(a) Energy consumption reduction versus average number of hops. is the compression ratio. The higher the number of hops from a cluster to a sink, the greater the reduction in energy consumption. If the average number of hops is small, the reduction in energy consumption is negative, showing that transmitting raw data directly to the sink is more energy efficient than compression. (b) Compression performance of different mapping periods. Each line indicates the compression ratio versus the normalized MSE. For a fixed error level, the shorter the mapping period is, the higher the compression ratio is. (c) Energy consumption reduction for different mapping period.