In this paper, a novel category of expectation propagation (EP) based frequency domain (FD) semi-blind receivers are proposed for single-carrier block transmissions. A recently proposed EP-based framework for deriving double-loop turbo detectors is extended to handle joint data-aided channel estimation along with EP-based soft interference cancellation (IC). When addressing this problem in a message passing framework, an unconventional probability density function prevent us from establishing analytical update functions for estimating data and channel estimates. This is solved with variational inference methods, such as mean-field (MF), expectation maximization (EM) or EP, using a three-loop receiver structure with flexible performance-complexity trade-off, thanks to fast Fourier transform (FFT) based processing.

This paper investigates the dynamic behaviour of doubly iterative bit-interleaved coded modulation (BICM) receivers based on expectation propagation (EP). When implemented in the frequency domain, for single-carrier (SC) systems, such receivers achieve attractive performance-complexity trade-offs in quasi-static wideband channels. With this category of receivers, conventional binary extrinsic information transfer (EXIT) functions are subject to a great number of parameters, including channel realizations, constellation and inner iteration parameters. Hence, this paper proposes a novel extrinsic information evolution analysis method which simplifies the receiver's EXIT function into independent inner transfer functions. The core idea is to track state-evolution dynamics of EP through numerically stable extrinsic variance/information transfer (EXVIT) functions. Numerical results attest to the accuracy of this method for tracking the asymptotic receiver behaviour.

This paper analyzes some emerging techniques from the broad area of Bayesian learning for the design of iterative receivers for single-carrier transmissions using bit-interleaved coded-modulation (BICM) in wideband channels. In particular, approximate Bayesian inference methods, such as expectation propagation (EP), and iterative signal-recovery methods, such as approximate message passing (AMP) algorithms are evaluated as frequency domain equalizers (FDE). These algorithms show that decoding performance can be improved by going beyond the established turbo-detection principles, by iterating over inner detection loops before decoding. A comparative analysis is performed for the case of quasistatic wideband communications channels, showing that the EP-based approach is more advantageous. Moreover, recent advances in structured learning are revisited for the iterative EP-based receiver by unfolding the inner detection loop, and obtaining a deep detection network with learnable parameters. To this end, a novel, mutual-information dependent learning cost function is proposed, suited to turbo detectors, and through learning, the detection performance of the deep EP network is optimized.

In satellite communications, the non-linear distortions introduced by the amplifier in the payload have to be overcome. When advanced mitigation techniques are considered at the receiver side, the current channel model is often based on Volterra series derived from an approximation of the non linear transfer function of the on-board amplifier. This nonlinear model is conditioning the performance at the receiver side. In this paper, a new non-linear model is proposed, leading to improved receiver performances. The polynomial approximation is improved considering both the usual model truncation to the 3rd order and the signal fluctuation at the input of the amplifier. First, the impact of the polynomial order of the AM/AM and AM/PM curve approximation is studied. Then, a non-linear model is derived based on a piecewise polynomial approximation of the amplifier response. Based on this refined nonlinear model, significant detection performance improvements are shown for both Nyquist and Faster-than-Nyquist rates.

Random Access (RA) protocols have considerably evolved in satellite communications, especially after the introduction of Contention Resolution Diversity Slotted Aloha (CRDSA). However, CRDSA finds itself in a deadlock when the number of users is important. A complementary treatment Multireplica Decoding using Correlation based Localization (MARSALA) has hence been proposed to unlock CRDSA. This is fulfilled by localizing then combining replicas of the same undecoded packets using correlations. Based on a prior knowledge of the potential frame content by the receiver, a random Shared POsition Technique for Interfered random Transmissions (SPOTiT) is proposed to reduce MARSALA's localization complexity. As a matter of fact, random SPOTiT highlights a manner for the receiver to be aware of time slot positions and the preamble used by each subscriber. Then it uses this information to target a lower number of slots for localization correlations. In this paper we propose a hybrid solution that mixes both DAMA and Random Access in order to lower the Packet Loss Ratio (PLR) floor. In fact, a centralized computing can manage replicas positions and preambles to use, in a way that no loops are created. This also allows to keep a simple packet localization as in SPOTiT. Hereafter, we provide an optimal distribution of frame content using two replicas per packet which is evaluated through simulation.

