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Monday, 15 December 2014

Wireless Media Communication

Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.The most common wireless technologies use radio
In wireless Of communication source originates a message, which could be a human voice, a television picture or data. The source is converted by an input transducer into an electrical waveform referred to as the baseband signal or message signal.
The transmitter modifies the baseband signal for efficient transmission. The transmitter generally consists of one or more of the following subsystems: a pre-emphasizer, a sampler, a quantizer, a coder and a modulator.

The channel is a medium through which the transmitter output is sent, which could be a wire, a coaxial cable, an optical fiber, or a radio link, etc. Based on the channel type, modern communication systems are divided into two categories: wireline communication systems and wireless communication systems.
Digital vs. Analog Communications :-
Analog and Digital Signals:-
Messages are digital or analog.
Digital messages are constructed with a finite number of symbols. For example, a text file is a digital message constructed from 50 symbols, consists of 26 letters, 10 numbers, a space and several punctuation marks. Similarly, a Morse-coded telegraph is a binary message, implying only two symbols –mark and space.
Analog messages are characterized by data whose values vary over a continuous range. For example, a speech waveform has amplitudes that vary over a continuous range. A picture is also an analog message.
Interface of Analog and Digital Systems:
(a)A/D and D/A Conversion:-
Sampling Theorem :A meeting ground exists for analog and digital signals: conversion of analog signals to digital signals. The backbone that supports the interface is Shannon's Sampling Theorem, which states that if the highest frequency in the signal spectrum is B (in hertz), then the signal can be recovered from its samples, taken at a rate not less than 2B samples per second.
(b)Quantization:- Each sample is approximated, or round off to the nearest quantized level, the information is thus digitalized. The quantized signal is an approximation of the original one. We can improve the accuracy of the quantized signal to any desired degree by increasing the number of levels.
(c)Coding:-
Source coding Convert the quantized signal into binary sequences.
Channel coding Introduces redundancy in a controlled manner to overcome the effects of noise and interferences.
Mapping Map binary sequence into symbols.
Transmission Symbols are applied to a transmitter filter, which produces a continuous signal for transmission over a continuous channel.



Cellular System Architecture:-
1.ô€‚„Radio Access: RF related signal processing and radio resource management. Mobile => base station  BSC or RNC => MSC.



2.Core Network: Main part is MSC (mobile switching center), performs user authentication, admission control, traffic control, roaming, billing, network support and maintenance etc.
3.Backbone networks: Providing voice services (PSTN, Public Switched Telephone Network), data services (through Internet), and emergency services. Wireless networks need to be connected to backbone networks to extend its service capabilities and geographic coverage.


For further study download the  handwritten notes of WMC...
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