### I. Introduction

### II. Propagation Environments

### 1. Urban Environment

*P*

*is the transmitted power,*

_{Tx}*P*

*is the received power,*

_{Rx}*G*

*and*

_{Tx}*G*

*are the antenna gain of the transmitter and receiver, respectively,*

_{Rx}*G*

*is the summed gain of the power amplifier and low-noise amplifier, and*

_{amp}*L*

*is the summed cable loss in the transmitting and receiving system.*

_{cable}### 2. Rural Environment

### III. Results

### 1. Measured Results

*P*

*. Three plots were drawn with three frequency band groups for clarity. As shown in Fig. 4(a)–(c), the measured path loss curves contain many null points because of the fading effect. To determine the appropriate reach distances at 95 dB of path loss, smooth curves were extracted from the measured data as follows.*

_{Rx}*L*is the path loss,

*α*is the slope coefficient by distance,

*β*is the floating offset value of the path loss,

*γ*is the difference coefficient by frequency,

*X*

*is the log-normal shadow fading factor, and*

_{σ}*σ*is the standard deviation of shadow fading. The distance

*d*and frequency

*f*are expressed in meters and gigahertz, respectively. Here, the parameter

*α*is not related to the frequency. Therefore, all fitted curves from the ABG model have the same slope, as shown in Fig. 4(a)–(c). With the AB model, the slope of each frequency curve could be different; however, this model is not recommended for multiple frequencies [13].

*α*,

*β*, and

*γ*were extracted from the measured path loss (Fig. 4) using the least squares method [13]. The derived values were

*α*= 2.26,

*β*= 30.99, and

*γ*= 2.04. These values are similar to those of the site-general model of ITU-R Recommendation P.1411–9 [8], which are

*α*= 2.12,

*β*= 19.2, and

*γ*= 2.11. Second, the smooth curves obtained from Eq. (1) were plotted in Fig. 4 (dotted lines). Finally, the appropriate reach distances at 95 dB of path loss were determined. The reach distances for the urban environment were 881, 680, 363, 252, 175, 135, 85, 50, and 39 m for 0.75, 1, 2, 3, 4.5, 6, 10, 18, and 24 GHz, respectively. The values are listed in Table 3. As expected, the reach distance was inversely proportional to the frequency.

*α*= 1.65,

*β*= 40.86, and

*γ*= 2.03.

*α*-value, and as a result, the reach distance was longer. This may have been caused by the absence of obstacles, such as buildings.