A novel multiuser multiple-input multiple-output (MU-MIMO) receiver for single-carrier frequency-division multiple-access (SC-FDMA) is proposed within the expectation propagation (EP) framework. Recent advances in iterative receiver design show the ability of low complexity EP-based iterative algorithms to achieve performance close to maximum a posteriori (MAP) detection. In this paper, based on the exact derivation of frequency-domain EP-based turbo receivers, we propose a novel spectrally and computationally efficient soft interference canceller (IC) with a doubly-iterative architecture. Asymptotic and finite-length analysis show that our proposal outperforms existing schemes with comparable complexity, in various spatial-multiplexing configurations.

This paper investigates the design and analysis of minimum mean square error (MMSE) turbo decision feedback equalization (DFE), with expectation propagation (EP), for single carrier modulations. Classical non iterative DFE structures have substantial advantages at high-data rates, even compared with turbo linear equalizers-interference cancellers (LE-IC), hence making turbo DFE-IC schemes an attractive solution. In this paper, we derive an iterative DFE-IC, capitalizing on the use of soft feedback based on expectation propagation, along with the use of prior information for improved filtering and interference cancellation. This turbo iterative DFE-IC significantly outperforms turbo LE-IC, especially at high-spectral efficiency and also exhibits performance improvements over existing DFE-IC variants. The proposed scheme can also be self-iterated, as done in the recent trend on EP-based equalizers, and it is shown to be an attractive alternative to linear self-iterated receivers. For time-varying (TV) filter equalizers, an efficient matrix inversion scheme is also proposed, considerably reducing the computational complexity relative to existing methods. Using finite-length and asymptotic analysis on a severely selective channel, the proposed DFE-IC is shown to achieve higher rates than known alternatives, with better waterfall thresholds and faster convergence, while keeping a similar computational complexity.

An original expectation propagation-based message passing framework is introduced, wherein transmitted symbols are considered to belong to the multivariate white Gaussian distribution family. This approach allows deriving a novel class of single-tap frequency domain (FD) receivers with a quasi-linear computational complexity in block length, thanks to fast-Fourier transform-based implementation. This framework is exposed in detail, through the design of a novel double-loop single-carrier FD equalizer (FDE), where self-iterations of the equalizer with the demapper and turbo iterations with the decoder provide numerous combinations for the performance and complexity tradeoff. Furthermore, the flexibility of this framework is illustrated with the derivation of an overlap FDE, used for time-varying channel equalization, among others, and with the design of an FD multiple-input multiple-output detector, used for spatial multiplexing. Through these different receiver design problems, this framework is shown to improve the mitigation of inter-symbol, inter-block, and multi-antenna interferences, compared to alternative single-tap FD structures of previous works. Thanks to finite-length and asymptotic analysis, supported by numerical results, the improvement brought by the proposed structures is assessed and then completed by also accounting for computational costs.

In this paper, we present a new data-aided carrier-recovery method for Continuous Phase Modulation (CPM) signals over frequency-selective channels. We first present a linear model of the received signal based on Mengali representation over selective channels and show how to use it to perform joint channel and carrier-frequency estimation. We also derive a low-complexity version of the estimator. Simulation results show that this method performs better than the optimal method suited to the Additive White Gaussian Noise (AWGN) channels.

Multisymbol receiver is an effective method to demodulate noncoherent sequences. However it is necessary to correlate an important number of symbols in a noncoherent scheme to reach the performances carried out by optimal coherent Maximum a Posteriori (MAP) detectors such as BCJR. In this paper, we propose an advanced multisymbol receiver by adding some memory to the decision process. The advanced receiver, called here Multisymbol With Memory (MWM) takes into account the cumulative phase information unlike multisymbol algorithm and thus it can be seen as a truncated BCJR. An exact mathematical derivation is performed for this truncated BCJR. Then an implementation of the MWM detector applied to a continuous phase frequency shift keying modulation is presented. Finally an asymptotic analysis is carried out based on the achievable Symmetric Mutual Information rate. The proposed system exhibits good performances compared to classical multisymbol receivers at the expense of increased complexity and can approach the performances of a coherent receiver.

In this paper, we consider a bit-interleaved coded modulation scheme (BICM) composed of an error correcting code serially concatenated with a M-ary non linear modulation with memory. We first compare demodulation strategies for both the coherent and the non coherent cases. Then, we perform an asymptotic analysis and try to show that the design of coding schemes performing well for both the coherent and the non coherent regimes should be done carefully when considering sparse graph based codes such as low-density parity-check (LDPC) codes. It will be shown that optimized coding schemes for the non coherent setting can perform fairly well when using coherent demodulation, while on the contrary, optimized coding schemes for the coherent setting may lead to “non stable” coding schemes in the non coherent setting.

