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1
Content available remote The Q-Best Spreading Sequences for Low-Complexity DS-CDMA IEEE 802.15 UltraWideBand Systems in Dense Multipath Channels
Gulfam S. M., Siddiqui A. M., Khaqan A., Ahmed A., Yasin A., Jamil M., Riaz S., Qureshi M., Abbasi S. N., Riaz R. A.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 6
88--92
EN
This paper presents an analysis for the selection of Q-Best spreading sequences of the synchronous Direct Sequence Code Division Multiple Access (DS-CDMA) UltraWideBand (UWB) system on the uplink using joint detection. It is shown that the time-domain cross correlation function between the spreading sequences is a prime interference measure for the synchronous DS-CDMA UWB users. Therefore auto and cross correlation funcitons of the spreading sequences, along with UWB IEEE 802.15 channel characteristics are amalgamated to obtain minimum Bit Error Rate (BER), using low complexity correlation joint detection scheme. Some well known classes of length Q sequences, such as m, Gold, Walsh and Random sequences are evaluated with respect to the aforementioned basic criteria. Explicitly, the performance of each sequence with length Q is shown in high Inter-Symbol Interference (ISI) and Multiple Access Interference (MAI) environment produced by dense multipath and multiuser.
PL
W artykule przedstawiono analizę metod rozpraszania widma z wykorzystaniem detekcji połączeń, dla metody dostępowej DS-CDMA w połączeniu z satelitą w systemie UltraWideBand. Wykazano, że wyznaczenie funkcji korelacji przejscia dziedziny czasu między sekwencjami rozpraszania powinno stanowić główny czynnik pomiarowy dla użytkowników systemu DS-CDMA UWB. W badaniach wykorzystano najlepiej znane klasy o długości sekwencji Q (Gold, Walsh, Random, m). Ich działanie sprawdzono w środowisku ISI oraz MAI stworzonym przez gęsty zbiór wielu scieżek i wielu użytkowników.
2
Content available remote Performance of Time Hopping Impulse Radio in Ultrawideband Propagation Channels: Implications of UWB and Diversity Order Selection
Khaqan A., Gulfam S. M., Riaz L., Yasin A., Ahmed A., Jamil M., Ali B., Ali H., Sharief H., Riaz R. A.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 7
69--73
EN
In this treatise, we quantify the effects of the UltraWideBand (UWB) on Time Hopping (TH) Impulse Radio (IR) operating in UWB propagation channels environment in terms of bandwidth utilization through diversity order selection. We select L strongest MultiPath Components (MPC) from Nr resolvable MPCs using Maximal Ratio Combining (MRC) in order to achieve maximum performance gain in single and full load scenarios. Three classical detectors have being used for analysis purposes named Correlation (Corr), Zero Forcing Detector (ZFD) and Minimum Mean Square Error (MMSE). Our results suggest that the diversity order L of 20 achieves maximum gain of 18dB and 12dB in single and full load Nu of 63 users scenarios, having spreading factor Ns of 63 over no diversity configuration. Hence, MPCs with delays greater than the TH chip time Tc are resolved by synchronization with the initial path of the received signal gives maximum performance gain.
PL
W artykule przedstawiono wyniki analizy dotyczącej działania techniki Time Hopping Impulse Radio, zastosowanej w komunikacji Ultra WideBand, pod kątem stopnia wykorzystania dostępnej przepustowości. W analizie zastosowano trzy typy detektorów: Corr, ZFD, MMSE. Wyniki badan wskazują, że gdy komponenty wielościeżkowe o opóźnieniach większych niż okres Time Hopping są synchronizowane z początkiem odbieranego sygnału, osiągana jest maksymalna efektywność działania.
3
Content available remote Estimation of Baseline Wander Characteristics in ECG Signals Using Adaptive Transversal Filter and Lomb’s Periodogram Analysis
Bakhshi A. D., Ahmed A., Gulfam S. M., Khaqan A., Yasin A., Iqbal S., Riaz S., Jamil M., Khawaja A., Riaz R. A.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 5
107-110
EN
A new technique is proposed to estimate the frequency and amplitude of baseline wander in ECG signals. The estimation has been performed in two stages. In the first stage, a QRS detector detects R peaks and signal samples between consecutive R peaks are passed through a weighted average adaptive filter. The cut-off frequency and order of the filter depends upon the time domain characteristics of the input samples and is automatically updated for each RR interval. In the second stage, Lomb’s periodogram is utilized to analyse the frequency response of the resultant unevenly sampled time series for estimating the baseline frequencies. These frequencies are then used to demodulate the signal for estimation of respective amplitudes. Results have been obtained using synthetic ECG signals with artificially introduced baseline wander containing single or multiple frequencies. The performance of the technique is evaluated by extracting baseline wander through three standard techniques and comparing the estimation errors.
