Analog integrated circuit design techniques for high-speed signal processing in communications systems

This work presents design techniques for the implementation of high-speed analog integrated circuits for wireless and wireline communications systems. Limitations commonly found in high-speed switched-capacitor (SC) circuits used for intermediate frequency (IF) filters in wireless receivers are explored. A model to analyze the aliasing effects due to periodical non-uniform individual sampling, a technique used in high-Q high-speed SC filters, is presented along with practical expressions that estimate the power of the generated alias components. The results are verified through circuit simulation of a 10.7MHz bandpass SC filter in TSMC 0.35mu-m CMOS technology. Implications on the use of this technique on the design of IF filters are discussed. To improve the speed at which SC networks can operate, a continuous-time common-mode feedback (CMFB) with reduced loading capacitance is proposed. This increases the achievable gain-bandwidth product (GBW) of fully-differential ampli- fiers. The performance of the CMFB is demonstrated in the implementation of a second-order 10.7MHz bandpass SC filter and compared with that of an identical filter using the conventional switched-capacitor CMFB (SC-CMFB). The filter using the continuous-time CMFB reduces the error due to finite GBW and slew rate to less than 1% for clock frequencies up to 72MHz while providing a dynamic range of 59dB and a PSRR- > 22dB. The design of high-speed transversal equalizers for wireline transceivers requires the implementation of broadband delay lines. A delay line based on a third-order linear-phase filter is presented for the implementation of a fractionally-spaced 1Gb/s transversal equalizer. Two topologies for a broadband summing node which enable the placement of the parasitic poles at the output of the transversal equalizer beyond 650MHz are presented. Using these cells, a 5-tap 1Gb/s equalizer was implemented in TSMC 0.35mu-m CMOS technology. The results show a programmable frequency response able to compensate up to 25dB loss at 500MHz. The eye-pattern diagrams at 1Gb/s demonstrate the equalization of 15 meters and 23 meters of CAT5e twistedpair cable, with a vertical eye-opening improvement from 0% (before the equalizer) to 58% (after the equalizer) in the second case. The equalizer consumes 96mW and an area of 630mu-m x 490mu-m

Adaptive equalizers for multipath compensation in digital microwave communications

SIGLEAvailable from British Library Document Supply Centre- DSC:D82998 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A High-speed Reconfigurable Free Space Optical Communication System Utilizing Software Defined Radio Environment

Free space optical (FSO) communication allows for high-speed data transmissions while also being extremely cost-effective by using visible or infrared wavelengths to transmit and receive data wirelessly through the free space channel. However, FSO links are highly susceptible to the effects of the atmosphere, particularly turbulence, smoke, and fog. On the other hand, FSO itself does not provide enough flexibility to address the issue of such blockage and obstruction caused by objects and atmospheric conditions. This research investigates, proposes, and evaluates a software defined multiple input multiple output (MIMO) FSO system to ensure link availability and reliability under weather conditions as part of the last mile access in the 5th generation, 6th generation, and beyond. Software defined radio (SDR) technology is adopted in order to provide a certain degree of flexibility to the optical wireless communications system. The scope of this research focuses on the design, validation, implementation, and evaluation of a novel adaptive switching algorithm i.e., activating additional transmitters of a MIMO FSO system using a software defined ecosystem. The main issues are the compactness of the experimental design; the limitation of software-oriented signal generation; robustness; reliability; and the quality of service. As part of the system design, the thresholding method, a decision-making process via the feedback link, and a spatial diversity technique is adopted to carry out the adaptive switching. The adaptive switching is performed via a feedback link in which the atmospheric loss and scintillation index are calculated for fog and turbulence respectively. The initial design is implemented in SDR/ GNURadio for a real-time emulation of the proposed system to enhance the system flexibility of a traditional MIMO FSO system. A bit-by-bit comparison is performed with the GNURadio signal processing block and BERT for a real-time BER estimation. However, based on the initial results, the switching mechanism can only overcome the effect of turbulence at a certain level. A new design to mainly mitigate the varying fog conditions is proposed based on the SDR-based adaptive switching for a gigabit ethernet (GbE) MIMO FSO system and tested in a 5 m dedicated atmospheric chamber. The proposed system is implemented using off-the-shelf components such as a media converter, small form pluggable transceivers, optical switch, and power meter to estimate the channel state information. A new Schmitt trigger-based thresholding method is also introduced. The proposed software defined GbE MIMO FSO with an adaptive switching algorithm is fabricated, implemented, and investigated. The results are also compared with the real-time simulated data. Since the purpose of this Ph.D. is to explain and demonstrate the proof of concept for the proposed SDR-MIMO FSO system, the emphasis has been on the design, evaluation, and minimal performance requirements rather than maximizing the data rate. The outcome of the thesis will be a huge degree of flexibility and mitigation property MIMO FSO can offer with the help of SDR. It will be shown that the designed system has the capability to provide data transmission with 99.999% availability with a packet error rate and data rate of 7.2 ×10−2 and ~120 Mbps respectively, under extremely harsh fog conditions with visibility V of < 11 m