In order to increase the capacity of future satellite communication systems, faster-than-Nyquist (FTN) signaling is increasingly considered. The gain in terms of transmission rate is obtained at the price of significant intersymbol interference (ISI) introduction. To benefit from an improved spectral efficiency (SE), many iterative detectors have already been investigated, demonstrating the interest of such a waveform in linear and non linear channels. A thorny point in FTN signaling remains its synchronization since the usual algorithms considered in the DVB-S2X standard cannot be applied on this waveform without significant loss on the performance. This paper proposes a synchronization scheme for FTN signaling in a satellite context. It is based on a Volterra decomposition of the received signal in order to fit both with linearized and non-linearized amplifiers which can be found in the satellite payload. Two steps, initialization and tracking are considered, based on training sequences fulfilling the DVB-S2Xs frames requirements. After start of sequence detection and frequency offset correction, the channel estimation is used for time offset issue in the two proposed schemes. Their performance are compared to the performance of a perfect synchronized detection.

In this paper, we investigate coded antenna selection for spectrally shaped Spatial Modulation (SM). Spectrally shaped SM aims at reducing the complex envelope fluctuations. This is done at the expense of a bandwidth expansion given by a roll-off factor β when root raised cosine (RRC) spectral filtering is considered. Nevertheless, this extra redundancy can be exploited by enabling the use of redundancy on the bit antenna selection stream. Indeed, we can associate a high performance error correcting code with a corresponding rate R = γ+β used to encode antenna selection bits and thus, we can achieve better performance at the receiver. Simulation results show that the proposed scheme exhibit a lower peak-to-average power ratio (PAPR) compared with the conventional SM scheme while achieving enhanced performance and diversity when an efficient coding scheme is used to improve antenna selection.

Increasing the sampling rate of Analog-to-Digital Converters (ADC) is a main challenge in many fields and especially in telecommunications. Time-Interleaved ADCs (TI-ADC) were introduced as a technical solution to reach high sampling rates by time interleaving and multiplexing several low-rate ADCs at the price of a perfect synchronization between them. Indeed, as the signal reconstruction formulas are derived under the assumption of uniform sampling, a desynchronization between the elementary ADCs must be compensated upstream with an online calibration and expensive hardware corrections of the sampling device. Based on the observation that desynchronized TI-ADCs can be effectively modeled using a Periodic Non-uniform Sampling (PNS) scheme, we develop a general method to blindly estimate the time delays involved in PNS. The proposed strategy exploits the signal stationarity properties and thus is simple and quite generalizable to other applications. Moreover, contrarily to state-of-the-art methods, it applies to bandpass signals which is the more judicious application framework of the PNS scheme.

Faster-than-Nyquist (FTN) signaling appears as an attractive method to improve spectral efficiency at the price of an increased complexity at the receiver. The receiver generally implements a turbo-equalization/detection scheme to benefit from all the promises of the FTN signaling. However, this is not the only limitation we have to deal with. Indeed, compressing in the time domain impact the emitted signal and it usually results in an increase of the envelope fluctuations. This leads to an inherent multi-objectives trade-off between performance, targeted spectral efficiency and limited Peak to Average Power Ratio (PAPR). The last aspect is crucial when considering a satellite communication link due to non-linear amplification effects that can occur on-board the satellite. Usually, FTN studies focus on spectral efficiency increase for a fixed modulation order, trying to trade-off between performance and PAPR properties. In this paper, we show that, for a given asymptotic spectral efficiency, we can compress low order modulations to increase the spectral efficiency of these schemes while controlling the PAPR increase to achieve a better PAPR than the non compressed scheme with a higher modulation order. Thus, for the same asymptotic spectral efficiency, we can achieve 1 dB gain in terms of PAPR and 2 dB gain in Bit Error Rate (BER) performances for a coded 8-PSK FTN system compared to a coded 16-APSK. For the same BER performances, the asymptotic spectral efficiency gain obtained in linear context is over 20 %, higher when non-linearities are taken into account.

