Abstract In this thesis integrated receiver channel techniques and circuit implementations for a pulsed time-of-flight (TOF) laser rangefinder are developed with the aim to achieve centimetre level accuracy within the dynamic range of > 1:10 000 of the input pulse amplitudes. The receiver channel converts the input current pulses produced by the photo detector to voltage pulses and produces a logic-level timing pulse for the time interval measurement. In addition to the minimization of noise, the main design challenge is the minimization of the timing walk error resulting from the varying amplitude of the received optical echo. In automotive perception laser radar application, which was the target application of this work, the input amplitude of the received echo varies in a range of 1:10 000 or even more due to changes in the measured distance and reflectivity and orientation of the target. Two receiver channel and timing discriminator architectures were developed and realized as integrated circuits in 0.35 μm BiCMOS technology, and finally verified by measurements. One of the receiver channels is based on the detection of the zero-crossing of the timing pulse produced with a unipolar-to-bipolar conversion at the input of the receiver. It achieved a timing walk error of ±8 mm in a dynamic range of 1:3000. Another receiver channel is based on the leading edge timing discrimination, in which the timing walk error is being compensated for in time domain by measuring the width of the timing pulse simultaneously with its leading edge time position. An important feature of this technique, suggested in this thesis, is that it is operative also beyond the linear range of the receiver channel, which is typically limited to < 1:100. The receiver channel with leading edge detection and pulse width compensation achieved a compensated walk error of ± 2–3 mm in a dynamic range of ~ 1:100 000. The bandwidth and input referred current noise of the channel were 230 MHz and <100 nArms, respectively. The single-shot timing precision was 120 ps (20 mm in distance) at the SNR of 10. The feasibility of the receiver electronics was verified by two laser radar prototypes. An accuracy of < ± 5 mm was measured in a measurement range from 1 to 55 m, which corresponds to the receiver dynamic range of > 1:10 000 taking into consideration the varying reflectivity of the target materials used. / Tiivistelmä Väitöskirjatyössä on suunniteltu integroituja vastaanotintekniikoita ja –piirejä valopulssin kulkuaikamittaustekniikkaan perustuvaan laseretäisyysmittaukseen. Tavoitteena on ollut saavuttaa senttimetriluokan tarkkuus laajalla tulopulssin amplitudin dynaamisella alueella > 1:10 000. Vastaanotinkanava muuntaa valoilmaisimelta saadun tulovirtapulssin jännitepulssiksi ja muodostaa siitä logiikkatasoisen ajoituspulssin aikavälimittauspiirille. Kohinan minimoimisen lisäksi toinen suuri suunnitteluhaaste on minimoida ajoitusvirhe, jota syntyy vastaanotetun optisen tulosignaalin amplitudin vaihdellessa laajalla alueella. Työssä kehitettyjen vastaanotinkanavien yksi sovelluskohdetavoitteista on ollut autoteollisuudessa käytettävät etäisyysmittarit. Näissä tulosignaalin taso vaihtelee erittäin laajalla dynaamisella alueella, joka voi olla > 1:10 000, johtuen laajasta etäisyysmittausalueesta sekä kohteen heijastavuuden ja orientaation vaihteluista. Väitöskirjatyössä kehitettiin ja valmistettiin kaksi vastaanotin- ja ajoitusilmaisurakennetta. Piirit valmistettiin 0,35 μm BiCMOS- teknologialla, ja niiden toiminta varmistettiin mittauksilla. Ensimmäinen vastaanotinkanava-arkkitehtuuri perustuu kanavan tulossa tapahtuvaan unipolaari-bipolaari muutokseen ja sen jälkeiseen nollaylityskohdan ilmaisuun. Piirillä saavutettiin ±8 mm ajoitusvirhe 1:3000 dynaamisella alueella. Toinen vastaanotinkanava-arkkitehtuuri perustuu etureunanilmaisuun, jossa ajoitusvirhe korjataan aikatasossa mittaamalla samanaikaisesti ajoituspulssin paikka ja leveys. Ajoitusvirheenkorjausmenetelmän tärkeä ominaisuus on, että se toimii laajemmalla kuin vastaanottimen lineaarisella alueella (< 1:100). Etureunanilmaisuun ja pulssinleveyden korjaukseen perustuvalla vastaanotinkanavalla saavutettiin korjattu ajoitusvirhe ± 2–3 mm 1:100 000 dynaamisella alueella. Kanavan kaistanleveys oli 230 MHz ja tulon redusoitu virtakohina < 100 nArms. Signaalikohinasuhteella 10 laseretäisyysmittauksen kertamittaustarkkuudeksi mitattiin 120 ps (20 mm etäisyydessä). Väitöskirjatyön yhteydessä valmistettiin lisäksi kaksi prototyyppilasertutkaa, joilla varmistettiin vastaanotinelektroniikan toiminta laajalla > 1:10 000 dynaamisella tulopulssin amplitudin vaihtelualueella. Lasertutkan ajoitusvirheeksi mitattiin < ± 5 mm 1–55 m:n mittausalueella.

