Marc Chenu-Tournier

Low complexity blind space-time identification of propagation parameters

The radio electrical transmissions often have multiple paths due to reflections on physical objects or due to the inhomogeneity of the propagation medium for example the ionospheric layers in a HF communication. This work presents a new algorithm for the blind estimation of the physical parameters in a multipath channel (direction of arrival, time delay and fading). The results exposed are useful for tactical applications such as HF radio-localization, or for radio communication systems, to combat the degradations due to the channel. The present study is based on the recent work done on blind deconvolution which estimates the channels impulse responses. Based on a physical path parametric model, a spatio-temporal parametric blind identification of the front wave is performed. These parameters are direction of arrival: DOA /spl theta/, relative time delay /spl tau/ and complex gain /spl phi/ (fading).

Space-frequency direction finding in wideband and multi-path contexts

Over the two last decades, a great number of narrow band direction finding methods have been developed in order to estimate the DOA (directions of arrival) of impinging sources received on an array of sensors. In a radiocommunication context, the signal of each emitter propagates through different multi-path channels. In this context, the emitted signals may have various spectrum characteristics, either narrow-band with normalized frequency channels or wideband such as PN (pseudo noise) spread spectrum signals. In order to take into account these frequency and wideband characteristics we can apply a space-frequency technique as presented by Grenier et al. (1989) and by Buckley (1986) for the DOA estimation. The first purpose of this paper is to adapt these algorithms for correlated sources such as in multi-path propagation channels and the second purpose is to decrease the high computation cost of this new method by simplifying the space-frequency criterion.

Multi-user detection applied to GSM communications

In this paper we propose to apply to the GSM system multi-user detection (MUD) techniques generally used in CDMA networks. The constraint of using the GSM wave form makes it impractical to use the optimum receiver due to its high complexity. Thus, in this paper, we derive the multi-user sub-optimum DFE-MMSE adapted to the GSM wave form. It relies on a linear approximation of the GSM modulation leading to a staggered modulation and thus requires a specific, (and multi-user in our case) equalizer to achieve good performances (Tu 1993). Not taking into account the fact that the modulation is staggered (as in Tripathi et al. 2000) leads to poor performances. The symbol detection is made possible by means of multiple antennas at the receiver. This technique is actually being tested on real data for underground transmissions in an IST funded project called ESCORT.

A Baseband Demonstrator Using Multi Antenna Techniques to Improve Capacity of Fixed Broadband Wireless Access

In the last five years, transmissions using multiple sensors at both ends of the link have been a major research topic. Many transmission schemes are studied such as point to point links using diversity coding, point to point links using multiplexing, tradeoffs between both and at last multi-point to point links. This last scheme was already covered by Space Division Multiple Access (SDMA) processing but a step forward was made with multiple subscriber detection. This paper asses the multi-point to point links for uplink and point to multi-point for the downlink based on OFDM waveform in the frame of the Wireless Metropolitan Area Network (WMAN) IEEE Std 802.16-2004 or HIPERMAN standard. It describes a realistic implementation of transceivers for Physical (PHY) layer to Medium Access Control (MAC) layer allowing a system capacity increase with minor modifications of the standard and with a low impact on the complexity of the subscriber equipment. In this context, this paper proposes to focus on based-band techniques: The Obèle algorithm based on the channel knowledge in the downlink and multiple-user detection in the uplink. The algorithm complexity and the tradeoffs for implementation are extensively discussed.

DOA estimation after blind identification of subspace channel vectors in multi-path contexts

Over the two last decades. a large number of narrow band direction finding techniques have been developed in order to estimate the DOAs (Directions Of Arrival) of impinging sources received on an array of sensors. To improve the classical methods in ambiguity robustness and accuracy. the blind-MUSIC method [51 has been proposed. It applies a separated DOA estimation of each independent source after a blind steering vector identification. In a radiocommunication context. the Signal of each emitter propagates through different paths and thus creates correlated sources at the receiver. The purpose of this paper is to apply a separated DOA estimation of independent emitters in a multi-path context taking into account both the large number of sources and the correlation due to the multi-path propagation. The approach is based on 2 steps: firstly a blind identification [2] [3] of emitters subspace channel is made and secondly a DOA estimation is applied to each estimated subspace channel. Using this new method. more sources than sensors can be identified.

Direct and turbo multi-user spatio-temporal channel estimation schemes for CDMA FDD UMTS uplink

Many multi-user receivers have been developed to mitigate the effects of both multipath and interference in CDMA radiocommunication networks. However, despite of these works, very few papers have been devoted to the implementation of these receivers and, more precisely, to the channel estimation problem in both the multi-user and FDD UMTS context. Assuming specular propagation channels and a multi-sensor receiver, the purpose of this paper is to present direct and turbo multi-user schemes for the joint estimation of the impulse response of the propagation channels between each user and each sensor for the FDD UMTS uplink. The quality of the latter are then evaluated through the bit error rate (BER) computation at the output of two receivers (2D-RAKE and decorrelator receiver) adapted to the FDD UMTS uplink.

Analytical Performance of a Frequency Offset Multi-user Multi-array System

Orthogonal Frequency Division Multiplexing (OFDM) modulation is a technique commonly used to deal with scattering environment. This is mainly due to the fact that it does not involve any complicated channel equalization, since each sub-carrier undergoes a flat fading channel. However this modulation is very sensitivity to frequency offset in the channel. The frequency offset causes two bad effects: the first is the reduction of the signal amplitude of each sub-carrier and the second is introduction of Inter Carrier Interferences (ICI) from the others carriers which are now no longer orthogonal. In a multi-users system the different transmitters got a independent local oscillator, then each transmitter is affected by a different frequency offset (in comparison to the receiver). The usual solution to deal with this problem in the single user case is to lock the frequency of the transmitter and the receiver using a phase lock loop. But in the case of multi-users transmission we cannot do it this way. The aim of this paper are twofold. First we first give an improved multi-users model including the frequency offset effects. Then using this model we derive the analytical performance at the channel decoder output. This paper is subdivided in three parts. First we describe our system. This model takes into account the effect of the frequency offset. Then by derivation of this model we describe the effect of the frequency offset as a noise floor, and we explain the analytical performance of our system according to the frequency offset of the different transmitters. In a