The estimation of the ionospheric delay by a GNSS receiver is quite simple when the receiver has access to signals located at different frequencies. However, when these two frequencies are very close, this estimation process becomes very noisy. The paper presents a technique to overcome this problem in the case of the reception of Galileo signals in the E5 band only. This technique is based on a local ionosphere model and the use of carrier phase dual frequency measurements. This paper also widen this investigation to the case of the reception of two GNSS constellations, GPS and Galileo, broadcasting in the same E5 band. The performance of the estimation process are shown to be very good in Europe with a standard deviation of the estimation error at L1 that is below 30cm for the worst case ionosphere conditions.

Procédé de calibration de linéariseur et composant électronique linéarisé. Le procédé comprend la pré-distorsion, dans un linéariseur par pré-distorsion (20, 34), d'un signal en amont d'un composant électronique (18, 28) pour compenser une distorsion non-linéaire. La détermination des paramètres de réglage de pré-distorsion comprend l'application au composant d'un signal de test bi-fréquence, la mesure d'amplitudes relatives des raies en sortie du composant. Une grandeur indicative du module |Kp| du coefficient de conversion AM/PM du composant est calculée sur la base ce ces mesures. Les paramètres de réglage de pré-distorsion sont ajustés de sorte à minimiser |Kp|. Le procédé peut notamment être mis en oeuvre dans un dispositif amplificateur linéarisé (12) et dans un banc de test d'amplificateurs (24).

This paper presents an analysis on the implementation on a GNSS signal of a Code Shift Keying (CSK) modulation: an orthogonal M-ary modulation specifically designed to increase the bandwidth efficiency of direct-sequence spread spectrum (DS-SS) signals. Two decoding methods are presented as suitable candidates to be implemented by a CSK modulation with a LDPC channel code: classical sequential decoding and Bit-interleaved coded Modulation – Iterative Decoding (BICM-ID). Afterwards, this paper presents the methodology used to construct CSK signals which increase the useful bit rate with respect to a BPSK signal but maintaining the same symbol rate. This methodology includes the calculation and comparison of signal demodulation performances in AWGN and mobile channels, the generation of CSK symbols allowing the desired bit rate and the determination of the codeword durations. Proposals for real signals have been made. Finally, this paper analyses the impact of processing a CSK modulated signal on a GNSS receiver with respect to a BPSK signal. This analysis includes the increase of complexity of the demodulator block and the possible performance degradation of the acquisition and, the carrier and code delay tracking.

Routing in mobile ad hoc networks (MANET) is a complex task due to the mobility of the nodes and the constraints linked to a wireless multihop network (e.g., limited bandwidth, collisions, bit errors). These adverse conditions impair not only data traffic but also routing signaling traffic which feeds route computation. In this contribution, we propose to use satellite communications to help in the distribution of MANET routing signaling. The Optimized Link-State Routing (OLSR) is chosen among several routing protocols to be extended with satellite-based signaling, yielding a version we call OLSR Hybrid signaling (OLSR-H). This new scheme is evaluated through simulations and yields improvements of ca. 10% in the data delivery ratio compared to a regular OLSR. This evaluation is conducted using two different network topology models, one being fit for representing forest firefighting operations.

GNSS and particularly GPS and GLONASS systems are currently used in some geodetic applications to obtain a centimeter-level precise position. Such a level of accuracy is obtained by performing complex processing on expensive high-end receivers and antennas, and by using precise corrections. Moreover, these applications are typically performed in clear-sky environments and cannot be applied in constrained environments. The constant improvement in GNSS availability and accuracy should allow the development of various applications in which precise positioning is required, such as automatic people transportation or advanced driver assistance systems. Moreover, the recent release on the market of low-cost receivers capable of delivering raw data from multiple constellations gives a glimpse of the potential improvement and the collapse in prices of precise positioning techniques. However, one of the challenge of road user precise positioning techniques is their availability in all types of environments potentially encountered, notably constrained environments (dense tree canopy, urban environments…). This difficulty is amplified by the use of multi-constellation low-cost receivers and antennas, which potentially deliver lower quality measurements. In this context the goal of this PhD study was to develop a precise positioning algorithm based on code, Doppler and carrier phase measurements from a low-cost receiver, potentially in a constrained environment. In particular, a precise positioning software based on RTK algorithm is described in this PhD study. It is demonstrated that GPS and GLONASS measurements from a low-cost receivers can be used to estimate carrier phase ambiguities as integers. The lower quality of measurements is handled by appropriately weighting and masking measurements, as well as performing an efficient outlier exclusion technique. Finally, an innovative cycle slip resolution technique is proposed. Two measurements campaigns were performed to assess the performance of the proposed algorithm. A horizontal position error 95th percentile of less than 70 centimeters is reached in a beltwayenvironment in both campaigns, whereas a 95th percentile of less than 3.5 meters is reached in urban environment. Therefore, this thesis demonstrates the possibility of precisely estimating the position of a road user using low-cost hardware.