PL
W artykule opisano propozycje estymatora częstotliwosci i amplitudy wahań osi podstawy dla sygnałów w badaniu EKG. Estymacja przebiega w dwóch etapach. Najpierw detektor QRS wykrywa impulsy R, a próbki sygnałów poddawane są filtracji w filtrze adaptacyjnym. W drugim kroku, korzystając z periodogramu Lomb’a, analizowana jest odpowiedź częstotliwosciowa będąca w postaci nierównomiernie pobieranych próbek. Tym sposobem uzyskuje się estymację częstotliwości odniesienia. Działanie algorytmu poddano weryfikacji na bazie symulowanych sygnałów EKG i porównano z trzema standardowymi technikami.
4
Content available remote DSP Based Hardware Implementation of Repetitive Current Controller for Interleaved Grid Connected Inverter
Jamil M., Sharief F., Yasin A., Ahmed A., Gulfam S. M., Khaqan A., Riaz R. A.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 2a
251-255
EN
The performance of the repetitive controller (RC) for classical inverters (e.g. two-level LCL filter based inverter) can decline if the system bandwidth is not sufficient enough due to much larger LCL filter component values. The novel interleaved inverters can provide higher bandwidth than the classical inverters because of low filter values. This paper reflects upon the analysis and hardware implementation of the RC for interleaved inverter using DSP. High quality (very low THD) output current is demonstrated through simulation and experimental results.
PL
W artykule przedstawiono analizę i implementację na DSP sterowania powtarzalnego dla badanego falownika typu interleaved. Przedstawione wyniki badań symulacyjnych, pokazują wysoką jakość (niskie THD) prądu wyjściowego przekształtnika.
5
Content available remote Design and Analysis of Odd-Harmonic Repetitive Control for Three-Phase Grid Connected Voltage Source Inverter
Jamil M., Latif I., Yasin A., Riaz R. A., Gulfam S. M., Ahmed A., Ali M.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 1a
292--295
EN
This paper presents a novel design and analysis of an odd-harmonic repetitive control (ORC) for a two-level three-phase grid connected voltage source inverter. An LCL filter between the inverter and the grid is used to attenuate high frequency PWM switching harmonics. The controller lowers the memory requirement, compared to a conventional repetitive controller. The control scheme contains a traditional conventional tracking controller with a dual loop feedback system, and a zero-phase noncasual filter with add-on ORC. Our analysis and simulation results suggest that the proposed control scheme is able to provide high quality output current (THD=1.8 %) even in worst case scenario.
PL
W artykule przedstawiono nową strategię sterowania ORC (ang. Odd-harmonic Repetitive Control) dla trójfazowego, dwupoziomowego sieciowego przekształtnika napięcia. Dodatkowo wykorzystano filtr wyjściowy LCL. Algorytm redukuje ilość wymaganej pamięci. Jego struktura opiera się na sterowniku nadążnym z podwójną pętlą sprzężenia zwrotnego, filtrze o zerowym przesunięciu fazy oraz ORC. Analiza i symulacje wykazały, że proponowane sterowanie może zapewnić wysokiej jakości prąd (THD=1,8%).
6
Content available remote Detection of ECG T-wave Alternans Using Maxima of Continuous-Time Wavelet Transform Ridges
Bakhshi A. D., Ahmed A., Gulfam S., Khaqan A., Yasin A., Riaz R., Alimgeer K., Malik S., Khan S., Dar A.H.
