Area C: in depth coverage of the network, or the level of intensity of the wide coverage area has been unable to further enhance the level of the whole network upgrade is part of the district to enhance the contribution, in terms of one cell coverage area is much smaller than the master interference area, so in the case of not enhance the power of the whole network, C the rate of increase will be slower than the rate of increase of I, resulting in the C / I is decreased, while with the increase in the average level, the power-restricted area are also increasing.