Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there are still considerable gaps in its effects especially on multi-carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi-carrier 2 dimensional (2D) spreading systems based on a combination of orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) and known as OFDM-CDMA. The contribution of this paper is multifold. First, we use some properties of random matrix and free probability theory to give a simplified expression of signal to interference and noise ratio (SINR) obtained after equalization and despreading. This expression is independent of the actual value of the spreading codes and depends mainly on the complex amplitudes of estimated channel coefficients. Secondly, we use this expression to derive new weighting functions which are very interesting for the radio frequency (RF) engineers when they design the frequency synthesizer. Therefore, based on these asymptotic results, we adapt a new method to predict the bit error rate (BER) at the output of the channel decoder by using an effective SINR value. We show by simulations the validity of our models and that at a given BER, the required signal to noise ratio (SNR) may easily increase due to the carrier phase noise.

In this paper, a low complexity multicode MMSE chip-level channel equalizer for the downlink UMTS FDD mode is proposed. This equalizer has a Rake-like structure and does not need the knowledge of the spreading codes to compute the equalizer filter coefficients. Moreover, the equalizer depth is determined automatically using the knowledge of the channel impulse response and the noise variance. Thus, the structure of the equalizer changes as the channel conditions change and the equalizer can be reduced to a Rake receiver if the depth is equal to one chip (e.g., in low signal-to-noise ratio conditions and/or in weak frequency selective channels). This property is very important and can be used to optimize the power consumption, which is a major constraint that has to be accounted for in the user equipment design.

This paper presents the impact of a carrier frequency offset on the performance of 2 dimensional spreading OFDM-CDMA systems. This is measured by the degradation of the Signal to Interference plus Noise Ratio (SINR) obtained after despreading and equalization. Using some properties of random matrix and free probability theories, a new expression of the SINR is derived. It is independent of the actual value of the spreading codes while still accounting for the orthogonality between codes. This model is validated by means of Monte-Carlo simulations. It is also exploited to compare the sensitivities of MC-CDMA and MC-DS-CDMA systems to carrier offset in a frequency selective channel. This work is carried out for zero forcing (ZF) and minimum mean square error (MMSE) equalizers.

In this paper, we propose a low complexity multi-code chip-level channel equalizer for the downlink UMTS FDD mode. Both block form and filter form implementations are considered. The proposed receiver can be of ZF or MMSE type, and consists of a linear equalizer followed by a bank of correlators corresponding to the spreading codes, and a decision device. It has a Rake-like structure and does not need the knowledge of the spreading codes to compute the equalizer filter coefficients. We show how to compute the equalization matrix at low complexity, and we give a measure of the upper-bound of the equalizer filter depth. Simulation results are given to corroborate the good performance of the equalizer in the high speed downlink packet access (HSDPA) scenario

In this paper, a new algorithm for multipath channel estimation by means of the Common Pilot Channel (CPICH) in downlink WCDMA-FDD is presented. The estimation is performed by using a Single Most Likely Replacement (SMLR) algorithm specifically derived for complex baseband signals where a Bernoulli-Gaussian (BG) model is introduced for the multipath channel. In the proposed algorithm, an interference cancelling technique is associated to the SMLR to enhance its performance. The proposed algorithm performs very well; it yields a satisfactory performance at a moderate extra computational cost compared to the SMLR.

This article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the Signal to Interference plus Noise Ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users' spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss the validity of this model.

The radio architecture of the UMTS is composed of two modes: the FDD mode (WB-CDMA) and the TDD mode (TD-CDMA). Both must be included in the future mobile terminal to provide all services promised by the 3G. A work of reconfiguration will take into account the specificity of these two modes and will improve their switch. This processing simplification of these two modes can be envisaged to facilitating their implementation and cohabitation in the same terminal. For the TDD mode, the receiver called "Ts-structure" (L.Ros et al., July 2001) has been chosen for his good performance and low complexity. For the FDD mode, up to now, the conventional receiver is the Rake. Sometimes, the channel profile will oblige to add an equalizer in order to improve the Rake performance. The objective of this paper is to present a FDD equalizer with architecture similar to the equalizer TDD "Ts-structure".

