Category: wireless Communication

Wireless Communication – WAN In the field of computers, the wide usage of group connections have become inevitable, which lead to the introduction of LANs (Local Area Networks). These LANs come under the category of small scale networks within a single building or campus. WANs are Wide Area Networks which cover a wider area such a city, or a limited area greater than LAN. Wireless Personal Area Networks (PANs) are the next step down from WLANs, covering smaller areas with low power transmission, for networking of portable and mobile computing devices such as PCs, Personal Digital Assistants (PDAs). Fundamentals of WLANs The technical issues in WLANs must be understood in order to appreciate the difference between wired networks and wireless networks. The use of WLANs and their design goals are then studied. The types of WLANS, their components and their basic functionalities are also detailed. IEEE 802.11 Standard This section introduces a prominent standard ion WLANs, the IEEE 802.11 standard. The medium access control (MAC) layer and the physical layer mechanisms are explained. This section also covers some of the optional functionalities such as security and quality of service (QoS). HIPERLAN Standard This section describes another WLAN standard, HIPERLAN standard, which is a European standard based on radio access. Bluetooth This section deals with the Bluetooth standard, which enables personal devices to communicate with each other in the absence of infrastructure. WLAN Fundamentals While both portable terminals and mobile terminals can move from one place to another, portable terminals are accessed only when they are stationary. Mobile Terminals (MTs), on the other hand, are more powerful, and can be accessed when they are in motion. WLANs aim to support truly mobile work stations. WLAN Uses Wireless computer networks are capable of offering versatile functionalities. WLANs are very flexible and can be configured in a variety of topologies based on the application. Some possible uses of WLANs are described below. Users would be able to surf the Internet, check e-mail, and receive Instant Messages on the move. In areas affected by earthquakes or other disasters, no suitable infrastructure may be available on the site. WLANs are handy in such locations to set up networks on the fly. There are many historic buildings where there has been a need to set up computer networks. In such places, wiring may not be permitted or the building design may not be conductive to efficient wiring. WLANs are very good solutions in such places. Design Goals The following are some of the goals which have to be achieved while designing WLANs − Operational simplicity − Design of wireless LANS must incorporate features to enable a mobile user to quickly set up and access network services in a simple and efficient manner. Power efficient operation − The power-constrained nature of mobile computing devices such as laptops and PDAs necessitates the important requirement of WLANs operating with minimal power consumption. Therefore, the design of WLAN must incorporate power-saving features and use appropriate technologies and protocols to achieve this. License-free operation − One of the major factors that affects the cost of wireless access is the license fee for the spectrum in which a particular wireless access technology operates. Low cost of access is an important aspect for popularizing a WLAN technology. Hence the design of WLAN should consider the parts of the frequency spectrum. For its operation which does not require an explicit Tolerance to interference − The proliferation of different wireless networking technologies both for civilian and military applications have led to a significant increase in the interference level across the radio spectrum. The WLAN design should account for this and take appropriate measures by way of selecting technologies and protocols to operate in the presence of interference. Global Usability − The design of the WLAN, the choice of technology, and the selection of the operating frequency spectrum should take into account the prevailing spectrum restriction in countries across the world. This ensures the acceptability of the technology across the world. Security − The inherent broadcast nature of wireless medium adds to the requirement of security features to be included in the design of WLAN technology. Safety requirements − The design of WLAN technology should follow the safety requirements that can be classified into the following. Interference to medical and other instrumentation devices. Increased power level of transmitters that can lead to health hazards. A well-designed WLAN should follow the power emission restrictions that are applicable in the given frequency spectrum. Quality of service requirements − Quality of Service (QoS) refers to the provisioning of designated levels of performance for multimedia traffic. The design of WLAN should take into consideration the possibility of supporting a wide variety of traffic, including multimedia traffic. Compatibility with other technologies and applications − The interoperability among different LANS is important for efficient communication between hosts operating with different LAN technologies. Network Architecture Network architecture describes the types of WLANs, the components of a typical WLAN and the services offered by a WLAN. Infrastructure based versus Ad Hoc LANs WLANs can be broadly classified into two types, namely Infrastructure networks and Ad hoc LANs, based on the underlying architecture. Infrastructure networks Infrastructure networks contain special nodes called Access Points (APs), which are connected via existing networks. APs are special in the sense that they can interact with wireless nodes as well as with the existing wired network. The other wireless nodes, also known as Mobile stations (STAs), communicate via APs. The APs also act as bridges with other networks. Ad hoc LANs Ad hoc LANs do not need any fixed infrastructure. These networks can be set up on the fly at any place. Nodes communicate directly with each other for forward messages through other nodes that are directly accessible. Learning working make money

