This thesis considers the development of synchronization and signal processing techniques for digital communication receivers, which is greatly influenced by the digital revolution of electronic systems. Eventhough synchronization concepts are well studied and established in the literature, there is always a need for new algorithms depending on new system re- quirements and new trends in receiver architecture design. The new trend of using digital receivers where the sampling of the baseband signal is performed by a free running oscil- lator reduces the analog components by performing most of the functions digitally, which increases the flexibility, configurability, and integrability of the receiver. Also, this new de- sign approach contributes greatly to the software radio (SWR) concept which is the natural progression of digital radio receivers towards multimode, multistandard terminals where the radio functionalities are defined by software. The first part of this research work introduces a new technique for jointly estimating the symbol timing and carrier phase of digital receivers with non-synchronized sampling clock for both data-aided and non-data-aided systems using a block-based feed-forward architec- ture. This technique is a practical, rapidly converging, fully digitally implemented synchro- nization concept based on a low-order polynomial approximation of the likelihood functions using the Farrow-based interpolator. A review of maximum likelihood theory, which is the basis for coherent theory of synchronization, defines first the criteria and general framework for developing near-optimum synchronization schemes for digital communication systems. Then, efficient Farrow-based polynomial approximations of the typical likelihood func- tions are derived for systematic symbol timing, carrier phase and fine acquisition frequency synchronization algorithms. Another important receiver functionality closely related to synchronization is propagation delay estimation which is the basis of positioning technologies. Mobile phone positioning is becoming unavoidable after the mandate imposed by communications regulatory bodies on emergency call positioning. The second part of this thesis reviews and develops new tech- niques with subchip resolution capabilities for estimating closely-spaced multipath delays in spread-spectrum CDMA systems. Generally, multipath delays caused by distant reflectors have relatively large delay spread, with more than one chip interval between different paths, that can be resolved using conventional delay-locked-loop techniques. However, shorter excess path delays result in overlapped fading multipath components that introduce signifi- cant errors to the line-of-sight path delay and gain estimation. Overlapping fading multipath components are considered as one of the major sources of error that have strong impact on high precision mobile positioning solutions, as well as, on mobile applications of dedicated systems like the Global Positioning System (GPS). An overview of the most promising ge- olocation positioning techniques for wireless systems that are being standardized is first provided with a survey of fundamental concepts and major problems in positioning. Then, the characteristics of different channel models and conventional multipath delay estimation techniques based on maximum likelihood theory are also discussed. Two new techniques with subchip resolution capabilities are proposed for estimating closely-spaced overlapped multipath components. These techniques are intended to improve the accuracy of location estimates by estimating correctly the delay of the line-of-sight path.

Synchronization and Multipath Delay: Estimation Algorithms for Digital Receivers

Accurate measurements of the Earth’s rotation rate can be obtained by using high quality gyroscopes, such as ring laser gyros (RLG) included in tactical grade inertial measurement units. However, such devices are bulky and expensive. As the Micro-Electro-Mechanical System (MEMS) technology has evolved rapidly during the last years, accurate low-cost gyroscopes are now available. Are the new MEMS gyros accurate enough to detect and measure the Earth’s rate? In this paper, we describe a method and algorithm that can be used to answer this question. To test the developed method, we used a modern MEMS gyroscope with specified bias stability less than 2 degrees per hour. The bias stability indicates that it is possible to measure the Earth’s rate. However, in order to do this, all the external factors that affect the gyro bias need to be carefully taken into account. For example, in order to observe the bias the gyroscope needs to be rotated sequentially. In the paper, we present a sequence of rotations that aims to maximize the signal to noise ratio and minimize the time needed to detect the Earth’s rotation rate. Furthermore, the influence of gravity in the bias can be examined with another sequence of rotations. For both cases, we use an accurate stepper motor to switch between different orientations. With this set up, we have successfully determined the Earth’s rotation rate. In addition, by using a Kalman filter we were able to estimate the magnitude of the rate with accuracy better than one degree per hour. The Kalman filter approach was used to improve convergence time and to enable error estimation. The results show that if the factors that affect the bias of the sensor are minimized and correctly modeled, the Earth’s rotation rate can be detected and estimated with new MEMS gyroscopes. This level of accuracy makes MEMS gyroscopes suitable for application areas where traditionally more expensive gyro technologies have been exploited.

Measuring the Earth's Rotation Rate Using a Low-Cost MEMS Gyroscope

Conversion of signals is fundamental to the interfacing of embedded systems. Such signal conversions include (i) analog-to digital (A/D) in order to translate an analog form of the signal to its sampled and quantized form for digital signal processing, (ii) digital-to-analog (D/A) in order to translate the digital samples to a corresponding boxcar signal for further low-pass filtering and recovery of the original signal, and (iii) digital-to-digital (D/D) to achieve new desired properties of the data. This paper focuses on teaching the delta-sigma (ΔΣ) A/D conversion that is often omitted from an interfacing course because it appears to be a difficult topic to comprehend and to teach. This new approach links the new ΔΣ conversion to the other classes of A/D conversion techniques explicitly, thus unifying and simplifying the teaching of signal conversions.

https://ojs.library.queensu.ca/index.php/PCEEA/article/download/5931/5653

Teaching delta-sigma signal conversion in an interfacing course

Two different thermal imagers are tested to find out their system noise properties such as the noise variance, the distribution of the system noise, the effect of the scanning element in the image and the possible uneven distribution of the temperature caused by the optics or other phenomena. The obtained results can be used for comparing the properties of different thermal imagers and in the process of designing optimal image processing algorithms. The system noise estimation is done with three different methods under certain assumptions. These methods are; the use of the two-dimensional autocorrelation-function and the fitted polynomial, the use of suitable high frequencies of the two-dimensional spectrum and the use of stable image series. The first two methods are closely related and can give the noise variance only. The shape of the system noise histogram can be approximated somewhat from the image series under suitable conditions. The variability between the even and the odd lines in image and other, possibly stable phenomena, are also analysed. These methods are first tested with simulated data sets and comparison between the methods is performed. Also real image series from two different cameras are used and conclusions regarding their performance are drawn.

Analysis of system noise in thermal imagers

Time Domain Reflectometry (TDR) diagnostic features of Ethernet physical transceiver chips are explored for evaluating their applicability for construction of an UTP-cable length-measurement and diagnostic instrument. The instrument is mainly intended as an aid during installation and for post-installation documentation. Dithering method is applied for length measurement to increase the resolution, based on physical patch-cable switchover and/or discrete component cable emulation and/or programmable delay-line delay-dithering. A practical experiment with length dithering using cable patches confirms the feasibility of the idea.

UTP cable length measuring instrument feturing TI's interface circuits

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and criticism in the Auditorium S1 at Tampere University of Technology, on the 7 th of May 2001, at 12 o'clock noon.

Olli Aumala

Papers

Dithering in Analogue-to-Digital Conversion