Types of mobility

User mobility Device portability

It refers to the user who access the same or similar

telecommunication services at different places

Here user can be MOBILE & system will follow him / her

(DOCOMO advertise )Eg. Call forwarding system of

BSNL

In this system communication device

moves with or without user Here the mechanism inside

the device takes care of communication continuation

even though the device moves from place to place

Eg. Mobile Phone

Wireless : Way of accessing network without wire ( no medium is required for wireless transmission)

Properties of communication device

1.Fixed & Wired : eg. Desktop in office 2.Mobile & Wired : eg. Laptops with a telephone

network or Modem3.Fixed & Wireless : eg. Used in historical buildings to

avoid wiring 4. Mobile & Wireless : No cable restrictions

Term Meaning Use Speed

DOB Digital Audio Broadcasting Music , news , road conditions , whether reports

1.5 Mbits/s

GSM Global System for Mobile Personal communication with Voice & Data

384 Kbits/s

GPS Global positioning System To determine the current position of the object

Satellite

Some important Wireless terms and their uses

Applications of Wireless networks & Mobile Communications

Vehicles Today we find many wireless communication systems working in a Car . It may use GPS or GSMtechniques along with satellite communication. If there is an accident occurs , not only the airbag triggers but the car automatically dial the nos.of ambulance , Police in emergency.In many situations now a days , the car was informed to slow down the speed to avoid the accident.

Emergencies If there is an accident took place , the current information of the injured person will be alreadypassed to the nearest hospital through wireless. All the necessary steps are taken in the hospital before the arrival of the injured person. In natural disasters , there is least possibilities of failure of wireless network than the wired network.

BusinessFrequent updating of the latest information such as stock exchange online on laptop on a person setting in vehicle back seat. A salesman requires latest prices , stock information frequently to his current location. Withwireless the laptop can be converted into mobile office.

Why does WLAN is replacement for cabling

In many applications cabling takes a long time and it is too inflexible

Wireless networks are used to replace wired networks in applications such as remote sensors , historic buildings .

Wireless networks provide up to date information at any location.

Location Dependant Services

1. Follow on Services : eg. Call forwarding technique with the existing telephone network.Wherever you are , just give u r temporary no. to u r phone and get all the calls transmitted from it to u r temporary phone no. Using mobile computers , this service will offer the same desktop environment as in office at any location wherever you are.

2. Location aware Services : eg. Printing a document from your personal laptop to others network printer in differnet locations other than your office.

Location Dependant Services

3. Privacy : access to the mails on your phone and don’t allow any phone calls to reach you when u r at some special task.Thus without showing the location , the information can be accessed by you.4. Information Services : Whenever we are in big cities we use the Maps or say wireless travel guide to find certain location.

Eg. Samsung mobiles provide locator Software. You can find the exact distance of yours from the location where u want to reach. 5. Support Services : Many applications are integrated in mobile to support it . Cache in mobiles use the information, get the user his/her work done offline when no network is available, and made the information available again , as soon as the coverage is available.

Sender

Transmission

Distance

Detection

Interference

Ranges for transmission, detection and interference

WirelessSignal Propagation

Path loss (or path attenuation)is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system.This term is commonly used in wireless communications and signal propagation. Path loss may be due to many effects, such as free-space loss, refraction, diffraction, reflection, aperture-medium coupling loss, and absorption. Path loss is also influenced by terrain contours, environment (urban or rural, vegetation and foliage), propagation medium (dry or moist air), the distance between the transmitter and the receiver, and the height and location of antennas.

Path loss normally includes propagation losses caused by the natural expansion of the radio wave front in free space (which usually takes the shape of an ever-increasing sphere), absorption losses (sometimes called penetration losses), when the signal passes through media not transparent to electromagnetic waves, diffraction losses when part of the radio wave front is obstructed by an opaque obstacle, and losses caused by other phenomena.

Line-of-sight propagation, electro-magnetic waves travelling in a straight line.

In wireless telecommunications, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings

In facsimile and television transmission, multipath causes jitter and ghosting, seen as a faded duplicate image to the right of the main image. Ghosts occur when transmissions bounce off a mountain or other large object, while also arriving at the antenna by a shorter, direct route, with the receiver picking up two signals separated by a delay.

In radar processing, multipath causes ghost targets to appear, deceiving the radar receiver. These ghosts are particularly bothersome since they move and behave like the normal targets (which they echo), and so the receiver has difficulty in isolating the correct target echo. These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height

Sonar System uses Multipath

Technique

In digital radio communications (such as GSM) multipath can cause errors and affect the quality of communications. The errors are due to intersymbol interference (ISI). Equalisers are often used to correct the ISI. Alternatively, techniques such as orthogonal frequency division modulation and rake receivers may be used

In a Global Positioning System receiver, Multipath Effect can cause a stationary receiver's output to indicate as if it were randomly jumping about or creeping. When the unit is moving the jumping or creeping is hidden, but it still degrades the displayed accuracy.

Multiplexing : the technique of sharing a common medium with minimum or without

interference with several users Types

Space Time Frequency Code

modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with respect to a modulating signal

Modulation Types

Analog Modulation

Digital Modulation

IMP : We can not use digital transmission directly …The Binary bit stream is first transmitted into analog signal first before transmission.Techniques used for digital data translation are … 1. ASK (Amplitude shift keying )2. FSK (frequency shift keying) 3. PSK (Phase Shift Keying )Types of Analog Modulation :4. Amplitude Modulation5. Frequency Modulation6. Phase Modulation

Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave.The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. The level of amplitude can be used to represent binary logic 0s and 1s.

Digital Modulation

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK). BFSK literally implies using a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency.

Digital Modulation

Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave).Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal — such a system is termed coherent (and referred to as CPSK).

Digital Modulation

AM Modulation

Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent. For example, changes in the signal strength can be used to specify the sounds to be reproduced by a loudspeaker, or the light intensity of television pixels.

FM Modulation

In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This is in contrast with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant. In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal amplitude. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.

PM Modulation

Phase modulation (PM) is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave.Unlike its more popular counterpart, frequency modulation (FM), PM is not very widely used for radio transmissions. This is because it tends to require more complex receiving hardware and there can be ambiguity problems in determining whether, for example, the signal has changed phase by +180° or -180°. PM is used, however, in digital music synthesizers such as the Yamaha DX7, even though these instruments are usually referred to as "FM" synthesizers