# Smart Gateway for Healthcare Networks Based on Beam Steering Technology
## 2 Smart Gateway Antenna
### Mean IQ-Value Method in Rice Propagation Environment  
In an indoor situation, even when the smart gateway antenna can be visible to the sensor device, i.e., an LOS environment, there is not only a strong direct wave coming from the sensor device attached to the human body, but there are also reflected and diffracted waves from the surrounding objects. This situation is known as a Rice propagation environment. Therefore, it is necessary to verify the AOA estimation accuracy in a multipath propagation environment, and a method to realize AOA estimation in Rician channels is described below. There is a great deal of difficulty in making interferometric AOA estimations when the direct wave is small in magnitude compared to the summation of the reflected waves, resulting in a small K-factor. This is due to the occurrence of significant phase perturbations caused by scattered reflected and diffracted waves. In [28; 29; 30], incoming waves are assumed to be plane waves, but multipath effects are not treated. In this paper, we propose a novel algorithm, called the mean IQ-value method (MIQ method), to extract the true angular information of incoming waves in severe Rician fading channels [24]. Figure 8 illustrates the schematic diagram that explains the MIQ method for estimating the angle of incoming waves. In Figure 8, the black symbols signify the complex samples of Rice fading signals. As shown in Figure 8, the random multipath scattered-field components are distributed around a coherent LOS component in the Rician fading channel. The magnitudes of the multipath scattered fields have the statistical characteristics of the Rayleigh response, meaning that the real and imaginary parts (in-phase and quadrature-phase: named the IQ components) of the multipath components have normal or Gaussian  
Figure 8: Mean IQ-value method for estimating the angle of incoming waves in a Rice propagation environment. distributions. The probability density functions (PDFs) of the IQ-multipath components have symmetrical bell-shaped curves, as illustrated in Figure 8. This symmetrical nature of the PDFs means that although there are considerable fluctuations for each sample point, their average values (denoted by \(\mu_{\rm I}\) and \(\mu_{\rm Q}\) in Figure 8 for in-phase and quadrature-phase components, respectively) maintain a certain constant value. Based on this theoretical consideration, we propose that the most probable angle of incoming waves can be extracted from the following equation:  
\[\angle E=\tan^{-1}\frac{\mu_{\rm Q}}{\mu_{\rm I}} \tag{6}\]  
To analyze the estimation accuracy of the proposed antenna in a Rician propagation environment, we describe an analytical investigation of channel modeling considering the Rice factor, which is the ratio of the direct wave power and the average scattered wave power, dependent multipath characterization. Figure 9a shows the Rice channel model, whereas Figure 9b is the vector diagram of signals in the complex plane. A Monte Carlo simulation was conducted using this model [31]. Hereafter, we consider the proposed antenna to be located at the center of the circle where the scatterer is placed, as depicted by the broken line in Figure 9a. The average power of multipath scattered waves is obtained as follows:  
\[P_{r}=\frac{1}{S}\sum_{s=1}^{S}|h_{s,r}|^{2} \tag{7}\]  
where \(S\) denotes the number of snapshots for the Monte Carlo simulation. \(h_{s,r}\) (illustrated as the blue arrow in Figure 9b) denotes the channel response of scattered fields and is represented by the following equation:  
\[h_{s,r}=\sum_{n=1}^{N}h_{n}\exp\biggl{\{}j\frac{2\pi d_{s}}{\lambda}\cos(\phi _{n}-\phi_{v})\biggr{\}}=\sum_{n=1}^{N}h_{s,nr} \tag{8}\]  
where \(N\) denotes the number of scatterers; \(h_{n}\) indicates the amplitude of the scattered wave; \(d_{s}\) is the moving distance of the antenna; \(\phi_{n}\) signifies the arrangement angle of the scatterers; and \(\phi_{v}\) is the moving direction of the antenna.