In this paper, the error performance of linear (MMSE-LE) and widely linear (MMSE-WLE) equalizers is analyzed in terms of mean square error (MSE) and bit error rate (BER). This analysis is done in a system using improper modulations of type Pulse Amplitude Modulations (PAM) having inter-symbol-interferences (ISI) and/or inter-user-interferences (IUI). For this scenario, we derive theoretical expressions of both MSE and BER for the two equalizers. Analytical expressions developed in this paper are verified by computer simulations. It is worth mentioning that these expressions are valid for any number of interferers and any channel delay spread.

When non second order circular (NSOC) signals are transmitted over time/frequency varying channels, classical linear equalization (LE) suffers from performance loss due to the signal's impropriety. For such signals, and signals corrupted by one single improper interference, it has been demonstrated that widely linear (WL) processing can enhance equalization performance. In this paper, we will study the limit of WL processing as a function of the number of interferers. We will carry simulations corroborated by analytical analysis and show that the performance of WL processing, in terms of bit error rate, decreases as the number of improper interferences increases.

In this paper, a new widely linear equalizer for single carrier systems using frequency domain equalization (SC-FDE) that takes into account up to K known interferers in the symbol estimation process is proposed. It was found out that the error performance of the proposed widely linear equalizer is nearly immune to the effect of one interferer, regardless of its power; when compared to its strictly linear version, the proposed structure also has a better error performance for up to three interferers.

In this paper, we propose three different approaches in order to multiplex N bits of data using very high efficiency differential chaos shift keying (VHE-DCSK) system. This system allows higher spectral efficiency than differential chaos shift keying (DCSK) and high efficiency differential chaos shift keying (HE-DCSK) systems. Using Gaussian approximation method and under a white Gaussian noise channel (AWGN), theoretical bit error rate (BER) are calculated. Simulations in this environment show good agreement with analytical expressions and allow us to conclude that the first approach gives better BER performances when the number of transmitted bit (N) is large or if the spreading factor (M) is small.

This study analyses the bit‐error‐rate (BER) performance of filter bank multicarrier (FBMC) systems with offset quadrature amplitude modulation in the presence of phase offset. The authors consider that the FBMC intrinsic‐interference has a Gaussian probability distribution, and they derive the BER analytical expressions for multilevel modulation over Rayleigh flat fading channels. Analytical expressions developed in this study are checked and confirmed by computer simulations.

The coexistence of broadband systems with currently deployed Professional Mobile Radio (PMR) communication systems like Public Protection and Disaster Relief (PPDR) has gained much deserved attention. In the recent literature, it has been suggested that LTE-like FBMC-OQAM system working on linear devices can coexist in PMR band, while conventional OFDM-based LTE system fails. When we take into account, the RF impairments in radio communication systems; it is inevitable to consider the non-linear nature of High Power Amplifiers (HPAs), as they add severe hindrance in this aspect. In this paper, we address this issue and show that LTE-like FBMC-OQAM system working on non-linear devices can still co-exist with PMR/PPDR systems, when suitable peak-to-average power ratio (PAPR) is applied.

Resource allocation for an uplink cooperative OFDMA system is considered in this paper. Relays are simple mobile users with advantageous positions to relay other users with bad channel conditions. Having their own data to transmit to the Base Station (BS), the relays multiplex their own data to relayed data before transmitting to BS using Decode and Forward (DF) scheme. The resource allocation is formulated as an optimization problem to minimize the transmit system power while ensuring a target data rate per user. The considered features to optimize are relay selection, power and Resource Blocks (RB) allocation. Dual decomposition is used for resolution. Both half and full-duplex users cases are studied and compared to non-cooperative system. Simulation results show that our proposed algorithm reduces system's power consumption while ensuring required QoS.

We investigate in this paper the resource allocation problem in an uplink cooperative MIMO OFDMA multiuser system. This system may be used in 5G in the context of green communications since we aim to save energy by reducing the system transmit power. We focus on multiplexing Decode and Forward (DF) relays that have their own data to transmit in addition to data to relay. Aiming to minimize the system transmit power with a required target data rate per user, the resource allocation problem is formulated as an optimization problem. The feature to optimize are relay selection, power allocation and resource block (RB) allocation. We propose a novel resolution algorithm based on dual method and Lagrangian decomposition. Moreover, at each user, Equal Power Allocation (EPA) and beamforming are studied and compared to allocate power to antennas. Simulation results show that the cooperative proposed algorithm leads to an important improvement comparing to a non-cooperative system.

