From Mobile Communications Engineering: Theory and Applications, Second Edition

8.5 Nonconstant Envelope Modulation

In the nonconstant envelope modulation, the information can be modulated on the amplitude of carrier frequency such as AM (amplitude mod- ulation) and SSB (single sideband), the common modulation schemes belonging to this family. The power spectrum efficiency of this kind of modulation is always higher than other kinds such as constant envelope modulation. However, in the mobile radio environment, the multipath fading distorts the signal envelope. Therefore, the information can be very hard to receive undistorted without any special treatment. For this reason, the nonconstant envelope modulation is not very popular in mobile radio or mobile wireless systems. The following section describes one of the nonconstant envelope modulations called QAM [17, 24, 25, 26].

QAM (quadrature amplitude modulation)

QAM signaling can be viewed as a combination of amplitude shift keying (ASK) and phase shift keying (PSK). It can also be viewed as an amplitude shift keying in two dimensions. In an M-ary QAM signal, the signal in each state I is

(8.106)

where A is a constant, representing the amplitude of the lowest state, and ( a i, b i) is a pair of identifying states in the constellation of the ith state. The 16-QAM constellation diagram is shown in Fig. 8.22.


Figure 8.22: The 16-QAM constellation diagram.

The probability of error for QAM can be determined from the probability of error for PAM. For the probability of error of a PAM is expressed as

(8.107)

Products & Services
RF Receivers
RF receivers are electronic devices that enable a particular radio signal to be separated from all others being received and converted into a format for video, voice, or data.
RF Transceivers
RF transceivers are electronic devices that receive and demodulate an RF signal, then modulate and transmit a new signal.
RF Modules
RF modules are partially finished circuits that can be incorporated into larger designs.
RF Transmitters
RF transmitters are electronic devices consisting of an oscillator, modulator, and other circuits that produce an RF signal.
Pressure Transmitters
Pressure transmitters translate the low level output of a sensor or transducer to a higher level signal suitable for transmission to a site where it can be further processed. These devices include pressure sensors, transducers, elements, and instruments.

Topics of Interest

8.6 OFDM Modem Orthogonal frequency division multiplexing (OFDM) is a modulation technique where source symbols are transmitted in parallel by applying to a large number of orthogonal subcarriers.

OVERVIEW Bandpass modulation techniques encode information as the amplitude, frequency, phase, or phase and amplitude of a sinusoidal carrier. These bandpass modulation schemes are known by their...

ACE active constellation extension ACI adjacent channel interference ACPR adjacent channel power ratio ADC analog-to-digital converter AM/PM amplitude modulation/phase modulation BCH Bose Chaudhuri...

OVERVIEW In this chapter we consider the principles and performance characteristics of digital modulation techniques that are frequently employed. Before dealing with bandwidth-efficient modulation...

QUADRATURE AMPLITUDE MODULATION The multilevel (M-ary) modulation methods utilized thus far encoded information as the parameters of the amplitude, frequency or phase of a sinusoidal carrier. The...