Frame synchronization for PSAM in AWGN and Rayleigh fading channels

Pilot Symbol Assisted Modulation (PSAM) is a good method to compensate for the channel fading effect in wireless mobile communications. In PSAM, known pilot symbols are periodically inserted into the transmitted data symbol stream and the receiver uses these symbols to derive amplitude and phase reference. One aspect of this procedure, which has not received much attention yet, is the frame synchronization, i.e. the method used by the receiver to locate the time position of the pilot symbols. In this study, two novel non-coherent frame synchronization methods are introduced in which only the magnitude of received signal is used to obtain the timing of the pilot symbol. The methods are evaluated for both AWGN and frequency non-selective slow Rayleigh fading channels. One synchronization technique is derived by standard maximum likelihood (ML) estimation formulation, and the other is obtained by using maximum a Posteriori probability (MAP) with a threshold test. Signal processing in the receiver uses simplifying approximations that rely on relatively high signal-to-noise ratio (SNR) as consistent with the reception of 16-QAM. Computer simulation has been used to test the acquisition time performance and the probability of false acquisition. Several lengths and patterns of pilot symbol sequences were tested where every 10th symbol was a pilot symbol and all other symbols were randomly selected data symbols. When compared with the other published synchronizers, results from this study show better performance in both AWGN and fading channels. Significantly better performance is observed in the presence of receiver frequency offsets

Wall Motion Score Index Predicts Persistent Moderate or Severe Secondary Mitral Regurgitation and its Prognostic Role in Patients Undergoing Percutaneous Coronary Intervention

Background: Patients with secondary mitral regurgitation (sMR) often present with greater mortality and comorbidity, which may be predicted by some risk factors. This study was designed to investigate the prognostic meaning of the echocardiographically detected wall motion score index (WMSI) in coronary artery disease (CAD) patients with moderate or severe baseline sMR who underwent percutaneous coronary intervention (PCI) therapy. Methods: The present study was a multi-center and prospective cohort of consecutive CAD patients with baseline moderate or severe sMR who underwent PCI. All underwent echocardiography at baseline and at follow-up after PCI to assess sMR and WMSI. The primary endpoint was the persistence of moderate or severe sMR after the second echocardiographic measurement. Logistic and Cox proportional hazards models were constructed for the primary (persistent moderate or severe sMR) and secondary (worsening heart failure [HF]; all-cause mortality; cardiovascular-specific mortality; and major adverse cardiovascular events [MACE]) endpoints. Results: Among 920 participants, 483 had WMSI values of ≥1.47, and 437 were less. Of all the participants, 366 (39.8%) continued to have moderate or severe sMR after the second echocardiogram measurement. After full adjustment for confounders, elevated WMSI after PCI was independently associated with the primary endpoint during 3–12 month follow-up. Similarly, elevated WMSI was associated with increased risk of worsening HF, all-cause mortality, cardiovascular-specific mortality, and MACE. Conclusions: Persistent moderate or severe sMR is common (approximately 40%) in PCI patients. Elevated WMSI in CAD patients after PCI is a predictor of persistent moderate or severe sMR and has independent negative prognostic value. Patients with CAD and sMR should be monitored for WMSI to identify those at higher risk of mortality and comorbidity