Marie-Laure Boucheret

Combining Adaptive Coding and Modulation With Hierarchical Modulation in Satcom Systems

We investigate the design of a broadcast system in order to maximize throughput. This task is usually challenging due to channel variability. Forty years ago, Cover introduced and compared two schemes: time sharing and superposition coding. Even if the second scheme was proved to be optimal for some channels, modern satellite communications systems such as DVB-SH and DVB-S2 rely mainly on a time sharing strategy to optimize the throughput. They consider hierarchical modulation, a practical implementation of superposition coding, but only for unequal error protection or backward compatibility purposes. In this article, we propose to combine time sharing and hierarchical modulation together and show how this scheme can improve the performance in terms of available rate. We introduce a hierarchical 16-APSK to boost the performance of the DVB-S2 standard. We also evaluate various strategies to group the receivers in pairs when using hierarchical modulation. Finally, we show in a realistic case, based on DVB-S2, that the combined scheme can provide throughput gains greater than 10% compared to the best time sharing strategy.

Iterative interference cancellation and channel estimation in multibeam satellite systems

This paper deals with the use of non-linear multiuser detection techniques to mitigate co-channel interference on the reverse link of multibeam satellite systems. These techniques allow more capacity efficient frequency reuse strategies than classical ones, as they make possible to cope with lower C/I. The considered system takes as a starting point the DVB-RCS standard, with the use of convolutional coding, and the use of the Ka-band. n n n nWe propose different iterative interference cancellation schemes, which operate at the beamformer outputs, and which use information from decoders. The proposed receivers assume an initial single-user synchronization step: frame synchronization and timing recovery, and then perform channel estimation: beamformer coefficients; signal carrier phases and signal amplitudes. n n n nIn a first step, these receivers are evaluated by simulation in terms of bit error rate and of channel estimation error on two interference configurations. For one of these receivers, sensitivity to imperfect timing recovery and to low-frequency offsets from user terminals is evaluated. n n n nIn a second step, since the receiver performances highly depend on the interference configuration, we propose an approach to evaluate performances on a multibeam coverage (by taking into account the variability of interference configurations on the coverage). This method is used to compare different receivers on an example based on a coverage designed on a digital focal array feed reflector antenna. Copyright

A Cooperative Network Coding Strategy for the Interference Relay Channel

In this paper, we study an interference relay network with a satellite as relay. We propose a cooperative strategy based on physical layer network coding and superposition modulation decoding for uni-directional communications among users. The performance of our solution in terms of throughput is evaluated through capacity analysis and simulations that include practical constraints such as the lack of synchronization in time and frequency. We obtain a significant throughput gain compared to the classical time sharing case.

Implementation of Code Shift Keying signalling technique in GALILEO E1 signal

One of limitations of the current GNSS signals is their low data information rate. This low data information rate does not allow, for example, the transmission of additional commercial services or the transmission of redundant ephemeris data. The Code Shift Keying (CSK) is a signaling technique specifically designed to increase the transmission bit rate of a spreading spectrum signal. Therefore, one solution to increase the data information rate of the GNSS signals is to introduce the CSK technique in them. In this paper, the implementation of the CSK technique into GNSS signals is inspected through the development and analysis of the likelihood ratio expression of the bits transmitted inside a CSK symbol, and through the identification of the best mapping between bits belonging to a word and bits transmitted inside a CSK symbol. Finally, the impact of the CSK technique on the GALILEO E1 signal is analyzed by calculating the CSK demodulation performance for a given scenario and the drawbacks of the technique on the signal acquisition and tracking processes.

A soft decision directed phase detector suited to satellite communications at very low signal to noise ratio

The introduction of data redundancy for the purpose of carrier synchronization over a Gaussian channel may be a profitable operation. We present in this paper the performance of a phase detector suited to 8 PSK receivers, based on the soft decoding of a single parity-check code. It is shown that in presence of phase noise and a quite important frequency error, the proposed synchronization scheme outperforms the classical non-data-aided and decision-directed algorithms, reducing the phase jitter in considerable proportions.

Beamforming for satellite communications in emergency situations

We consider a multi-beam Ka-band satellite communication system aimed at operating in emergency situations where terrestrial communications systems are no longer effective. In contrast to most systems which use one single beam to cover a large area, we study here the feasibility of a one beam per user concept, where a beamformer is calculated for each user. This should allow to guarantee the maximum antenna gain towards each user. We assess the performance of the minimum variance distortionless response (MVDR) beamformer and of a beamformer using a training sequence in realistic scenarios including channel, steering vector and synchronisation errors. We show that both beamformers provide a sufficiently high output signal to noise ratio in a DVB-RCS system.

Proposal of a satellite system for emergency situations

In emergency situations or in the case of disasters (cyclone, flood...), there is a vital need for communications services such as voice, video or useful data (logistical, medical data, support for stricken population...) in order to assist populations. Satellite links seem to be a cost effective way to ensure secure and high data rate communications in these situations where users are scattered all over the area. This article deals with the setting up of such a satellite communication system that would operate in Ka-band. Estimating the frequency reuse factor, a first analysis of the systems performance is proposed.

Iterative Multiuser Detection and Channel Estimation in a Multibeam Satellite Communication System

This paper deals with the use of non-linear multiuser detection techniques to mitigate co-channel interference on the reverse link of multibeam satellite systems. The considered system is inspired by the DVB-RCS standard, with the use of convolutional coding. The proposed scheme consists of an iterative parallel interference cancellation algorithm with semi-blind channel estimation. The main contributions of this paper are the assumption of unknown beamformer coefficients for the receiver design, the introduction a low complexity scheme for a symbol asynchronous channel, and sensitivity evaluations with imperfect timing recoveries or reduced frequency offsets. The proposed algorithm allows close to single user performance on configurations characterized by very low C/I

Optimization of an OFDM waveform suited to the forward link of a flxed broadband satellite system

This paper proposes an OFDM receiver for the forward link of a flxed broadband satellite system. We focus on the synchronization tasks in the receiver. Our objective is to reduce to the minimum the needed overhead, in order to improve spectral e‐ciency compared to a single carrier waveform system. Indeed, a non pilot aided algorithm is used for flne synchronization stage. It is preceded by a coarse synchronization stage, in which a limited overhead is necessary (short cyclic preflx associated to a few number of pilots).