Interface air pour systèmes de navigation en bande S : étude détaillée des signaux OFDM

Positioning in urban or indoor environment is a hot topic, either due to regulations such as the E911 requiring US mobile telecommunication operators to be able to locate their subscribers in case of emergency, or due to the market development, with the extension of location - based services targeting the mass market concentrated in metropolitan areas. In urban or indoor areas, it is generally recognized that satellite - based positioning systems are not suitable (alone) to provide a continuous, reliable and accurate position to the user. Therefore, alternative positioning techniques may be useful to complement or replace satellite positioning in these environments. This PhD study ha s studied the possibility of using a mobile TV system based on the DVB - SH standard as system of opportunity for positioning. The advantage s of using a DVB - SH system for positioning are multiple. First, such system has a good availability in metropolitan areas, including indoor. Secondly, the emitters are synchronized and their density should be sufficient to track signals from several emitters simultaneously. This opens the possibility of using timing measurements from several emitters to find a position by trilateration . Also, the large bandwidth of the TV signal, required for the transmission of video content, should be beneficial for the accuracy of the timing measurements and for the robustness against multipath . Therefore, DVB - SH system seems to be an interesting candidate as system of opportunity for positioning. However, several challenges are to be solved for such a solution to be relevant. First, the signals propagate in the urban environment, which creates challenging conditions for positioning su ch as strong power fading, blockage of the desired line - of - sight signal or large echoes. Secondly, the DVB - SH standard uses an OFDM modulation, which has not been studied for positioning purpose. Therefore, techniques for fine tracking of the first receive d signal replica will have to be developed. Finally, a particularity of modern broadcast system is the use of a Single Frequency Network, in which all emitters send the same signal on the same carrier frequency. Therefore emitter identification in a Single Frequency will be another issue to be solved. This PhD study has proved the feasibility of positioning using DVB - SH signals. The main contributions of this work are the propositions of (1) an OFDM signal delay tracking method working in urban propagation channels, and (2) a modification to the network deployment permitting emitter identification and (3) a first assessment of the position accuracy using the proposed algorithms. These two methods have very low impact on the initial TV broadcasting service if the right set of signal parameters is chosen: no signal modification is required and the network deployment modification uses a feature already present in the DVB - SH standard. The positioning method was simulated using real urban propagation channel measurements. The obtained position has root mean square error of 4 0m. The main error contribution comes from tracking a non - line - of - sight signal. Further work would be required to deal with this issue, which would lower the position root mean square error to 7 m, which has been locally observed in the simulation for good tracking conditionsLe positionnement en environnement urbain est un domaine de recherche actif, de par la croissance des services grand public liées à la localisation, et à cause de réglementations émergentes liées aux situations d'urgence (E911). En environnement urbain ou à l'intérieur des bâtiments, il est communément admis que les systèmes de positionnement basés sur des satellites ne sont pas suffisants pour fournir une position précise, fiable et de manière continue. Des techniques de positionnement alternatives sont donc développées afin de remplacer ou compléter les systèmes de positionnement par satellite. Cette thèse étudie la possibilité de fournir un service de positionnement utilisant un futur système de diffusion de télévison vers les mobiles basé sur le standard DVB-SH. Le principal attrait de ce système pour du positionnement est sa bonne couverture en milieu urbain, ainsi que l'utilisation d'un réseau d'émetteurs synchronisés. Il est donc possible d'employer des mesures de temps d'arrivée des signaux afin de réaliser une triangulation pour calculer la position d'un récepteur. Afin de fournir ce service innovant, des techniques spécifiques d'estimation de pseudo-distance et d'identification d'émetteurs ont été développées dans le cadre de cette thèse. Le principal résultat de cette étude est d'avoir montré la faisabilité du positionnement utilisant un système DVB-SH, ne nécessitant que de légères modifications du système qui n'apportent aucune dégradation auservice de diffusion TV. De premières simulations ont montré une précision de positionnement autour de 40m en utilisant des mesures réalistes de canal de propagation urbain

Equalizer's Use Limitation for Complexity Reduction in a Green Radio Receiver

International audienceThis work is about reducing energy consumption in the receiver chain by limiting the use of the equalizer. It is to make the radio receiver aware of its environment and able to take decision to turn on or off the equalizer according to its necessity or not. When the equalizer is off , the computational complexity is reduced and the rate of reduction depends on the percentage of time during which this component is disabled. In order to achieve this scenario of adapting the use of the equalizer, we need to develop a decision making technique that provides to the receiver the capacities of awareness and adaptability to the state of its environment. For this, we improve a technique based on a statistical modeling of the environment by defining two metrics as channel quality indicators to evaluate the effect of the inter-symbol interferences and the channel fading. The statistical modeling technique allows to take into account the impact of the uncertainties of the estimated metrics on the decision making