Frequency Shift Keying

Adaptive decision-aided algorithm for coherent optical communication systems

Full information (i.e., the amplitude and phase) of the optical electric field can be preserved in digital coherent receivers. Accordingly, rather than using an optical phase-locked loop to lock the phase of the LO laser to the transmitter laser—which is sensitive to feedback delay in ultra-high-speed (e.g., 100Gbits/s) optical systems—an LO laser can run freely (i.e., require no extra control to adjust frequency and phase) where we are able to recover its dithering phase using a digital signal processing (DSP) phase-estimation algorithm. A conventional scheme The latter refers to the influence of the chosen memory length on the accuracy of the estimated carrier phase. A shorter filter length is preferred for tracking rapidly varying phase noise, and vice versa. Additional research is required to apply the Mth power to quadrature amplitude modulation (QAM) formats, such as those used for increasing channel capacity. To get around these problems, we propose using adaptive decision-aided phase estimation, which is capable of adjusting the filter weight based on the received signal information.

To eliminate the block-length effect found in other phase-estimation algorithms and improve performance, we introduce a first-order adaptive filter to assign different weights α and 1−α to the previous and current phase reference.

Quadrature Amplitude modulation | Classle

Quadrature amplitude modulation Quadrature amplitude modulation (QAM) (Pronounced kwaːm or kăm) is a modulation scheme which conveys two digital bit streams or two analog message signals by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. These two waves, usually sinusoids, are out of phase with each other by 90 ° and are thus called quadrature carriers or quadrature components — hence the name of the scheme. The modulated waves are summarized, and the resulting waveform is a combination of both phase shift keying (PSK) and amplitude-shift keying (ASK), or in the analog case of phase modulation (PM) and amplitude modulation (AM). In the digital QAM case, a finite number of at least two phases, and at least two amplitudes are used. PSK modulators are often designed using the QAM principle, but are not considered as QAM since the amplitude of the resulting signal is constant. Overview Like all modulation schemes, QAM conveys data by changing some aspect of a carrier signal, or the carrier wave, (usually a sinusoid) in response to a data signal. In the case of QAM, the amplitude of two waves, 90 degrees out-of-phase with each other (in quadrature) are changed (modulated or keyed) to represent the data signal. Amplitude modulating two carriers in quadrature can be equivalently viewed as both amplitude modulating and phase modulating a single carrier. Phase modulation (analog PM) and phase-shift keying (digital PSK) can be regarded as a special case of QAM, where the magnitude of the modulating signal is a constant, with only the phase varying. This can also be extended to frequency modulation (FM) and frequency-shift keying (FSK), for these can be regarded as a special case of phase modulation. Analog QAM When transmitting two signals by modulating them with QAM, the transmitted signal will be of the form: where I(t) and Q(t) are the modulating signals and f0 is the carrier frequency. At the receiver, these two modulating signals can be demodulated using a coherent demodulator. Such a receiver multiplies the received signal separately with both a cosine and sine signal to produce the received estimates of I(t) and Q(t) respectively. Because of the orthogonality property of the carrier signals, it is possible to detect the modulating signals independently.

Digital transmission systems

The art of electronics

Logic and foundations of mathematics, selected contributed papers of the Tenth International Congress of Logic, Methodology, and Philosophy of Science, Florence, August 1995

Phase-locked loops

Digital Communication System Using System VUE