What is Wireless Communication Transmitting voice, data, video and other services data using electromagnetic waves in open space (atmosphere) Electromagnetic waves Travel at speed of light (c = 3x108 m/s) Has a frequency (f) and wavelength (λ) c = f x λ Where c = wave speed Higher frequency means higher energy The higher the energy the more penetrating are the radiations What is Wireless Communication The speed of electromagnetic waves is constant in a vacuum, it can change when the wave travels through different media. The speed of a wave in a particular medium is determined by the medium’s refractive index (n), which is given by the following equation: n = c/vm Here, vm is the speed of the wave in the medium, and n is the refractive index. As the refractive index increases, the speed of the electromagnetic wave decreases. For example, the refractive index of air is approximately 1.0003, while that of water is about 1.33. As a result, light travels slower in water than in air Electro Magnetic radiation Spectrum The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. Strengths and Weaknesses of Wireless Mobile computing and wireless communication networks are playing an increasingly important role in our professional and personal lives Large numbers of subscribers to mobile telephones (more than a billion in 2004) use mobile devices on a daily basis. Wireless Ethernet (also known as Wi-Fi, abbreviation of Wireless Fidelity) LANs are being rapidly deployed in offices, homes , shopping malls, “hotspots,” and apartment buildings. The result is a very large number of business, government, military, educational, and social applications. Strengths and Weaknesses of Wireless The strengths of wireless systems that are driving their growth are: Strengths and Drivers Social and cultural factors: In our personal and business lives, our employees, partners, customers, relatives, and friends are always moving around. Wireless systems fit well in this increasingly mobile environment with the need for information/transactions anytime and anywhere. Advances in wireless networks: increase in flexibility, in wireless s data rates, 802.11g yield data rates in the range of 50 Mbps and can be deployed almost anywhere. Strengths and Weaknesses of Wireless Niche applications. In some cases, wireless is the only option. Special situations. Wireless communications make more sense in several situations, In the war-torn. Country of Angola, Telkom (South Africa) also prefers (wireless) technology in corridor between Soweto and the District of Pretoria. Wireless for older buildings Developments in mobile devices. Increased revenue and productivity possibilities Weaknesses and Issues A major limitation is security of wireless systems because wireless communications are technically easier to eavesdrop and intrude. All the weaknesses can be discussed in terms of social, business, and technology issues. Social Issues Business Issues Technology Issues Mobile Business, Mobile Government and Mobile Life Mobile Business: A great deal of activity in mobile computing and wireless communications at present falls under the umbrella of m-business. M-Business goes beyond e-business to take advantage of the wide range of mobile, in many cases handheld devices. M-Business = e-Business + Wireless Networks + Mobile Devices Mobile Business, Mobile Government and Mobile Life Mobile Government: M-Government, a subset of e-government, is the use of mobile computing and wireless communication technologies to improve the activities of public sector organizations. The goal of m-government is to make public information and government services available “anytime, anywhere” to citizens and officials. Examples C2G (Citizen-to-Government) and G2C m-communications . Governments recognize that the public has access to mobile devices. Thus, these devices are being used to improve communication between the government and the general public Mobile Business, Mobile Government and Mobile Life Mobile Government: Examples B2G (Business-to-Government) support through mobile devices. Many business-to-government (and government-to-business , of course) activities can benefit from mobility. m-Transactions: Mobile devices can also be used to make payments (e.g., taxes, fines) and other transactional services. For example, Norway has introduced a mobile tax collecting system. In Finland, tickets for Helsinki’s public transport system can be ordered by sending a text message. Wireless Networks Overview of Wireless Networks Wireless networks, as the name implies, are interconnected devices that do not use wires. The unique features of wireless Networks are: Government regulations restrict the bandwidths, and consequently data rates, of communication channels . The government policies allow only a few frequenc y ranges for wireless communications. The communication channel between senders/receivers is often impaired by noise, interference, and weather fluctuations. Overview of Wireless Networks Types of Wireless Networks are: Wireless LANs (WLANs) IEEE 802.11 LANs, and Bluetooth are also known as Wireless Personal Area Networks (WPANs) Wireless metropolitan area networks (WMANs) Wireless local loop (WLL) Wireless WANs (WWANs) Analog and Digital ANALOG Refers to something