Use of antenna arrays at both sides of the communication link can result in high channel capacities provided that the propagation medium is rich scattering. Previous studies on MIMO wireless structures have mostly considered Rayleigh fading conditions. Here a study is made on the capacity of Rician channels; it is shown that depending on the number of antennas, the MIMO capacity achieved under the condition of Rician fading may be greater or smaller than the capacity in the case of Rayleigh fading. In particular, for a large number of antennas, Rician channels exhibit smaller capacity than Rayleigh channels. On the other hand, for Rician channels, if the line-of-sight component is not very significant, the increase in capacity by an increase in the number of antennas can still be considerable.

MIMO channels can attain high capacities provided that the propagation medium contains enough scatterers. The capacity of MIMO channels can further be increased by performing optimal power distribution over transmit antennas. This, in turn, necessitates knowledge of the channel at the transmitter. It is shown in this paper that for low signal-to-noise ratios (SNR) and small number of antennas, this increase in capacity can be of interest. Rayleigh fading conditions are considered.

In the downlink TD/CDMA multiple access scheme through a multipath channel, the use of a short complex code enables a strategy of multi-user detection with great sensibility improvement compared to the traditional matched filter. Nevertheless, the performances are damaged compared to the situation with an ideal channel, more especially as the number of users increases. In this paper, we first use the cross-spectral matrix of the aliased coded channels to recall linear multi-user detector (ZF and MMSE) and express a degradation factor of interference and noise to signal ratio due to a non-ideal channel, with or without fading. The degradation and bit error probability are then computed in the concrete situation of indoor and pedestrian channel environments in order to show the great benefit of one or two supplementary sensors at the reception system.

This paper concerns the equalization problem of an underwater high rate transmission system. As the channel delay spread is large compared with the data duration, we have developed an equalizer in order to minimize the calculus burden. Test on real data is also made.

Proposes a receiver which performs fast self-recovering adaptive identification and equalization based on decision feedback equalization and reduced maximum likelihood sequence estimation. It runs on binary-phase-shift keying signals through underwater acoustic channels. Considerations for its implementation are discussed. Its performance is demonstrated both on experimental data from a long-range deep water channel and on simulated data from two discrete-time channels with severe amplitude distortion and additive white Gaussian noise.

We present a new M-ary wideband communication system based on use of binary spread-spectrum sequences and a correlation receiver. The proposed system offers a significant savings in receiver complexity compared to classical M-ary systems as only one correlator is required and also the word synchronization can be automatically made. The sequences used here were primarily described by Yates and Holgate (1979) and generalized by Potter (1980). A set of Yates-Holgate (Y-H) sequences is constructed from a single m-sequence called the "parent". When any sequence in the set is cross correlated with the "parent", the obtained cross-correlation function (CCF) has a shape that simply and uniquely identifies that sequence-in the same time it defines the word synchronization. The transmitter associates k information bits to a sequence of N chips selected in a Y-H set of M=2/sup k/ sequences. The receiver correlates the received sequence with the parent and hence can decide what sequence has been transmitted. In this way, the receiver can recover the k information bits. In this paper (Part I of two), we present the performance of this system in a nonfading channel with additive white Gaussian noise and in some multipath channels.>