Terms in Mobile Telephony Among the various terms used in Mobile telephony, the most used ones will be discussed here. Mobile Station (MS) − The Mobile Station (MS) communicates the information with the user and modifies it to the transmission protocols of the air interface to communicate with the BSS. The user information communicates with the MS through a microphone and speaker for the speech, keyboard and display for short messaging and the cable connection for other data terminals. The mobile station has two elements Mobile Equipment (ME) and Subscriber Identity Module (SIM). Mobile Equipment (ME) − ME is a piece of hardware that the customer purchases from the equipment manufacturer. The hardware piece contains all the components needed for the implementation of the protocols to interface with the user and the air-interface to the base stations. Subscriber Identity Module (SIM) − This is a smart card issued at the subscription to identify the specifications of a user such as address and type of service. The calls in the GSM are directed to the SIM rather than the terminal. SMS are also stored in the SIM card. It carries every user”s personal information which enables a number of useful applications. Base Station (BS) − A base station transmits and receives user data. When a mobile is only responsible for its user”s data transmission and reception, a base station is capable to handle the calls of several subscribers simultaneously. Base Transceiver Station (BTS) − The user data transmission takes place between the mobile phone and the base station (BS) through the base transceiver station. A transceiver is a circuit which transmits and receives, i.e., does both. Mobile Switching Center (MSC) − MSC is the hardware part of the wireless switch that can communicate with PSTN switches using the Signaling System 7 (SS7) protocol as well as other MSCs in the coverage area of a service provider. The MSC also provides for communication with other wired and wireless networks as well as support for registration and maintenance of the connection with the mobile stations. The following image illustrates the parts of different sub-systems. HLR, VLR, EIR and AuC are the sub-systems of Network sub-system. Channels − It is a range of frequency allotted to particular service or systems. Control Channel − Radio channel used for transmission of call setup, call request, call initiation and other beacon or control purposes. Forward Control Channel(FCC) − Radio channel used for transmission of information from the base station to the mobile Reverse Channel(RC) − Radio channel used for transmission of information from the mobile to base station. Voice Channel(VC) − Radio channel used for voice or data transmission. Handoff − It is defined as the transferring a call from the channel or base station to another base station. Roamer − A mobile station which operates in a service area other than that from which service has been subscribed Transceiver − A device capable of simultaneously transmitting and receiving radio signals. Learning working make money

Wireless Communication – Bluetooth Bluetooth wireless technology is a short range communications technology intended to replace the cables connecting portable unit and maintaining high levels of security. Bluetooth technology is based on Ad-hoc technology also known as Ad-hoc Pico nets, which is a local area network with a very limited coverage. History of Bluetooth WLAN technology enables device connectivity to infrastructure based services through a wireless carrier provider. The need for personal devices to communicate wirelessly with one another without an established infrastructure has led to the emergence of Personal Area Networks (PANs). Ericsson”s Bluetooth project in 1994 defines the standard for PANs to enable communication between mobile phones using low power and low cost radio interfaces. In May 1988, Companies such as IBM, Intel, Nokia and Toshiba joined Ericsson to form the Bluetooth Special Interest Group (SIG) whose aim was to develop a defacto standard for PANs. IEEE has approved a Bluetooth based standard named IEEE 802.15.1 for Wireless Personal Area Networks (WPANs). IEEE standard covers MAC and Physical layer applications. Bluetooth specification details the entire protocol stack. Bluetooth employs Radio Frequency (RF) for communication. It makes use of frequency modulation to generate radio waves in the ISM band. The usage of Bluetooth has widely increased for its special features. Bluetooth offers a uniform structure for a wide range of devices to connect and communicate with each other. Bluetooth technology has achieved global acceptance such that any Bluetooth enabled device, almost everywhere in the world, can be connected with Bluetooth enabled devices. Low power consumption of Bluetooth technology and an offered range of up to ten meters has paved the way for several usage models. Bluetooth offers interactive conference by