Quadrature amplitude modulation

Quadrature phase shift keying, quadrature amplitude modulation. 

Transmission of the encoded facsimile signal makes use of signaling techniques based on ITU-T recommendations V.27 (standard) and V.29 (optional addition). The former utilizes 8-phase modulation at 4800 b/s, and the latter employs 16-QAM quadrature amplitude modulation (QAM) at 9600 b/s with adaptive. 

Frequency modulation (FM) has been the most widely used modulation. However, advances in digital voice and video compression have led to the widespread use of digital modulation methods such as quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) (Schwartz, 1990 Sklar, 1988). 

Quadrature amplitude modulation (QAM) A process that allows two different signals to modulate a single carrier frequency. The two signals of interest amplitude modulate two samples of the carrier that are of the same frequency, but differ in phase by 90°. The two resultant signals can be added and transmitted. Both signals may be recovered at a decoder when they are demodulated 90° apart. 

SSB S3MQAM TFM TSI QPSK Single SideBand Staggered class 3 Quadrature Amplitude Modulation Tamed Frequency Modulation Two-Symbol-Interval QPSK Low and High capacity radio... 

WQAM XPSK Weighted Quadrature Amplitude Modulation Crosscorrelated PSK Includes most digital schemes... 

DQPSK 3MQAM 4MQAM 12PM3 k/4. shift DQPSK with a = 0.35 raised cosine filtering Class 3 Quadrature Amplitude Modulation Class 4 Quadrature Amplitude Modulation 12 state PM with 3 bit correlation IS-54 TDMA voice and data... 

It is worth noting that the four-fold symmetry of hexadecapole moment is revealed only at the synchronous pumping and, what is important, at time moments when the hexadecapole moment is precisely aligned with one of its symmetry axis along the linear polarization of the field and the atomic coherence p 2, 2 in the M-system has its maximal value. The periodic change of the optical properties of atomic medium modulates the angle of tight polarization that leads to the FM NMOR resonances. If the time-dependent optical rotation is measured at the first harmonic of (.lm, a resonance is seen when Qm = k Ql which allows one to separate the NFS produced by different atomic PM. Indeed, in the experiment the in-phase and quadrature amplitudes of optical rotation,... 

As for ID data, fi quadrature detection requires two data sets to be collected which differ in phase by 90 , thus providing the necessary sine and cosine amplitude-modulated data. Since the fi dimension is generated artificially, there is strictly no reference rf to define signal phases so it is the phase of the pulses that bracket ti that dictate the phase of the detected signal. Thus, for each tj increment two data sets are collected, one with a 90 preparation pulse (ti sine modulation), the other with 90j, (ti cosine modulation), and both stored separately (Fig. 5.17). These two sets are then equivalent to the... 

With amplitude modulation the cosine and sine components may be handled in two ways to achieve quadrature detection in fl. They may be acquired in subsequent scans by either incrementing the pulse or receiver phase and the data co-added in the computer memory or they may be acquired sequentially and stored separately. With the first approach direct Fourier transformation yields frequency discrimination in fl but no absorptive lineshapes whilst with the second approach additional processing steps are necessary to achieve both, frequency discrimination and absorptive lineshapes. 

Quadrature-amplitude-shift keying (QASK) A digital modulation scheme in which both the phase and... 

Figure 9 Magnetic-field dependence of the FM NMOR signals, showing quadrupole resonances at B = 143.0 fj,G, and the hexadecapole resonances at 71.5 /liG. Laser modulation frequency is 200 Hz, and modulation amplitudes is 40 MHz peak to peak the central frequency is tuned to the low-frequency slope of the F = 2 — F = 1 absorption line. Plots (a) and (b) show the in-phase component of the signal at two different light powers plot (c) shows the quadrature component. Note the increase in the relative size of the hexadecapole signals at the higher power. The insets show zooms on hexadecapole resonances.

Figure 7.46. In-phase (solid) and quadrature (dashed) potential-modulated ATR-SEIRA spectra of 4-mercaptopyridine (PySH) SAM on 20-nm-thick (80-nm-size particles) Au evaporated electrode in 0.1 M HCIO4. Modulation frequencies are shown. Amplitude of potential modulation was 400 mV, between -0.1 and 0.3 V (SCE). Spectra were recorded using Bio-Rad FTS 60A/896 FTiR spectrometer equipped with dc-coupled MCT detector and bandpass optical filter transmitting between 4000 and 1000 cm. Spectrometer was operated in step-scanning mode using setup shown in Fig. 4.56. Reprinted, by permission, from K. Ataka, Y. Hara, and M. Osawa, J. Electroanal. Chem. 473, 34 (1999), p. 39, Fig. 6. Copyright 1999 Elsevier Science S.A.

---