## 4 Experimental Results
### Discussion  
The present work represents a platform development and methodology based on the ILA of commercial RF PAs with LTE applications. It is based on sweeping the signal from the AD9361 dual transceiver using a virtual PA for QPSK and 64-QAM modulation. The achieved metric to evaluate the system is 8 dB of spectral reduction achieved. The developed system reaches a value of 7.5% of EVM, which is the primary specification that quantifies the performance of digital modulation. The system represents a preliminary platform for DPD applications based on LTE digital multiplexing schemes operating in the 2.5 GHz band. Its operating range allows modeling and linearization in licensed and unlicensed bands and bandwidths of 200 KHz to 56 MHz. Table 4 shows a comparison of the application ranges in frequency; the developed system explores an integration of CFR-clipping that can be joint helps to increase the PA efficiency, while simultaneously provide a better linearity performance, for wide-range applications from 47 MHz-6 GHz. The CFR-clipping method before the DPD stage allows achieving PAPR reductions compared with seminal works. Most of the works summarized in Table 4 are based on a signal baseband generation defined as CW Source, VSG or simulation, these approaches involve a limited transceiver system, and the tuning is limited for specified applications. Table 5 shows the wide range of digital applications to achieve spectral reduction and improvement with multi-carrier systems. OFDM and W-CDMA applications predominate towards 5G, in addition to bandwidths of 5-20 MHz. It can be seen that the developed work is an integration of a system based on CFR technique-clipping based in closed-loop iterative process, which achieves a reduction of up to 3.3 dB in PAPR. The system is based on more than 60 OFDM symbols for each of the 600 subcarriers, in addition to an EVM study (%) with an improvement from 5.7% to 31.39% with the CFR approach of 5-MHz, in addition to an EVM improvement (%) from 5.46% to 39.21% with CFR 10-MHz. In this work, a platform was developed to validate the robustness of the CFR-clipping algorithm with experimental results, they can be scaled in various digital multiplexing schemes such as OFDM or W-CDMA with multi-carriers, where the systematic tuning can be automated controlled for the whole SDR system. The developed algorithm is dependent on the digital domain, unlike the other reported works [26; 28]; these approaches are based mainly on vector signal generator (VSG), or vector signal transceiver to generate the I/Q baseband data samples [18; 24], which is more expensive test equipment, and the signals are predefined. In this context, our proposed CFR-clipping system can be fully controlled for LTE 5-MHz and LTE 10-MHz applications, from 47-MHz to 6-GHz. This algorithm links a CFR-clipping stage before a DPD block. The system can control the power spectra of carrier frequency by varying the power scale factor in the board, which is associated with CFR and clipping procedures that are detailed in the subsection CFR Model Identification with Joint PAPR Clipping. This work evaluates different CFR-clipping levels to improve the precision and spectral reduction of a DPD technique integrated with the CFR-clipping algorithm. In this developed work, the CFR algorithm it is validated with a commercial RF PA from Mini-Circuits ZX60-5916 MA+ for LTE applications as a DUT in the platform. The on-board transmit power monitor can be used as a power detector, enabling highly accurate TX power measurements; in the case of the compared works, it is not so precise if a VSG is used as the input device instead of a development board. This is the primary key and purpose of utilizing a software defined radio (SDR) board for scalability between applications for sub-6 GHz frequency bands.