In this study, a new non‐coherent communication system, i.e. very high efficiency differential chaos shift keying system, is proposed. This system is a generalised form of the high efficiency differential chaos shift keying (HE‐DCSK) system, with an arbitrary number ( N ) of transmitted bits per frame. The major advantage of this new proposition is its ability to significantly improve the spectral efficiency compared with DCSK and HE‐DCSK. The theoretical bit error rate of this system is found using the Gaussian approximation method under different communication channels: additive white Gaussian noise and two‐ray Rayleigh fading channels. Simulations in both environments show a perfect match with the analytical expressions for large spreading factors. Simulation results for the two‐ray Rayleigh fading channel show clearly the diversity gain compared with the single‐ray Rayleigh channel.

The Filter bank multi-carrier (FBMC) with offset-quadrature amplitude modulation (OQAM) gained lot of attention recently. Both orthogonal frequency division multiplexing (OFDM) and FBMC-OQAM suffer from high peak-to-average power ratio (PAPR). The classical PAPR reduction schemes suggested for OFDM signals cannot be directly applied on the OFDM-OQM, due to the overlapping structure. In this paper we investigate the problem of PAPR reduction in FBMC-OQAM systems and a trellis-based selected mapping (TSLM) scheme with dynamic programming (DP) has been proposed, which probes for optimal phase rotation vectors. With selected mapping (SLM) scheme, multiple patterns of the modulated signal are generated. Theoretical and numerical analyses indicate that TSLM offer better PAPR reduction performance as compared to symbol-by-symbol approach. Simulation results show that performance of FBMC-OQAM system with this method is not only superior to any scheme based on symbol-by-symbol approach, but also outperforms that of the OFDM with classical SLM scheme. It has also been shown that this result holds for different prototype filter impulse responses that are more or less localized in time or frequency.

Filter Bank based Multicarrier communication with Offset Quadrature Amplitude Modulation (FBMC/OQAM) has been gaining considerable interest as an important competitor to Orthogonal Frequency Division Multiplexing system (OFDM). However, FBMC/OQAM signal inherits the same drawback of High Peak to Average Power Ratio as OFDM signal. Because of the overlapping structure of FBMC/OQAM symbols, the direct application of the conventional PAPR reduction scheme originally proposed for OFDM is not effective. In this paper, we investigate the performance of Smart Gradient Project Active Constellation Extension (ACE-SGP) and Tone Reservation (TR) approaches in PAPR reduction for FBMC/OQAM signals. Indeed, we introduce three PAPR reduction schemes for FBMC/OQAM system based on ACE-SGP, TR and a hybrid one. The performance of the three schemes are presented and compared with those of the OFDM system.

In this paper, we investigate receiver techniques for nonlinear high power amplifier distortion compensation in Orthogonal Frequency Division Multiplexing (OFDM) systems. We introduce a new method for the detection of the nonlinearly distorted symbols received by the OFDM transmission system receiver. The proposed approach allows the determination of the position of the symbol in error and based on the Bussgang theorem application and the fast fourier transform (FFT), we create a set of a simultaneous equations which, when solved, return the true symbols before they were distorted. The numerical performance evaluation shows that the proposed method enables significant performance improvement compared to conventional receivers.

The Filter Bank Multi-Carrier (FBMC) along with Offset Quadrature Amplitude Modulation (OQAM), is emerging to be one of the serious candidates for the next generation radio access technology. This multi-carrier modulation technique, and like its counterparts, suffers from high Peak to Average Power Ratio (PAPR). When a FBMC/OQAM modulated signal crosses a nonlinear Power Amplifier (PA), the transmitted signal exhibits in-band as well as out-of-band distortions. In such a scenario, it's mandatory to add dedicated signal processing, at the transmitter or at the receiver side, in order to reduce the impact of the PA nonlinear distortion. According to the Bussgang's theorem, the in-band distortion induced by a nonlinear PA can be modeled with a complex gain and an independent additive noise term. The complex gain can be computed from analytical formula or estimated jointly with the channel response. However, for the additive noise we will investigate, in this paper, the use of an iterative technique for PA Nonlinearity Cancellation (PANC), at the receiver side. The Bit Error Rate (BER) performance of the FBMC/OQAM system in presence nonlinear PA and iterative PANC receiver will be evaluated over Rayleigh fading channel.

The Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) is emerging as one of the alternatives to Orthogonal Frequency Division Multiplexing (OFDM) for next generation broadband wireless access systems. In this paper, we focus on the nonlinear distortion effects in a FBMC-OQAM system when the signal is passed through a nonlinear High Power Amplifier (HPA) which is modeled as Saleh's one exhibiting amplitude and phase distortions. First, we develop an analysis showing that the FBMC-OQAM signals are more sensitive to the phase distortion than OFDM signals. Then, we address the problem of the compensation of these distortions in FBMC-OQAM systems using digital predistortion (DPD) at the transmitter. Therefore, two DPD schemes are considered in this investigation and their performance are compared in OFDM and FBMC-OQAM systems.

This paper discusses the resource allocation problem in an uplink multi-cell OFDMA system. The classical LTE model considers two areas in the cell: the cell center and the cell border and divides the resources in four sets. The users in the cells center zones use the same subset of subcarriers whereas the users of the border zones use the remaining resources with a Fractional Frequency Reuse (FFR) equal to 3. Considering the same cell zones, we present in this work a different FFR model and prove with a theoretical analysis that the system throughput can be improved. The resource allocation is then performed considering the Weighted Proportional Fair (WPF) algorithm. Simulation results illustrate the performance improvements of the proposed solution in comparison to the classical model. The fairness for the different models is also studied and compared.

Relevance of Filter Bank Multi-Carrier (FBMC) systems along with Offset Quadrature Amplitude Modulation (OQAM) for 5G Radio Access Technology (RAT) cannot be ruled out. FBMC-OQAM modulation technique has many attractive features over OFDM that make it more appealing to be the radio waveform in 5G. However, being a multi-carrier modulation technique, it has high PAPR and prone to spectral regrowth in the presence of a non-linear high power amplifier (HPA), which is a vital component in contemporary modern communication systems. This spectral regrowth indicate that the excellent frequency localization property of the FBMC-OQAM signals no longer holds in the presence of a non-linear HPA. So, there is a dire need to predict the extant of spectral regrowth induced by the HPA non-linearities. With cumulants, it is possible to predict the power spectral density (PSD) of the HPA output. Prediction of spectral regrowth in the case of OFDM systems was already done and in this paper it is extended to FBMC based systems. HPA of Salehs model is used for simulations but prediction can be done for any measured or modeled HPA after polynomial fitting of its AM/AM and AM/PM distortion characteristics.

We investigate in this paper the resource allocation problem in an uplink OFDMA multiuser system. We focus on the Proportional Fairness approach which aims to maximize the system throughput and while ensuring fairness between users. In this paper, we propose a Weighted Proportional Fair algorithm for resource allocation that introduces priorities between users to better exploit good channel conditions in the cell center. We also perform a theoretical analysis to compare both standard and weighted proportional fair algorithms. Simulation results, compared to existing algorithms, show that the proposed algorithm approaches the max sum rate upper bound but still maintains sufficient fairness between users.

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.

When the transmitter does not have channel state information (CSI), linear precoding can be used in multicarrier systems in order to minimize the degradation of the overall bit error rate (BER) caused by deep fades appearing on subchannels. Within the multicarrier systems family, filterbank multicarrier (FBMC) systems were proposed to overcome the poor frequency localization together with the bandwidth/energy waste caused by the use of the cyclic prefix in classical Orthogonal Frequency Division Multiplexing (OFDM) systems. Previous work [1] has focused on BER performance of precoded FBMC systems with perfect equalization at the receiver. In this paper we extend our analysis taking into account the effect of the intersymbol interference (ISI) stemming from non-completely equalized subchannels in these systems, specially when the transmission channel is highly frequency selective. An analytical expression of the error performance of single-input single-output (SISO) precoded FBMC systems with linear minimum mean square error (MMSE) equalization is established taking into account the ISI resulting from imperfect equalization, which causes a loss of diversity. This expression is for uncoded transmissions and matches accurately Monte Carlo simulation results.

