Example(continue) The Shannon formula gives us 6 Mbps,the upper limit. For better performance we choose something lower,4 Mbps,for example.Then we use the Nyquist formula to find the number of signal levels. 4Mbps=2×1MHz×log2 L=4 Shannon定理给出了信道容量的理论上限， 而Nyquist定理给出了信号离散等级的数量Example (continue) The Shannon formula gives us 6 Mbps, the upper limit. For better performance we choose something lower, 4 Mbps, for example. Then we use the Nyquist formula to find the number of signal levels. Shannon定理给出了信道容量的理论上限， 而Nyquist定理给出了信号离散等级的数量