## What is the peak amplitude value of the constellation ask?

Draw the constellation diagram for the following: a. ASK, with peak amplitude values of 1 and 3 b. BPSK, with a peak amplitude value of 2

## What is the constellation diagram used for?

The constellation diagram is useful for understanding the effect of interference on the signal. In Figure 4.12, quadrant I illustrates the effect of a continuous wave (CW) interfering signal in the passband of the receiver.

## Can more than two parameters be modified in a constellation diagram?

In certain cases, more than two parameters can be modified for a given symbol (in the temporal or frequency domain), so that a constellation diagram with N dimensions can be adopted to represent N independent parameters, for a given frequency, as indicated in Figure 3.14 (b).

## What are previous and variant constellations used for?

Previous constellations provide information on the coding efficiency for a given symbol in the temporal domain or more precisely here, in the frequency domain. A variant can be used by integrating the frequency axis (or the time axis depending on the type of coding) to graphically display the generated ID.

## How many dB is OSNR?

With this technique, the OSNR was evaluated from** 22 to 38 ** dB in a 10-Gb/s NRZ-DPSK signal. 92 OSNR monitoring has also been demonstrated for RZ-DPSK and RZ-DQPSK formats. In this case, the histogram differs from that of the NRZ-DPSK waveform. It is comprised of two distribution peaks corresponding to the RZ pulse peak and the level of waveform valley between the pulses. OSNR reduction due to the change in ASE noise level causes a waveform fluctuation due to signal beating with ASE noise. Waveform fluctuation results in a reduced ratio between the histogram peak height and histogram height at median level, as shown in Figure 12.16. This phenomenon enables evaluation of the OSNR from 17 to 27 dB for the RZ-DPSK signal and from 17 to 30 dB for the RZ-DQPSK signal. 92 In this range the parameter scales linearly with the OSNR.

## How to create a histogram?

The histogram is** created by first sorting the samples by their value. ** The values are mapped onto histogram bins that uniformly divide the dynamic range of sample values into n levels. The histogram is formed by counting the number of amplitude samples falling into each of the bins and plotting the count as a function of the bin value. An example of an amplitude histogram for a 10-Gb/s RZ-DPSK signal is shown in Figure 12.16. The horizontal axis of the histogram represents the number of sample points in respective bins, while the vertical axis corresponds to the sample value. The peaks of the histogram correspond to the valley and the peak of signal waveform, respectively. The samples in between the peaks correspond to the crossover points of the rising and falling edge. In order to analyze the shape of the histogram, a distribution is fitted to each of the peaks. Histogram parameters reflect the properties of signal waveform. Therefore, by tracking the statistical properties of the histogram, it is possible to evaluate the level of impairments affecting the optical signal.

## What is the simplest demodulation scheme?

There are a few different options for demodulation, including zero-IF (direct conversion), low-IF, or high IF.** Zero-IF ** is the simplest scheme as it does not require an extra stage of demodulation at the intermediate frequency (IF), and zero-IF will only work for an IQ system. The overview of a QAM system is given in Figure 13.13.

## How are DRACs clocked?

The DRACs are clocked in tact of differential quadrature upconverting** clocks ** IP, IN, QP, and QN. 2 According to Fig. 6.1, the four quadrants of the constellation diagram must be addressed by the modulator. The switching between quadrants can be achieved by swapping between IP / IN or/and between QP / QN according to the sign bits of IBB-up and QBB-up. The DRAC outputs are connected to a power combiner that facilitates the conversion of the upconverted digital signals into the reconstructed RF output. In fact, the digital I/Q modulator represents an RFDAC. In this approach, however, the primary challenge is related to the orthogonal summing of the I and Q DRAC outputs in order to reliably reconstruct the modulated RF signal [ 26, 116–118 ].

## What is the purpose of the I and Q channels?

Transmitting data using I and Q channels becomes** a way of encapsulating magnitude and phase data if we consider the I and Q channels in the same way as ** complex data (real and imaginary). The data can then be described graphically using a “constellation” diagram, where the values of instantaneous data are plotted on an X–Y graph.

## What causes the constellation to blur?

**Random noise (quadrant III) ** causes each point in the constellation to “blur,” somewhat as with CW interference, except that the spreading of the point tends to be more nearly uniform within the circle, and the circle does not have a well-defined radius.

## What is phase noise in quadrant 2?

Quadrant II illustrates the effect of phase noise on the signal. Phase noise is introduced when a local oscillator has significant phase noise. It can also be shown to occur when the transmission channel does not have a response that is symmetrical about the carrier.