Mitigation of nonlinear transmission effects for OFDM 16-QAM optical signal using adaptive modulation

The impact of the fiber Kerr effect on error statistics in the nonlinear (high power) transmission of the OFDM 16-QAM signal over a 2000 km EDFA-based link is examined. We observed and quantified the difference in the error statistics for constellation points located at three power-defined rings. Theoretical analysis of a trade-off between redundancy and error rate reduction using probabilistic coding of three constellation power rings decreasing the symbol-error rate of OFDM 16-QAM signal is presented. Based on this analysis, we propose to mitigate the nonlinear impairments using the adaptive modulation technique applied to the OFDM 16-QAM signal. We demonstrate through numerical modelling the system performance improvement by the adaptive modulation for the large number of OFDM subcarriers (more than 100). We also show that a similar technique can be applied to single carrier transmission

Power pre-emphasis for suppression of FWM in coherent optical OFDM transmission

Four-wave-mixing (FWM) due to the fiber nonlinearity is a major limiting factor in coherent optical OFDM transmission. We propose to apply power pre-emphasis, i.e. to allocate the transmitted power nonuniformly among subcarriers in order to suppress the FWM impairment. The proposed technique was numerically investigated for both single channel 15.6 Gbs CO-OFDM transmissions and 7-channel WDM transmissions, showing that up to 1 dB improvement in the system's Qfactor can be achieved without considering sophisticated power loading algorithms developed for wireless communications

Identifying Extreme PAPR in Coherent Optical Communications

We apply well established concepts of adaptive wave front shaping used in imaging through turbid medium to detect detrimental phase modulated sequences in multi-carrier optical communications that can cause extreme power fluctuations due to dispersion enhanced interference of information symbols

Neurons along the auditory pathway exhibit a hierarchical organization of prediction error

Perception is characterized by a reciprocal exchange of predictions and prediction error signals between neural regions. However, the relationship between such sensory mismatch responses and hierarchical predictive processing has not yet been demonstrated at the neuronal level in the auditory pathway. We recorded single-neuron activity from different auditory centers in anaesthetized rats and awake mice while animals were played a sequence of sounds, designed to separate the responses due to prediction error from those due to adaptation effects. Here we report that prediction error is organized hierarchically along the central auditory pathway. These prediction error signals are detectable in subcortical regions and increase as the signals move towards auditory cortex, which in turn demonstrates a large-scale mismatch potential. Finally, the predictive activity of single auditory neurons underlies automatic deviance detection at subcortical levels of processing. These results demonstrate that prediction error is a fundamental component of singly auditory neuron responses

Stimulus-specific adaptation and deviance detection in the auditory cortex

Tesis por compendio de publicaciones[EN] Neurons in primary auditory cortex, thalamus and midbrain show stimulus-specific adaptation (SSA), a reduction in response to repetitive stimuli that does not affect neuronal responses to deviant tones. This has been proposed as a neuronal correlate of the mismatch negativity (MMN), a special evoked potential in response to deviant tones. However, three important requirements remain to be demonstrated in order to support the SSA-MMN link: (1) MMN is generated mainly within higher-order auditory cortical areas, whereas cortical SSA has only been recorded in A1 of different species. (2) MMN is a mid-long latency response, peaking between 100-200 ms in humans, whereas SSA has only been observed in early responses of A1 neurons. And finally, (3) neuronal responses to oddball stimulation have not been tested for deviance detection–enhancement of responses to deviant events—in addition to SSA, which is an essential property of any bona-fide mismatch response. In this study, I set specific objectives to investigate the relation between SSA and MMN, and moreover, I will test the Hierarchical Predictive Coding account for the MMN at the neuronal level, showing that single neuron responses to oddball stimulation represent prediction error, which is hierarchically organized along the auditory system

Robust effects of corticothalamic feedback and behavioral state on movie responses in mouse dLGN

Neurons in the dorsolateral geniculate nucleus (dLGN) of the thalamus receive a substantial proportion of modulatory inputs from corticothalamic (CT) feedback and brain stem nuclei. Hypothesizing that these modulatory influences might be differentially engaged depending on the visual stimulus and behavioral state, we performed in vivo extracellular recordings from mouse dLGN while optogenetically suppressing CT feedback and monitoring behavioral state by locomotion and pupil dilation. For naturalistic movie clips, we found CT feedback to consistently increase dLGN response gain and promote tonic firing. In contrast, for gratings, CT feedback effects on firing rates were mixed. For both stimulus types, the neural signatures of CT feedback closely resembled those of behavioral state, yet effects of behavioral state on responses to movies persisted even when CT feedback was suppressed. We conclude that CT feedback modulates visual information on its way to cortex in a stimulus-dependent manner, but largely independently of behavioral state