This question concerns cellular telephony. a. In the LTE downlink, an OFDM symbol is described mathematically by s(t) = x(i)e2m t %3D i=1 Identify and explain K, X(i), and T;. b. For the symbol in part a, briefly explain how the fast Fourier transform (FFT) can be used to modulate and demodulate the symbol. c. In LTE, the physical resource block (PRB) contains 7 OFDM symbols, described in part a, with each symbol using 12 subcarriers. Suppose each symbol is selected from a 16-QAM constellation, and suppose four symbols from the entire PRB are used as reference symbols to estimate the channel, and cannot be used for data. If the PRB lasts 0.5 ms, what is the peak data rate of a PRB (in bits/s)? d. A city of size 42 km? is to be covered by a digital cellular phone network. The spectrum re-use cluster size is 3 cells, and each cell has area 0.2 km. Assume that the cells perfectly fit the city size without overlap. If the system bandwidth is 35 MHz, and FDM is used where each user is allocated 25 kHz including guard band, how many users can simultaneously use the system? How many can simultaneously use the system per cell?