TABLE OF CONTENTS Modulation is the process of changing the amplitude, frequency, or phase of a radio frequency carrier signal (a carrier) to change with the information signal (such as voice or data). The CDMA radio channel uses two types of modulation: BPSK and QPSK. The analog radio channel uses frequency modulation FM for voice channels and frequency shift keying (FSK) for control channels.
Binary phase shift keying (BPSK) is a modulation process that converts binary bits into phase shifts of the radio carrier without substantially changing the frequency of the carrier waveform. The phase of a carrier is the relative time of the peaks and valleys of the sine wave relative to the time of an unmodulated "clock" sine wave of the same frequency. BPSK uses only two phase angles, corresponding to a phase shift of zero or a half cycle (that is, zero or 180 degrees of angle).
Quadrature phase shift keying (QPSK) is a type of modulation that uses 4 different phase shifts of a radio carrier signal to represent the digital information signal. These shifts are typically 90 and 180 degrees.
The CDMA system uses different types of quadrature modulation on the forward and reverse channels. The forward channel uses quadrature phase shift keying (QPSK) and the reverse channel uses offset quadrature phase shift keying (O-QPSK).
The difference between QPSK and O-QPSK is that offset quadrature phase shift keying requires that the transmitter does not pass through the...
