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Dynamic efficiency degradation of BAN antennas due to the movement of the arms
Abstract
This paper presents analytical results with respect to dynamic shadowing properties of BAN antennas due to the movement of the arms. Particular emphasis is placed on the identification of important parameters for designing BAN systems, such as radiation efficiency and dissipated power, which can not be obtained only by experimental approaches.
... In contrast, a BAN system is used in a state where the human body moves in an environment that shows severe sig- nal fading because of shadowing caused by the movement of the arms compared with the Rayleigh propagation environ- ment. To analyze this situation, studies have been conducted to assess the communication quality, such as the signal bit error rate (BER), when the combined outcome of shadowing and multipath fading occurs simultaneously in an off-body situation [7], [11], [12]. However, the dynamic characteriza- tion of the BAN diversity antenna due to the movement of a human body in a shadowing-fading combined environment has not been fully examined. ...
... The measured results also show that the average value of the maximum swing angle of the left arm is +37.0 • in the forward direction and −13.5 • in the backward direction. Thus, in this study, a model of the arm-swinging motion is determined to be +40 • and −15 • , respectively, for the for- ward and backward directions in comparison with the previ- ous studies [7], [11], [12] in which the maximum angles of the arm-swinging motion were set to ±40 • . ...
... As compared with the measured results of the arm-swinging motion, the triangle model has a root mean square error of 4.0 • , whereas that of the sine-wave model is 1.7 • . Although in our previ- ous studies [7], [11], [12] we used the triangle model in the simulation, we found in the present study that the sine-wave model has a lesser error than the triangle model, as shown in Fig. 5. This result means that the sine-wave model is more appropriate to represent the swing motion of the arms. ...
This paper presents the shadowing analysis of a body area network (BAN) diversity antenna based on the statistical measurements of the human walking motion. First, the dynamic characteristics of the arm-swing motion were measured using human subjects, and a statistical analysis was then carried out using the measured data to extract useful information for the analysis of a BAN diversity antenna. Second, the analytical results of the shadowing effects of the BAN antenna were shown based on the statistical data of the swing motion. The difference between the typical and the realistic arm-swinging models significantly affected the bit error rate (BER) characteristic of the BAN antenna. To eliminate the shadowing caused by the movement of the arms, a BAN diversity antenna was used. Particular emphasis was placed on the evaluation of the spatial separation of the diversity antennas to attain reduction of the signal-to-noise ratio (SNR) required to achieve a specific BER performance, considering the combined outcome of shadowing and multipath fading unique to BAN antenna systems. We determined that an antenna angle separation of greater than 80 degrees is required to reduce the shadowing effects when the diversity antenna is mounted at the left waist in a symmetrical configuration. Further, an antenna angle separation of 120 degrees is required when the diversity antenna is mounted in an asymmetric configuration.
This paper presents analytical results on the BER degradation of QPSK signals for BAN antennas for the case where the combined outcome of shadowing and multipath fading emerge simultaneously and different types of human walking models are employed in the analysis. The results show that a probability of a low signal level is higher than that for the Rayleigh distribution owing to shadowing caused by the movement of the arms, resulting in the significant impact of arm-swinging on the BER performance of body-attached BAN devices. Furthermore, statistical measurements of human walking motion using a number of human subjects are conducted. Using the measured data, dynamic analytical models are created to show that different types of human walking models have appreciable effects on the BER performance of BAN antenna systems.
This paper presents a newly developed arm-waving dynamic phantom that can simulate the walking and running motion of a human. The arm-waving phantom has unique features, in that waving of the right and left arms and the direction and speed of waving can be controlled independently, leading to excellent capability to replicate a variety of natural walking and running styles of an average human. Using the phantom, we have attempted to develop a dynamic channel characterization for BAN systems, such as shadowing properties and path loss characteristics, when the geometrical relationships between the arms and the human body change continuously due to the movement of the arm for both off-body and on-body situations. Furthermore, assessments of the communication quality, such as the signal bit error rate, have been conducted in order to gain useful knowledge about the way in which arm-waving has a significant impact on the performance of body-attached BAN devices.
In this paper, a new radiation efficiency based on the available power is defined with regard to a normal mode helical antenna at 150 MHz placed close to the human abdomen, so that the power loss caused by impedance mismatch and by the resistance of the antenna itself can be taken into consideration in the treatment. In this way, the variation of the effective radiation efficiency of the antenna in a practical situation caused by the antenna length and the distance to the human body is analytically derived. Further, by deriving the loss power in each section, the factors causing degradation of the radiation efficiency are analyzed and the mechanisms for efficiency degradation are clarified. Based on the results, the possibility of improved radiation efficiency of the antenna near the human body is discussed. It is shown that the radiation efficiency of the antenna near the body is less than −20 dB, that its main cause is impedance mismatch, and that improvement of the radiation efficiency by more than 10 dB is possible by always maintaining conjugate match near the human body. These findings are experimentally confirmed. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 23–33, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1115