Abstract The main aim of this work was to design CMOS receiver channels for the integrated receiver chip of a pulsed time-of-flight (TOF) laser rangefinder. The chip includes both the receiver channel and the time-to-digital converter (TDC) in a single die, thus increasing the level of integration of the system, with the corresponding advantages of a cheaper price and lower power consumption, for example. Receiver channels with both linear and leading edge timing discriminator schemes were investigated. In general the receiver channel consists of a preamplifier, a postamplifier and a timing comparator. Since a large systematic timing error may occur due to high variation in the amplitude of the received echo, a leading edge timing discriminator scheme with time domain walk error compensation is proposed here, making use of the TDC already available in the chip to measure the slew rate of the pulse and using that information to evaluate the timing error. This compensation scheme benefits from the fact that compensation can be continued even though the signal is clipped in the amplitude domain, because the slew rate continues to increase even then. The receiver channel with leading edge detection and time domain walk error compensation achieved a compensated timing walk error of ±4.5 mm within a dynamic range of more than 1:10000. The standard deviation in single shot precision was less than 25 mm with an SNR of more than 20. The usability of the receiver channel in pulsed TOF laser rangefinders was verified by making actual time-of-flight measurements on a calibrated measurement track. The linearity of the receiver chip was better than ±5 mm in a measurement range from 3 m to 21 m, with the dynamic range of the receiver channel reaching more than 1:2000. An integrated CMOS laser diode pulser was also demonstrated to prove its functionality for generating ampere-scale peak current pulses through a low ohmic load and a laser diode. The CMOS pulser achieved a peak current pulse with the amplitude of ~1 A, an optical pulse width of ~2.5 ns and a rise time of ~1 ns with a 5 V power supply. / Tiivistelmä Työn ensisijaisena tavoitteena oli suunnitella CMOS-vastaanottimia valopulssin kulkuajan mittaukseen perustuvan lasertutkan integroituun vastaanotinpiiriin. Vastaanotinpiiri sisältää sekä vastaanotinkanavan että aika-digitaalimuuntimen yhdellä integroidulla sirulla. Tällöin systeemin integrointiastetta saadaan kasvatettua, mikä merkitsee esimerkiksi halvempaa hintaa ja pienempää tehon kulutusta. Työssä on tutkittu vastaanotinkanavia, jotka käyttävät joko lineaariseen ilmaisuun tai etureunailmaisuun perustuvaa ajoitusilmaisutekniikkaa. Yleisesti vastaanotinkanava sisältää esivahvistimen, jälkivahvistimen ja ajoituskomparaattorin. Vastaanotetun signaalin tason voimakas vaihtelu saattaa aiheuttaa suuren systemaattisen virheen etureunailmaisuun perustuvassa ajoitusilmaisussa. Tässä työssä on esitetty etureunailmaisua käyttävä ajoitusilmaisin, jossa syntyvää ajoitusvirhettä voidaan korjata mittaamalla pulssin nousunopeutta aika-digitaalimuuntimella, joka on integroitu samalle sirulle. Aikatasossa tapahtuvan virheenkorjauksen etuna on mahdollisuus jatkaa virheenkorjausta amplituditasossa tapahtuvan signaalin leikkautumisen jälkeenkin, koska signaalin nousunopeus kasvaa leikkaantumisesta huolimatta. Etureunailmaisua käyttävällä vastaanotinkanavalla, jossa ajoitusvirhettä korjattiin pulssin nousunopeutta mittaamalla, saavutettiin ±4,5 mm ajoitusvirhe 1:10000 dynaamisella alueella. Kertamittaustarkkuuden keskihajonta oli vähemmän kuin 25 mm, kun signaalikohinasuhde oli enemmän kuin 20. Vastaanotinkanavan käytettävyys osana lasertutkaa todettiin tekemällä tutkamittauksia kalibroidulla mittaradalla. Mittauksissa saavutettu lineaarisuus oli ±5 mm mittausalueen vaihdellessa 3 metristä 21 metriin ja signaalin dynamiikan ollessa enemmän kuin 1:2000. Lisäksi työssä esitellään integroitu CMOS-pulssitin, joka pystyy tuottamaan ampeeri-luokan virtapulsseja laserdiodiin. CMOS-pulssittimella voitiin tuottaa 5 V käyttöjännitteellä ~1 A virtapulsseja optisen pulssin leveyden ja nousuajan ollessa ~2,5 ns ja ~1 ns.

