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.
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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
( no medium is required for wireless transmission)
Properties of communication device
Fixed & Wired : eg. Desktop in office
Mobile & Wired : eg. Laptops with a telephone network or Modem
Fixed & Wireless : eg. Used in historical buildings to avoid wiring
Mobile & Wireless : No cable restrictions
Today we find many wireless communication systems working in a Car . It may use GPS or GSM
techniques 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
If there is an accident took place , the current information of the injured person will be already
passed 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
Frequent 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. With
wireless the laptop can be converted into mobile office.
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.
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.
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.
Ranges for transmission, detection and interference
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 signalpropagation. Path loss may be due to many effects, such as free-space loss, refraction, diffraction, reflection, aperture-mediumcoupling 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 lossescaused 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 losseswhen 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 wirelesstelecommunications, multipath is the propagationphenomenon that results in radiosignals 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 televisiontransmission, 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
modulationis the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with respect to a modulating signal
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 …
ASK (Amplitude shift keying )
FSK (frequency shift keying)
PSK (Phase Shift Keying )
Types of Analog Modulation :
Amplitude-shift keying (ASK) is a form of modulation that represents digitaldata 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.
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.
Phase-shift keying (PSK) is a digitalmodulation 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).
Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radiocarrier 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.
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. Digitaldata can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.
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