●● ●●●● ●●●●● In contrast to analog modulation, ●●●● ●●●●0 ●●●● digital modulation has: ●●●色 ●● 与模拟调制相比，数字调制有下面的好处 1more efficient use of the radio spectrum. 更有效利用射频频谱 2usually requires less power.CDMA 通常所需的功率小 3over a fading communications channel. 克服通信信道的衰落 4more compatible with the use of error correcting codes.便于与纠错兼容 Need wider frequency bands. 9 ①more efficient use of the radio spectrum. 更有效利用射频频谱  ②usually requires less power. CDMA 通常所需的功率小  ③over a fading communications channel. 克服通信信道的衰落  ④more compatible with the use of error correcting codes.便于与纠错兼容  Need wider frequency bands. In contrast to analog modulation, digital modulation has: 与模拟调制相比，数字调制有下面的好处 9