Research On Digital Predistortion Technology For Carrier Aggregation

With the rapid development of wireless communication systems,carrier aggregation(CA)technology has been proposed to satisfy the user's demand by making sufficient use of the spectrum resource,which lead to the change of the traditional transmitter architecture.Nowadays,multi-band and multi-mode signals can be amplified through the new transmitter architecture with only one power amplifier.The new transmitter architecture not only reduces the consumption of the power but also makes the miniaturization of base station possible.Power amplifier serves as the key component of the transmitter,however due to its intrinsic nonlinearity,it's hard to place the balance between efficiency and linearity.Especially in the new CA application scenarios,harmonic distortion which can be easily filtered in the old days may also cause interference to the whole system.At the meantime,the in-band distortion and the intermodulation distortion caused by the amplification of multi ?band signals are also need to be suppressed.Digital predistortion is a promising power amplifier linearization technique with the advantage of high precision,good stability,and reasonable cost-effectiveness.With the change of application scenarios,digital predistortion technology also needs to be changed accordingly to meet new requirements.In this paper,the research focus on the digital predistortion technique under the carrier aggregation scenarios.In the frequency division duplexing(FDD)intra-band CA scenario and cognitive radio scenario,we propose the frequency selective digital predistortion to eliminate the harmonic emission at the target frequency.We use particle swarm optimization algorithm to solve the predistortion coefficients.Compared with the traditional gradient based optimization solutions,it speeds up the convergence process with a better convergent result.The simulation results indicate that the harmonic can be well suppressed with our proposed method.The second order harmonic and the third order harmonic can be suppressed by 40.4dB,and 28.8dB respectively.For the dual-band transmitting scenario,we propose the two-dimension piecewise digital predistortion based on self-organizing maps(SOM).We use SOM network to divide the dual-band signal into different segments according to the characteristics of input signal.Compared with the traditional K-Means algorithm,SOM provide a robust way to cluster input signals.The principle component analysis method is introduced to the indirect predistortion learning architecture.With the order reduction method,the predistortion coefficients in each segment are controlled in a reasonable range.We use the web-based platform with actual power amplifier to verify our proposed method,the measurement results demonstrate the validity of our proposed method.For the dual-band WCDMA signal,the ACPR can be improved by 15.3dBc;for the dual-band GSM/OFDM signal,the lower band GSM signal's IMR can be improved by 13.3dBc and upper band OFDM's ACPR can be improved by 12.2dBc;or the dual-band OFDM signal,the ACPR can be improved by 14.1dBc.