《Wireless Communications Principle and Practice 2nd Edition by Rappaport》 第三章课后习题：Compare the received power for the exact(Equation 4.47) and approximate (Euation 4.52) expressions for the two-ray ground reflection model. Assume the height of the transmitter is 40m and the height of the receiver is 3 m. The frequency is 1800 MHz, and unity gain antennas are used. Plot the received power for both models continuously over the range of 1 km to 20 km, assuming the ground reflection coefficient of -1 for horizontal polarization, d0=1km and Pr(d0)=1uw.