In order to provide high data rate over wireless channels and improve the system capacity, Multiple-Input Multiple-Output (MIMO) wireless communication systems exploit spatial diversity by using multiple transmit and receive antennas. Moreover, to achieve high date rate and fulfill the power, MIMO systems are equipped with High Power Amplifiers (HPAs). However, HPAs cause nonlinear distortions and affect the receiver's performance. In this paper, we investigate the joint effects of HPA nonlinearity and frequency selective channel on the performance of MIMO receiver. Then, we propose two equalization schemes to compensate simultaneously nonlinear distortions and frequency selective channel effects. The first one is based on a feedforward Neural Network (NN) named (NN-MIMO-Receiver) and the second uses NN technique and LMS equalizer (LMS-NN-MIMO). The Levenberg-Marquardt algorithm (LM) is used for neural network training, which has proven [1] to exhibit a very good performance with lower computation complexity and faster convergence than other algorithms used in literature. These proposed methods are compared in term of Symbol Error Rate (SER) running under nonlinear frequency selective channel.

This study deals with a multiple-access transmission scheme based on random permutations, which allows one to obtain both spectrum spreading and time spreading. In particular, one is interested by the multi-user detection when the transmission is achieved in the context of asynchronous frequency-selective and time-varying channels. For this detection, it is assumed that the channel coefficients and delays are unknown at the receiver side. Instead, only rough estimates of the minimum and maximum delays are available. However, it is supposed that the transmitter sends pilot signals, that is, training bit sequences, which allow the receiver to perform an LMS (least-mean-square)-type detection. This study provides theoretical performance results. Moreover, this random permutation-based transmission scheme is compared with the DS-CDMA system, for which a similar LMS receiver is defined, under the same assumptions. It is then shown that, for time-varying channels, the permutation-based system presents lower bit-error rates than the DS-CDMA system, since the former provides time diversity.

Interference at the radio receiver is a key source of degradation in quality of service of wireless communication systems. In this paper, we address the impact of imperfect inter-cell synchronization on the performance 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 useful analytical method for computing the average error rates is derived considering the frequency correlation fading between adjacent interfering subcarriers.

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.

In this paper, we investigate the interference caused by Non Linear (NL) power amplifiers together with timing errors for multicarrier OFDM/FBMC transmissions. This kind of interference will be found in Cognitive Radio systems where users are non synchronized. We found that the global interference can be computed by adding the NL effect with the unsynchronized one. Finally, simulation results are presented and are in good agreement with the developed theoretical model.

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.

Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

In this paper, a new way to predict the performance of single user differential chaos shift keying communication system over an m-distributed fading channel is presented. Since the Gaussian approximation used to compute the performance leads to inaccurate results especially for low spreading factor, this new approach based on the chaos bit energy distribution gives accurate results. Computer simulations verify the precision of our approach to compute the performance of this chaos-based communication system.

This paper addresses the effect of timing synchronization errors for two different multicarrier techniques CPOFDM and FBMC. Such errors degrade the performance of the reference receiver by causing multi user interference. This interference occurs when the signals from different transmitters arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of orthogonality between subcarriers. In this paper, we propose a model of interference that provides a useful computational tool in order to analyze the performance of an OFDM/FBMC receiver in frequency selective fading environment. Finally, simulation results confirmed the accuracy of the proposed model.

The combination of Multiple-Input Multiple-Output (MIMO) with Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for achieving high performance with very high data rates in 4G broadband wireless communications. Nevertheless, one major disadvantage of MIMO-OFDM systems lies in a prohibitively large Peak-to-Average Power Ratio (PAPR) of the transmitted signal on each antenna. Indeed, the performance of the receivers is very sensitive to nonlinear distortions caused by the High Power Amplifier (HPA). Furthermore, Crosstalk can take place before or after the power amplifiers designated herein as nonlinear and linear crosstalk, respectively. In this paper, we extend the efficient Neural Network Predistorter (NNPD) proposed in [1] to MIMO-OFDM systems and equally demonstrate that nonlinear crosstalk significantly affects the performance of NNPD. Along, we propose a new Crossover Neural Network Predistorter (CO-NNPD) model to compensate simultaneously for crosstalk and HPA nonlinearity in MIMO-OFDM systems. The Levenberg-Marquardt algorithm (LM) is used for neural network training, which has proven [3] to exhibit a very good performance with lower computation complexity and faster convergence than other algorithms used in literature. This paper is supported with simulation results for the Alamouti STBC MIMO OFDM system in terms of Bit Error Rate (BER) in Rayleigh fading channel.

In this paper, we propose a new approach to compute the exact bit error rate expression for asynchronous chaos-based DS-CDMA system over multipath channel. Perfect estimation of the channel coefficients with the associated delays and chaos synchronization are assumed. A simple RAKE receiver structure is considered. A stationary multipath channel with constant gain is assumed. An asynchronous multi-user chaos-based DS-CDMA system is then defined and the BER is derived in terms of the energy distribution, the number of paths, the noise variances, and the number of users.

