Didier Le Ruyet

Transmit Processing Techniques Based on Switched Interleaving and Limited Feedback for Interference Mitigation in Multiantenna MC-CDMA Systems

In this paper, we propose transmit processing techniques based on novel switched interleaving, chipwise linear precoding, and limited feedback for both downlink and uplink multicarrier code-division multiple access (MC-CDMA) multiple-antenna systems. We develop transceiver structures with switched interleaving, linear precoding, and detectors for both uplink and downlink using limited-feedback techniques. In the proposed schemes, a set of possible chip interleavers is constructed and prestored at both the base station (BS) and mobile stations (MSs). For the downlink, a new hybrid transmit processing technique based on switched interleaving and chipwise precoding is proposed to suppress the multiuser interference. The BS and MSs are also equipped with another codebook of quantized downlink channel-state information (CSI). Each MS quantizes its own downlink CSI and feeds the index back to the BS through a low-rate feedback channel. Then, the selection function at the BS determines the optimum interleaver based on the CSI of all users. Moreover, a transmit processing technique for the uplink of multiple-antenna MC-CDMA systems, which requires a very low rate of feedback information, is also proposed. Codebook design methods for both interleavers and quantized CSI are also proposed. Simulation results show that the performance of the proposed techniques is significantly better than prior art.

On the Use of Filter Bank Based Multicarrier Modulation for Professional Mobile Radio

Our main emphasis is on the use of enhanced OFDM and filter bank based multicarrier (FB-MC) waveforms for utilizing effectively the available fragmented spectrum in heterogeneous radio environments. Special attention is on the broadband-narrowband coexistence scenario of the Professional Mobile Radio (PMR) evolution. The target here is to provide broadband data services in coexistence with narrowband legacy services of the TETRA family. The core idea is a multi-mode radio platform, based on variable filter bank processing, which is able to perform modulation/detection functions simultaneously for different signal formats with adjustable center frequencies, bandwidths and subchannel spacings.

MIMO Signal Processing in Offset-QAM Based Filter Bank Multicarrier Systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.

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.

Channel tracking using particle filtering in unresolvable multipath environments

We propose a new timing error detector for timing tracking loops inside the Rake receiver in spread spectrum systems. Based on a particle filter, this timing error detector jointly tracks the delays of each path of the frequency-selective channels. Instead of using a conventional channel estimator, we have introduced a joint time delay and channel estimator with almost no additional computational complexity. The proposed scheme avoids the drawback of the classical early-late gate detector which is not able to separate closely spaced paths. Simulation results show that the proposed detectors outperform the conventional early-late gate detector in indoor scenarios.

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.

Intrinsic interference reduction in a filter bank-based multicarrier using QAM modulation☆

Abstract The offset QAM-based filter-bank multicarrier (FBMC/OQAM) has recently attracted a lot of research interest thanks to its high spectral efficiency. The data in the FBMC/OQAM are carried by real-valued symbols transmitted at each half period ( T / 2 ). At the receiver side, the received symbols are corrupted by pure imaginary intrinsic interference terms which prevent the application of some well-known schemes such as Alamouti coding and maximum likelihood (ML) detection in spatial multiplexing (SM) systems. Receiver schemes with interference cancellation are not always effective, due to error propagation. Interference cancellation can be effective when the signal-to-interference ratio is beyond a certain threshold. In this paper, we propose reducing the intrinsic interference power by modifying the conventional FBMC/OQAM system by transmitting QAM data symbols instead of OQAM ones. Consequently, the real orthogonality condition is no longer satisfied. On the other hand, we can show that, by using receivers based on iterative interference cancellation, we can successfully remove the intrinsic interference. We test the proposed FBMC/QAM in both schemes: 2 × 1 Alamouti coding scheme and 2 × 2 SM with ML detection. The bit-error rate performance is assessed and illustrated by Monte Carlo simulations.

Adaptive resource allocation and decoding strategy for underlay multi-carrier cooperative cognitive radio systems

This paper proposes a resource allocation and decoding strategy at the secondary system for underlay and interweave multi-carrier cooperative cognitive radio. The objective is to maximise the sum rate of both primary and secondary systems, taking into account the interference threshold constraint and the fact that the primary receiver always considers interference as noise. The decoding method at the secondary receivers is either Successive Interference Cancellation or treating interference as noise, depending on their channel gains. The rationale for this strategy is the extension of the Han–Kobayashi capacity-achieving strategy on the Gaussian interference channel to the studied cognitive scenario. The proposed resource allocation algorithm is composed of a subcarrier allocation procedure to avoid intercell interference between secondary cells and of an iterative power allocation algorithm that maximises the sum rate on the primary and secondary cells, respectively. The proposed algorithm achieves high data rate improvements for the secondary systems while maintaining a low degradation on the primary systems rate. It also benefits from multi-user diversity and is robust to the distance variations. Copyright

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.

Decoding schemes for FBMC with single-delay STTC

Orthogonally multiplexed Quadrature Amplitude Modulation (OQAM) with Filter-Bank-based MultiCarrier modulation (FBMC) is a multicarrier modulation scheme that can be considered an alternative to the conventional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) for transmission over multipath fading channels. However, as OQAM-based FBMC is based on real orthogonality, transmission over a complex-valued channel makes the decoding process more challenging compared to CP-OFDM case. Moreover, if we apply Multiple Input Multiple Output (MIMO) techniques to OQAM-based FBMC, the decoding schemes are different from the ones used in CP-OFDM. In this paper, we consider the combination of OQAM-based FBMC with single-delay Space-Time Trellis Coding (STTC). We extend the decoding process presented earlier in the case of transmit antennas to greater values of . Then, for , we make an analysis of the theoretical and simulation performance of ML and Viterbi decoding. Finally, to improve the performance of this method, we suggest an iterative decoding method. We show that the OQAM-based FBMC iterative decoding scheme can slightly outperform CP-OFDM.