Abstract Iterative receiver techniques, multiple-input – multiple-output (MIMO) processing, and orthogonal frequency division multiplexing (OFDM) are amongst the key physical layer technologies when aiming at higher spectral efficiency for a wireless communication system. Special focus is put on iterative detection, decoding, and channel estimation for a MIMO-OFDM system. After designing separately efficient algorithms for the detection, channel decoding, and channel estimation, the objective is to optimize them to work together through optimizing the activation schedules for soft-in soft-out (SfISfO) components. A list parallel interference cancellation (PIC) detector is derived to approximate an a posteriori probability (APP) algorithm with reduced complexity and minimal loss of performance. It is shown that the list PIC detector with good initialization outperforms the K-best list sphere detector (LSD) in the case of small list sizes, whereas the complexities of the algorithms are of the same order. The convergence of the iterative detection and decoding is improved by using a priori information to also recalculate the candidate list, aside from the log-likelihood ratios (LLRs) of the coded bits. Unlike in pilot based channel estimation, the least-squares (LS) channel estimator based on symbol decisions requires a matrix inversion in MIMO-OFDM. The frequency domain (FD) space-alternating generalized expectation-maximization (SAGE) channel estimator calculates the LS estimate iteratively, avoiding the matrix inversion with constant envelope modulation. The performance and computational complexity of the FD-SAGE channel estimator are compared to those of pilot based LS channel estimation with minimum mean square error (MMSE) post-processing exploiting the time correlation of the channel. A time domain (TD) SAGE channel estimator is derived to avoid the matrix inversion in channel estimation based on symbol decisions for MIMO-OFDM systems also with non-constant envelope modulation. An obvious problem, with more than two blocks in an iterative receiver, is to find the optimal activation schedule of the different blocks. It is proposed to use extrinsic information transfer (EXIT) charts to characterize the behavior of the receiver blocks and to find out the optimal activation schedule for them. A semi-analytical expression of the EXIT function is derived for the LS channel estimator. An algorithm is proposed to generate the EXIT function of the APP algorithm as a function of the channel estimate’s mutual information (MI). Surface fitting is used to get closed form expressions for the EXIT functions of the APP algorithm and the channel decoder. Trellis search algorithms are shown to find the convergence with the lowest possible complexity using the EXIT functions. With the proposed concept, the activation scheduling can be adapted to prevailing channel circumstances and unnecessary iterations will be avoided.

