RESUMO
Noise uncertainty and signal-to-noise ratio (SNR) wall are two very serious problems in spectrum sensing of cognitive radio (CR) networks, which restrict the applications of some conventional spectrum sensing methods especially under low SNR circumstances. In this study, an optimal dynamic stochastic resonance (SR) processing method is introduced to improve the SNR of the receiving signal under certain conditions. By using the proposed method, the SNR wall can be enhanced and the sampling complexity can be reduced, accordingly the noise uncertainty of the received signal can also be decreased. Based on the well-studied overdamped bistable SR system, the theoretical analyses and the computer simulations verify the effectiveness of the proposed approach. It can extend the application scenes of the conventional energy detection especially under some serious wireless conditions especially low SNR circumstances such as deep wireless signal fading, signal shadowing and multipath fading.
RESUMO
OBJECTIVE: To observe the influence of electroacupuncture (EA) stimulation with different electrical current intensities and therapeutic intervals on learning-memory ability and expression of ß-amyloid peptide Aß 1-40 and arginine vasopressin (AVP) genes in the hippocampal CA 1 region in vascular dementia (VD) rats, so as to provide evidence for treatment of VD. METHODS: A total of 48 male SD rats were randomly divided into sham, model, 0.5 mA-5 d-EA, 1.5 mA-5 d-EA, 0.5 mA-1 d-EA and 1.5 mA-1 d-EA groups (n=8 in each group). The VD model was established using modified 4-vessels occlusion method. EA (alternative 2 Hz/15 Hz, 0.5 mA, 1.5 mA) was applied to "Baihui" (GV 20) and "Dazhui" (GV 14) for 30 min, once a day (1 d) or once every 5 d for 10 times. The learning-memory ability was detected using Morris water maze tests (place navigation task and spatial probe trials), and the expression of Aß 1-40 and AVP genes in hippocampal CA 1 region was determined using real time-PCR. RESULTS: In comparison with the sham group, the average escape latency of place navigation task, and the duration for crossing the target-platform for the 1st time (spatial navigation task) were significantly increased (P<0.05), and the times to cross the target-platform within 2 min (spatial probe trials) were significantly decreased in the model group (P<0.05), suggesting a reduction of learning-memory ability. The expression level of Aß 1-40 mRNA was remarkably increased (P<0.05), and that of AVP mRNA notably decreased in the model group (P<0.05). Following EA intervention, the increased escape latency and the duration of crossing the target-platform for the 1st time and the increased Aß 1-40 mRNA expression, and the decreased target-platform crossing times within 2 min as well the down-regulated AVP mRNA expression level were reversed in the 4 EA groups compared with the model group (P<0.05). The therapeutic effects of higher stimulating intensity (1.5 mA-1 d-EA and 1.5 mA-5 d-EA) were markedly superior to those of lower intensity (0.5 mA-1 d-EA and 0.5 mA-5 d-EA), and the effects of higher frequency of EA intervention (0.5 mA-5 d-EA and 1.5 mA-5 d-EA) were obviously superior to those of lower frequency of EA (0.5 mA-1 d-EA and 1.5 mA-1 d-EA) in suppressing the increased 3 indexes and the decreased 2 indexes mentioned above (P<0.05). CONCLUSIONS: EA can improve the learning-memory ability of VD rats, which Feb be related to its effects in inhibiting the expression of Aß 1-40 mRNA and up-regulating the expression of AVP mRNA in hippocampal CA 1 region; and the therapeutic effects of higher stimulating intensity and higher intervention frequency are obviously better than those of lower stimulating intensity and lower therapeutic frequency.