Unit 11 Wireless Modulation Techniques

Experimental Techniques, 2004

This article shows some modulation techniques for wireless network which is also called : Spread Spectrum Frequency-Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum(DSSS) Orthogonal Frequency Division Multiplexing(OFDM) and Variant CDMA(Code Division Multiple Access) Comparision All Techniques

2004

Complex modulation may be achieved by imposing multiple modulation techniques on a single carrier, as in quadriture phase shift key amplitude modulation (QPSKAM) and the use of the FM carrier for both the FM modulation and the subsidiary communication authorization (SCA) modulation, or by using a succession of modulated carriers to modulate a higher level carrier, as in Bell System frequency domain multiplexing (FDM). Unintentional complex modulation is also frequently the result of poor filtering and unintended feedback loops.

After studying this chapter, you should be able to:

Experimental Techniques, 2004

We use the word modulation to mean the systematic alteration of one waveform, called the carrier, according to the characteristic of another waveform, the modulating signal or the message. In Continuous Wave (CW) modulation schemes, the carrier is a sinusoid. We use () c t and (), m t to denote the carrier and the message waveforms respectively. The three parameters of a sinusoidal carrier that can be varied are: amplitude, phase and frequency. A given modulation scheme can result in the variation of one or more of these parameters. Before we look into the details of various linear modulation schemes, let us understand the need for modulation.

Digital communication is a transfer of information from source to destination in the form of discrete signals. These signals are manipulated by electronic circuits (analog or digital) for making it possible to transmit and receive the data or information. Digital transmission is the physical transfer of data over a point-to-point or point-to-multipoint communication channel such as copper wires (guided and unguided channels), optical fibres, wireless communication channels, and storage media. The data is represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal. In communication systems, the noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. If we transmit the baseband signals directly, the signals from different transmitters will get mixed up and the information will be lost. Because of these reasons, we use the technology of modulation, for transmitting message signals effectively for long distances Modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted. The main goal of modulation today is to squeeze as much data into the least amount of spectrum possible. That objective, known as spectral efficiency, measures how quickly data can be transmitted in an assigned bandwidth expressed in terms of bits per second per Hz (b/s/Hz). Multiple techniques have emerged to achieve and improve spectral efficiency. There are various analog and digital modulation techniques used to transmit the signals. Due to various advantages of digital signals over analog signals, digital modulation techniques are preferred widely. This paper presents a brief study of different digital modulation methods and their uses for a particular application.