Improved Reception Schemes for Digital Video Broadcasting Based on Hierarchical Modulation

In this paper, we first provide an overview of Hierarchical Modulation (HM) along with the opportunities offered by this modulation in the context of the recent Digital Video Broadcasting standard for Satellite to Handheld devices (DVB-SH).With HM, the binary data is partitioned into a “high-priority” (HP) and a “low-priority” (LP) bit stream that are separately and independently encoded before being mapped on non-uniformly spaced constellation points. We will show that the robustness of the HP stream is obtained at the expense of performance degradation of the less protected LP stream with respect to a non-hierarchical modulation. To overcome this inherent drawback of HM, we propose two different reception schemes for improving the bit error rate performance of the less protected LP stream, while keeping the HP decoding performance unchanged. The important point is that in one of the proposed reception schemes, the performance improvement is achieved together with the reduction of the receiver’s complexity

Precision and neuronal dynamics in the human posterior parietal cortex during evidence accumulation

Primate studies show slow ramping activity in posterior parietal cortex (PPC) neurons during perceptual decision-making. These findings have inspired a rich theoretical literature to account for this activity. These accounts are largely unrelated to Bayesian theories of perception and predictive coding, a related formulation of perceptual inference in the cortical hierarchy. Here, we tested a key prediction of such hierarchical inference, namely that the estimated precision (reliability) of information ascending the cortical hierarchy plays a key role in determining both the speed of decision-making and the rate of increase of PPC activity. Using dynamic causal modelling of magnetoencephalographic (MEG) evoked responses, recorded during a simple perceptual decision-making task, we recover ramping-activity from an anatomically and functionally plausible network of regions, including early visual cortex, the middle temporal area (MT) and PPC. Precision, as reflected by the gain on pyramidal cell activity, was strongly correlated with both the speed of decision making and the slope of PPC ramping activity. Our findings indicate that the dynamics of neuronal activity in the human PPC during perceptual decision-making recapitulate those observed in the macaque, and in so doing we link observations from primate electrophysiology and human choice behaviour. Moreover, the synaptic gain control modulating these dynamics is consistent with predictive coding formulations of evidence accumulation