In this work, we apply Spatial Modulation (SM) to in the so-called spectrally shaped SC-OFDM (SS SC-OFDM) at the transmitter. The idea behind SS SC-OFDM lies in applying a frequency window between the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT) in order to lower the side-lobes of the resulting time domain generated waveform. Thus, we can avoid the peak-to-average power ratio (PAPR) problem encountered in multicarrier systems. At the receiver, a reduced-rank (rr) Least Square (LS) channel estimation and a combining Minimum Mean Square Error (MMSE) equalization are used to retrieve the transmitted block of information bits, considering two flight scenarios for different environments.

The spatial coupling is an efficient technique that improves the threshold of Low Density Parity Check (LDPC) codes. In this paper, we investigate the performance of the serial concatenation of Continuous phase modulation (CPM) and LDPC convolutional codes over a memoryless additive white Gaussian noise channel. We show that coupling protographs optimized for CPM improves their performance and helps designing very good `small' protographs. Inspired from convolutional codes and thanks to the inner structure of CPM, we also introduce a new termination without rate loss but that still exhibits a coupling gain and it thus has a very good threshold. We will illustrate the behavior of different LDPC convolutional codes with different termination methods by giving some examples and studying their performance using multidimensional EXIT analysis.

In this paper, we provide a proof for the conjecture made by Abu Surra et al. [1] to simplify the computation of ensemble input output weight enumerators for protograph-based low density parity check (LDPC) codes. Furthermore, we propose a new method to compute more efficiently the ensemble weight enumerator. This approach can be applied particularly to lighten the computations for high rate codes, generalized LDPC codes or spatially coupled LDPC codes.

In this paper, we investigate on some efficient channel estimation methods for the aeronautical multipaths channel. The proposed methods exploit both the particular form of the channel impulse response and a priori knowledge of some parameters (mainly delays) that can be inferred from geometrical considerations based on geolocation. The first estimation method is based on a parametric multipath channel model while the second tries to exploit the relative sparsity of the channel impulse response. In both cases, this reduces the number of variables to be estimated and it provides better performance compared to a direct classical least-square estimation of the discrete equivalent channel impulse response.

This paper proposes a new method for data reception over a random access channel in a satellite communication system. The method is called Multi-replicA decoding using corRelation baSed locALisAtion (MARSALA). It uses the same transmission scheme as in Contention Resolution Diversity Slotted Aloha (CRDSA) where each user sends several replicas of the same packet over the frame. MARSALA is a new decoding technique that localises all the replicas of a packet using a correlation based method, then combines them to decode the data. With MARSALA, the system can achieve a normalized throughput higher than 1.2, resulting in a significant gain compared to CRDSA, while adding a relatively low implementation complexity at the receiver. We also highlight on the practical issues related to channel estimation and how to perform coherent signal combination in MARSALA.

In recent random access methods used for satellite communications, collisions between packets are not considered as destructive. In fact, to deal with the collision problem, successive interference cancellation is performed at the receiver. Generally, it is assumed that the receiver has perfect knowledge of the interference. In practice, the interference term is affected by the transmission channel parameters, i.e., channel attenuation, timing offsets, frequency offsets and phase shifts, and needs to be accurately estimated and canceled to avoid performance degradation. In this paper, we study the performance of an enhanced channel estimation technique combining estimation using an autocorrelation based method and the Expectation-Maximization algorithm integrated in a joint estimation and decoding scheme. We evaluate the effect of residual estimation errors after successive interference cancellation. To validate our experimental results, we compare them to the Cramer-Rao lower bounds for the estimation of channel parameters in case of superimposed signals.

In this paper, we derive an asymptotic analysis for a capacity approaching design of serially concatenated turbo schemes with low density parity check (LDPC) codes and continuous phase modulation (CPM) based on Laurent decomposition. The proposed design is based on extrinsic mutual information evolution and Gaussian approximation. By inserting partial interleavers between LDPC and CPM and allowing degree-1 variable nodes under a certain constraint we show that designed rates are very close to the maximum achievable rates. Furthermore, we discuss the selection of low complexity receivers that works with the same optimized profiles.

In this paper, we derive an asymptotic analysis and optimization of coded CPM systems using both unstructured and protograph-based LDPC codes ensembles. First, we present a simple yet effective approach to design unstructured LDPC codes : by inserting partial interleavers between LDPC and CPM, and allowing degree-1 and degree-2 variable nodes in a controlled pattern, we show that designed codes perform that can operate very close to the maximum achievable rates. Finally, the extension to protograph based codes is discussed. We provide some simple rules to design good protograph codes with good threshold properties.

