# Smart Gateway for Healthcare Networks Based on Beam Steering Technology
## 5 Radio Propagation Experiments in an LOS Environment  
To examine the effectiveness of the beam steering function in the proposed antenna, this section presents the radio propagation experiments conducted to evaluate the receiving level performance according to beam steering, which is dependent on the movement of a human who is attached to the sensor device. In this indoor situation, we performed two types of measurements: one with K-factor estimation in an LOS propagation environment with short-term fading, and one with received level characteristics from long-term fading. Figure 23a shows the top view of the indoor measurement environment, which is a 10 m \(\times\) 5 m classroom at the University of Toyama. The distance from the floor to the ceiling is 3 m. A study involving humans requires us to obtain an informed consent statement from the participants, and moreover, the repeatability of measurement with real humans tends to be poor. As an alternative, we previously developed an arm-swinging dynamic phantom that can simulate the natural walking style of humans [40]. This phantom was created to be a realistic geometrical representation of an average Japanese male [41]. The head and body are approximated by circular cylinders, the dimensions of which are 18 cm in diameter by 25 cm in height, and 22 cm in diameter by 135.5 cm in height, respectively. The circular cylinders contain a mixed solution that simulates the electrical properties of a human [42]. Figure 23: Radio propagation experiment performed in an indoor situation: (**a**) top view of the indoor measurement environment and (**b**) measurement setup in the classroom. With regard to a sensor device mounted on a human being, dynamic channel variations caused by arm swinging while walking must be considered [43]. The shadowing effects are attributed to the sensor device attached to the person and should not be included in the evaluation of the gateway system. However, variation in the direction of the incoming wave due to human movement is very important. Therefore, a half-wavelength sleeve dipole antenna, which represents a sensor device, was attached to the waist of a human phantom without arms. Moreover, the human phantom was placed on a truck and was moved at a constant speed on rails. The gap between the dipole antenna and the surface of the body was set to 1 cm. The height from the floor to the sensor device and the gateway antenna was set to 1 m. The distance from the human phantom to the wall was 1.5 m, while the distance from the proposed antenna to the wall was 0.5 m.  
Figure 23b depicts a photograph of the measurement setup in a classroom. The output signal of the signal generator (SG) is radiated from the half-wavelength sleeve dipole antenna attached to the human phantom, and the received signal of the proposed antenna is measured by a spectrum analyzer (SA). The transmit signal is set to continuous wave, and the measured frequency is 2 GHz. To assess the K-factor in the indoor situation, we conducted an experiment using the human phantom. To achieve short-term fading in off-body communication, the travel distance of the phantom was set to 0.9 m (6 \(\lambda\)) from the start point. The maximum difference in the free-space path loss on the moving distance was 0.4 dB, indicating the propagation loss variation was very small. The receiving antenna used is a half-wavelength dipole antenna, which is omnidirectional on the horizontal plane, to evaluate incoming wave characteristics. Figure 24 shows the cumulative distribution function (CDF) characteristics of the measured instantaneous response. The received power is normalized by its median value. The black solid curve is that of measured results. The black broken curve is the theoretical CDF characteristic for the K-factor estimated from the measured data. The theoretical curve for Rayleigh response is also included as a red broken line in the Figure. In Figure 24, the estimated K-factor is 4 dB, despite the short-distance communication.