Cooperative communication techniques have been proposed in order to improve the quality of the received signals at the receivers by using the diversity added by duplication of signals sent by relays situating between each transmission pair. This paper proposes a new on-demand cooperative transmission technique concerned with the interoperability issues between nodes with cooperative functionality and legacy nodes. Based on the standard IEEE 802.11, the proposed method can switch its transmission mode for each data frame between a cooperative mode and a non-cooperative mode automatically. Moreover, it can work with the IEEE medium access method in the basic mode and in the optional RTS/CTS mode. An original method is proposed, where the relay node acts as a proxy that is in charge of data retransmissions when needed. Interest of the proposition is to improve the transmission performance by decreasing the number of retransmissions due to frame errors. Moreover, the proposition avoids inappropriate routing processes that are costly in time and bandwidth. Evaluation of the proposition is done by simulation. Analysis of the results is mainly based on the Packet Delivery Ratio (PDR) and on the Number of Route Discovery and Maintenance (NRDM) per second.

In this paper several turbo receivers for Interleave-Division Multiple-Access (IDMA) systems will be discussed. The multiple access system model is presented first. The optimal, Maximum A Posteriori (MAP) algorithm, is then presented. It will be shown that the use of a precoding technique at the emitter side is applicable to IDMA systems. Several low complexity Multi-User Detector (MUD), based on the Gaussian approximation, will be next discussed. It will be shown that the MUD with Probabilistic Data Association (PDA) algorithm provides faster convergence of the turbo receiver. The discussed turbo receivers will be evaluated by means of Bit Error Rate (BER) simulations and EXtrinsic Information Transfer (EXIT) charts.

This paper addresses the problem of bit detection for a chaos-based multiple-access system. In particular, one considers the differential chaos shift keying modulation. It is assumed that the transmission channels are frequency-selective. Moreover, the channel coefficients and the channel delays are unknown to the receiver. It is only assumed that vague estimates of the minimum and maximum channel delays are available for the user of interest. In this context, the detection is achieved using a training sequence from which an LMS detector is derived. The theoretical performance results are compared to those of the optimal detector for which all channel characteristics are known. Simulation results are given, which confirm the theoretical study.

In order to improve the communication efficiency without using multi-antennae terminals, cooperative communications implement one or several single antenna relays to assist the transmission between a source and a destination. The design of such a cooperative network, involves several layers of the OSI model. Transmission and multiplexing techniques are addressed at the physical layer whereas the management of the cooperative network (activation of a cooperative mode, selection of relays) is done at the Medium Access Control (MAC) layer and the layers above. After an overview of protocols that have been designed in this domain, we propose an original framework of a cooperative network, at the system level. Inspired from models of the ITU normative organization, our cooperative network model is based on two planes: a data plane and a control plane. A validation of the framework is given by modeling an existing cooperative MAC protocol.

Interleavers used to be considered with a temporal approach. Hence, no work has ever proposed a theoretical study of the frequency effect of an interleaver and we propose here to address this issue. This work is chiefly motivated by the recent use of interleavers as a spread spectrum tool. For that purpose, we first point out the equivalence between periodic clock changes (PCC) and interleavers. Furthermore, because of its linear periodic time varying (LPTV) nature, a PCC turns any wide sense stationary (WSS) process into a wide sense cyclostationary process (WSC). Then, we propose to stationarize the output of a PCC in order to derive a theoretical expression of the output power spectral density (PSD). Thanks to the previous equivalence, this result can be applied to any interleaver and we propose to investigate the frequency effect of the matrix interleaver

This paper presents a solution to enhance the navigation of LEO satellites by mitigating the multipath influence. In several cases, navigation of LEO satellites needs a very high accuracy in positioning, while GPS receivers suffer from leak of accuracy. As multipath is a major source of inaccuracy, we propose to use a neural networks (NN) technique in the range domain in order to estimate and compensate for phase and code (delay) tracking errors. In this paper we present a rich discussion of the NN application in the range domain and the major factors influencing its performance.

