## 5 Conclusions and Future Work  
In this work, a clipping-based algorithm was developed to reduce the PAPR of OFDM signals using a FPGA-based system. The proposed CFR algorithm is experimentally validated in terms of PAPR, ACPR, and residual spectral regrowth performance improvement. The conditioning waveform with the simplest approach clip and filter method not only aids to take clipped points, but also from the actual signal preserve its feature when a factor clipping is applied. The CFR model identification with joint PAPR clipping is applied to operate the PA with better energy efficiency in order to affect the amplified signal to introduce in its linear region. A reduction of 3.3 dB is obtained for the transmitter in the 10-MHz and 2.93 dB for the Tx for a 5-MHz bandwidth. The CFR algorithm performance is done on a commercial amplifier for 64-QAM OFDM LTE applications with bandwidths of 5-MHz and 10-MHz with an average increase of the EVM obtained as 39.94% and 12.82% for 10-MHz. For future work, we expect to implement in the FPGA system robust algorithms based on the direct and indirect learning architectures, to identify the coefficients for the real-time signals and explore new DPD systems, with its CFR algorithm associated under a parameters preservation approach. Conceptualization, J.A.G.-A. and J.R.C.-V.; methodology, J.A.G.-A., L.F.-H. and J.R.C.-V.; software, L.F.-H., E.I.-G. and C.V.-R.; validation, J.A.G.-A., J.R.C.-V., E.I.-G. and C.V.-R.; \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Related** & **Fundamental** & **Predistortion** & **Baseband Signal** \\
**Work** & **Frequency** & **Technique** & **Generation** \\ \hline This work & 47 MHz-6 GHz & CFR-Clipping and & FPGA RF Agile Transceiver \\  & & Memory polynomial model & \\ [PERSON], et al. [7] & 1.9–2.6 GHz & 2-D power distribution reshaping & CW Source \\ [PERSON], et al. [14] & Not specified & new spectrum constrained-CFR & VSG \\ [PERSON] [15] & 1952–1965 MHz & DPD-CFR & VSG \\ [PERSON] [16] & 3.3–3.8 GHz & clipping-and-bank & Arbitrary waveform \\  & & filtering & generator \\ [PERSON], et al. [17] & Not specified & DPD-least squares (LS) & FPGA-Transceiver \\  & & optimization & \\ [PERSON], et al. [19] & Not specified & Clipping signal & Not specified \\  & & Iterative clipping & VSG \\  & & and weighted error filtering & \\  & & & Monte Carlo Simulation \\  & & & Tone Reservation & Simulated WiMax 802.16a \\  & & clipping method & system \\  & & MPM Modeling & VSG \\ [PERSON] and [PERSON] [27] & 3.44–3.60 GHz & Not specified & Not specified \\  & & Clipping-Filtering and & Not Specified \\  & & Peak-Shrinking Interpolating & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparative table for the CFR technique, linearization method and signal generation. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Digital Application** & **Achieved Precision and Spectral Improvement** & **Spectral Reduction Technique** \\ \hline LTE 1.4 MHz [26] & \(-\)36.9 dB NMSE & Augmented MP \\ QPSK, 8-PSK and 16-QAM 10/20 MHz [27] & \(-\)35.62 10 MHz, \(-\)37.40 20 MHz & ANN, Rapp model \\ LTE, V-CDMA [29] & PAPR 4 dB & CFR techniques-Clipping based \\
16 QAM, and 64 QAM, OFDM [17] & PAPR 4 dB & CFR techniques-Clipping based \\ OFDM, WiMax 802.16e [20] & PAPR not specified & Clipping based \\ OFDM, WiMax 802.16e [20] & PAPR not specified & Clipping based \\ OFDM [21] & PAPR not specified & iterative clipping noise \\ OFDM [19] & PAPR 9.5 dB & Iterative clipping \\  & and BER improvement & and filtering \\ Not specified [16], general purpose & PAPR 3 dB & CFR and DPD neural networks (NN) based \\ W-CDMA multi-carrier [15] & PAPR 8.6 dB & CFR and envelope clipping \\ OFDM, 64-QAM [14] & PAPR 8.6 dB & CFR and envelope clipping \\ LTE 10-MHz [7] & 0.3 to 0.8 dB Power improvement & 1D-CFR \\ OFDM, LTE-10 and 5-MHz [This work] & PAPR 3 dB (5-MHz) & CFR technique \\  & PAPR 3.3 dB (10-MHz) & Clipping based \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of spectral improvements and applied techniques for digital applications.