establishing an adhoc network of laptops. Bluetooth usage model includes cordless computer, intercom, cordless phone and mobile phones. Piconets and Scatternets Bluetooth enabled electronic devices connect and communicate wirelessly through shortrange devices known as Piconets. Bluetooth devices exist in small ad-hoc configurations with the ability to act either as master or slave the specification allows a mechanism for master and slave to switch their roles. Point to point configuration with one master and one slave is the simplest configuration. When more than two Bluetooth devices communicate with one another, this is called a PICONET. A Piconet can contain up to seven slaves clustered around a single master. The device that initializes establishment of the Piconet becomes the master. The master is responsible for transmission control by dividing the network into a series of time slots amongst the network members, as a part of time division multiplexing scheme which is shown below. The features of Piconets are as follows − Within a Piconet, the timing of various devices and the frequency hopping sequence of individual devices is determined by the clock and unique 48-bit address of master. Each device can communicate simultaneously with up to seven other devices within a single Piconet. Each device can communicate with several piconets simultaneously. Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave piconets. There is no direct connection between the slaves and all the connections are essentially master-to-slave or slave-to-master. Slaves are allowed to transmit once these have been polled by the master. Transmission starts in the slave-to-master time slot immediately following a polling packet from the master. A device can be a member of two or more piconets, jumping from one piconet to another by adjusting the transmission regime-timing and frequency hopping sequence dictated by the master device of the second piconet. It can be a slave in one piconet and master in another. It however cannot be a master in more than once piconet. Devices resident in adjacent piconets provide a bridge to support inner-piconet connections, allowing assemblies of linked piconets to form a physically extensible communication infrastructure known as Scatternet. Spectrum Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHZ, using a spread spectrum hopping, full-duplex signal at a nominal rate of 1600 hops/sec. the 2.4 GHZ ISM band is available and unlicensed in most countries. Range Bluetooth operating range depends on the device Class 3 radios have a range of up to 1 meter or 3 feet Class 2 radios are most commonly found in mobile devices have a range of 10 meters or 30 feet Class 1 radios are used primarily in industrial use cases have a range of 100 meters or 300 feet. Data rate Bluetooth supports 1Mbps data rate for version 1.2 and 3Mbps data rate for Version 2.0 combined with Error Data Rate. Learning working make money

Wireless Communication Tutorial Job Search Wireless Communication is an advanced branch of communication engineering. This tutorial helps to develop an overview on the existing trends of wireless communication and the concepts related to it. Audience This tutorial has been developed for the beginners to help them understand the basic concepts and developing trends of wireless communications. Prerequisites This is a basic tutorial that any reader with a little knowledge of analog and digital communication can easily understand. Learning working make money

Cellular Wireless Networks Cellular network is an underlying technology for mobile phones, personal communication systems, wireless networking etc. The technology is developed for mobile radio telephone to replace high power transmitter/receiver systems. Cellular networks use lower power, shorter range and more transmitters for data transmission. Features of Cellular Systems Wireless Cellular Systems solves the problem of spectral congestion and increases user capacity. The features of cellular systems are as follows − Offer very high capacity in a limited spectrum. Reuse of radio channel in different cells. Enable a fixed number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region. Communication is always between mobile and base station (not directly between mobiles). Each cellular base station is allocated a group of radio channels within a small geographic area called a cell. Neighboring cells are assigned different channel groups. By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells. Keep interference levels within tolerable limits. Frequency reuse or frequency planning. Organization of Wireless Cellular Network. Cellular network is organized into multiple low power transmitters each 100w or less. Shape of Cells The coverage area of cellular networks are divided into cells, each cell having its own antenna for transmitting the signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station transmitter, receiver and its control unit. The shape of cells can be either square or hexagon − Square A square cell has four neighbors at distance d and four at distance Root 2 d Better if all adjacent antennas equidistant Simplifies choosing and switching to new antenna Hexagon A hexagon cell shape is highly recommended for its easy coverage and calculations. It offers the following advantages − Provides equidistant antennas Distance from center to vertex equals length of side Frequency Reuse Frequency reusing is the concept of using the same radio frequencies within a given area, that are separated by considerable distance, with minimal interference, to establish communication. Frequency reuse offers the following benefits − Allows communications within cell on a given frequency Limits escaping power to adjacent cells Allows re-use of frequencies in nearby cells Uses same frequency for multiple conversations 10 to 50 frequencies per cell For example, when N cells are using the same number of frequencies and K be the total number of frequencies used in systems. Then each cell frequency is calculated by using the formulae K/N. In Advanced Mobile Phone Services (AMPS) when K = 395 and N = 7, then frequencies per cell on an average will be 395/7 = 56. Here, cell frequency is 56. Learning working make money

