Dominique Lacroix

Pilot-aided channel estimation for OFDM/OQAM

OFDM/offsetQAM is an interesting alternative to classical OFDM modulation, as it does not require the use of guard interval. This characteristic makes its spectral efficiency optimal. On the other hand, this modulation is less robust to Rayleigh fading channel. Indeed, when classical channel estimation used for OFDM modulation is applied straightforwardly to OFDM/OQAM modulation, an intrinsic inter-symbol-interference is observed. This deeply degrades its performances. In this paper, we theoretically explain this phenomenon and propose a reliable method to significantly reduce it. Results of different methods of pilot-aided channel estimation over delay-Doppler channels are shown in this paper.

OFDM with guard interval versus OFDM/offsetQAM for high data rate UMTS downlink transmission

OFDM modulation using a guard interval, denoted OFDM/QAM, in this paper, is well known for its robustness to multipath time varying propagation channels, and therefore used in several broadcasting and high data rate radio LAN standards. OFDM/OQAM modulation is an alternative to it, which has the advantage not to require the use of a guard interval, which leads to a gain in spectral efficiency. In this paper, we recall the main characteristics of OFDM/OQAM, and compare it to the OFDM/QAM in a realistic 3G context. We propose optimized modulation parameters and provide simulation results. The study confirms the interest of considering OFDM modulation for high data rate UMTS downlink transmission. Besides, in that context, the gain in spectral efficiency allows OFDM/OQAM to outperform OFDM/QAM performances.

A study of OFDM parameters for high data rate radio LANs

This paper presents the technical advantages of using a multicarrier OFDM modulation for high data rate wireless LANs. It investigates a way of choosing the key parameters of a coded-OFDM (COFDM) system dedicated to such networks. As an example, the broadband radio access network called HIPERLAN/2 is studied. The comparison of two differential subcarrier modulation schemes specific to OFDM modulation, in the frequency domain and in the time domain, is more particularly detailed, through simulations and a theoretical analysis. Furthermore, considering the necessity for the system to be robust to noise as well as to frequency offset, turbo-codes are proposed. Information on FFT complexity is finally provided.

On the choice of a radio interface for high speed radio lan’s

This paper describes parameters and options relevant to OSI layers 1 and 2 when designing a broadband radio interface. For each layers, statements are illustrated with the description of possible options for the specification of Hiperlan type 2 standard, such as: the modulation, system parameters, architecture, duplex schemes, interworking with network protocols. Then, it is briefly described which parameters are essentials for the joint optimisation of layers 1 and 2: switching frequency time, turnaround time, mac-pdu, frame duration, collision detection and radio measurements.RésuméCet article décrit les paramètres et options à considérer au niveau des couches 1 et 2 du modèle OSI lors de la définition d’une interface radio large bande. Pour chaque couche, les discussions sont illustrées par la description des choix possibles pour la normalisation du système Hiperlan type 2, notamment: la modulation, les paramètres systèmes, l’architecture, le mode de duplex, l’interfonctionnement avec les protocoles réseaux. Enfin, il est brièvement décrit quels sont les paramètres essentiels à considérer pour l’optimisation commune des couches 1 et 2, soit: le temps de changement de fréquence, le temps de changement de sens de transmission, le PDU-MAC, la durée de trame, la détection de collision et les mesures radios.