Complex sentence: Thirdly, because users are mobile, the traffic of each BTS fluctuates (called'tide effect'), and as a result, the average utilization rate of individual BTS is pretty low.
Split into simpler sentences: Thirdly, because mobile users are moving from one place to another, the traffic of each BTS is fluctuating very much from time to time, which is called'tide effect'. As a result, the average utilization rate of individual BTS is pretty low.