Wireless Communication – Overview Wireless communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors. Wireless communication is a broad term that incorporates all procedures and forms of connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices. Features of Wireless Communication The evolution of wireless technology has brought many advancements with its effective features. The transmitted distance can be anywhere between a few meters (for example, a television”s remote control) and thousands of kilometers (for example, radio communication). Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones. Wireless – Advantages Wireless communication involves transfer of information without any physical connection between two or more points. Because of this absence of any ”physical infrastructure”, wireless communication has certain advantages. This would often include collapsing distance or space. Wireless communication has several advantages; the most important ones are discussed below − Cost effectiveness Wired communication entails the use of connection wires. In wireless networks, communication does not require elaborate physical infrastructure or maintenance practices. Hence the cost is reduced. Example − Any company providing wireless communication services does not incur a lot of costs, and as a result, it is able to charge cheaply with regard to its customer fees. Flexibility Wireless communication enables people to communicate regardless of their location. It is not necessary to be in an office or some telephone booth in order to pass and receive messages. Miners in the outback can rely on satellite phones to call their loved ones, and thus, help improve their general welfare by keeping them in touch with the people who mean the most to them. Convenience Wireless communication devices like mobile phones are quite simple and therefore allow anyone to use them, wherever they may be. There is no need to physically connect anything in order to receive or pass messages. Example − Wireless communications services can also be seen in Internet technologies such as Wi-Fi. With no network cables hampering movement, we can now connect with almost anyone, anywhere, anytime. Speed Improvements can also be seen in speed. The network connectivity or the accessibility were much improved in accuracy and speed. Example − A wireless remote can operate a system faster than a wired one. The wireless control of a machine can easily stop its working if something goes wrong, whereas direct operation can’t act so fast. Accessibility The wireless technology helps easy accessibility as the remote areas where ground lines can’t be properly laid, are being easily connected to the network. Example − In rural regions, online education is now possible. Educators no longer need to travel to far-flung areas to teach their lessons. Thanks to live streaming of their educational modules. Constant connectivity Constant connectivity also ensures that people can respond to emergencies relatively quickly. Example − A wireless mobile can ensure you a constant connectivity though you move from place to place or while you travel, whereas a wired land line can’t. Learning working make money

Wireless Communication – Satellite A satellite is an object that revolves around another object. For example, earth is a satellite of The Sun, and moon is a satellite of earth. A communication satellite is a microwave repeater station in a space that is used for telecommunication, radio and television signals. A communication satellite processes the data coming from one earth station and it converts the data into another form and send it to the second earth station. How a Satellite Works Two stations on earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a relay station for their communication. One earth station transmits the signal to the satellite. Uplink frequency is the frequency at which ground station is communicating with satellite. The satellite transponder converts the signal and sends it down to the second earth station, and this is called Downlink frequency. The second earth station also communicates with the first one in the same way. Advantages of Satellite The advantages of Satellite Communications are as follows − The Coverage area is very high than that of terrestrial systems. The transmission cost is independent of the coverage area. Higher bandwidths are possible. Disadvantages of Satellite The disadvantages of Satellite Communications are as follows − Launching satellites into orbits is a costly process. The bandwidths are gradually used up. High propagation delay for satellite systems than the conventional terrestrial systems. Satellite Communication Basics The process of satellite communication begins at an earth station. Here an installation is designed to transmit and receive signals from a satellite in orbit around the earth. Earth stations send information to satellites in the