that is Continuous CONTINUOUS A set of specific points of data and all possible points between them DIGITAL Refers to something that is Discrete DISCRETE A set of specific points of data with no points in between Analog and Digital Signals Analog Signal It is a continuous waveform that changes smoothly over time. Digital Signal A digital signal is discrete. It can have only a limited number of defined values, often as simple as 1s and 0s . Signals Generally, the information is not in a form that can be transmitted over a Link The binary digits must be converted into a form that Transmission Medium can accept The data stream of 1s and 0s must be turned into Signals A series of waves that carry a sound, picture, or other information. Signal characteristics Period Amount of time ( in seconds) a signal need to complete one cycle. Frequency Number of cycles completed in one second., (Frequency) F = 1 / T (Time Period) T = 1 / F Peak Amplitude is the maximum value or strength of the signal over time Aperiodic: in which the signal pattern isn’t repeated over time Frequency Units Frequency is measured in hertz, There are 5 units used in Hertz: Hertz Kilohertz Megahertz Gigahertz Terahertz Relationship between Data rate and Bandwidth There is a direct relationship between the Data rate and its bandwidth: The greater the bandwidth, the higher the information-carrying capacity Bit Interval: Time required to send one single bit unit seconds Bit rate: Bit rate, Number of bits sent per second is called Bit rate Unit bps Baud rate: The baud rate refers to the number of signal changes (or symbols) per second in a digital communication system. Relationship between Data rate and Bandwidth Data rate: data rate is the amount of data that is transferred per second or Data rate is the speed at which data is transferred between two devices, measured in Kilo/Mega bits per second (Kbps and mbps). Bandwidth: is the maximum amount of data that can be transmitted in a fixed amount of time. It is the range of lowest to highes t frequency. In digital devices, it is measured as bps, and in analog devices, it is measured as cycles per second or hertz. Or In other words , Bandwidth refers to the range of the component frequencies. How to calculate Bandwidth of digital signal Method 1: If you know the baud rate and modulation schema of a signal, the multiplication of the baud rate and modulation schema provides the bandwidth of the signal. Bandwidth = baud rate * Modulation Method 2: The minimum bandwidth required for a digital signal is twice the highest frequency component present in the signal (Nyquist Theorem) Bandwidth=2×Bitrate Calculating Bandwidth in digital signals 3In a digital communication system, the bitrate of the transmitted signal is 4 Mbps (megabits per second). Calculate the minimum bandwidth required for accurately transmitting this digital signal. 4 A satellite communication link uses a digital modulation scheme with a bitrate of 10 Mbps. Determine the minimum bandwidth needed for transmitting this digital signal without loss. Signal to Noise ratio The signal-to-noise ratio (SNR) is a measure used in communication systems to quantify the ratio of the power of a signal (such as an audio or radio signal) to the power of background noise present in the system. In wireless communication, for example, the SNR represents the ratio of the power of the transmitted signal to the power of the noise present in the channel. A higher SNR indicates that the signal is stronger relative to the noise, which typically results in better communication performance and higher data rates. SNR(dB)=10×log 10(Signal Power/Noise Power) Analog and Digital Data Transmission A Data communication system is made up of 5 components: Data or Messages Sender and Receiver Protocols Transmission Medium Channel Capacity The maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions is referred to as the channel capacity. The greater the bandwidth, the greater the channel capacity. Data rate: This is the rate, at which data can be communicated. Bandwidth: This is the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium, expressed in cycles per second, or Hertz. Noise: is an unwanted signal which interferes with the original message signal and corrupts the parameters of the message signal. Error rate: This is the rate at which errors occur, where an error is the reception of a 1 when a 0 was transmitted or the reception of a 0 when a 1 was transmitted. Transmission Media Transmission medium is the path(physical or any) between transmitter and receiver. Transmission media can be classified as guided or unguided. In both cases, communication is in the form of electromagnetic waves. Guided media, the waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, or optical fiber. The atmosphere and outer space are examples of unguided media, which provide a means of transmitting electromagnetic signals but do not guide them Satellite A communication satellite is, in effect, a microwave relay station. It is used to link two or more ground-based microwave transmitter /receivers, known as earth stations, or ground stations. The satellite receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink). A single orbiting satellite will operate on a number of