宽带通信的升压效率

　　宽带通信的升压效率

　　军事和航空通信的关键要求是避免窃听的能力。由于拦截技术变得更加复杂，因此必须采用调制和加密方案的传输系统。军事和航空电子通信系统现在使用高度灵活的无线通信，从频段跳频频段，以及采用宽带协议允许有效的数据加密，在效果上，使传输越来越像噪音，窃听者。

　　然而，转移到更复杂的调制方案和宽带，扩频通信技术的压力增加功率放大器用于RF，这通常是在一个相对狭窄的频带调整效率。尝试使用这些设备在低能效的宽带操作结果。类似的过程也影响了商业环境。

　　For example， in commercial protocols such as GSM， Gaussian minimum shift keying technique was chosen because it allows a linear power amplifier to operate in its most efficient， saturated region. More complex modulation schemes， such as quadrature amplitude modulation， provide greater spectral efficiency， allowing more data to be packed into a smaller bandwidth or provide greater headroom for encryption. As these modulation schemes alter phase and amplitude rather than just the phase of GMSK， the power amplifier needs to drop further into its linear region， which is less power-efficient than working close to the saturated region.

　　As the modulation schemes get more complex， the peak-to-average ratio or crest factor worsens. For comparisons from the commercial environment， LTE takes peak-to-average values to 10 dB， compared to the 7 dB of 3G UMTS and the 3 dB of GSM. This in turn has led to the development of circuit-level techniques that make it possible to deliver wideband communications without loss of efficiency.