Michel Terre

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.

Impact of Clear Channel Assessment Mode on the Performance of ZigBee Operating in a WiFi Environment

ZigBee is a standard optimised for radio networks used in applications such as interconnecting sensors, monitoring and automating home, medical, industrial, and agricultural systems where low levels of data throughput and low-power consumption are needed. The physical (PHY) and medium access control (MAC) layers of ZigBee are defined by the IEEE 802.15.4 standard. One of the operational frequency bands of ZigBee is the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band which is also used by WiFi. Several ZigBee and WiFi devices may operate in the same environment, which may result in the two systems performance degradation. Before transmitting, WiFi and ZigBee devices perform the clear channel assessment (CCA) according to three different modes defined in the standards. In this paper, ZigBee throughput is obtained for the different CCA modes used by both ZigBee and WiFi systems operating in the same environment. Simulation results show that, ZigBee performance can be optimised by choosing the suitable CCA mode with respect to the interference level at the receiver

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.

Low-Cost Transparent Radio-Over-Fiber System for In-Building Distribution of UWB Signals

This paper investigates hybrid fiber-radio networks for in-building distribution of ultrawideband (UWB) signals, in order to extend UWB radio coverage area. An original multipoint to multipoint UWB-over-fiber system, proposed in the frame of BILBAO project, is presented and discussed. System link gain and noise figure are evaluated through theoretical analysis. A simulation model is used to study the impact of E/O transceivers nonlinearity on UWB signals. Experimental results show good agreement with simulation results. A high data rate file transfer, with UWB radio propagation and transmission over 100 m of multimode fiber, has been also successfully demonstrated.

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.

Spectral Efficiency Analysis in OFDM and OFDM/OQAM Based Cognitive Radio Networks

The future wireless communication is expected to be able to improve the efficiency of spectrum usage. To solve the challenge of spectrum shortage, an innovative opportunistic spectrum access strategy, called cognitive radio (CR) has been proposed. Conventional orthogonal frequency division multiplexing (OFDM) has already been suggested as a physical layer candidate for CR system. Herein another potential candidate for CR, OFDM offset quadrature amplitude modulation (OFDM/OQAM) is introduced, and its spectral efficiency for coded multicarrier transmission is compared with cyclic prefix based OFDM (CP-OFDM) and raised cosine windowed OFDM (RC-OFDM) in CR context. Simulated results of spectral efficiency comparison (SEC) for different multicarrier systems are interpreted by theoretically analyzing the out-of-band radiation of their prototype pulses shaping. Both theoretic analysis and experimental results can show that OFDM/OQAM is a more natural candidate than CP-OFDM and RC-OFDM for CR networks application.

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.

A hybrid single-carrier/multicarrier transmission scheme with power allocation

We propose a flexible transmission scheme which easily allows to switch between cyclic-prefixed single-carrier (CP-SC) and cyclic-prefixed multicarrier (CP-MC) transmissions. This scheme takes advantage of the best characteristic of each scheme, namely, the low peak-to-average power ratio (PAPR) of the CP-SC scheme and the robustness to channel selectivity of the CP-MC scheme. Moreover, we derive the optimum power allocation for the CP-SC transmission considering a zero-forcing (ZF) and a minimum mean-square error (MMSE) receiver. By taking the PAPR into account, we are able to make a better analysis of the overall system and the results show the advantage of the CP-SC-MMSE scheme for flat and mild selective channels due to their low PAPR and that the CP-MC scheme is more advantageous for a narrow range of channels with severe selectivity.

Major characteristics of UWB indoor transmission for simulation

We present a ray tracing approach adjusted for the special purposes of an UWB signal to estimate the characteristics of an indoor channel. Main dependencies between physical parameters involved in an UWB transmission, such as the characteristics of antennas, the duration of signals and the channel properties, are outlined. The simulated results are compared with measurements and finally semi-empirical propagation formula are proposed.

Spectral correlation of multicarrier modulated signals and its application for signal detection

Spectral correlation theory for cyclostationary time-series signals has been studied for decades. Explicit formulas of spectral correlation function for various types of analog-modulated and digital-modulated signals are already derived. In this paper, we investigate and exploit the cyclostationarity characteristics for two kinds of multicarrier modulated (MCM) signals: conventional OFDM and filter bank based multicarrier (FBMC) signals. The spectral correlation characterization of MCM signal can be described by a special linear periodic time-variant (LPTV) system. Using this LPTV description, we have derived the explicit theoretical formulas of nonconjugate and conjugate cyclic autocorrelation function (CAF) and spectral correlation function (SCF) for OFDM and FBMC signals. According to theoretical spectral analysis, Cyclostationary Signatures (CS) are artificially embedded into MCM signal and a low-complexity signature detector is, therefore, presented for detecting MCM signal. Theoretical analysis and simulation results demonstrate the efficiency and robustness of this CS detector compared to traditionary energy detector.