronous orbit. These satellites can cover the earth if all are inclined at an angle of 120o to each other.

Television communication

Television is one of the most popular forms of communication in the world today. Everyone in the world owns a television and watches it at least for 1 hour per day. This is a sign that this form of communication is successful. With televisions you can get your local stations, cable or choose from the many types of satellite providers. With these few great options, you will have access to this great form of communication in your own home.

By watching television shows, news and movies are a great way to keep up with the times and the newer forms of communication. Television is used for entertainment, fun, relaxation and to keep up with the the news around the world. This form of communication that gives you the opportunity to learn about the events around the world. Television does not have to bad for you if you watch the appropriate TV shows. There are many television shows that promote violence and other negative characteristics. Just because they are on TV does not mean that you have to watch it. Television provides information and entertainment to the masses in a way like no other form of communication does.

TVs can be purchased for as little as Rs.5000! This is a great deal for a TV that works well and can deliver a great form of communication directly to your home. Of course there are many great new technologies that have made it possible to create new forms of televisions for new generations. The plasma TV is one of the newest styles of televisions available today. This great new TV is allowing more improved forms of communication to be seen throughout the entire world.

Communication through TV has been going on for so many years now, that this is the reason for its improvement. With all the years of TV communication, there are so many people in the world that are not aware that they are taking part in any form of communication at all. This makes TV that much more effective. People are being affected by their TV and the shows that they watch without even realizing it. This can be a good thing, if you are being effected in a good way.

No matter what type of TV that you have you still experience the amazing communication that TV offers you. This form of communication is something that cannot be replaced and has been incredibly successful from the very beginning. TV is something that will never go out of style.

Mobile communication

Communication is one of the integral parts of science that has always been a focus point for exchanging information among parties at locations physically apart. After its discovery, telephones have replaced the telegrams and letters. Similarly, the term `mobile' has completely revolutionized the communication by opening up innovative applications that are limited to one's imagination. Today, mobile communication has become the backbone of the society. All the mobile system technologies have improved the way of living. Its main plus point is that it has privileged a common mass of society.

Evolution of Mobile Radio Communications

The rst wireline telephone system was introduced in the year 1877. Mobile communication systems as early as 1934 were based on Amplitude Modulation (AM) schemes and only certain public organizations maintained such systems. With the demand for newer and better mobile radio communication systems during the World War II and the development of Frequency Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems began to witness many new changes. Mobile telephone was introduced in the year 1946. However, during its initial three and a half decades it found very less market penetration owing to high costs and numerous technological drawbacks. But with the development of the cellular concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising eld of expanse which could serve wider populations. Initially, mobile communication was restricted to certain social users and the cellular concept was never even dreamt of being made commercially available. Moreover, even the growth in the cellular networks was very slow. However, with the development of newer and better technologies starting from the 1970s and with the mobile users now connected to the Public Switched Telephone Network (PSTN), there has been an astronomical growth in the cellular radio and the personal communication systems. Advanced

Mobile Phone System (AMPS) was the rst U.S. cellular telephone system and it was deployed in 1983. Wireless services have since then been experiencing a 50% per year growth rate. The number of cellular telephone users grew from 25000 in 1984 to around 3 billion in the year 2007 and the demand rate is increasing day by day.

Present Day Mobile Communication

Since the time of wireless telegraphy, radio communication has been used extensively. Our society has been looking for acquiring mobility in communication since then. Initially the mobile communication was limited between one pair of users on single channel pair. The range of mobility was denied by the transmitter power, type of antenna used and the frequency of operation. With the increase in the number of users, accommodating them within the limited available frequency spectrum became a major problem. To resolve this problem, the concept of cellular communication was evolved. The present day cellular communication uses a basic unit called cell. Each cell consists of small hexagonal area with a base station located at the center

of the cell which communicates with the user. To accommodate multiple users Time Division multiple Access (TDMA), Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA) and their hybrids are used. Numerous mobile radio standards have been deployed at various places such as AMPS, PACS, GSM, NTT, PHS and IS-95, each utilizing di
erent set of frequencies and allocating different number of users and channels.

Fundamental Techniques

By definition, mobile radio terminal means any radio terminal that could be moved during its operation. Depending on the radio channel, there can be three different types of mobile communication. In general, however, a Mobile Station (MS) or subscriber unit communicates to a xed Base Station (BS) which in turn communicates to the desired user at the other end. The MS consists of transceiver, control circuitry, duplexer and an antenna while the BS consists of transceiver and channel multiplexer along with antennas mounted on the tower. The BS are also

linked to a power source for the transmission of the radio signals for communication and are connected to a xed backbone network. Figure 4.1 shows a basic mobile communication with low power transmitters/receivers at the BS, the MS and also the Mobile Switching Center (MSC). The MSC is sometimes also called Mobile Telephone Switching Oce (MTSO). The radio signals emitted by the BS decay as the signals travel away from it. A minimum amount of signal strength is needed in order to be detected by the mobile stations or mobile sets which are the hand-held

personal units (portables) or those installed in the vehicles (mobiles). The region over which the signal strength lies above such a threshold value is known as the coverage area of a BS. The xed backbone network is a wired network that links all the base stations and also the landline and other telephone networks through wires.

Radio Transmission Techniques

Based on the type of channels being utilized, mobile radio transmission systems may be classified as the following three categories which is also shown in Fig.4.2:

Simplex System: Simplex systems utilize simplex channels i.e., the communication is unidirectional. The rst user can communicate with the second user. However, the second user cannot communicate with the rst user. One example of such a system is a pager.

Half Duplex System: Half duplex radio systems that use half duplex radio channels allow for non-simultaneous bidirectional communication. The first user can communicate with the second user but the second user can communicate to the rst user only after the rst user has finished his conversation. At a time, the user can only transmit or receive information. A walkie-talkie is an example of a half duplex system which uses `push to talk' and `release to listen' type of switches.

Full Duplex System: Full duplex systems allow two way simultaneous communications. Both the users can communicate to each other simultaneously. This can be done by providing two simultaneous but separate channels to both the users. This is possible by one of the two following methods:

• Frequency Division Duplexing (FDD): FDD supports two-way radio communication by using two distinct radio channels. One frequency channel is transmitted downstream from the BS to the MS (forward channel).A second frequency is used in the upstream direction and supports transmission from the MS to the BS (reverse channel). Because of the pairing of frequencies, simultaneous transmission in both directions is possible. To mitigate self-interference between upstream and downstream transmissions, a minimum amount of frequency separation must be maintained between the frequency pair, as shown in Fig. 4.3.
• Time Division Duplexing (TDD): TDD uses a single frequency band to transmit signals in both the downstream and upstream directions. TDD operates by toggling transmission directions over a time interval. This toggling takes place very rapidly and is imperceptible to the user.

A full duplex mobile system can further be subdivided into two category: a single MS for a dedicated BS, and many MS for a single BS. Cordless telephone systems are full duplex communication systems that use radio to connect to a portable handset to a single dedicated BS, which is then connected to a dedicated telephone line with a specific telephone number on the Public Switched Telephone Network (PSTN). A mobile system, in general, on the other hand, is the example of the second category of a full duplex mobile system where many users connect among themselves via a single BS.