This research project aimed to develop a condition monitoring system for the final production quality of pharmaceutical tablets and detection capping and lamination during powder compression process using the acoustic emission (AE) method. Pharmaceutical tablet manufacturers obliged by regulatory bodies to test the tablet's physical properties such as hardness, dissolution and disintegration before the tablets are released to the market. Most of the existing methods and techniques for testing and monitoring these tablet's properties are performed at the tablet post-compression stage. Furthermore, these tests are destructive in nature. Early experimental investigations revealed that the AE energy that is generated during powder compression is directly proportional to the peak force that is required to crush the tablet, i. e. crushing strength. Further laboratory and industrial experimental investigation have been conducted to study the relationship between the AE signals and the compression conditions. Traditional AE signal features such as energy, count, peak amplitude, average signal level, event duration and rise time were recorded. AE data analysis with the aid of advanced classification algorithm, fuzzy C-mean clustering showed that the AE energy is a very useful parameter in tablet condition monitoring. It was found that the AE energy that is generated during powder compression is sensitive to the process and is directly proportional to the compression speed, particle size, homogeneity of mixture and the amount of material present. Also this AE signal is dependent upon the type of material used as the tablet filler. Acoustic emission has been shown to be a useful technique for characterising some of the complex physical changes which occur during tabletting. Capping and lamination are serious problems that are encountered during tabletting. A capped or laminated tablet is one which no longer retains its mechanical integrity and exhibit low strength characteristics. Capping and lamination can be caused by a number of factors such as excessive pressure, insufficient binder in the granules and poor material flowabilities. However, capping and lamination can also occur randomly and they are also dependent upon the material used in tabletting. It was possible to identify a capped or laminated tablet by monitoring the AE energy level during continuous on-line monitoring of tabletting. Capped tablets indicated by low level of AE energy. The proposed condition monitoring system aimed to set the AE energy threshold that could discriminate between capped and non-capped tablets. This was based upon statistical distributions of the AE energy values for both the capped and non-capped tablets. The system aims to minimise the rate of false alarms (indication of capping when in reality capping has not occurred) and the rate of missed detection (an indication of non capping, when in reality capping has occurred). A novel approach that employs both the AE method and the receiver operating characteristic (ROC) curve was proposed for the on-line detection of capping and lamination during tabletting. The proposed system employs AE energy as the discriminating parameter to detect between capped and non-capped tablets. The ROC curve was constructed from the area under the two distributions of both capped and non-capped tablet. This curve shows a trade-off between the probabilities of true detection rate and false alarm rate for capped and non-capped tablet. A two-graph receiver operating characteristic (ROC) curve was presented as a modification of the original ROC curve to enable an operator to directly select the desired energy threshold for tablet monitoring. This plot shows the ROC co-ordinate as a function of the threshold value over the entire threshold (AE energy) range for all test outcomes. An alternative way of deciding a threshold based on the slope of the ROC curve was also developed. The slope of the ROC curve represents the optimal operating point on the curve. It depends upon the penalties cost of capping and the prevalence of capping. Sets of guidelines have been outlined for decision making i.e. threshold setting. These guidelines take into account both the prevalence of capping in manufacturing and the cost associated with various outcomes of tablet formation. The proposed condition monitoring system also relates AE monitoring to non-AE measurement as it enable an operator predicting tablet hardness and disintegration form the AE energy, a relationship which was established in this research.

Radar warning systems are life saving equipment in modern fighter aircraft. It is therefore vital that the system can tell the difference between a threat genuine frequency) and a false signal (spurious frequency). This thesis presents a model aimed at predicting the frequencies and other parameters in the RF converter of the radar warning system. The components of the RF converter have been studied, measured, and modelled. The modelling tool has been the Simulink toolbox for Matlab. Extreme accuracy has been sacrificed in order to make the model easy to use for the working engineer. Instead, this model presents a rough estimate of some of the most important properties of the radar warning system with just a few data sheet figures as input. The simulation results are satisfactory as a whole. Simulink is the limiting factor in the implementation of the model. Significantly improved results can probably be obtained by working in another software environment.

