Yahia Medjahdi

Performance Analysis in the Downlink of Asynchronous OFDM/FBMC Based Multi-Cellular Networks

This paper provides a theoretical performance evaluation of the downlink of asynchronous orthogonal frequency division multiplexing (OFDM) and filter bank based multicarrier (FBMC) cellular radio communication systems. An accurate derivation, for the interference caused by the timing synchronization errors in the neighboring cells, is developed. The multipath effects on the interfering and desired signal are also considered. Based on computing the moment generating functions of the interference power, exact expressions are derived for average error rates of OFDM and FBMC systems considering the frequency correlation fading in the case of block subcarrier assignment scheme.

Spectral efficiency comparison of OFDM/FBMC for uplink cognitive radio networks

Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

Inter-cell interference analysis for OFDM/FBMC systems

Multicarrier communication technologies are promising candidates for 4G wireless access systems. In this paper, we focus on the downlink of multicellular networks and we investigate the influence of the inter-cell interference in an unsynchronized frequency division duplex (FDD) context with a frequency resuse of 1. We compare the conventional orthogonal frequency division multiplexing with cyclic prefix modulation (CP-OFDM) and the filter bank based multi-carrier modulation (FBMC). Two tables modeling the mean interference power are given and show that, in FBMC case, the interference is more localized than in OFDM case. Finaly, these tables are used to evaluate performance in terms of average capacity in FBMC multi-cell networks compared to CP-OFDM ones.

Theoretical analysis of BER performance of nonlinearly amplified FBMC/OQAM and OFDM signals

In this paper, we introduce an analytical study of the impact of high-power amplifier (HPA) nonlinear distortion (NLD) on the bit error rate (BER) of multicarrier techniques. Two schemes of multicarrier modulations are considered in this work: the classical orthogonal frequency division multiplexing (OFDM) and the filter bank-based multicarrier using offset quadrature amplitude modulation (FBMC/OQAM), including different HPA models. According to Bussgang’s theorem, the in-band NLD is modeled as a complex gain in addition to an independent noise term for a Gaussian input signal. The BER performance of OFDM and FBMC/OQAM modulations, transmitting over additive white Gaussian noise (AWGN) and Rayleigh fading channels, is theoretically investigated and compared to simulation results. For simple HPA models, such as the soft envelope limiter, it is easy to compute the BER theoretical expression. However, for other HPA models or for real measured HPA, BER derivation is generally intractable. In this paper, we propose a general method based on a polynomial fitting of the HPA characteristics and we give theoretical expressions for the BER for any HPA model.

Interference tables: a useful model for interference analysis in asynchronous multicarrier transmission

In this paper, we investigate the impact of timing asynchronism on the performance of multicarrier techniques in a spectrum coexistence context. Two multicarrier schemes are considered: cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM) with a rectangular pulse shape and filter bank-based multicarrier (FBMC) with physical layer for dynamic spectrum access and cognitive radio (PHYDYAS) and isotropic orthogonal transform algorithm (IOTA) waveforms. First, we present the general concept of the so-called power spectral density (PSD)-based interference tables which are commonly used for multicarrier interference characterization in spectrum sharing context. After highlighting the limits of this approach, we propose a new family of interference tables called ‘instantaneous interference tables’. The proposed tables give the interference power caused by a given interfering subcarrier on a victim one, not only as a function of the spectral distance separating both subcarriers but also with respect to the timing misalignment between the subcarrier holders. In contrast to the PSD-based interference tables, the accuracy of the proposed tables has been validated through different simulation results. Furthermore, due to the better frequency localization of both PHYDYAS and IOTA waveforms, FBMC technique is demonstrated to be more robust to timing asynchronism compared to OFDM one. Such a result makes FBMC a potential candidate for the physical layer of future cognitive radio systems.

On ISI cancellation in MIMO-ML detection using FBMC/QAM modulation

In this paper, the filter-bank multicarrier (FBMC) system is considered, and we deal with the presence of the inherent intersymbol interference (ISI). Indeed, the transmitted data symbols in FBMC are OQAM (Offset QAM) modulated, and the received data symbols are corrupted by inherent interference terms which complicate the detection in a maximum likelihood (ML) sense in the spatial multiplexing scheme. Detection schemes with ISI estimation and cancellation are not always effective due to the error propagation. We propose in this paper to modify the conventional FBMC system by transmitting QAM data symbols instead of OQAM ones in order to reduce the inherent interference. Then, we propose a receiver based on ISI estimation and cancellation. A simple tentative detector is first used to attempt to cancel the ISI before applying the ML detection. We show by simulation that with the proposed FBMC/QAM system, the ISI cancellation is effective and the performance converges to the optimum one.

Multicarrier Interference Evaluation with Jointly Non-Linear Amplification and Timing Errors

In this paper, we investigate the interference caused by Non Linear (NL) power amplifiers together with timing errors for multicarrier OFDM/FBMC transmissions. This kind of interference will be found in Cognitive Radio systems where users are non synchronized. We found that the global interference can be computed by adding the NL effect with the unsynchronized one. Finally, simulation results are presented and are in good agreement with the developed theoretical model.

On spectral efficiency of asynchronous OFDM/FBMC based cellular networks

The growing demand for wireless communication makes it important to determine the capacity limits of the different multicarrier systems. In this paper, we address the impact of imperfect inter-cell synchronization on the average capacity of orthogonal frequency division multiplexing (OFDM) and filter bank based multicarrier (FBMC) multi-cellular networks. Based on computing the moment generating functions of the asynchronous interference power, a simple new expression for the exact evaluation of the average capacity is derived considering the frequency correlation fading between adjacent interfering subcarriers.

Closed-Form BER Expression for (QAM or OQAM)-Based OFDM System With HPA Nonlinearity Over Rayleigh Fading Channel

Nonlinear distortions caused by high-power amplifiers are considered the key impairment in multicarrier techniques-based communication systems. However, there are few past investigations addressing their effect on the performance of filter bank multicarrier-based systems. In this letter, we derive a closed-form expression for the BER of Gray-coded M-ary [quadrature amplitude modulation (QAM) or offset QAM]-based OFDM running under a frequency-flat-fading Rayleigh channel, which is valid for any memoryless nonlinearity model and can be evaluated without a numerical integration method.

Asynchronous OFDM/FBMC interference analysis in selective channels

This paper addresses the effect of timing synchronization errors for two different multicarrier techniques CPOFDM and FBMC. Such errors degrade the performance of the reference receiver by causing multi user interference. This interference occurs when the signals from different transmitters arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of orthogonality between subcarriers. In this paper, we propose a model of interference that provides a useful computational tool in order to analyze the performance of an OFDM/FBMC receiver in frequency selective fading environment. Finally, simulation results confirmed the accuracy of the proposed model.