A Novel Method of Removing the Influence of Continuous Electromagnetic Wave Disturbances in OFDM Systems

Abstract

This paper describes a novel technique for removing the influence of a continuous wave (or narrowband) electromagnetic disturbance in orthogonal frequency division multiplexing (OFDM) systems with quadrature amplitude modulation (QAM) or phase-shift keying (PSK) modulation schemes. The technique relies on a mathematical derivation of how a continuous wave electromagnetic disturbance induces spectral leakage in the OFDM system. Using this derivation, an algorithm is obtained that aims to cancel the continuous wave electromagnetic disturbance by estimating its frequency, retrieving its amplitude and phase from the corrupted OFDM frame. Note that the algorithm does not require any prior information about the disturbance. The proposed algorithm is validated through thorough simulations, covering different modulations, noise variations and spectral leakage cases, and compared with standard OFDM performance without the algorithm. Through our experimentation it has been demonstrated that for a disturbance frequency not equal to one of the OFDM subcarriers, the algorithm can estimate the disturbance frequency with high precision, resulting in a gain of more than 80 dB when compared to the case without the algorithm. For a disturbance frequency equal to one of the OFDM subcarriers, a simple coding technique such as Hamming & interleaving enables the user to remove the disturbance.

Influence of AWGN on the Possibility to Remove a Continuous Wave EM Disturbance in OFDM systems

“…To assist the reader in the understanding of the CW EMD removal algorithm, we provide here a summary of Section II of [6]. The algorithm starts by predicting the error mismatch E * m (m is a subcarrier number) between the received signal and the demodulated symbols.…”

“…1. The CW EMD excision procedure in OFDM at the receiver's side [6] 4. When all the CW EMD parameters are known, the CW EMD error is calculated:…”

“…The further demodulation of the improved DFT symbols will result in recovered symbols. An in-depth mathematical derivation of the algorithm can be found in [6].…”

“…spectral leakage. In this case, the subcarriers close to the actual CW EMD frequency are affected the most [6]. This can result in bit flips and incorrect signal demodulation which is intolerable in safety-critical applications like autonomous driving or industry 4.0 applications where the OFDM technique is used.…”

“…CW EMD or a narrowband EMD has recently been tackled by different research groups. A novel CW EMD removal algorithm for OFDM systems was proposed [6]. The mathematical model that is used as a basis for that algorithm works in the following fashion.…”