Multiuser Detection Assisted Time- and Frequency-Domain Spread Multicarrier Code-Division Multiple-Access

In this contribution, we study a reduced-complexity multiuser detection aided multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) scheme, which employs both time (T)-domain and frequency (F)-domain spreading. We investigate the achievable detection performance in the context of synchronous TF-domain spread MC DS-CDMA when communicating over an additive white Gaussian noise (AWGN) channel. Five detection schemes are investigated, which include the single-user correlation based detector, the joint TF-domain decorrelating multiuser detector (MUD), the joint TF-domain MMSEMUD, the separate TF-domain decorrelating/MMSE MUD, and the separate TF-domain MMSE/decorrelating MUD. Our simulation results show that the separate TF-domain MUD schemes are capable of achieving a similar bit error rate (BER) performance to that of the significantly more complex joint TF-domain MUD schemes. Index Terms—Code-division multiple-access (CDMA), decorrelating, frequency-domain spreading, joint detection, minimum mean square error (MMSE), multicarrier (MC), multiuser detection, separate detection, time-domain spreading

Adaptive Filters Revisited - RFI Mitigation in pulsar observations

Pulsar detection and timing experiments are applications where adaptive filters seem eminently suitable tools for radio-frequency-interference (RFI) mitigation. We describe a novel variant which works well in field trials of pulsar observations centred on an observing frequency of 675 MHz, a bandwidth of 64 MHz and with 2-bit sampling. Adaptive filters have generally received bad press for RFI mitigation in radio astronomical observations with their most serious drawback being a spectral echo of the RFI embedded in the filtered signals. Pulsar observations are intrinsically less sensitive to this as they operate in the (pulsar period) time domain. The field trials have allowed us to identify those issues which limit the effectiveness of the adaptive filter. We conclude that adaptive filters can significantly improve pulsar observations in the presence of RFI.Comment: Accepted for publication in Radio Scienc

A mixed-signal integrated circuit for FM-DCSK modulation

This paper presents a mixed-signal application-specific integrated circuit (ASIC) for a frequency-modulated differential chaos shift keying (FM-DCSK) communication system. The chip is conceived to serve as an experimental platform for the evaluation of the FM-DCSK modulation scheme, and includes several programming features toward this goal. The operation of the ASIC is herein illustrated for a data rate of 500 kb/s and a transmission bandwidth in the range of 17 MHz. Using signals acquired from the test platform, bit error rate (BER) estimations of the overall FM-DCSK communication link have been obtained assuming wireless transmission at the 2.4-GHz ISM band. Under all tested propagation conditions, including multipath effects, the system obtains a BER = 10-3 for Eb/No lower than 28 dB.Ministerio de Ciencia y Tecnología TIC2003-0235

The theory of bootstrapped algorithms and their applications to cross polarization interference cancelation

Dual-polarized transmission has become an important method for frequency re-use, particularly in satellite and microwave radio communication. Nevertheless, cross-polarization interference, which is inherent to this method, may cause degradation in system performance. Different canceler [sic] structures have been proposed to mitigate the effect of cross-polarization. Among these are the diagonalizer, the least mean square (LMS) canceler [sic] and the bootstrapped cancelers [sic]. Bootstrapped canceler [sic] schemes have been proposed and implemented in different applications, such as satellites, tactical communications, and quadrature amplitude madulation [sic] (QAM) dual polarized microwave radio. Nevertheless, no attempt was made in the past to quantify the probability of error of dual polarized transmission systems when such cancelers [sic] are used, nor were important issues such as stability and the dynamic behavior of algorithms controlling such cancelers [sic] studied. In this thesis, the error probability performance of dual polarized QAM transmission, for nondispersive fading channels and different configurations of bootstrapped cross-pol cancelers [sic], is derived and compared to the performance for other cancelers [sic]. Stability analyses of different canceler [sic] configurations are investigated, and an application of orthogonal perturbation sequences in controlling the bootstrapped cancelers [sic] is considered. It is shown that the error probability performance of the bootstrapped canceler [sic] is always better than that of other cancellers, such as the LMS canceler [sic]. It is also shown that, when the bootstrapped canceler [sic] is designed to meet certain conditions, it is asymptotically stable in converging to the calculated optimal points. Controlling the cancelers [sic] with adaptive algorithms using orthogonal dithering sequences is shown to be satisfactory; the canceler [sic] converges in the mean to the optimal condition. The results indicate that bootstrapped algorithms are faster than other algorithms. Considering the fact such cancelers [sic] do not require decision feedback for their operation, we can conclude that bootstrapped algorithms are not only advantageous for cross polarization cancelation [sic], but perhaps suitable for other adaptive signal processing applications, as well

