Table of Contents
Advertisement
OVERVIEW: iDEN Digital Modulation Technology
Chapter 1
iDEN SYSTEM OVERVIEW
1.1
iDEN Digital Modulation Technology
The Integrated Digital Enhanced Network or iDEN of the i425/i290 operates in multiple modes: phone, private, data,
and group; and uses two digital modulation technologies: Quad QAM, and Time Division Multiple Access (TDMA).
Quadrature Amplitude Modulation (QAM) is a modulation technique that transmits information by altering the
amplitude and phase of the radio frequency (RF) signal. Data is converted into complex symbols, which alter the RF
signal and transmit the information. When the signal is received, the amplitude and phase are converted back into
symbols and then into the original data.
The i425/i290 uses 16QAM only for voice and data applications. In 16QAM, there are 16 possible combinations of 4
bits. The traditional 25 kHz channel used for two-way radios is split into four QAM signals (sub-carriers) that are
transmitted simultaneously. This technique can transmit 64 Kbps in a single 25 kHz channel.
The iDEN system requires approximately 10 Kbps to transmit a compressed voice; therefore, 64 Kbps can
accommodate 6 voice channels or 3 voice channels in enhanced systems.
The signal spectrum of the Quad 16QAM is shown in Figure 2
Frequency from Desired Channel Center (kHz)
Figure:2. Spectrum of iDEN Quad 16QAM
6880401P26-O
17
Advertisement
Table of Contents
