寬帶通信的升壓效率

　　軍事和航空通信的關鍵要求是避免竊聽的能力。由于攔截技術變得更加復雜，因此必須采用調制和加密方案的傳輸系統。軍事和航空電子通信系統現在使用高度靈活的無線通信，從頻段跳頻頻段，以及采用寬帶協議允許有效的數據加密，在效果上，使傳輸越來越像噪音，竊聽者。

　　然而，轉移到更復雜的調制方案和寬帶，擴頻通信技術的壓力增加功率放大器用于RF，這通常是在一個相對狹窄的頻帶調整效率。嘗試使用這些設備在低能效的寬帶操作結果。類似的過程也影響了商業環境。

　　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.