Realization Limits of Impulse-Radio UWB Indoor Localization Systems

In this work, the realization limits of an impulse-based Ultra-Wideband (UWB) localization system for indoor applications have been thoroughly investigated and verified by measurements. The analysis spans from the position calculation algorithms, through hardware realization and modeling, up to the localization experiments conducted in realistic scenarios. The main focus was put on identification and characterization of limiting factors as well as developing methods to overcome them

Оптическая корреляционная спектроскопия для дистанционного обнаружения загрязнений

Досягнення в галузі спектрально-кореляційної обробки сигналів створюють перспективу підвищення чутливості виявлення сигналів, що мають складний спектр, таких, наприклад, як сигнали раманівського лідара, що використовує комбінаційне розсіяння. При оптичній спектрально-кореляційній обробці результуючий сигнал являє собою міру подібності не окремих ліній спектру, а комбінації багатьох спектральних ліній. Це дає можливість подолати проблему виявлення сигналів від цілей типу хімічних речовин, що мають малий переріз розсіяння, дозволяє використовувати раманівський лідар для багатьох практичних застосувань, таких, наприклад, як виявлення слідів наркотичних речовин в ручній поклажі або в багажі. В роботі розглянуто принцип дії, проаналізовано результати експериментальних досліджень та відмічені перспективи побудови оптичного спектрально-кореляційного раманівського лідара для дистанційного виявлення типових хімічних речовин на фоні матеріалів промислового та природного походження. При цьому оптичний сигнал обробляється до етапу фотодетектування.Recent advances in spectral correlation signal processing can enhance the detection sensitivity of spectrally complex signals, such as those generated by a Raman lidar. By means of optical correlation, the resulting optical signal is a direct measure of the similarity of the received unknown and known reference spectra, being responsive not to the intensity of individual spectral lines, but to the combination of many spectral lines thus creating an increased sensitivity. It overcomes the small cross-sections of target chemicals and makes Raman lidar practical for many important applications. In particular, the short-range, stand-off detection of explosive residue or narcotics on the exterior of packages, luggage and vehicles now appears to be possible. This paper presents the theory of operation, the results of initial proof of principle experiments and the projected performance of an optical correlation spectroscopy Raman lidar when used to remotely detect typical chemical agents in the presence of common industrial materials and natural backgrounds which could interfere with the detection process. These experiments also mark the first known instance where a received optical signal is analyzed and processed prior to photodetection.Достижения в спектрально-корреляционной обработке сигналов дают шанс повышению чувствительности обнаружения сигналов со сложным спектром, таких, например, как сигналы рамановских лидаров, основанных на комбинационном рассеянии. При оптической спектрально-корреляционной обработке результирующий сигнал представляет собой меру подобия неизвестного и референтного спектров, то есть меру подобия не отдельных линий спектра, а комбинации множества спектральных линий. Это дает возможность преодолеть проблему обнаружения сигналов от целей типа химических веществ, имеющих малое сечение рассеяния, и обеспечивает использование рамановского лидара для многих практических применений, таких, например, как обнаружение следов наркотических веществ на ручной клади или в багаже. В работе рассмотрен принцип действия, проанализированы результаты экспериментальных исследований и отмечены перспективы построения оптического спектрально-корреляционного рамановского лидара для дистанционного обнаружения типичных химических веществ на фоне материалов промышленного и естественного происхождения. При этом оптический сигнал обрабатывается до этапа фотодетектирования

Development of a set of optimum synchronization codes for a unique decoder mechanization

Synchronization requirements are specified for and a unique decoder mechanization is associated with a particular communication system. Optimum synchronization codes, defined as codes which are the least susceptible to false synchronization indications, are sought. Existing sets of optimum codes are investigated for applicability. This Thesis shows how these sets were developed from selected criteria and demonstrates why their theoretical nature produces unsatisfactory results in the present application wherein all parameters are known. A computer program was written to examine code pattern performance in the specified decoder under actual operating conditions. From an analysis of the results, a recommended set of optimum synchronization codes was developed --Abstract, page ii

Fisher Hartwig determinants, conformal field theory and universality in generalised XX models

We discuss certain quadratic models of spinless fermions on a 1D lattice, and their corresponding spin chains. These were studied by Keating and Mezzadri in the context of their relation to the Haar measures of the classical compact groups. We show how these models correspond to translation invariant models on an infinite or semi-infinite chain, which in the simplest case reduce to the familiar XX model. We give physical context to mathematical results for the entanglement entropy, and calculate the spin-spin correlation functions using the Fisher-Hartwig conjecture. These calculations rigorously demonstrate universality in classes of these models. We show that these are in agreement with field theoretic and renormalization group arguments that we provide