N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 9 - Wireless Systems and Technologies                                                                                   Slide 6 of 80                                                                                                    ________________

    How Information is Transmitted Over an Electromagnetic Wave

                                  Single Radio Frequency

                                  Information Transmission Type (Analogue or Digital)

                                  Access Methodologies

                                  Modulation Techniques

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A channel to carry information consists of radio frequencies. The information in a channel can be transmitted in analogue or digital form. In an analogue transmission voice or data in analogue form is superimposed on the channel carrier frequency. In a digital transmission the digitized voice or data in binary form is superimposed on the channel carrier frequency. This superimposition is obtained by a modulation process. The access methodologies carry more than one message at a time.

Access Methodologies - Access methodologies vary with applications. FDMA, TDMA and CDMA access methodologies are used in the wireless networks.

Modulation Techniques - Many types of modulation techniques are used to pump more information into a channel. PSK, QAM, CDPD, OFDM and DSSS are commonly used modulation techniques in the wireless networks.