In this paper, we investigate a sub-optimal but efficient receiver structure for the equalization of aeronautical communications via a satellite link. The structure is based on the inherent sparsity of the equivalent discrete baseband channel model that enables an efficient implementation based on simple parallel trellis using Maximum A Posteriori (MAP) detection combined with iterative residual interference estimation and cancellation. The proposed scheme is shown to be very efficient while significantly decreasing the complexity compared to a MAP receiver that does not exploit the sparsity of the aeronautical channel.

This article deals with Minimum Mean Square Error (MMSE) turbo equalization of nonlinear interference using a volterra series decomposition of the underlying nonlinear channel. Although it has been often argued that linear MMSE based equalization is unsuited for cancelling nonlinear interference, we show that this common belief is not true in a strict sense. By a proper derivation of the linear based MMSE soft equalizer, we are able to show that the underlying structure of the equalizer is equivalent to a Soft Interference Canceller (SIC) treating both the linear and nonlinear interference. Based on these results, approximations are provided for lowering the computational complexity. Links to previously proposed “nonlinear” SIC are emphasized showing that the previously proposed structures are nothing but approximations of a linear MMSE receiver applied to nonlinear ISI channels. Simulations show that significant improvements can be achieved by using the proposed exact and approximate MMSE based turbo-equalizers.

In this paper, we derive the exact outage probability of a hybrid satellite-terrestrial cooperative system (HSTCS). A selective decode-and-forward scheme is implemented between a source node (the satellite) and a destination node (a terrestrial station), and a selection of the best relay terminal is performed. In this proposed system, a two time-slot scenario is considered. During the first time slot, the satellite is broadcasting the information to the terrestrial relays and the destination. In the second time slot, only the best relay is transmitting toward the destination node. Then, both signals are combined using the maximum ratio combining (MRC) technique. The analytical expression of the outage probability is evaluated and is then verified with the simulation. The results show that our analytical expression matched well to the simulation results.

Broadcasting systems have to deal with channel variability in order to offer the best spectrum efficiency to the receivers. However, the transmission parameters that optimize the spectrum efficiency generally leads to a large link unavailability. In this paper, we study the performance of hierarchical and non-hierarchical modulations in terms of spectrum efficiency and link unavailability for DVB-S2 systems. Our first contribution is the design of the hierarchical 16-APSK for the DVB-S2 standard. Then we introduce the link unavailability to compare the performance of hierarchical and non-hierarchical modulations in terms of spectrum efficiency and link unavailability. The results show that hierarchical modulation is a good alternative to non-hierarchical modulation for the DVB-S2 standard.

In this paper, we study the Symbol Error Probability (SEP) performance of a hybrid/integrated satellite-terrestrial cooperative network. In particular, we focus on the case of mobile relays that forward the satellite signal to a masked mobile destination node. The Selective Decode-and-Forward (SDF) transmission scheme is implemented and only the relay nodes which can successfully decode the satellite message are selected to retransmit the signal. The destination node exploits the spatial diversity advantages by implementing a typical Maximum Ratio Combining (MRC) technique. The closed-form expressions for the exact average SEP of the arbitrary M-ary phase shift keying and M-ary quadrature amplitude modulation signaling with MRC diversity reception over independent but not necessarily identically distributed fading channels are derived using a Moment Generating Function (MGF) approach. These closed-form expressions are represented in terms of a finite sum of Lauricella hypergeometric functions. The analytical expressions show excellent agreement with the simulation results. Numerical results show that for a system using QPSK under the frequent heavy shadowed fading condition, the diversity gain of approximately 7 dB can be obtained at the SEP of 10-1with respect to the direct transmission, when only one relay is used. It increases to around 12 dB in the case of 3 relays.

This paper proposes a new modulation format suited to power- and band-limited, non-frequency selective channels. It is considered here for satellite broadcast and broadband applications. The proposed format uses combinations of Gold sequences transmitted through a spectral-efficient multi-carrier format with orthogonal frequency-division multiplexing (OFDM). We present the modulation design as well as an analytical approximation of the performances and a comparison with existing modulations. The focus is put on the power efficiency improvement. Moreover, the multi-carrier format alleviates the receiver synchronization and improves the spectral efficiency. The critical issue of Peak-to-Average-Power Ratio (PAPR) distribution and reduction is finally discussed.

