Broadband amplifiers have been used in modern wireless communication systems. However, the accompanying disadvantage is that there is more nonlinear interference in the available operating frequency band. In addition to the in-band intermodulation distortion which affecting adjacent frequency bands the most important is harmonic distortion. In this letter we present a robust and low complex digital harmonic canceling model called cross-disturbing harmonic (CDH) model for broadband power amplifiers (PAs). The approach introducing cross terms is used to enhance the robustness of the model, thereby significantly increase the stability of the system. The CDH model still has excellent performance when actively reducing the number of coefficients. Comparisons are conducted between the CDH model and the other state-of-the-art model called memory polynomial harmonic (MPM) model. Experimental results show that the CDH model can achieve comparable performance as the MPM model but with much fewer (43%) coefficients.

Orthogonal frequency division multiplexing (OFDM) technique has been widely used in communication systems in pursuit of the most efficient utilization of spectrum. However, the increase of the number of orthogonal subcarriers will lead to the rise of the peak-to-average power ratio (PAPR) of the waveform, thus reducing the efficiency of the power amplifiers. In this letter we propose a phase-changed PAPR reduction technique based on windowing function architecture for OFDM systems. This technique is based on the idea of phase change, which makes the spectrum of output signal almost free of regrowth caused by peak clipping. It can reduce more than 28dBc adjacent channel power ratio (ACPR) compared with the traditional peak windowing clipping methods in situation that peak is maximally suppressed. This technique also has low algorithm complexity so it can be easily laid out on hardware. The proposed algorithm has been laid out on a low-cost field-programmable gate array (FPGA) to verify its effectiveness and feasibility. A 64-QAM modulated 20M LTE-A waveform is used for measurement, which has a sampling rate of 245.67M.