Pulse Amplitude Modulation Data Research Articles

Light absorptance of algal films for photosynthetic rate determinations

A Reflectance Absorptance Transmittance (RAT) meter, developed for routine measurements of Abtλ nm on leaves, was used to measure absorptance of algal films mounted on glass fibre filter disks for use in PAM (Pulse Amplitude Modulation) fluorometry. Absorptance readings (Abtλ nm) are essential to quantitate the photosynthetic electron transport rate from PAM data and are also helpful if algal disks are used in an IRGA (InfraRed Gas Analyzer). Measurements were made on Synechococcus R-2 (Cyanophyceae), Acaryochloris marina (Chlorobacteria), Chlorella vulgaris (Chlorophyceae), Chaetoceros sp. (Bacillariophyceae) and Isochrysis sp. (Haptophyta) in blue (445 nm), green (525 nm) and red (625 nm) light. Plots of Abtλ vs. Chl a (mg Chl a m-2) or Chl d for Acaryochloris (mg Chl d m-2) of the algae followed exponential saturation curves (Abt%λ = Abt%λ, ∞ (1-e-k×Chl)) usually reaching asymptotes in the blue light used by blue-diode PAM machines. Synechococcus, Chlorella, Chaetoceros and Isochrysis Abt%445nm saturates ≈ 50-100 mg Chl a m-2 (Synechococcus: Abt%445 nm, max = 77.3±0.94, ±95% conf. limits, Chlorella: Abt%445 nm, max = 77.0±2.06, Chaetoceros: Abt%445 nm, max = 80.6±1.87; Isochrysis: 83.2±8.06 mg Chl a m-2); Acaryochloris above about 100 mg Chl d m-2. Asymptotic loading of cells was in general easily achieved in blue light in the case of Synechococcus, Chlorella and Acaryochloris but not in green, red or “white” light. It was difficult to achieve asymptotic loading for Chaetoceros and Isochrysis due to mucilaginous blockage of the filter disks.

Ground Based Hyperspectral Imaging to Characterize Canopy-Level Photosynthetic Activities

Improving plant photosynthesis provides the best possibility for increasing crop yield potential, which is considered a crucial effort for global food security. Chlorophyll fluorescence is an important indicator for the study of plant photosynthesis. Previous studies have intensively examined the use of spectrometer, airborne, and spaceborne spectral data to retrieve solar induced fluorescence (SIF) for estimating gross primary productivity and carbon fixation. None of the methods, however, had a spatial resolution and a scanning throughput suitable for applications at the canopy and sub-canopy levels, thereby limiting photosynthesis analysis for breeding programs and genetics/genomics studies. The goal of this study was to develop a hyperspectral imaging approach to characterize plant photosynthesis at the canopy level. An experimental field was planted with two cotton cultivars that received two different treatments (control and herbicide treated), with each cultivar-treatment combination having eight replicate 10 m plots. A ground mobile sensing system (GPhenoVision) was configured with a hyperspectral module consisting of a spectrometer and a hyperspectral camera that covered the spectral range from 400 to 1000 nm with a spectral sampling resolution of 2 nm. The system acquired downwelling irradiance spectra from the spectrometer and reflected radiance spectral images from the hyperspectral camera. On the day after 24 h of the DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) application, the system was used to conduct six data collection trials in the experiment field from 08:00 to 18:00 with an interval of two hours. A data processing pipeline was developed to measure SIF using the irradiance and radiance spectral data. Diurnal SIF measurements were used to estimate the effective quantum yield and electron transport rate, deriving rapid light curves (RLCs) to characterize photosynthetic efficiency at the group and plot levels. Experimental results showed that the effective quantum yields estimated by the developed method highly correlated with those measured by a pulse amplitude modulation (PAM) fluorometer. In addition, RLC characteristics calculated using the developed method showed similar statistical trends with those derived using the PAM data. Both the RLC and PAM data agreed with destructive growth analyses. This suggests that the developed method can be used as an effective tool for future breeding programs and genetics/genomics studies to characterize plant photosynthesis at the canopy level.

Ultrafast pulse-amplitude modulation with a femtojoule silicon photonic modulator

Ultrahigh-speed optical interconnects are essential to future cloud computing. Further increase in optical transmission speed has been hindered by power consumption and limited bandwidth resources, for which integrated optical transceivers using advanced modulation formats, such as pulse-amplitude modulation (PAM), are a promising solution. We report 80 Gb/s PAM operation of a silicon microring modulator (MRM) with an ultralow power consumption below 7 fJ/bit. We also report the first demonstration of PAM-8 modulation of MRMs in the Gb/s order, achieving error-free capability at 45 Gb/s, using 1 fJ/bit. To the best of our knowledge, these results feature the lowest power consumption, per transmitted bit, ever demonstrated at such high data rates. We further demonstrate PAM data transmission up to 64 Gb/s over 5 km. Simultaneous achievement of ultrafast modulation and ultralow power consumption is a critical step toward next-generation optical interconnects.

Blind equalisation of multilevel PAM data for nonminimum phase channels via second- and fourth-order cumulants

This paper introduces a new blind equalisation algorithm for the pulse amplitude modulation (PAM) data transmitted through nonminimum phase (NMP) channels. The algorithm itself is based on a noncausal AR model of communication channels and the second- and fourth-order cumulants of the received data series, where only the diagonal slices of cumulants are used. The AR parameters are adjusted at each sample by using a successive over-relaxation (SOR) scheme, a variety of the ordinary LMS scheme, but with a faster convergence rate and a greater robustness to the selection of the ‘step-size’ in iterations. Computer simulations are implemented for both linear time-invariant (LTI) and linear time-variant (LTV) NMP channels, and the results show that the algorithm proposed in this paper has a fast convergence rate and a potential capability to track the LTV NMP channels.

Optimum Detection of Quantized PAM Data Signals

The degree of complexity of a digital signal processor is closely related to the precision with which samples of an incoming analog waveform are represented. There is considerable interest in determining how coarse this representation can be without seriously degrading performance from that of an ideal processor of unquantized samples. This question is examined for a receiver of noisy, linearly distorted pulse amplitude modulation (PAM) signals. An optimum [maximum likelihood (ML)] detector, analogous to the Viterbi detector for unquantized samples, is derived for the case of a quantized sample sequence. Performance is evaluated under the assumption of high signal-to-noise ratio (SNR), and the resultant error probability is a good approximation for coarse quantization, and an upper bound for any degree of quantization. For a specified error probability, the degree of quantization suggested by this approach is conservative. Since receiver complexity is closely associated with the length of the digital representation of an input sample, an upper bound on receiver complexity is also suggested. Numerical evaluation of the error probability is quite tedious for an arbitrary channel; however, system performance may be readily evaluated for partial-response (PR) signaling. For the PR channels

Standard-quadrature-rules approach to the evaluation of error probability in multilevel digital systems

A method for computing the probability of error for multilevel pulse-amplitude modulation data transmission systems is presented. It is based on the use of standard quadrature rules, and allows one to obtain very accurate results in a short computer time. Results and comparisons with previously known methods show the satisfactory performance of the proposed approach, even in critical situations.