The correct answer is: A. Assigning different group of channels.
Interference between neighboring base stations is a major problem in cellular networks. It can cause dropped calls, slow data speeds, and other problems for users. There are a number of ways to avoid interference, but one of the most effective is to assign different groups of channels to neighboring base stations. This ensures that each base station is using a unique set of frequencies, which prevents them from interfering with each other.
The other options are not as effective at avoiding interference. Using transmitters with different power levels can help to reduce interference, but it is not a perfect solution. If two base stations are using the same frequencies, even if they are using different power levels, there is still a chance that they will interfere with each other. Using different antennas can also help to reduce interference, but it is not as effective as assigning different groups of channels. This is because antennas can only be so directional, and there is always a chance that they will pick up signals from neighboring base stations. Using different base stations is the most effective way to avoid interference, but it is also the most expensive. This is because it requires building new base stations, which can be a significant investment.
In conclusion, the best way to avoid interference between neighboring base stations is to assign different groups of channels to them. This is the most effective and efficient way to prevent interference, and it is relatively inexpensive to implement.