Suppressing the OFDM CFO-Caused Constellation Symbol Phase Deviation by PAPR Reduction

Adriana Lipovac,Pamela Njemčević,Vlatko Lipovac

doi:10.1155/2018/3497694

Abstract

The well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM), namely, the transmitter versus receiver Carrier Frequency Offset (CFO), and the Peak-to-Average Power Ratio (PAPR) of the transmitted OFDM signal, may degrade the error performance, by causing Intercarrier Interference (ICI), as well as in-band distortion and adjacent channel interference, respectively. Moreover, in spite of the utmost care given to CFO estimation and compensation in OFDM wireless systems, such as wireless local networks or the mobile radio systems of the fourth generation, e.g., the Long-Term Evolution (LTE), still some residual CFO remains. With this regard, though so far the CFO and the PAPR have been treated independently, in this paper, we develop an Error Vector Magnitude (EVM) based analytical model for the CFO-induced constellation symbol phase distortion, which essentially reveals that the maximal CFO-caused squared phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR. This implies that any PAPR reduction technique, such as simple clipping or coding, indirectly suppresses the CFO-induced phase deviation, too. The analytically achieved results and conclusions are tested and successfully verified by conducted Monte Carlo simulations.

Highlights

Orthogonal Frequency-Division Multiplexing (OFDM) has become widely accepted due to its excellent transmission performance and high data rate under multipath fading conditions [1]
Two major inherent weaknesses of the OFDM-based stateof-the art wireless systems, such as the Long-Term Evolution (LTE), are Carrier Frequency Offset (CFO) and Peak-to-Average Power Ratio (PAPR), which compromise the orthogonality of subcarriers and introduce cochannel and adjacent channel interference, respectively
With this regard, we develop an Error Vector Magnitude (EVM)-based analytical model for the constellation symbol phase, unveiling that the CFO-caused maximal squared phase deviation is linear with the instantaneous PAPR

Summary

Introduction

Orthogonal Frequency-Division Multiplexing (OFDM) has become widely accepted due to its excellent transmission performance and high data rate under multipath fading conditions [1]. Though OFDM performance has been subject to extensive investigations in the last two decades, with regard to practical local area wireless networks (WiFi) and the fourth-generation (4G) mobile communication systems, the Long-Term Evolution (LTE) in particular [2,3,4], still it remains affected mainly by two OFDM drawbacks These are the shift between the carrier frequency at the transmitter and the one used at the receiver, which is commonly referred to as Carrier Frequency Offset (CFO), and the excessive Peak-to-Average Power Ratio (PAPR) that is inherent to the transmitted OFDM signal, being effectively a sum of many sinusoids, which can mutually combine either constructively, or destructively [5, 6].

CFO-Induced EVM and Constellation Symbol Phase-Deviation Model

MTs nMTs

Peak CFO-Induced Phase Deviation versus PAPR Model

Verification of Peak CFO-Induced Phase Deviation

Findings

Conclusion