frequency bands , called transponder channels, or simply transponders Satellite Frequency Band Satellite communications occur over a wide range of frequency bands, from 137 MHz for mobile satellite service to 18 GHz for satellite television The higher frequency bands typically give access to wider bandwidths , but are also more susceptible to signal degradation due to various atmospheric factors Satellite Orbits 1. Geostationary Earth Orbit (GEO) This circular orbit is 35,785 km from the Earth’s surface. For many years, satellite communication systems were implemented with GEO orbits The apparent position of a GEO satellite in the sky, when viewed by an observer on Earth, does not change because it orbits the Earth at the same angular speed as the Earth’s rotation, and thus appears stationary in the sky From their high altitude, satellite communication systems achieve nearly complete Earth coverage using only three satellites, placed 120 degrees apart in longitude Applications for GEO satellites include weather forecasting, satellite television, satellite radio, and other types of global communications. However, GEO satellites have long propagation delays, which are problematic for time-sensitive communications Satellite Orbits 2. Medium Earth Orbit (MEO) This orbit ranges from 2,000 to 36,000 km above the Earth MEO satellites have historically been used for Global Positioning System (GPS) and other navigation systems. Approximately 32 satellites in MEO can cover any given spot on the Earth at any time during the day To determine the position of a point on Earth, four satellites must be visible at the same time from that particular point on the Earth’s surface The Main Parts of a Communications Satellite Most communications satellites have the same basic components, pointed out in this diagram Solar cells and batteries to power the satellite systems Antennas to receive and transmit signals Transponder to alter the frequency of incoming signals (avoiding interference with outgoing signals) and to amplify signals before transmitting them back to Earth Orientation and propulsion systems to keep the antennas pointed at Earth, and the satellite in the right orbit Multiplexing To make efficient use of the transmission system, it is desirable to carry multiple signals on a single medium. This is referred to as multiplexing. There are n inputs to a multiplexer. The multiplexer is connected by a single data link to a DE multiplexer Frequency Division multiplexing FDM takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal. A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency and the carrier frequencies are sufficiently separated so that the bandwidths of the signals do not overlap. Figure 2.12a depicts a simple case. Six signal sources are fed into a multiplexer that modulates each signal onto a different frequency (f1,…f6) Each signal requires a certain bandwidth centered on its carrier frequency , referred to as a channel. To prevent interference, the channels are separated by guard bands, which are unused portions of the spectrum (not shown in the figure). Time Division multiplexing TDM takes advantage of the fact that the achievable bit rate (sometimes, unfortunately, called bandwidth) of the medium exceeds the required data rate of a digital signal. Multiple digital signals can be carried on a single transmission path by interleaving portions of each signal in time. The interleaving can be at the bit level or in blocks of bytes or larger quantities. For example, the multiplexer in Figure 2.12b has six inputs that might each be, say, 9.6 kbps. A single line with a capacity of 57.6 kbps could accommodate all six sources. Analogously to FDM, the sequence of time slots dedicated to a particular source is called a channel. One cycle of time slots (one per source) is called a frame Wavelength Division multiplexing Multiple communications channels are consolidated and then transmitted on lightwaves with different wavelengths The WDM approach is more common in telecommunication systems and computer networks that use laser systems to send light signals over fiber optic cables WDM variations include coarse WDM and dense WDM (DWDM), which put fewer or more channels of information, respectively, on the medium at the same time. Code Division multiplexing A sequence of bits called the spreading code is assigned to each signa l to distinguish one signal from another. The spreading code is combined with the original signal to produce a new stream of encoded data, which is then transmitted on a shared medium. A demux that knows the code can then retrieve the original signals by subtracting out the spreading code, a process called dispreading CDM is widely used in digital television and radio broadcasting and in 3G mobile cellular networks Orthogonal Frequency Division multiplexing Orthogonal frequency-division multiplexing (OFDM) is a digital communication technique initially developed for use in cable television systems. In wireless communications, OFDM has become an alternative to single -carrier modulation techniques such as frequency division multiple access (FDMA), time-division multiple access (TDMA), and code-division multiple access (CDMA) It is used in applications including digital video broadcasting, digital