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To solve the sparse channel estimation problem in Orthogonal Frequency Division Multiplexing (OFDM) systems, this paper presents a pilot design algorithm based on multi-pilot parallel searching and binary coding. Under the Mutual Incoherence Property (MIP), we consider the deterministic pilot design problem by minimizing the coherence of the dictionary matrix. The pilot is also required to be placed within the effective subcarrier range for more practical purposes. In this scheme, the pilot set is binary coded. In each iteration, the sequence of the binary code segment is recombined to update the approximately optimal pilot position. The update of some coding segments can change multiple pilot positions at the same time. It can increase the diversity of pilots, and reduce the complexity of computation. Experimental results show that, compared with the existing pilot optimization methods, this algorithm can find a smaller MIP measurement matrix. Therefore, the corresponding pilot mode can significantly improve the performance of channel estimation.

Objective To discuss the clinical features of ischemic stroke caused by intracranial artery fenestration, and to explore possible correlation between ischemic stroke and intracranial artery fenestration. Methods and Results We retrospectively studied 11 cases of ischemic stroke caused by intracranial artery fenestration from December 2012 to October 2017. Cranial MRI showed the infarcts were located in pons (5 cases, 5/11), posterior limb of internal capsule (3 cases, 3/11), left thalamus (one case, 1/11), left centrum semiovale (one case, 1/11) and bilateral occipital lobes combined with left internal carotid artery (ICA) aneurysm (one case, 1/11). MRA showed fenestration in basilar artery (BA) was found in 9 cases (9/11), fenestration in left vertebral artery (VA) was found in one case (1/11), fenestration in right posterior cerebral artery (PCA) was found in one case (1/11). Five cases of pontine infarction were caused by BA fenestration (4 cases) and right PCA fenestration (one case); 3 cases of internal capsule posterior limb infarction were caused by BA fenestration; one case of left thalamic infarction was caused by left VA fenestration; one case of left centrum semiovale infarction was caused by BA fenestration; one case of bilateral occipital lobes infarction was caused by BA fenestration. All patients were treated by antiplatelet aggregation, lipid regulation and scavenging free radical. No patient recurred ischemic stroke. Conclusions Intracranial artery fenestration may results in focal hemodynamic changes, and is closely related to ischemic stroke. [ABSTRACT FROM AUTHOR]