In this paper is studied the performance of a spread-spectrum system based on random permutations, in the case of a transmission over frequency-selective time-varying channels. The detection is achieved using a linear minimum mean-square error approach. The obtained detector is compared to the detector derived in the same context for the DS-CDMA system. This comparison shows that this new system performs in general better when the channels are time-varying

This article deals with the joint detection of bits for a spread-spectrum system based on random permutations, in the case of a transmission over frequency-selective channels. A linear minimum mean-squares error approach is studied, whose objective consists of mitigating both the multi-access interference and the intersymbol interference. The proposed system is compared with the DS-CDMA system. The theoretical study is confirmed by simulation results.

This paper is focused on the design of a set of orthogonal linear periodic time varying (LPTV) filters and proposes to apply this result to spread spectrum multiuser transmissions. The construction method of such an orthogonal set is presented, emphasizing that only an invertible LPTV filter is required, since the full set is then deduced from this kernel element. Based on this theoretical result, a spread spectrum multiuser transmission is proposed. In order to appreciate the performance of the proposed system, simulations are performed and results are compared to a classical DS-CDMA system.

This paper studies the joint detection of bits for a new spread-spectrum system based on random permutations. The proposed technique can be regarded as a special case of discrete linear periodic time varying filters. As any spread-spectrum technique, this method generates multi-access interference, which must be mitigated in order to retrieve the users' bits with acceptable bit-error-rate. Thus, different detection strategies must be analysed regarding their performance, their complexity and the available a priori information. In this paper, an asynchronous model is considered, and a linear minimum mean-square error (MMSE) detector fitted to this model is investigated. Theoretical and simulated results are provided, along with a comparison with the corresponding detector for CDMA systems.

Since the apparition of turbocodes in 1993, this topic has been a great success and the subject of much research. But the performance of these coding systems are often presented only in terms of bit-error-rate (BER) or frame-error-rate (FER). These parameters are not the only ones to take into account when designing a communication system. Other properties of the error distribution are also important when analysing the performance of the system at higher levels such as the networking layer. This paper presents some properties of the errors at the output of a turbo decoding system. It also presents a model that is able to describe the error burst length when using the max-log-MAP decoding algorithm.

We propose a class of invertible linear periodically time varying (LPTV) filters. After introducing modulator and MIMO representations of LPTV filters, we associate a matrix formulation for these two representations. The inversion problem is then studied leading to a matrix inversion problem. Under a condition on the LPTV construction, the LPTV modulator matrix becomes circulant. Using the diagonalization properties of circulant matrices, the problem of inverting the N periodic LPTV filter reduces to the inversion of N linear time invariant (LTI) filters. An analytic expression of the LPTV inverse filter is given. Such invertible LPTV filters define a general set of LPTV filters in which, for example, convolutional interleavers are included. To illustrate the good LPTV properties of this class of LPTV filters, simulation results emphasize the spreading efficiency of this class.

The paper deals with the multi-user detection in the context of random permutations. Random permutations, as a special class of discrete linear periodic time varying filters, are a tool to generate multiple access, for which it is important to develop appropriate receiver detectors. The case of the synchronous model is considered, for which two detectors are developed: the matched-filter detector and the decorrelating detector. Theoretical probabilities of error are given, which are confirmed by Monte-Carlo simulations. A comparison with decorrelating techniques for CDMA systems is provided, along with a discussion on the choice of the permutations.

This paper proposes a novel on-line method to predistort the nonlinear high power amplifier (HPA) on-board the satellite by neural networks (NN). The proposed method consists of two NNs: a NN to model the HPA on-line and another NN to pre-distort it. The updating rules of the predistortion NN depend on the instantaneous parameters of the modeling NN. The ordinary gradient descent algorithm suffers from a long transient phase and a slow convergence speed since the two NNs evolves si-multaneously. Using the natural gradient descent exhibits good convergence speed and more accurate model and pre-distorter in a short time.

One of the characteristics of the Viterbi algorithm is that errors at the output appear grouped in bursts. The knowledge of these error burst statistics is very useful in designing a communication system. This paper presents a simple model of Viterbi decoder burst-error statistics derived from the code distance properties. The puncturing process is also modeled. Results are validated through additional computer simulations. The advantage of the model is that it may be used to generate Viterbi error sequences quickly when a very large amount of data is needed. The complete analysis of the convolutional code used in Digital Video Broadcasting (DVB) standards is shown.

In this paper we investigate the effects of a special class of discrete Linear Periodic Time Varying (LPTV) filters on stationary signals. Periodic discrete clock changes are applied to a stationary sequence changing x(n) in x(n+f(n) where f(n) is a periodic and bijective function. Such a LPTV is a permutation of the samples of sequence x(n). We study in the paper the power spectral density of the filtered sequence together with the possible application of discrete LPTV to multiple access.

