Select the correct statement(s) regarding OFDM.

a. in the frequency domain, each subcarrier must be separated by a guard channel

b. subcarriers in the frequency domain overlap one another at a specified spacing that prevents adjacent subchannel interference

c. OFDM is considered a spread spectrum technology

d. b and c are correct

What is true about terrestrial microwave systems?

a. use of directional parabolic antennas are typically required for high data rate applications

b. since transmission frequencies are very high, line-of-sight between communicating antennas is required

c. security is poor since transmissions are easily intercepted

d. all are true