Przegląd Elektrotechniczny
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2012
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R. 88, nr 12b
35-38
EN
Prognostic utility of microvolt T-wave alternans (TWA) has been established since its clinical acceptance as marker for malignant ventricular arrhythmias, leading to sudden cardiac death. Accurate detection of TWA from surface ECG is a challenge because of invisible nature of the phenomenon. A novel TWA detection scheme based upon analysis of continuous time wavelet ridges (CTWR) of consecutive ventricular repolarization complexes is presented. The CTWR is computed using maxima of wavelet energy coefficients of continuous wavelet transform. Variety of simulated alternans waveforms, wavelet functions, frequency bands and noise levels are used to test the algorithm. The study concludes that CTWR can successfully characterize the alternation of cardiac repolarization and detect TWA phenomenon.
PL
Diagnostyka sygnału TWA odgrywa dużą rolę w badaniach jako marker arytmii powodującej zawał serca. Sygnał TWA jest wykrywany jako składowa sygnału elektrokardiogramu. W artykule opisano wykorzystanie ciągłej transformaty falkowej do analizy tego sygnału. (Detekcja składowej TWA sygnału EKG bazująca na wykorzystaniu ciągłej transformaty falkowej)
7
On multiobjective nonlinear programming with support functions
Husain I., Ahmed A., Mattoo R. G.
Journal of Applied Analysis
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2010
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Vol. 16, nr 2
171-187
EN
A multiobjective programming problem containing support functions is considered. Wolfe and Mond-Weir type vector duals to this problem are constructed and various duality results are validated under invexity and generalized invexity assumptions. Special cases are generated from these results.
8
Sufficiency and duality in control problems with generalized invexity
Husain I, Ahmed A., Ahmed B.
Journal of Applied Analysis
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2008
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Vol. 14, nr 1
27-42
EN
Sufficient optimality criteria are derived for a control problem under generalized invexity. A Mond-Weir type dual to the control problem is proposed and various duality theorems are validated under generalized invexity assumptions on functionals appearing in the the problems. It is pointed out that these results can be applied to the control problem with free boundery conditions and have linkage with results for nonlinear programming problems in the presence of inequality and equality constraints already established in the literature.
9
Content available remote L^3 : A Linear Language with Locations
Ahmed A., Fluet M., Morrisett G.
Fundamenta Informaticae
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2007
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Vol. 77, nr 4
397-449
EN
We present a simple, but expressive type system that supports strong updates-updating a memory cell to hold values of unrelated types at different points in time. Our formulation is based upon a standard linear lambda calculus and, as a result, enjoys a simple semantic interpretation for types that is closely related to models for spatial logics. The typing interpretation is strong enough that, in spite of the fact that our core programming language supports shared, mutable references and cyclic graphs, every well-typed program terminates. We then consider extensions needed to model ML-style references, where the capability to access a reference cell is unrestricted, but strong updates are disallowed. Our extensions include a thaw primitive for re-gaining the capability to perform strong updates on unrestricted references. The thaw primitive is closely related to other mechanisms that support strong updates, such as CQUAL's restrict.
10
Content available remote Servo tracking of targets at sea
Ahmed A., Brdyś M. A.
International Journal of Applied Mathematics and Computer Science
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2006
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Vol. 16, no 2
197-207
EN
This paper details a proposal for the position control system of a two-axis ship-mounted tracker. Aspects of the non-linear dynamics governing Line-Of-Sight (LOS) errors between the tracker and the target are presented. It is shown that the regulation of LOS errors can be achieved by introducing a feed-forward term based on the target’s velocity. This velocity is not measurable, and an estimator is required. Given that the tracking problem is non-linear, the classical separation principle does not hold, and cascading the estimator and regulator together may not lead to an optimal position control system. The ‘LQAdaptive’ system proposed here aims therefore to improve conformity to the separation principle. Simulation trials show that tracking is improved under the LQAdaptive system in comparison to a simple estimator-regulator structure.
11
Optimality conditions and duality for multiobjective control problems
Gulati T. R., Husain I., Ahmed A.
Journal of Applied Analysis
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2005
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Vol. 11, nr 2
225-245
EN
Fritz John and Kuhn-Tucker type necessary optimality conditions for a Pareto optimal (efficient) solution of a multiobjective control problem are obtained by first reducing the multiobjective control problem to a system of single objective control problems, and then using already established optimality conditions. As an application of Kuhn-Tucker type optimality conditions, Wolfe and Mond-Weir type dual multiobjective control problems are formulated and usual duality results are established under invexity / generalized invexity, relating properly efficient solutions of the primal and dual problems. Wolfe and Mond-Weir type dual multiobjective control problems with free boundary conditions are also presented.
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