Abstract
It is well known that human body shadowing is a significant propagation effect in indoor communications especially at frequencies higher than 10 GHz. Thus, in this work, human body shadowing in directive short range channel is measured at 28 GHz. A distance of 10 m between the transmitting antenna and the receiving one is used in the measurement campaign. Two body orientations are used in this study. Four persons have participated in the measurement campaign as objects. Shadowing results are given for single person case and two person case. It is shown that maximum body shadowing occurs when the body is near to the transmitting or receiving antenna. Minimum shadowing occurs at almost the half of the distance between the transmitting and receiving antennas. It is shown that, body shadowing loss is low when the body is not in the center line between the transmitting and receiving antennas. At an antenna height of 1.2 m and 1.4 m, height and weight of the person under study affect the shadowing loss. In general, higher person and heavier person give a rise to higher shadowing loss. Crossing the line between the transmitting antenna and the receiving one, body shadowing loss of 10–36 dB is noticed. For the first orientation, shadowing loss due to two persons reaches to 36.5 dB when one of them moving along the line between the transmitting antenna and the receiving one and the other is at 5 ms from the transmitting antenna. A shadowing loss of 50.1 dB is observed when the third person is at 9.5 m from the transmitting antenna a d the fourth one is at 0.5 m from the transmitting antenna.
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Appendix
Appendix
When a person exists in the line between the transmitting antenna and the receiving one, the rays that contribute in the received signal are the attenuated direct ray with three diffracted rays, two of them form the lateral part of the body and the third one the diffracted ray from the head (Fig. 14).
Attenuated direct ray with two diffracted rays for an object at the central line where the diffracted ray from the head is not depicted (first body orientation case)
When a person exists out of the line between the transmitting antenna and the receiving one, the rays that contribute in the received signal are, the direct ray with two diffracted rays from the lateral part of the body (Fig. 15).
Direct ray with two diffracted rays for an object with lateral displacement (first body orientation case)
Due to the geometry of the scenario at which measurements have been carried out and the antenna used, the maximum value that the system can measure with a small error is limited to a given value whatever high is the dynamic range of the measurement system. Figure 16 depicts the measured loss versus the possible body shadowing loss. The lower limit represents the case when the residual scenario resultant ray and the ray due to the human being shadowing are in phase. The upper limit represents the case when the residual scenario resultant ray and the ray due to the human being shadowing are out of phase. It can be seen that at a measured loss of 60 dB, possible body shadowing is 59.72 dB up to 60.3 dB. Also, it can be seen that at a measured loss of 70 dB, possible body shadowing is 67.8 dB up to 74.7 dB. Such high shadowing loss occurs with multi body obstructing the LoS ray.
Measured loss and possible measurement error versus the measured loss
The worst-case (occurs when the sidewall reflection and the ceil reflection are in phase) limit of measurements whatever high is the dynamic range of the measurement system is almost 65 dB (with 1 dB error). A more practical limit could be 68 dB.
A measure to increase the scenario measurement limit is to use absorbing material around the specular reflection point. It is worth mentioning that multi-reflection has insignificant effect on the scenario measurement limit (Fig. 16).
Figure 17 presents the maximum limit of body shadowing loss as a function of the dynamic range of the measurement system and the scenario loss limit due to the geometry of the scenario and the used antennas. Here maximum limit of 77 dB of body shadowing loss is shown. A more practical upper limit could be 70 dB.
Maximum limit of body shadowing loss as a function of the dynamic range of the measurement system and the scenario loss limit
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Ahmed, B.T. Human Body Shadowing at 28 GHz. Wireless Pers Commun 110, 621–635 (2020). https://doi.org/10.1007/s11277-019-06746-8
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DOI: https://doi.org/10.1007/s11277-019-06746-8