Wireless and Cellular Telecommunications, Third Edition
Just in time for the rebounding wireless industry, this updated classic text offers an in-depth engineering guide for both voice and data services, Wi-Fi, 3G, WiMAX, and more.
TABLE OF CONTENTS Wireless and Cellular Telecommunications, Third Edition
Chapter 4: Digital Cellular Systems (2G Systems)
Many digital cellular and cordless phone systems have been developed. The cellular systems are GSM, NA-TDMA, CDMA, PDC, and 1800-DCS, and the cordless phone systems are DECT and CT-2 schemes. Although analog cellular systems are limited to using frequency-division multiple-access (FDMA) schemes, digital cellular systems can use FDMA, time-division multiple-access (TDMA), and code-division multiple-access (CDMA). When a multiple-access scheme is chosen for a particular system, all the functions, protocols, and network are associated with that scheme. This chapter covers GSM, NA-TDMA, and CDMA in great detail and briefly describes other systems. At the begining of this chapter, a general description of digital systems is provided.
4.1 INTRODUCTION TO DIGITAL SYSTEMS
4.1.1 Advantages of Digital Systems
In an analog system, the signals applied to the transmission media are continuous functions of the message waveform. In the analog system, either the amplitude, the phase, or the frequency of a sinosoidal carrier can be continuously varied in accordance with the voice or the message.
In digital transmission systems, the transmitted signals are discrete in time, amplitude, phase, or frequency, or in a combination of any two of these parameters. To convert from analog form to digital form, the quantizing noise due to discrete levels should be controlled by assigning a sufficient number of digits for each sample, and a sufficient number of samples is needed to apply the Nyquist rate for sampling an analog waveform.
One advantage of converting message signals into digital form is the ruggedness of the digital signal. The impairments...
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