1,720,964 research outputs found
FPGA Implementation and Performance of Joint Crest Factor Reduction and Adaptive Predistortion
No full textNon-linear distortion caused by power amplifliers is one of the impairments that limit the performance of digital transmission systems. The detrimental effects of non-linear distortion can be mitigated by predistortion. However, since the peak output power of the amplifier is constrained, one has to accept a compromise between output power and distortion. One method to put the compromise under control is that of reducing the crest factor of the signal before predistortion, taking the crest-limited signal as a desired output signal. In this paper, we present experimental results obtained by a system implemented on FPGA that consists of the cascade of crest factor reduction, adaptive predistortion and a synthetic memoryless model of the power amplifier. The results show that, with a Gaussian input signal, crest factor reduction is the key parameter that allows to optimize the trade-off between output power and signal distortion. Also, the results show that our implementation achieves virtually optimal performance with moderate use of FPGA resources
Upper and Lower Bounds to the Information Rate Transferred Through First-Order Markov Channels With Free-Running Continuous State
Get PDFStarting from the definition of mutual information, one promptly realizes that the probabilities inferred by Bayesian tracking can be used to compute the Shannon information between the state and the measurement of a dynamic system. In the Gaussian and linear case, the information rate can be evaluated from the probabilities computed by the Kalman filter. When the probability distributions inferred by Bayesian tracking are nontractable, one is forced to resort to approximated inference, which gives only an approximation to the wanted probabilities. We propose upper and lower bounds to the information rate between the hidden state and the measurement based on approximated inference. Application of these bounds to multiplicative communication channels is discussed, and experimental results for the discrete-time phase noise channel and for the Gauss-Markov fading channel are presented
On discrete-time modeling of the filtered and symbol-rate sampled continuous-time signal affected by Wiener phase noise
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Analog nonlinear MIMO receiver for optical mode division multiplexing transmission
No full textThe complexity and the power consumption of digital signal
processing are crucial issues in optical transmission systems
based on mode division multiplexing and coherent multiple-input
multiple-output (MIMO) processing at the receiver. In this paper
the inherent characteristic of spatial separation between fiber
modes is exploited, getting a MIMO system where joint
demultiplexing and detection is based on spatially separated
photodetectors. After photodetection, one has a MIMO system with
nonlinear crosstalk between modes. The paper shows that the
nonlinear crosstalk can be dealt with by a low-complexity and
non-adaptive detection scheme, at least in the cases presented in
the paper
Direct detection analog nonlinear MIMO for mode-division multiplexing in fiber
No full textComplexity of digital multiple-input multiple-output (MIMO) signal processing based on coherent detection affects the development of mode division multiplexing systems. The inherent characteristics of fiber modes is here exploited to get a nonlinear MIMO system based on direct detection by circular photodiodes and analog non-adaptive electrical network
Phase noise impact on directly detected optical OFDM transmission in uncompensated links
No full textThe impact of large phase noise, typical of cost-effective energy-efficient sources such as VCSELs, on the transmission of a single side-band optical OFDM signal in case of direct detection over uncompensated fiber tracks is investigated thanks to Monte Carlo simulations. Comparison with the results achieved by a semi-analytical approach is reported, in particular when the laser linewidth is comparable to the OFDM subcarrier spacing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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