Le dépistage du cancer colorectal par IRM à des stades précoces exige l'obtention des images avec une résolution spatiale suffisante. L'acquisition d'images de résolution spatiale submillimétrique peut être réalisée avec des capteurs endoluminaux placés au plus proche de la zone à explorer. Les développements de ce type de capteur ont été compromis par des aspects liés à la sécurité du patient en raison des échauffements localisés qui ont lieu avec une liaison galvanique reliant le capteur au système d'imagerie. Pour pallier ces problèmes de sécurité, nous proposons de développer un capteur magnétique déporté grâce à une transmission par fibre optique. Deux points importants doivent être traités pour réaliser ce capteur : le découplage actif de la boucle endoluminale et le transport optique de l'information RMN. Un système de découplage actif optique a été réalisé puis caractérisé sur banc et en IRM (in-vitro). Les résultats montrent que le découplage optique est efficace et ses performances sont comparables avec un système de découplage conventionnel. Le transport optique du signal RMN a été réalisé en couplant un cristal Electro-Optique à la boucle résonnante endoluminale. Ce cristal permet une modulation de l'état de polarisation du faisceau optique. Les résultats de caractérisation du capteur en termes de linéarité, dynamique et sensibilité sur un banc optique montrent sa faisabilité / Detection of colorectal cancer by MRI at its early stages requires images with high spatial resolution. Submillimetric spatial resolution images can be achieved with MRI endoluminal receiver coil placed as close as possible to the region of interest. However using this type of receiver is always limited by security issues related to patient safety due to localized heating which appear with a galvanic connection between the receiver coil and the imaging system. To address this problem, we propose to develop an non-invasive optically deported characterization of NMR Radiofrequency signal. Two important points need to be addressed to achieve this receiver: active endoluminal loop decoupling and optical signal transport. A system of active optical decoupling has been achieved and characterized on bench and in MRI (in-vitro). The results show that the optical decoupling is efficient and its performance is comparable to a conventional decoupling system. The optical transmission of the NMR signal has been achieved by associating a passive Electro-Optical crystal transducer to the resonant receiver coil. This crystal allows a modulation of the polarization state of the laser probe beam. The results of sensor’s characterization on an optical bench concerning its linearity, its sensitivity and its dynamic, show the feasibility

Maintaining or even improving image quality while lowering patient dose is always the desire in clinical computed tomography (CT) imaging. Iterative reconstruction (IR) algorithms have been designed to allow for a reduced dose while maintaining or even improving an image. However, we have previously shown that the dose-saving capabilities allowed with IR are different for different clinical tasks. The channelized scanning linear observer (CSLO) was applied to study clinical tasks that combine detection and estimation when assessing CT image data. The purpose of this work is to illustrate the importance of task complexity when assessing dose savings and to move toward more realistic tasks when performing these types of studies. Human-observer validation of these methods will take place in a future publication. Low-contrast objects embedded in body-size phantoms were imaged multiple times and reconstructed by filtered back projection (FBP) and an IR algorithm. The task was to detect, localize, and estimate the size and contrast of low-contrast objects in the phantom. Independent signal-present and signal-absent regions of interest cropped from images were channelized by the dense-difference of Gauss channels for CSLO training and testing. Estimation receiver operating characteristic (EROC) curves and the areas under EROC curves (EAUC) were calculated by CSLO as the figure of merit. The one-shot method was used to compute the variance of the EAUC values. Results suggest that the IR algorithm studied in this work could efficiently reduce the dose by similar to 50% while maintaining an image quality comparable to conventional FBP reconstruction warranting further investigation using real patient data. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Este informe técnico propone el diseño de un bloque llamado Amplificador Limitador que se encuentra en los equipos que trabajan con fibra óptica o con altas tasas de transmision de datos y que estan integrados en una pastilla de silicio. El objetivo principal es aumentar el ancho de banda de un Amplificador Limitador mediante la aplicación de la técnica Inductive Peaking para lograr velocidades que corresponden a una portadora óptica OC-192 equivalente a 10 Gbps bajo el estándar SONET. Haciendo uso de tecnología CMOS con transistores de 130 nm de ancho de canal. A su vez se propone disminuir el consumo de potencia y el área ocupada en la pastilla de Silicio utilizando inductores activos y la eliminación de los capacitores de desacople DC entre etapas. Los resultados finales Post Layout demuestran que es posible extender el ancho de banda con las técnicas mencionadas anteriormente, reducir el consumo total y el área ocupada en la pastilla de Silicio y cumplir con las especificaciones técnicas requeridas. This technical report proposes the design of a block called Limiting Amplifier which is found in equipment that works with optical fiber or with high rates of data transmission and that are integrated in a silicon wafer. The main objective is to increase the bandwidth of a limiter amplifier by applying the Inductive Peaking technique to achieve speeds that correspond to an OC-192 optical carrier equivalent to 10 Gbps under the SONET standard, making use of CMOS technology with 130 nm channel width transistors. At the same time, it is proposed to reduce the power consumption and the area occupied in the chip using active inductors and the elimination of DC decoupling capacitors between stages. The final results of Post Layout show that it is possible to extend the bandwidth with the techniques mentioned above, reducing the total consumption and the area occupied in the silicon pellet and accomplishing with the required technical specifications.