For pt. I see ibid., vol.43, no.1, p.127, 1995. We present a new M-ary wideband communication system based on use of binary spread-spectrum sequences and a correlation receiver. The proposed system offers a significant savings in receiver complexity compared to classical M-ary systems as one correlator is required and also the word synchronization can be automatically made. The sequences used here were primarily described by Yates and Holgate (1979) and generalized by Potter (1980). A set of Yates-Holgate (Y-H) sequences is constructed from a single m-sequence called the "parent". When any sequence in the set is cross-correlated with the "parent", the cross-correlation function (CCF) obtained has a shape that simply and uniquely identifies that sequence; at the same time, it defines the word synchronization. The transmitter associates k information bits to a sequence of N chips selected in a Y-H set of M=2/sup k/ sequences. The receiver correlates the received sequence with the parent and hence can decide what sequence has been transmitted. In this way, the receiver can recover the k information bits. We give results from a communication experiment that we conducted with this system and have compared it with a classical M-ary communication system using a set of Gold sequences with same parameters (energy, duration, bandwidth). The obtained performance shows that the system is quite robust.>

We use the concept of Bayesian estimation for estimating the time delays in multipath ocean acoustic tomography (MOAT). The time delay estimation (TDE) from a signal waveform can be seen as a full inversion problem which has to be associated to the geophysical inversion (GI) scheme. Using as a consequence some Bayesian algorithms, they cope with some problems which classically happen in MOAT (unstability and poor signal to noise ratio data). A supplementary reason to use Bayesian algorithms is that it is easy to find some pertinent prior information. Bayesian TDE gives a chance for the tomographic tool to apply in difficult oceanic conditions.>

An adaptive algorithm called FOLMS is proposed. The algorithm has two novel characteristics: it is self-optimized, and it outperforms LMS (least-mean-square) and RLS (recursive-least-squares) algorithms in all the cases when the model to identify is alternatively stationary and nonstationary. Moreover, it requires a small computational cost (4N+3 add, 4N+5 mult). This algorithm is particularly interesting in nonstationary cases when the optimal step-size value has large variations, i.e. mainly when the minimum MSE is not only a function of the noise power but also of the model to identify impulse response, as in underwater equalization and all inverse identification problems.>

The tracking behaviour of the fast RLS (recursive least squares) and LMS (least mean squares) algorithms is investigated in the multipath underwater transmission case. The convergence properties of the algorithms are discussed, and the algorithms are applied to an underwater experiment in a constant-time context. Several cases of fluctuating underwater data transmission are simulated by varying the typical multipath parameters: magnitude ratio of the paths, delays, phases and SNR (signal/noise ratio). The simulation results clearly indicate that the SNR is of a great importance in the tracking capability of an equalizer. For a low SNR, (5 dB, for example), an optimal FLS (fast least squares) algorithm is useless for tracking magnitude ratio or path phase variations. For a high SNR (>20 dB), a FLS algorithm can perform better for compensating fast magnitude variations. In the phase fluctuation case, the algorithms performed equally well.>

For oceanic tomography, it is essential to identify and estimate the arrival times of the acoustic paths. The classical method, which uses large WT signals and correlations, may be no longer sufficient to separate and identify the different time delays. The authors present a method that performs a multidimensional filtering on the successive correlation data and obtains a good delay separation by some kind of deconvolution. Simulation results and real acoustic experimental results demonstrate the good performance of the method.>

We are interested in optimal linear estimation of signals transmitted over a noisy multipath channel. The impulse response of the channel is assumed known. The problem is similar to the telecommunication equalization problem. The optimal linear discrete causal and stable filter (a Wiener-type filter) is given ; different structures are studied and their performance calculated : i) a pure transversal structure, ii) a mixed recursive and transversal structure which is simple and well-adapted to the model of channel. Some results are exhibited. This last structure has been found robust enough versus an error on the channel estimated parameters.

When the transmission is fluctuating (with respect to the elementary transmission duration) diversity techniques enable to improve the performance. In a first part the Rayleigh model has been tested in long distance submarine acoustics transmission and we present some experimental results of explicit frequential diversity. In the general delay and Doppler dispersive case, we present some results of implicit diversity in order to decrease the error probability and we show the consequences of this concept on to the signal design problem. We have applied this study particularly in two cases : the multipath transmission and the fast-fading modulation case.