We present two adaptive predistortion techniques for non-linear satellite amplifiers. The amplifier gives two kind of distortions: amplitude distortion (AM/AM conversion) and phase distortion (AM/PM conversion). We compare the performance of these predistortion techniques applied to the same amplifier. Both predistortions are realized with multilayer perceptron (MLP) neural networks (NN) associated with the backpropagation (BP) algorithm. The first adaptive predistortion technique identifies the inverse AM/AM conversion with one NN and the direct AM/PM conversion with another one. The second one realizes directly the predistortion by training an input NN at the input of the amplifier. This NN contains one structure for the inversion of the AM/AM conversion and one for the AM/PM conversion.

We present a neural network architecture that belongs to the multilayer perceptron family, associated with two different algorithms: the ordinary gradient and the natural gradient, we compare the performances of those algorithms. The identification of a non-normalized power amplifier yielded to the introduction of an additional weight in the classical multilayer perceptron structure. The application of this network is space telecommunications: identification of satellite communication channels, and especially the down link. This link is made up with two elements. The first one is a high power amplifier (non-linearity). The second one is a filter (memory).

Many models based on hidden Markov models were developed to model errors bursts in communication channels. These models allow the computation of error distributions as well as the capacity expression of a channel. In this paper, we evaluate the effect of interleaving on the capacity of the widely used Gilbert model. An expression of this capacity is derived and is illustrated by simulation. This allows, when having an identified error model, simulation in an easy manner of the effects of any interleaving depth on the capacity of the channel.

Many models based on hidden Markov models were developed to model error bursts in communication channels. In this paper, we evaluate the effect of interleaving for the widely used Gilbert-Elliot model. An expression of the transition probability matrix is then derived. This allows, when having an identified error model, to simulate in an easy way the effects of any interleaving depth. Therefore, the choice of an interleaving degree and a forward error correction code (FEC) can be done easily.

This paper presents results obtained by applying periodic clock changes multiple access (PCCMA) to the uplink of mobile multiuser communication systems. Emitted signals are subjected to periodic clock changes based on linear time variant filters. At the reception side, we transpose the system in the time invariant domain and apply inverse filtering.

The presence of nonlinear devices in several communication channels, such as satellite channels, causes distortions of the transmitted signal. These distortions are more severe for non-constant envelope modulations such as 16-QAM. Over the last years neural networks (NN) have emerged as competitive tools for linear and nonlinear channel equalization. However, their main drawback is often slow convergence speed which results in poor tracking capabilities. The present paper combines simple NN structures with conventional equalizers. The NN techniques are shown to efficiently approximate the optimal decision boundaries which results in good symbol error rate (SER) performance. The paper gives simulation examples (in the context of satellite mobile channels) and compares neural network approaches to classical equalization techniques.

Privacy and security of radio communications becomes increasingly important. In this context, modulation techniques with embedded scrambling properties are suitable. The aim of this paper is to present a new transmitting technique using linear time varying filters with hopping in the frequency domain.

The paper proposes a neural network approach to equalize time varying nonlinear channels. The approach is applied to a satellite UMTS channel composed of time invariant linear filters, a non-linear memoryless amplifier and a time varying multipath propagation channel. The neural network equalizer has a radial basis function structure. The usual k-mean clustering algorithm is replaced by a Kohonen (1995) learning rule. This results in an RBF-SOM equalizer which outperforms the LMS equalizer, and which has better recovering abilities (after passing through a high fading area) than the former RBF equalizer.

The paper proposes a radial basis function (RBF) neural network (NN) approach to satellite universal mobile telecommunication system (S-UMTS) channel equalization. Two main problems arise in S-UMTS communications: (i) non-linear distortions which are caused by the onboard nonlinear power amplifiers, and (ii) multipath propagation. This paper shows that RBF networks are particularly well suited to overcome these problems. The paper presents several simulation results which show that RBF networks outperform classical equalization techniques for different configurations of the mobile channel (mobile speed, noise level, number of paths, etc.).

This paper is concerned with evolutionary ARMA modelling of randomly time-variant impulse responses. This modelling is applied to mobile radio channels subjected to multipaths and characterized by a time-variant impulse response. We present the principle of evolutionary ARMA models and derive a parameter estimator based upon an eigenformulation for the optimization condition of a chosen criterion.