form of high powered, high frequency (GHz range) signals. The satellites receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite. Satellite”s footprint is the area which receives a signal of useful strength from the satellite. The transmission system from the earth station to the satellite through a channel is called the uplink. The system from the satellite to the earth station through the channel is called the downlink. Satellite Frequency Bands The satellite frequency bands which are commonly used for communication are the Cband, Ku-band, and Ka-band. C-band and Ku-band are the commonly used frequency spectrums by today”s satellites. It is important to note that there is an inverse relationship between frequency and wavelength i.e. when frequency increases, wavelength decreases this helps to understand the relationship between antenna diameter and transmission frequency. Larger antennas (satellite dishes) are necessary to gather the signal with increasing wavelength. Earth Orbits A satellite when launched into space, needs to be placed in certain orbit to provide a particular way for its revolution, so as to maintain accessibility and serve its purpose whether scientific, military or commercial. Such orbits which are assigned to satellites, with respect to earth are called as Earth Orbits. The satellites in these orbits are Earth Orbit Satellites. The important kinds of Earth Orbits are − Geo-synchronous Earth Orbit Geo-stationary Earth Orbit Medium Earth Orbit Low Earth Orbit Geo-synchronous Earth Orbit (GEO) Satellites A Geo-synchronous Earth orbit Satellite is one which is placed at an altitude of 22,300 miles above the Earth. This orbit is synchronized with a side real day (i.e., 23hours 56minutes). This orbit can have inclination and eccentricity. It may not be circular. This orbit can be tilted at the poles of the earth. But it appears stationary when observed from the Earth. The same geo-synchronous orbit, if it is circular and in the plane of equator, it is called as geo-stationary orbit. These Satellites are placed at 35,900kms (same as geosynchronous) above the Earth’s Equator and they keep on rotating with respect to earth’s direction (west to east). These satellites are considered stationary with respect to earth and hence the name implies. Geo-Stationary Earth Orbit Satellites are used for weather forecasting, satellite TV, satellite radio and other types of global communications. The above figure shows the difference between Geo-synchronous and Geo- Stationary orbits. The Axis of rotation indicates the movement of Earth. The main point to note here is that every Geo-Stationary orbit is a Geo-Synchronous orbit. But every Geo-Synchronous orbit is NOT a Geo-stationary orbit. Medium Earth Orbit (MEO) Satellites Medium earth orbit (MEO) satellite networks will orbit at distances of about 8000 miles from earth”s surface. Signals transmitted from a MEO satellite travel a shorter distance. This translates to improved signal strength at the receiving end. This shows that smaller, more lightweight receiving terminals can be used at the receiving end. Since the signal is travelling a shorter distance to and from the satellite, there is less transmission delay. Transmission delay can be defined as the time it takes for a signal to travel up to a satellite and back down to a receiving station. For real-time communications, the shorter the transmission delay, the better will be the communication system. As an example, if a GEO satellite requires 0.25 seconds for a round trip, then MEO satellite requires less than 0.1 seconds to complete the same trip. MEOs operates in the frequency range of 2 GHz and above. Low Earth Orbit (LEO) Satellites The LEO satellites are mainly classified into three categories namely, little LEOs, big LEOs, and Mega-LEOs. LEOs will orbit at a distance of 500 to 1000 miles above the earth”s surface. This relatively short distance reduces transmission delay to only 0.05 seconds. This further reduces the need for sensitive and bulky receiving equipment. Little LEOs will operate in the 800 MHz (0.8 GHz) range. Big LEOs will operate in the 2 GHz or above range, and Mega-LEOs operates in the 20-30 GHz range. The higher frequencies associated with Mega-LEOs translates into more information carrying capacity and yields to the capability of real-time, low delay video transmission scheme. High Altitude Long Endurance (HALE) Platforms Experimental HALE platforms are basically highly efficient and lightweight airplanes carrying communications equipment. This

Wireless Communication – WAP WAP stands for Wireless Application Protocol. WAP represents a suite of protocols rather than a single protocol. WAP aims at integrating a simple lightweight browser also known as a micro-browser into handheld devices, thus requiring minimal amounts of resources such as memory and CPU at these devices. WAP tries to compensate for the shortfalls of the wireless handheld devices and the wireless link by incorporating more intelligence into the network nodes such as the routers, web servers, and BSs. The primary objectives of the WAP protocol suite are the following. Independence from the wireless network standards Interoperability among service providers Overcoming the shortfalls of the wireless medium Overcoming the drawbacks of handheld devices Increasing efficiency and reliability Providing security, scalability, and extensibility The WAP Model WAP adopts a client-server approach. It specifies a proxy server that acts as an interface between the wireless domain and core wired network. This proxy server, also