SIGNAL QUALITY ENHANCEMENT FOR POWER AND SPECTRUM EFFICIENT 4G/5G COMMUNICATION

Abstract

High peak-to-average-power ratio of OFDM-based 3G/4G and 5G communication signals forces the power amplifier (PA) at the transmitter to work at reduced efficiency. In order to operate the PA with maximum possible efficiency, the OFDM-based signals are processed before transmission such that their PAPR is reduced. Clipping and filtering is one of the simplest and most effective methods to reduce the peak power of multi-carrier signals. Although it reduces PAPR efficiently, the in-band distortion and out-of-band distortion produced post-clipping operation degrades the system performance. The former leads to signal quality degradation deteriorating the bit error rate (BER) performance of the system and the latter is responsible for spectral fading. The present work analyzes the variants of conventional clipping and filtering technique so as to achieve optimum PAPR reduction. A signal smoothening technique is also proposed that is intended to suppress the frequency distortion due to signal clipping. Based on this approach, two algorithms viz. two-point polyBLAMP and four-point polyBLAMP are presented and tested for sinusoidal, harmonic and LTE signals. The results show that the aforementioned technique works well with sinusoidal and harmonic signals producing aliasing suppression of more than 10 dB. In order to mitigate the clipping noise distortion and restore the BER performance of the system, several receiver-based processing techniques are presented. Based on this, an RRC-OFDM system is proposed which involves optimized iterative clipping and filtering at the transmitter and receiver-based iterative recovery of clipping noise. It includes the use of root-raisedcosine (RRC) filtering in order to improve the spectral efficiency in OFDM-based communication. The simulation results show significant increase in power efficiency of PA (  21%) after the application of transmitter-based optimized clipping algorithm with relatively lesser increase in SNR (  2 dB) to achieve the same BER performance as that of the non-clipped case.