BackgroundNon-invasive fetal electrocardiogram (NIFECG) is an evolving technology in fetal surveillance which is attracting increasing research interest. There is however, only limited data outlining the reference ranges for normal cardiac time intervals (CTIs). The objective of our group was to carry out a systematic review to outline normal fetal CTIs using NIFECG.MethodsA systematic review of peer reviewed literature was performed, searching PUBMED,Ovid MEDLINE and EMBASE. The outcomes of interest included fetal CTIs (P wave duration, PR interval, QRS duration and QT interval) and a descriptive summary of relevant studies as well. The outcomes were grouped as early pre-term (≤ 32 weeks), moderate to late pre-term (32–37 weeks) and term (37–41 weeks).Results8 studies were identified as suitable for inclusion. Reference ranges of CTIs were generated. Both PR interval and QRS duration demonstrated a linear correlation with advancing gestation. Several studies also demonstrated a reduction in signal acquisition between 27 and 32 weeks due to the attenuation by vernix caseosa. In this group, both the P wave and T waves were difficult to detect due to signal strength and interference.ConclusionNIFECG demonstrates utility to quantify CTIs in the fetus, particularly at advanced gestations. Larger prospective studies should be directed towards establishing reliable CTIs across various gestations.
In this paper, we address the decision making criteria of a secondary user (SU) for deciding whether to transmit or not upon performing spectrum sensing and detecting the presence of any primary user (PU) in the environment in a cognitive radio network (CRN). We propose a reinforcement learning (RL) based approach by a Markov process at the SU node and present novel analytical methods to analyze the performance of such approaches. In particular, we define the probability of interference Pi and the probability of wastage Pw, and compare these metrics with a RL based and a non-RL based approach for SU transmission. The simulations show the presence of a tradeoff in the two probability metrics Pw and Pi, based on the Markov process. The simulation results are compared in the form of the transmitter operating characteristics (ToC) curves. Using our approach, one could control the interference to the PU by trading off with the spectral wastage.
Ongoing developments of the LTE standard will allow for device-to-device (D2D) communications, which will enable direct connection of user equipments (UEs). Since UEs are becoming increasingly more powerful both in computational power and in the role they have in the network, a concrete threat is that a hand-held D2D-enabled device could be deployed to jam intentionally ongoing transmissions of other D2D users. In this context, a natural concern for operators will be the resilience of the legitimate user (LU) against a jammer's (J) attack. In this work, we model an LTE D2D system made of a pair of LUs and a J that tries to impair their communication. We model the adversarial scenario between the transmitting LU and J as a zero-sum game: in this game, J's target is to minimize the throughput of the legitimate D2D pair. We show the achievable channel rate of the D2D pair under jamming attacks and the existence of a Nash equilibrium. Finally, when both players learn each other strategy over time, e.g., employing fictitious play, such equilibrium becomes the system's operating point.
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