Wireless Communication Basics
Which is a general characteristic of radio waves in millimeter-wave bands such as the 28 GHz band used in 5G, compared with bands below 6 GHz?
- ATheir long wavelength lets them bend easily into the shadows of buildings, so one base station can cover a wide area
- BThey are hardly affected by rain or the human body, so they suit long-distance outdoor links
- CWide bandwidths are easy to secure, enabling high-speed communication, but propagation loss is large and they are easily blocked by obstacles, so the coverage area is small
Show answer and explanation
Answer: C. Wide bandwidths are easy to secure, enabling high-speed communication, but propagation loss is large and they are easily blocked by obstacles, so the coverage area is small
Millimeter-wave bands are high in frequency and large contiguous blocks are easier to secure, so wide bandwidths of several hundred MHz can be used for high-speed communication. On the other hand, the short wavelength makes it hard for the waves to bend around obstacles, they are easily blocked by buildings, people and trees, and they are attenuated by rain. As a result, the area covered by one base station (a cell) becomes small, and beamforming with many antenna elements concentrates the waves toward the terminal to make up for the loss.
- A. These are characteristics of lower bands below 6 GHz. Millimeter waves have short wavelengths and do not bend easily into the shadows of obstacles.
- B. Millimeter waves are readily attenuated by rain and the human body and do not suit long-distance links.
- C. Correct. They are fast thanks to wide bandwidth, but their reach is short.