known as a WAP gateway, is responsible for a wide variety of functions such as protocol translation and optimizing data transfer over the wireless medium. Wireless network parts consist of − Content provider (Application or origin server) Mobile device (WAP client) WAP gateway WAP proxy The WAP Architecture has been designed to closely follow the web. The only difference is the presence of the WAP gateway is translating between HTTP and WAP. WAP Client The three sections to be mentioned regarding WAP client are WAE user agent, WTA user agent and WAP stack. WAE user agent − Wireless application environment user agent is the browser that renders the content for display. WTA user agent − Wireless telephony application agent receives compiled WTA files from WTA server and executes them. WAP stack − WAP stack allows the phone to connect to the WAP gateway using the WAP Protocols. Application Server The element in the network where the information (web, WAP) applications reside are WAP proxy, WAP gateway or WAP server − Proxy − This is an intermediary element acting both as a client and as a server in the network it is located between client and server. The client sends requests to it and it retrieves and caches the information needed by contacting the origin Server. Gateway − This is an intermediary element usually used to connect two different types of networks. WAP Gateway is basically software that is placed between a network that supports WAP and IP packet network such as Internet. The WAP Protocol Stack WAP protocol stack is shown in the following figure − Application Layer The application layer provides an application environment intended for the development and execution of portable application and services WAE consists of two different user agents located on client side. The WAE user agent consists of browser and the text message editor along with the WTA user agent. Session Layer The session layer supplies methods for the organized exchange of content between Client/Service applications. WAP contains the following components − Connection Oriented Session Services − These operate over WTP. Connectionless Session Services − These operate directly over WDP. Session services − These functionalities help to set up a connection between a client and server using primitive messages. Primitives messages are defined as messages that client sends to the server to request a service facility. The client sends request primitives and receive confirm primitive and the server can send response primitives and receive indication primitives. The connectionless session service provides only non-confirmed service. To start session, the client invokes a WSP primitives that provide some parameters, such as the server address, client address and client headers. In some respects, WSP is basically a binary form of HTTP. Transaction Layer Provides different methods for performing transaction to varying degree of reliability. Security Layer Optional layer that provides, when authentication, privacy and secure connection is present, between applications. It is based on SSL (Secure Socket Layer). It provides services that ensure privacy, server authentication, client authentication and data integrity. A Standard SSL session is opened between the web server and the WAP gateway, and WTLS session is initialized between the gateway and the mobile device. The encrypted content is send through this connection from the server to the gateway, which translates it and sends it to mobile phone. The transaction between SSL and WTLS takes place in the memory of the WAP gateway. Transport Layer This is the bottom layer, connected with the bearer service offered by the operator. Bearer services are the communication between the mobile phone and the base stations. They include SMS, CSD, USSD, GSM, GPRS, DECT, CDMA, FDMA, and TDMA. The physical layer prepares the data to be sent from the mobile device over the air services and sends the data using bearer service implemented in the network that the device is operating in. WDP has an interface with various bearer networks, so it must have a bearer specific implementation. WDP is the only layer that must be rewritten to support different bearer networks. The WTP layer implements a simple request-response transaction oriented protocol instead of the three-way-handshake connection mechanism. Learning working make money

Wireless Communication – Internet The advent of the Internet has caused a revolutionary change in the use of computers and the search for information. The Internet has affected the traditional way of information exchange and now almost every city, every town, and every street has access to the Internet. Homes, schools and businesses connect to the Internet today using a variety of different methods. One method, wireless Internet service, provides Internet access to customers without the need for underground copper, fiber, or other forms of commercial network cabling. Compared to more established wired services like DSL and cable Internet, wireless technology brings added convenience and mobility to computer networks. The below sections describe each popular type of wireless Internet service available. Satellite Internet Introduced in the mid1990s, satellite became the first mainstream consumer wireless Internet service. Compared to other forms of wireless Internet service, satellite enjoys the advantage of availability. Requiring only a small dish antenna, satellite modem and subscription plan, satellite works in almost all rural areas not serviced by other technologies. However, satellite also