Filtered OFDM: An Insight Into Intrinsic In-Band Interference and Filter Frequency Response Selectivity

Juquan Mao,Pei Xiao,Konstantinos Nikitopoulos,Lei Zhang

doi:10.1109/access.2020.2997316

Juquan Mao, Pei Xiao + Show 2 more

Open Access

https://doi.org/10.1109/access.2020.2997316

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Abstract

The future mobile networks will face challenges in support of heterogeneous services over a unified physical layer, calling for a waveform with good frequency localization. Filtered orthogonal frequency division multiplexing (f-OFDM), as a representative subband filtered waveform, can be employed to improve the spectrum localization of orthogonal frequency-division multiplexing (OFDM) signal. However, the applied filtering operations will impact the performance in various aspects, especially for narrow subband cases. Unlike existing studies which mainly focus its benefits, this paper investigates two negative consequences inflicted on single subband f-OFDM systems: in-band interference and filter frequency response (FFR) selectivity. The exact-form expression for the in-band interference is derived, and the effect of FFR selectivity is analyzed for both single antenna and multiple antenna cases. The in-band interference-free and nearly-free conditions for f-OFDM systems are studied. A low-complexity block-wise parallel interference cancellation (BwPIC) algorithm and a pre-equalizer are proposed to tackle the two issues caused by the filtering operations, respectively. Numerical results show that narrower subbands suffer more performance degradation compared to wider bands. In addition, the proposed BwPIC algorithm effectively suppresses interference, and pre-equalized f-OFDM (pf-OFDM) considerably outperforms f-OFDM in both single antenna and multi-antenna systems.

Highlights

Orthogonal frequency-division multiplexing (OFDM) has strengths such as robustness against multi-path fading, a simple implementation based on fast Fourier transform (FFT) algorithms, and perfect compatibility with multiple-inputmultiple-output (MIMO) technique, and so on
We propose a novel PIC algorithm customized for filtered OFDM (f-OFDM) systems, namely, block-wise parallel interference cancellation (BwPIC)
1) the derived system model and interference power induced by filters with different settings, 2) the BER performance of f-OFDM single antenna systems under additive white Gaussian noise (AWGN) channels,4 and the different performance enhancement techniques represented in Section III-D and Section IV-A, 3) the BER performance of f-OFDM/pre-equalized f-OFDM (pf-OFDM) multiantenna systems under multi-path fading channels

Summary

Introduction

Orthogonal frequency-division multiplexing (OFDM) has strengths such as robustness against multi-path fading, a simple implementation based on fast Fourier transform (FFT) algorithms, and perfect compatibility with multiple-inputmultiple-output (MIMO) technique, and so on. To address the mentioned limitations of OFDM, several candidate waveforms and their variants, such as filter bank multicarrier (FBMC) [3], [4], generalized frequency division multiplexing (GFDM) [5], [6], universal filtered multicarrier (UFMC) [7] are being studied and promoted The comparisons among these schemes with respects to different criteria can be found in [2], [8], [9]. The system bandwidth is divided into arbitrary numbers of subbands, each containing a legacy OFDM signal

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