Laboratoire de communications et d'intégration de la microélectronique

Underwater wireless information transfer is of great interest to the military, industry, and the scientific community, as it plays an important role in tactical surveillance, pollution monitoring, oil control and maintenance, offshore explorations, climate change monitoring, and oceanography research. In order to facilitate all these activities, there is an increase in the number of unmanned vehicles or devices deployed underwater, which require high bandwidth and high capacity for information transfer underwater. Although tremendous progress has been made in the field of acoustic communication underwater, however, it is limited by bandwidth. All this has led to the proliferation of underwater optical wireless communication (UOWC), as it provides higher data rates than the traditional acoustic communication systems with significantly lower power consumption and simpler computational complexities for short-range wireless links. UOWC has many potential applications ranging from deep oceans to coastal waters. However, the biggest challenge for underwater wireless communication originates from the fundamental characteristics of ocean or sea water; addressing these challenges requires a thorough understanding of complex physio-chemical biological systems. In this paper, the main focus is to understand the feasibility and the reliability of high data rate underwater optical links due to various propagation phenomena that impact the performance of the system. This paper provides an exhaustive overview of recent advances in UOWC. Channel characterization, modulation schemes, coding techniques, and various sources of noise which are specific to UOWC are discussed. This paper not only provides exhaustive research in underwater optical communication but also aims to provide the development of new ideas that would help in the growth of future underwater communication. A hybrid approach to an acousto-optic communication system is presented that complements the existing acoustic system, resulting in high data rates, low latency, and an energy-efficient system.

A tracking scenario comprising a mobile emitter node moving through an indoor environment covered by multiple anchor receivers is investigated in this work. A localization method based on received signal strength indicators (RSSI) and making use of the extended Kalman filter (EKF) and circularly polarized (CP) antennas is proposed. The EKF implements the position-velocity (PV) model, which assumes that the target is moving at a near-constant velocity during any given short time interval Δt. The measurement vector is composed of velocities in addition to RSSI values, which allow to deal with the error term between measurements and the propagation model directly. CP antennas are used on both the anchor nodes and the mobile node. These antennas are known to reduce the effects of multipath, especially those caused by single reflections. As a result, the RSSI values received in line of sight are more accurate and stable than those received from linearly polarized antennas. We tested our approach by tracking the movement of a robot following a predefined trajectory. The maximum location estimation error (LEE) is found to be 0.52 m. In addition, velocity changes are easily tracked during the target movement, which demonstrates the effectiveness of the proposed approach.

Parallel subband digital predistortion (DPD) has emerged as a promising approach for linearizing power amplifiers (PA) in wireless communication systems. This solution has the advantage of relaxing the bandwidth constraints on the feedback path analog to digital converter (ADC) which digitizes the PA distorted output which may spread over several hundreds MHz in the latest generations of mobile communications. However, the subband approach still has some limitations such as signal reconstruction and subband aliasing which limits its implementation on a wide scale. In this paper, an FFT-Based DPD technique that enables to compute the predistorter without interpolating signals is presented. Thanks to the frequency domain approach, the subband signals can be combined easily to compute the fullband predistorter directly. Moreover, the proposed technique offers the possibility of selecting specific frequency bins for the computation. In particular, the subband edges can be ignored which will result in relaxed bandwidth constraints and selectivity for the subband ADCs. Simulations show that the proposed FFT based subband DPD performs as good as the conventional time domain least-square approach even while excluding up to 13% of the FFT bins at the band edges.

Evolutive algorithms have demonstrated their potential as optimizers in a wide variety of applications. Automated evolutionary design of analog filters, antennas, logical gates and micro-electro-mechanical systems (MEMS) has resulted in unexpected but efficient topologies and configurations. In this paper, we present an automated design procedure for digital filters based on the use of a genetic algorithm (GA) and high level primitives such as delays, bit shift operators and adders. Given the performance criteria, the proposed algorithm autonomously decides on the components use and circuit configuration. Compared to traditional infinite impulse response (IIR) and canonical signed digits (CSD)-IIR filters, synthesis results show that the evolutionary designed (ED) filter can attain a twofold increase in speed and requires less hardware resource.

In military communication applications, tactical scenarios demand octave range tunability and high power handling. As a main component of a highly tunable filter, low-loss switches are desired to dynamically select components which tune the filters. This paper presents the design, the simulation, the manufacturing and the testing of tunable filter with in-line and integrated RF micro switches that operates in Band 3+ (1.35 to 2.7 GHz). The four states tunable filter is a microstrip half-wavelength resonator. The filter is wideband (1.597 to 2.295 GHz) and very selective with relative bandwidth from 1.6% to 4%. This operation band requires in general large-scale filter size and loss. The proposed design takes less than 1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and has acceptable insertion loss. Several micro switches are used with resonators to commute large scale surface to form a four-state tunable filter. The switches and resonators are designed such that the complete tunable filter is fabricated during the same manufacturing process.

The purpose of this paper is to present the impact of intentional electronic countermeasures using a high-speed repeater jammer on a single input single output (SISO) OFDM communication system. The jammer is composed of high-speed ADCs, DACs and a high performance FPGA used to implement a digital radio frequency memory (DRFM) and other jammers. This jammer can repeat a modified version of the input signal by continuously changing the amplitude or delay. The DRFM method can then be used to generate advanced jamming techniques capable of replicating fast fading channels similar to multipath environments. It can also add a continuous wave, broadband or partial band noise. In this study, WiMAX signals are subjected to these different types of jamming. The resulting EVM measures are converted using simple probability equations relating EVM to BER. The signal's immunity to jamming can be extracted by measuring the needed Signal-to-Interference-Ratio (SIR) required to reach a predetermined BER threshold. The most effective jammers are then determined. Power-to-power comparisons show that the best intelligent jammer is only 2 dB less efficient compared to an ideal "genie-aided" noise jammer which knows which band to target.

To reduce energy consumption of transmission sys-tems, the power amplifier in transceiver systems is a key element to be improved. The energy consumption associated with this component represents a major part of the total consumption of transmission systems. Moreover it plays an essential role in the quality of the transmitted signals. Digital predistortion (DPD) is a technique that aims at linearizing power amplifiers and thus allows energy efficiency improvements. However, this technique requires, in the feedback path, wideband and high dynamic range analog-to-digital converters (ADC) and usually large computational resources. Subband digitization with subband DPD algorithm have been proposed to relax the design constraints of the feedback path ADC and the digital processing unit. We present in this article a subsampled RLS-based subband DPD algorithm. We show that the gain in terms of number of multiplications and/or additions per second (MAC/s), between the conventional wideband approach and the subsampled algorithm, tends to the number of subbands. Simulations show that the convergence speed by RLS iteration of the subsampled algorithm is maintained. Therefore, the subsampled algorithm converges with the same number of iterations as the conventional wideband approach. After conver-gence, the residual mean-square-error (MSE) is approximately -76 dB for the conventional wideband algorithm and -70 dB for the proposed algorithm.