For phase-shift keying (PSK) modulation schemes, the noise Z ~ retains its statistical properties after the division [20], as the phase of circular complex Gaussian random variables is uniformly distributed and thus has the same probability distribution after the division.
First, speckle may be reduced by averaging successive image frames because tissue motion that may occur between frames will cause some spatial modulation of the noise pattern.
The experiments showed the same trends as the simulations, but with slightly lower variability, possibly implying modulation of the noise through metabolism and cell division, leading to the phenotypic response.
In general, operating at higher modulation frequencies reduces the noise, such as laser fluctuations, although sufficient light must fall on the camera to fill the well to ensure shot noise operation.
At around 200 averages the DC noise increases due to drift and at 2000 averages the modulation depth noise starts to flatten out, this is the noise floor of the data acquisition system and is the level at which the performance of the system cannot be improved by averaging – this is the ultimate performance limit of the current system.
The final feature of the proposed method is that the performance of the estimation algorithm depends on the choice of the modulation sequences to resist the noise effects.
The core requirements about the modulation-based behavior of the noise reduction subsystem, however, lead to measurements exposing side effects or imprecise results, like shown in Figure 9. Therefore, the results shown in that figure need to be discussed further.
The imaging performance of the screens was assessed by experimental determination of the modulation transfer function (MTF) and the noise transfer function (NTF).
Modern demapping algorithms for APSK modulation incorporate the mean of the noise distribution as a shift in the received symbol centroids, e.g., obtained by pilot symbols [13, 14]; however, these works retain the assumption of equal noise variance across the constellation.
The design of the modulation sequences when noise is present is given in Section 3.2.