This paper analyses the congestion on a LEO satellite architecture with intermittent connectivity. The satellites are used to sense and gather data from ground terminals. The DTN (Delay Tolerant Networking) architecture allows the terminals to wait for the next contact when the satellite is not in the line of sight. The lack of connectivity of the network may create starvations for some stations. A model of the network is provided using Queueing Theory which allows to determine a probability of loss. This derivation proves that loss depends more on the number of terminals than on packet lifetime. The proposed scheduler and protocol allow to distribute traffic and loss fairly among stations. A testbed has been designed to validate the protocol.

Cognitive radios promise to revolutionize the performance of wireless networks in general and multi-hop wireless networks in particular by making efficient use of the portion of the licensed spectrum left un-utilized. Realizing this promise, however, requires revisiting many of the current network architectures and protocols, which is the subject of a very active research effort. In this work, we focus on Quality of Service routing and more specifically, admission control. We consider a multi-hop cognitive radio network where every node is equipped with multiple transceivers. Because the research and development of a widely accepted MAC protocol for these networks is still ongoing, we assume a bare-bones TDMA protocol at the link layer. We show that, for the network considered, the problem of finding the maximum end-to-end bandwidth of a given path is NP-Complete. Given this result, we consider a relaxed version of the problem wherein the slot allocations are carried out at each node by selecting at random the required number of slots among those available. For this case, we provide a linear time algorithm for computing the average residual end-to-end bandwidth. We perform an extensive numerical analysis that demonstrates its accuracy and enabling value for performing admission control.

This paper analyses the congestion on a LEO satellite architecture with intermittent connectivity. The satellites are used to sense and gather data from ground terminals. The DTN (Delay Tolerant Networking) architecture allows the terminals to wait for the next contact when the satellite is not in the line of sight. The lack of connectivity of the network may create starvations for some stations. A model of the network is provided using Queueing Theory which allows to determine a probability of loss. This derivation proves that loss depends more on the number of terminals than on packet lifetime. The proposed scheduler and protocol allow to distribute traffic and loss fairly among stations. A testbed has been designed to validate the protocol.

With most internet connections being short-lived (i.e. 10 segments), it is very tempting to enlarge the TCP Initial Window (IW). This would save two of the three RTTs needed to transfer most of the web pages through a legacy slow start. However it has been demonstrated that the bursts created by a larger IW greatly impair global performance. An intuitive solution is the TCP Pacing. By spreading the transmission over the whole RTT, Pacing smoothes the bursts and delays the congestion. While postponing congestion provides good performance for short-lived connections, it could significantly deteriorate global network performance insofar as the reaction to congestion is also delayed. This paper analyzes the weaknesses of large IW and TCP Pacing and proposes a fast Start-Up mechanism to speed up short-lived connections while preserving long-term connections. Extensive simulations and analysis demonstrate that our solution is as efficient as a larger IW would be in an uncongested network and better than current mechanisms in congested environments.

Passive inter-modulation products between transmitted signals may prevent the correct operation of satellite receivers using the same antenna. In many cases, these passive products do not obey the classical rule of 3 dB/dB slope as a function of carrier input power and they cannot be modeled using the classical theory based on polynomials. This has prevented the exact computation of carrier to inter-modulation ratio in multicarrier conditions from 2-carrier measurements. This has led to the use of higher than necessary margins. We present non-analytic models that generate non-integer inter-modulation slopes identical to that obtained in measurements and permit to predict multicarrier results.