SCIENCE CHINA Information Sciences, Volume 62, Issue 2: 022304(2019) https://doi.org/10.1007/s11432-017-9420-y

## An enhanced digital predistortion algorithm based on polynomial model identification

• AcceptedMar 29, 2018
• PublishedDec 26, 2018
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### Abstract

To improve the accuracy of the nonlinear distortion correction for the radio frequency (RF) power amplifier (PA), it is necessary to precisely obtain the reverse function of the PA nonlinear model. However, the direct inversion of the PA nonlinear model involves solving a high-order univariate polynomial, which is difficult to apply in engineering. In this study, based on the envelope memory polynomial (EMP) model, the high-order terms of the nonlinear model are approximated by their previously calculated values through iterations and considered as known constants in the polynomial solution finding process, thereby resulting in a significant reduction in computational complexity. Compared with the direct inversion method, model of a 9th-order nonlinear, the proposed method reduces the calculation time in the coordinated rotation digital computer (CORDIC) algorithm by at least 80%. The simulation results show that for a long-term evolution (LTE) downlink signal, the results obtained by the proposed simplified method agree well with those obtained by direct inversion method.

### Acknowledgment

This work was supported in part by National Natural Science Foundation of China (Grant Nos. 61771107, 61701075, 61771115, 61531009, 61471108), National Major Projects (Grant No. 2016ZX03001009), the Project Funded by China Postdoctoral Science Foundation, and the Fundamental Research Funds for the Central Universities.

### References

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• Figure 1

The DPD structure based on polynomial model identification.

• Figure 2

Estimation errors of the two methods.

• Figure 3

Performance comparison of the DPD algorithms on inhibition of spectral regeneration in LTE-A system.

• Table 1   Complexity analysis of QR decomposition algorithm
 Number of multiplications Number of divisions CORDIC iteration times $\frac{1}{2}P^{3}+6P^{2}-\frac{1}{2}P$ $P$ $\frac{5}{2}P^{3}+\frac{3}{2}P^{2}-2P$
• Table 2   Simulation parameters of the signal source
 Source type Subcarrier number Signal bandwidth Signal power LTE-A 5 100 MHz $-$10 dBm
• Table 3   NMSE comparison of the DPD functions
 DPD methods NMSE (dB) PA modeling error $-$80.00 Error of the precise method in [13,14] $-$72.70 Error of the precise method in [9] $-$80 Error of (30) in this paper with $P=7$ $-$79.24 Error of (30) in this paper with $P=5$ $-$78.12

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