Many buildings have poor cellular coverage or dead zones indoors, which is an issue for occupants considering that 80% of calls are made indoors. There are many factors that inhibit cellular signals, such as the size and construction of the building, environmental obstacles, and the location of towers. The number of users on a network (known as “loading”) can also affect cellular coverage since networks are dynamic and grow or shrink based on inter-cell interference levels. This is why coverage may vary based on time of day, or day of the week.