A Low Complexity Non-Distortion Clipping Technique PAPR Reduction of MIMO-OFDM Systems

Introduction

There exist several types of algorithms in the literature to mitigate the high PAPR problem of MIMO –OFDM systems. These algorithms or methods can be categorized into three groups: signal distortion such as clipping and filtering (Yang et al., 2018), signal scrambling such as partial transmit sequences (PTS) (Iwasaki & Ohuchi, 2019) and selective mapping (SLM) (Ta¸spınar & Yıldırım, 2015), and coding techniques such as linear block codes (Jones et al., 1994) and Golay codes and Reed-Muller code (Davis & Jedwab, 1997).

One of the more realistic and simpler approaches available to reduce PAPR is clipping and filtering which can cut down the signal at the transmitter so as to reduce the high peaks (Rahmatallah & Mohan, 2013). Amplitude clipping is one of the most popular techniques used to reduce PAPR. This technique does not demand side information; therefore, there is no reduction in the system’s data throughput. However, clipping causes not only in-band signal distortion, resulting in performance degradation, but also out-of-band distortion, as shown in Figure1. Out-of-band distortion results in out-of-band interference signals to adjacent channels. The out-of-band interference caused by clipping can however be reduced by filtering. Unfortunately, the reduction in out-of-band interference comes at the cost of peak regrowth (Li & Cimini, 1998) and (Singha & Kumarbad, 2016).

To overcome this problem, this research proposes a low complexity non- distortion clipping technique for MIMO-OFDM system. The main concept of this method is how to convert the generated distortion (in-band and out-of-band signals distortion) when using clipping at transmitter to impulse noise (error) which is possible easily be covered by using a simple coding technique to cover error at the receiver that it does not clip the signal in time domain. Instead, the clipping occurs for discrete samples directly after IFFT.

This work suggests a useful method for reduction of PAPR that offers several advantages: very low complexity, very good performance with the ability to reduce PAPR considerably and possibly eliminate the resulting the distortion. Moreover, the relationship between PAPR and power amplifier is explained and analyzed and approximate values of achievable PAPR will be determined. The relationship between PAPR with crest factor (CF) is also discussed. The second part will explain the PAPR problems where the input-back-off and out-back-off are given and how PAPR reduces the power amplifier efficiency.

Figure 1.

PSD Shows In-band distortion and Out-of-band radiation

This research is arranged in several sections. Section one presents an introduction to the subject. Section two gives a description of MIMO-OFDM system with its problems and focuses on the PAPR problem. Section three presents analysis and studies of PAPR reduction methods in MIMO-OFDM system to deduce the difference between the conventional clipping and the proposed non- distortion clipping technique to reduce PAPR of MIMO-OFDM systems. Then, the rest of sections study and analyze the relationship between PAPR and power amplifier. Finally, simulation results obtained are presented concerning the performance of the proposed method with QAM modulation. Several conclusions and some useful suggestions are given for future work.

Systems Model Of Mimo-Ofdm

Due to the importance of OFDM and MIMO systems, it is essential to integrate both to realize high speed wireless communication systems of 5G and beyond. MIMO-OFDM systems can achieve coding gain and diversity gain by the use of space-time coding. In our proposed scheme, at the transmitting end, an arbitrary number of antennas may be utilized. Data bit stream is encoded using space-time coding (Jankiraman,2004), and modulated by OFDM with the non-distortion clipping technique proposed here, and eventually fed to the antennas for transmission, as shown in Figure 2. At the receiver, arriving signals are fed into a signal discoverer and handled before recovering the prime signal.

Figure 2.

MIMO-OFDM System with Non-Distortion clipping technique