| Frequency-hopping communication systems are widely used in military and civilian applications because of their good anti-interference characteristics.In order to improve the utilization of spectrum resources,using high-order modulation in frequency-hopping systems will bring a higher peak-to-average power ratio to the signal,when passing through the RF power amplifier,there will be serious non-linear distortion of the power amplifier.However,the digital predistortion technology used in mobile communication systems is only applicable to RF power amplifiers with a fixed carrier frequency,and cannot be directly applied to frequency-hopping communication systems with constantly changing carrier frequencies.In response to this problem,this paper studies a frequency-hopping digital predistortion algorithm,the research content includes:First,the frequency-hopping predistortion nonlinear model is analyzed and designed.For the frequency-hopping communication system,from the perspective of computational complexity and predistortion effect,the nonlinear model is analyzed.Since the nonlinear distortion of the power amplifier can be regarded as approximately unchanged in adjacent frequency bands,in order to reduce the number of nonlinear model coefficients,frequency-hopping points in the same frequency range using the same set of coefficients is proposed.Second,design a calculation algorithm of frequency-hopping predistortion coefficient,which can choose the suitable calculation method in different application scenarios,including the predistortion coefficient offline extraction method and the predistortion coefficient online update method.The former is based on the indirect learning architecture and least squares method,and uses an independent high-performance digital signal processing module to calculate the frequency-hopping predistortion coefficients corresponding to different frequencies at one time.This method has a large amount of calculation,a high complexity but accurate calculation results,and is suitable for initializing the predistortion coefficient when the frequency-hopping transmitter leaves the factory.The latter is based on the indirect learning architecture and adaptive filtering principle,iteratively updates the predistortion coefficients of a single frequency-hopping frequency.With low computation and complexity,it is suitable to update the predistortion coefficient when the predistortion effect deteriorates.Third,the proposed digital predistortion algorithm for the frequency-hopping power amplifier is validated through the simulation.By setting up a pre-distortion simulation link with one thousand hops per second,it verifies the frequency-hopping predistortion technology at four frequency-hopping frequencies.It is verified that when the baseband signal adopts 16 QAM modulation mode and the signal bandwidth is 10 MHz and the nonlinear distortion causes the ACPR of the power amplifier output signal to reach-32 dBc,the frequency-hopping predistortion can reduce the ACPR by more than 23 dBc.This paper studies the frequency-hopping digital predistortion algorithm.It analyzes the nonlinear model,the extraction and update algorithm of the model coefficient when applying the traditional digital predistortion algorithm to the frequency-hopping communication system.The results can be used to solve the nonlinear problem of power amplifiers in frequency-hopping systems. |
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