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Linearization of Concurrent Dual-Band Power Amplifier Using Digital Predistortion

Naraharisetti, Naveen
http://rave.ohiolink.edu/etdc/view?acc_num=osu1406151856

Abstract Details

2014, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
With the current demand for higher data-rate transmissions, complex envelop techniques like wideband code division multiple access (WCDMA) and orthogonal frequency division multiplexing (OFDM) techniques are employed because of their high spectral efficiency. However these modulated schemes which feature non-constant envelop signals with high peak to average power ratio (PAPR) also impose strict linearity requirements on the PAs. A digital predistortion is used to linearize the PA for its robustness and easy implementation on an FPGA. The complexity of the DPD design is alleviated using widely spaced carriers and frequency selective technique. A new direct learning (DL) technique using 2D quasi exact inverse (2D-QEI) of a power amplifier (PA) model for linearizing concurrent dual band PA is developed. In contrast to indirect learning (IL) architecture, where the coefficients are extracted by swapping the input and output variables in any PA model, a QEI of a PA model can be used in the digital predistorter (DPD). An FPGA test bench integrating the concurrent dual band RF system is utilized to verify the linearization performance of the new DL technique. A 10W PA is excited with two WCDMA signals of 3.84MHz bandwidth which are 310 MHz apart. The measurement results demonstrate that in the presence of additive noise, there is a noticeable improvement in terms of normalized mean square error (NMSE) and adjacent channel power ratio (ACPR) when using the QEI model for DPD. This improvement is achieved in one iteration as in practical DPD systems where data is never played twice. To relish the advantages provided by the piece-wise polynomials, two different types of 2D cubic-spline digital predistorters are developed for linearizing a power amplifier used in dual band transmitters. In the first 2D cubic-spline (2D-CS) representation, the gain functions must be extracted along each axis sequentially. The gain values at the knots should be calculated using an alternate basis, typically 2D polynomials. Secondly, in the new 2D least-square cubic-spline (2D-LSCS) approach, a 2D cubic-spline basis is introduced such that the basis weights can be extracted directly from measured data using the least square method. Inside the FPGA, the 2D basis functions are calculated from 1D basis functions to reduce the signal-processing resource usage in the real-time implementation. Two different test scenarios involving 3 carrier WCDMA and long term evolution (LTE) signals which are 310 MHz apart are considered. The experimental results show that the in-band intermodulation distortion products are reduced by 20 dBc, with an ACPR by less than -50dbc and NMSE by less than -40dB for a 10 W dual-band PA. The 2D-LSCS basis improves performance by upto 3 dB in both ACPR and NMSE when compared to the conventional 2D polynomial model and 2D-CS approaches. At the same time, it uses reduced FPGA resources and features a faster extraction process.
Patrick Roblin (Advisor)
Joanne E. Degroat (Committee Member)
Furrukh Khan (Committee Member)
Cynthia A. Gerhardt (Committee Member)
110 p.
Electrical Engineering

Recommended Citations

Citations

  • Naraharisetti, N. (2014). Linearization of Concurrent Dual-Band Power Amplifier Using Digital Predistortion [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406151856

    APA Style (7th edition)

  • Naraharisetti, Naveen. Linearization of Concurrent Dual-Band Power Amplifier Using Digital Predistortion. 2014. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1406151856.

    MLA Style (8th edition)

  • Naraharisetti, Naveen. "Linearization of Concurrent Dual-Band Power Amplifier Using Digital Predistortion." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406151856

    Chicago Manual of Style (17th edition)

osu1406151856
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This open access ETD is published by The Ohio State University and OhioLINK.