This paper proposed a modified tone reservation (TR) technique that can reduce the peak-to-average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) system and is able to correct errors to avoid channel interference. The TR technique is a widely used PAPR reduction technique, which divides subcarriers of the OFDM system into two sets to generate peak-canceling signals and transmit modulated data. The subcarriers used to reduce the PAPR are called the peak reduction tone sets. The mechanism of peak-canceling signal generation is a primary factor in determining the quality of the PAPR reduction performance of the TR technique. Currently, two signal generation mechanisms exist: TR-gradient-based and TR-clipping-based techniques. Although TR techniques can effectively reduce the high PAPR in the OFDM system, TR techniques lack the ability to correct errors. Therefore, this paper combined block coded modulation codes and TR techniques to provide the modified TR techniques with error correction abilities. From the simulation results, the modified TR techniques had a superior effect on PAPR reduction performance compared with the conventional TR technique. The modified TR technique also possessed the ability to correct errors during signal transmission. 749Numerous techniques improving the high PAPR of the OFDM system have been proposed successively [6], such as amplitude clipping [7], partial transmit sequence (PTS) [8,9], selected mapping (SLM) [10,11], and tone reservation (TR) [12][13][14][15][16]. The amplitude clipping technique adopts the method of filtering signals to reduce the high PAPR. In other words, with a predetermined transmitted signal amplitude threshold, the amplitude clipping technique replaces the transmitted signal amplitude with the threshold when the transmitted signal amplitude is higher than the threshold; conversely, the original transmitted signal is used for transmission when the transmitted signal amplitude is lower than or equal to the threshold. Because the amplitude clipping technique easily induces distortion of transmitted signals, massive calculations must be conducted at the receiving end to improve distortion. Meanwhile, PTS and SLM techniques are categorized as multiple signal representation (MSR) techniques that generate multiple sets of candidate signals, using phase changes during signal transmission and selecting the signal with the minimum PAPR from candidate signals for transmission. Although PTS and SLM techniques can effectively reduce the high PAPR, side information (SI) must be transmitted from the transmission end to the receiving end to identify the candidate signal selected for transmission, thereby facilitating a precise and perfect recovery of transmitted data at the receiving end. The TR technique can also be considered as an MSR technique. However, in contrast to PTS and SLM techniques, the TR technique does not need to transmit additional SI to the receiving end. The TR technique reserves a number of the subcarriers ready to transmit data...
Orthogonal frequency division multiplexing (OFDM) is a popular transmission technique used in wireless communication systems. However, OFDM has deficiencies that must be improved, including a high peak-to-average power ratio (PAPR) in the transmission signal. The tone reservation (TR) scheme is an efficient PAPR reduction method used in OFDM systems. Although the TR scheme can achieve good PAPR performance, it does not have inherent error correction capability and requires extra channel coding to counteract the detrimental effect of channel interference. This paper proposes a TR scheme based on the |u|u + v| construction of Reed-Muller (RM) codes to reduce the PAPR of OFDM signals. The proposed TR-RM scheme uses the |u|u + v| construction to divide the RM code into the direct sum of a correcting subcode for encoding information bits and a scrambling subcode for assigning the number of peak reduction tones (PRTs). Numerical results show that the TR-RM scheme achieves better performance in PAPR reduction than the conventional TR scheme. The TR-RM scheme also has better error correction capability than the conventional TR scheme.
BackgroundThe symptom of tongue deviation is observed in a stroke or transient ischemic attack. Nevertheless, there is much room for the interpretation of the tongue deviation test. The crucial factor is the lack of an effective quantification method of tongue deviation. If we can quantify the features of the tongue deviation and scientifically verify the relationship between the deviation angle and a stroke, the information provided by the tongue will be helpful in recognizing a warning of a stroke.MethodsIn this study, a quantification method of the tongue deviation angle was proposed for the first time to characterize stroke patients. We captured the tongue images of stroke patients (15 males and 10 females, ranging between 55 and 82 years of age); transient ischemic attack (TIA) patients (16 males and 9 females, ranging between 53 and 79 years of age); and normal subjects (14 males and 11 females, ranging between 52 and 80 years of age) to analyze whether the method is effective. In addition, we used the receiver operating characteristic curve (ROC) for the sensitivity analysis, and determined the threshold value of the tongue deviation angle for the warning sign of a stroke.ResultsThe means and standard deviations of the tongue deviation angles of the stroke, TIA, and normal groups were: 6.9 ± 3.1, 4.9 ± 2.1 and 1.4 ± 0.8 degrees, respectively. Analyzed by the unpaired Student’s t-test, the p-value between the stroke group and the TIA group was 0.015 (>0.01), indicating no significant difference in the tongue deviation angle. The p-values between the stroke group and the normal group, as well as between the TIA group and the normal group were both less than 0.01. These results show the significant differences in the tongue deviation angle between the patient groups (stroke and TIA patients) and the normal group. These results also imply that the tongue deviation angle can effectively identify the patient group (stroke and TIA patients) and the normal group. With respect to the visual examination, 40% and 32% of stroke patients, 24% and 16% of TIA patients, and 4% and 0% of normal subjects were found to have tongue deviations when physicians “A” and “B” examined them. The variation showed the essentiality of the quantification method in a clinical setting. In the receiver operating characteristic curve (ROC), the Area Under Curve (AUC, = 0.96) indicates good discrimination. The tongue deviation angle more than the optimum threshold value (= 3.2°) predicts a risk of stroke.ConclusionsIn summary, we developed an effective quantification method to characterize the tongue deviation angle, and we confirmed the feasibility of recognizing the tongue deviation angle as an early warning sign of an impending stroke.
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