In this paper, we analyze the performance of Successive Interference Cancelation (SIC) receivers in the context of the ARGOS satellite system. Multi-user SIC receivers are studied in presence of imperfect estimates of signal parameters. We derive performance graphs that show the parameter ranges over which a successful demodulation of all users is possible. First, the graphs are derived in the context of perfect parameter estimation. Then, imperfect parameter estimation is considered. Erroneous estimations affect both the amplitude and the time delay of the received signal. Carrier frequencies are assumed to be accurately measured by the receiver. ARGOS SIC receivers are shown to be both robust to imperfect amplitude estimation and sensitive to imperfect time delay estimation.

This paper introduces an iterative multiuser detection scheme, including channel estimation, for the reverse link of (narrowband) multibeam satellite communication systems with convolutional coding. After a derivation of the algorithm on a symbol-asynchronous time-invariant channel, we discuss and evaluate possible adaptations to the more realistic case of frequency offsets affecting user terminals.

In this letter, we present an analysis tool for the convergence of a turbo decoder using the min-sum algorithm. First of all, we classify cycles on a turbo code factor graph. We define and develop a quantity which characterizes the trellis convergence and a probability of a message round on a cycle. Our analysis is then applied to an interleaver design for a turbo decoder using the min-sum algorithm. Since the probability of a message round is closely related to the convergence property, the constructed interleaver optimizes the convergence property. The performance is compared with several referential interleavers.

In this paper, we present a phase synchronization algorithm which exploits the data redundancy brought by a single parity-check code. The symbol decoding of a parity equation is discussed first. Then, a soft detection directed (SDD) estimation technique is derived for any modulation scheme. The performance of the developed SDD phase estimator is evaluated with 8PSK modulation in very low SNR condition. It appears to greatly outperform the non data aided Viterbi and Viterbi estimator. Quite robust to phase noise, it seems well suited to the context of satellite burst transmissions

We introduce in this paper a carrier phase detector suited to transmissions at very low signal to noise ratio. Based on the soft decoding of parity check equations, the synchronization scheme proposed here for a QPSK modulation outperforms a classical decision directed algorithm over a Gaussian channel, and is notably well adapted to satellite applications.

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.

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.

Most of GEO satellite telecommunication systems today aim at providing multimedia access services to low cost and power-limited user terminals by implementing performant regenerative onboard processing techniques (demodulation, routing). In order to meet high QoS performance at low SNR, especially on the satellite uplink, performant coding schemes such as turbo codes are necessary. We focus on the critical point of the on-board demodulator: the carrier phase recovery performed in presence of powerful turbo decoding. Non-data aided (NDA) and TD estimators are presented and analysed in terms of characteristics for transmissions using recursive systematic convolutional (RSC) codes that can be used for turbo codes. We show that TD estimation can operate down to E/sub c//N/sub 0/=0 dB with frequency offset up to 10/sup -3/.

In this paper, we describe and analyze a new feedforward carrier-phase algorithm suited to on-board digital implementation. The algorithm studied here (for phase recovery of M-ary phase-shift keying signals) has the particularity to perform all calculations in polar coordinates in order to reduce the implementation complexity. The defined phase estimator is operating at very low signal-to-noise ratio with small frequency offsets. Its performance is close to those of the Viterbi and Viterbi algorithm.

We present a multiuser synchronization scheme for tracking the mobile's uplink time and frequency offsets. It uses the redundancy introduced by the cyclic prefix and does not need additional pilots. We show performance results of an orthogonal frequency division multiplexing (OFDM)-based radio interface based on the universal mobile telecommunication system (UMTS) parameters. For a UMTS-typical mobile channel environment, the performance of a coherent system employing the scheme is virtually indistinguishable from the performance of a perfectly synchronized system. In a differentially modulated system, synchronization errors decrease the system performance by about 0.7 dB compared to a perfectly synchronized system.

Filter banks able to demultiplex channels of different sizes are necessary on board the satellite when a single bit-rate channel is assigned to each user. In this paper, the method referred to as the fast convolution filter bank is analyzed for regenerative payloads. The size of the input fast Fourier transform (FFT) depends on the narrowest channel, while the inverse fast Fourier transform (IFFT) number of points is relative to the decimation ratio associated with each channel. In order to reduce the complexity, most of the frequency coefficients are forced to zero, leading to a violation of the overlap-and-save (OS) condition. It is shown that the resulting error can be modeled as a cyclostationary process, and an optimization method based on minimization of the associated mean-square error (MSE) is proposed. Fast convolution is then compared with multistage implementation in terms of flexibility, reconfigurability, and complexity.