offers relatively low performing wireless Internet. Satellite suffers from high latency (delay) connections due to the long distance signals must travel between Earth and the orbiting stations. Satellite also supports relatively modest amounts of network bandwidth. Public Wi-Fi Networks Some municipalities have built their public wireless Internet service using Wi-Fi technology. These so-called mesh networks join numerous wireless access points together to span larger urban areas. Individual Wi-Fi hotspots also provide public wireless Internet service in select locations. Wi-Fi is a low-cost option relative to other forms of wireless Internet service. Equipment is inexpensive (many newer computers have the needed hardware built in), and Wi-Fi hotspots remains free in some locales. Fixed Wireless Broadband Fixed wireless is a type of broadband that utilizes mounted antennas pointed at radio transmission towers. Mobile Broadband Cell phones have existed for decades, but only recently have cellular networks evolved to become a mainstream form of wireless Internet service. With an installed cellular network adapter, or by tethering a cell phone to a laptop computer, Internet connectivity can be maintained in any area with cell tower coverage. Mobile broadband service will not function without having an Internet data subscription in place from some provider. The classical wired networks have given rise to a number of application protocols such as TELNET, FTP and SMTP. The wireless application protocol (WAP) architecture aims at bridging the gap at the application level, between the wireless users and the services offered to them. Wireless Internet Wireless Internet refers to the extension of the services offered by the Internet to mobile users, enabling them to access information and data irrespective of their location. The inherent problems associated with wireless domain, mobility of nodes, and the design of existing protocols used in the Internet, require several solutions for making the wireless Internet a reality. The major issues that are to be considered for Wireless Internet are the following − Address mobility Inefficiency of transport layer protocols and Inefficiency of application layer protocols Address Mobility The network layer protocol used in the Internet is Internet Protocol (IP) which was designed for wired networks with fixed nodes. IP employs a hierarchical addressing with a globally unique 32-bit address which has two parts Network identifier and Host identifier. The network identifier refers to the subnet address to which the host is connected. The addressing scheme was used to reduce the routing table size in the core routers of the Internet, which uses only the network part of the IP address for making routing decisions. This addressing scheme may not work directly in the wireless extension of the Internet, as the mobile hosts may move from one subnet to another, but the packets addressed to the mobile host may be delivered to the old subnet to which the node was originally attached. Inefficiency of Transport Layer Protocols The transport layer is very important in the Internet and it ensures setting up and maintaining end-to-end connections, reliable end-to-end delivery of data packets, flow control and congestion control. TCP is the predominant transport layer protocol for wired networks, even though UDP, a connectionless unreliable transport layer protocol is used by certain applications. Wireless Internet requires efficient operation of the transport layer protocols as the wireless medium is inherently unreliable due to its time varying and environment dependent characteristics. Traditional TCP invokes a congestion control algorithm in order to handle congestion in the networks. If a data packet or an ACK packet is lost, then TCP assumes that the loss is due to congestion and reduces the size of the congestion window by half. With every successive packet loss, the congestion window is reduced, and hence TCP provides a degraded performance in wireless links. Even in situations where the packet loss is caused by link error or collision, the TCP invokes the congestion control algorithm leading to very low throughput. The identification of the real cause that led to the packet loss is important in improving the performance of the TCP over wireless links. Some of the solutions for the transport layer issues include − Indirect TCP (ITCP) Snoop TCP and Mobile TCP Inefficiency of Application Layer Protocols Traditional application layer protocols used in the Internet such as HTTP, TELNET, simple mail transfer protocol (SMTP), and several markup languages such as HTML were designed and optimized for wired networks. Many of these protocols are not very efficient when used with wireless links. The major issues that prevent HTTP from being used in Wireless Internet are its stateless operation, high overhead due to character encoding, redundant information carried in the HTTP requests, and opening of a new TCP connection with every transaction. The capabilities of the handheld devices are limited, making it difficult to handle computationally and bandwidth wise expensive application protocols. Wireless application protocol (WAP) and optimizations over traditional HTTP are some of the solutions for the application layer issues. Learning working make money

Discuss Wireless Communication Wireless Communication is an advanced branch of communication engineering. This tutorial helps to develop an overview on the existing trends of wireless communication and the concepts related to it. Learning working make money