audio broadcasting, digital cable television, and orthogonal frequency division multiplexing line (OFDML) Web and Internet Although the Web and the Internet are usually confused with each other in popular literature, they are two different technologies. Figure 3.1 shows a conceptual view of how Web content is accessed from regular Web browsers What is internet Internet is a network based on TCP/IP Protocol stack. The TCP/IP was developed by Defense Advanced Research Projects Agency (DARPA) in late 1960. TCP/IP was developed for interconnecting many computers in Advanced Research Projects Agency Networks (ARPANET). ARPANET initially consisted five protocols TCP/IP Protocol Suite Transmission Control Protocol / Internetworking Protocol Developed Prior to OSI Model Widely used in the Internet Today Wireless and Mobile Communication Transmission Control Protocol (TCP) is a connection-oriented Layer 4 protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack. In a connection-oriented environment, a connection is established between both ends before the transfer of information can begin. TCP is responsible for breaking messages into segments, reassembling them at the destination station, resending anything that is not received, and reassembling messages from the segments. TCP supplies a virtual circuit between end-user applications. Wireless and Mobile Communication User Datagram Protocol (UDP) is the connectionless transport protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams, without acknowledgments or guaranteed delivery. Error processing and retransmission must be handled by higher layer protocols. UDP uses no windowing or acknowledgments so reliability, if needed, is provided by application layer protocols. UDP is designed for applications that do not need to put sequences of segments together. UDP TFTP (Trivial File Transfer Protocol) SNMP (Simple Network Management Protocol) DHCP (Dynamic Host Control Protocol) DNS (Domain Name System) IP Overview Transmission Control Protocol (TCP) and Internet Protocol (IP) are the best-known protocols in the IP stack (they operate roughly at layer 3 and 4 of OSI). TCP/IP has dramatically grown in popularity in the last 20 years and is supported very widely. For example, TCP/IP can be used to transfer files between IBM, SUN , HP, IBM PCs and several other machines. IP, the lowest protocol in this Suite, can reside on a very wide variety of physical networks such as Ethernets, FDDI based fiber optic LANs, dial-up lines, X.25 -based packet switching networks, wireless networks, or ISDN digital networks. TCP, the layer above IP, supports a very wide variety of higher-level (application) protocols which allow users to emulate terminals, transfer files, and send/receive mail between different computers Switching Techniques For transmission of data beyond a local area, communication is typically achieved by transmitting data from source to destination through a network of intermediate switching nodes; The switching nodes are not concerned with the content of the data; rather their purpose is to provide a switching facility that will move the data from node to node until they reach their destination. The end devices that wish to communicate may be referred to as stations. The stations may be computers, terminals, telephones, or other communicating devices. Switching Techniques Figure illustrates a simple network. Signals entering the network from a station are routed to the destination by being switched from node to node. For example, information from station A intended for station F is sent to node 4. It may then be routed via nodes 5 and 6 or nodes 7 and 6 to the destination. Several observations are in order CIRCUIT SWITCHING Circuit switching has been the dominant technology for both voice and data communications. Communication via circuit switching implies that there is a dedicated communication path between two stations. That path is a connected sequence of links between network nodes. On each physical link, a channel is dedicated to the connection. The most common example of circuit switching is the telephone network. Circuit switching involves three phases: Circuit Establishment Information Transfer Circuit Disconnect Packet Switching Data are transmitted in blocks, called packets. A typical upper bound on packet length is 1000 octets (bytes). If a source has a longer message to send, the message is broken up into a series of packets Each packet consists of a portion of the data (or all of the data for a short message) that a station wants to transmit, plus a packet header that contains control information. The control information, at a minimum, includes the information that the network requires in order to be able to route the packet through the network and deliver it to the intended destination. At each node route, the packet is received, stored briefly, and passed on to the next node. Asynchronous Transfer Mode Asynchronous Transfer Mode Also known as Cell Relay is someway similar to packet switching technique ATM involves the transmission of data in discrete chunks called Cells ATM allows multiple logical channels to be multiplexed on a single physical interface ATM is streamlined protocol with minimum error and flow control capabilities