Abstract This Thesis examines low complexity receiver structures for impulse-radio (IR) ultra-wideband (UWB) systems to be used in wireless sensor network applications. Such applications require radio communication solutions characterized by low cost, low complexity hardware and low power consumption to provide very long battery life. Analysis of several auto-correlation receiver (AcR) structures is performed in the presence of additive white Gaussian noise to identify receiver structures that offer a good compromise between implementation complexity and data communication performance. The classes of receiver that demonstrate the best complexity/performance trade-off are shown to be the AcR utilising transmitted-reference with binary pulse amplitude modulation signaling, and the energy detector (ED) utilising binary pulse position modulation. The analysis of these two schemes is extended to consider multipath fading channels. Numerically integrable bit error rate probability (BEP) expressions are derived in order to evaluate the receivers' performance in the presence of fading distributions characterized by closed form characteristic functions. Simulations utilising widely accepted UWB channel models are then used to evaluate the BEP in different indoor environments. Since UWB systems share frequency spectrum with many narrowband (NB) systems, and need to coexist with other UWB systems, the performance of low complexity receivers can be seriously affected by interference. In the presence of NB interference, two cases have been considered: 1) single NB interference, where the interfering node is located at a fixed distance from the receiver, and 2) multiple NB interference, where the interfering nodes are scattered according to a spatial Poisson process. When considering UWB interference, the case of multiple sources of interference has been considered. For both the multiple NB and the multiple UWB interference cases, the model derived considers several interference parameters, which can be integrated into BEP formulations for quick performance evaluations. The framework is sufficiently simple to allow tractable analysis and can serve as a guideline for the design of heterogeneous networks where coexistence between UWB systems and NB systems is of importance. The very large bandwidth of UWB signals offers an unprecedented possibility for accurate ranging operations. Signal leading-edge estimation algorithms based on average maximum likelihood estimators are derived considering different multipath channel fading distributions. Suboptimal solutions are proposed and investigated in order to support ranging capabilities in low complexity receiver structures. The ability to identify line-of-sight and non-line-of-sight conditions with the ED-based receiver is also addressed. An example of an IR-UWB low complexity transceiver based on ED for sensor network applications is proposed in this Thesis. Ad-hoc solutions for pulse transmission, synchronization and data detection are developed.

Abstract The present dissertation deals with initial synchronization in Code Division Multiple Access (CDMA) networks. In the first part of this thesis an extensive and up-to-date review of the literature is presented. The basic theory of code acquisition as well as different techniques and structures used to achieve the initial synchronization are discussed. A survey of the most common theoretical approaches allowing performance characterization of the acquisition process is included. The effect of noise, interference, carrier Doppler, multipath propagation, fading and data modulation on system performance are reviewed. Advanced code acquisition approaches exploiting interference suppression techniques and multiple antennas are also described. A summary of the results obtained within the area of code acquisition in CDMA networks is also embraced by this thesis. The distinctive assumption is to consider the actual variable effect of multiple access interference on the delay-domain search process, instead of the usual constant approximation. Three directions of research are followed. Models for code acquisition in quasi-synchronous and asynchronous CDMA networks are first developed and analysed. Closed-form expressions for the main performance figures of the acquisition process are derived and analysed. Results show a strong dependence of the mean acquisition time with the nature of the multiple access interference. In the second area of research the previous results are extended to consider code acquisition with a multi-branch (Rake) receiver in a multipath channel. A generic model for Rake receiver code acquisition is considered and developed, in which the synchronization takes place in two phases. The first detected path is allocated to the first finger during the initial synchronization phase, whereas the remaining fingers are successively allocated to other available paths in the postinitial synchronization phase. Performance measures for this acquisition process are also derived and analysed. Finally, based on the use of an antenna array and beamforming techniques, conventional delay-domain code acquisition is extended to the angular domain, resulting in a two-dimensional (delay-angle) search. This technique is found to be feasible, outperforming the synchronization approach exploiting a single-antenna. It is found that there exists an optimal number of antennas that minimises the mean acquisition time. Two-dimensional code acquisition is studied in a variety of scenarios, including single and multipath channels, fixed and fading channels, and with uniform and nonuniform spatial distributions of interference. Different two-dimensional search strategies are studied. A clear dependence of acquisition performance with the search strategy and the particular distribution of interference is pointed out. The performance of two-dimensional code acquisition is found to be seriously deteriorated by the presence of spatially nonuniform interference. Schemes based on search strategy and adaptive detector structures are considered and analysed to combat the performance degradation in the mentioned case. A comparative study of code acquisition exploiting multiple antennas is also presented.