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In third generation (3G) mobile communication systems, linear amplification is required for linear modulations. Nonlinear amplification yields inter-modulation distortion (IMD) products and results in unacceptable spectral regrowth in adjacent channels. To achieve linear amplification, linearization techniques are usually employed. Various techniques have been developed to reduce IMD products in high power amplifiers. Generally, three main linearization methods are used. They are the feedforward method, the feedback method and the predistortion method. Adaptive techniques are usually employed to improve the linearization performance.

Adaptive feedforward Method with DSB Pilot

The feedforward method is a commonly used approach, which provides a significant improvement in the linearity of power amplifiers.1–5 The mechanism used in a feedforward amplifier is to cancel the inter-modulation products produced by the main amplifier. The diagram of the feedforward amplifier with a DSB pilot is shown in Figure 1. The purpose of the DSB pilot is to obtain a better adaptive cancellation.