Which of these is primarily used to prevent signal interference in communication systems?

The primary purpose of a guard band is to prevent signal interference in communication systems. A guard band is a small frequency range that is deliberately left unused between two channels. This buffer helps to reduce the risk of overlapping signals that can occur due to variations in signal propagation, increasing the overall reliability of the communication system. By providing this separation, a guard band minimizes the possibility of crosstalk between adjacent channels, ensuring clearer and more reliable communication.

While the other options serve important roles in communication systems, they do not specifically target the prevention of interference in the same way. For instance, channel spacing refers to the separation between allocated frequency channels but does not inherently include a buffer; frequency modulation is a technique used to encode information on a carrier wave, and signal amplification increases signal strength but does not address interference issues directly. Therefore, guard bands are critical for maintaining signal integrity by specifically preventing unwanted interference.