Wyniki 1-9 spośród 9 dla zapytania: authorDesc:"Shahid A. KHAN"

Atmospheric influences on satellite communications

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Among other atmospheric regions, ionosphere, which is ionized region of the atmosphere, is considered to impose serious limitations on satellite communication. At higher frequencies, radio waves pass through the ionosphere and are attenuated due to the free electrons present in ionosphere. This paper discusses atmospheric effects on high frequency radio waves illustrating the attenuation and losses it may come across like attenuation due to atmospheric gases, rain, clouds, beam spreading loss and noise temperature. Data used to summarize the influence of atmospheric phenomena is obtained from ITU-R models and processed using MATLAB. Streszczenie. Spośród różnych warstw atmosfery szczególnie jonosfera wpływa niekorzystnie na komunikację za pośrednictwem satelitów. Przy wyższych częstotliwościach fale radiowe są silnie tłumione w jonosferze. Artykuł przedstawia analizę wpływu czynników atmosferycznych w jonosferze na tłumienie i straty w radiowej komunikacji wysokoczęstotliwościowej. (Wpływ atmosfery na jakość komunikacji satelitarnej) Keywords: Radio propagation, Ionosphere, Rain attenuation, cross polar discrimination. Słowa kluczowe: propagacja fal radiowych, komunikacja satelitarna Introduction The ionosphere is the upper part of the atmosphere where sufficient ionization exists to influence radio wave propagation. The ionosphere usually consists of two layers: the E layer which is about 80 to 113 km above the earth’s surface and reflects radio waves of lower frequency. Above E layer is F layer which reflects higher frequency radio waves. The F layer is then further sub divided into F1 and F2 layers. The F1 layer is lower portion of F layer and exists from 150 to 200 km above the earth’s surface, whereas F2 layer is the upper portion and exists at a height of 200 to 500 km. F2 layer is mainly responsible for reflection of HF waves during day and night. Since the ionization is mainly caused by solar radiations, it is dep[...]

Planar monopole UWB antenna with 5GHz dual notched band characteristics

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These days most of the research work in the area of antenna design is focused on monopole antennas for UWB communications due to their high data rate, precision and low complexity. However, interference effect increases within the Ultra wide Band due to the increasing growth of 802.11a wireless LAN in the frequency band of 5 GHz in many countries. To minimize this closely found in-band interference effect, antennas with closely found notch band characteristics are becoming essential. The idea of band notch is extended in this paper by the placement of parasitic strips at different positions on the bottom of the substrate to achieve dual notches in 5 GHz band. Experimental results show that this technique can be employed to generate sharp controllable notch and/or dual notch bands with reasonable accuracy. Streszczenie. Przedstawiono projekt anteny do szerokopasmowej komunikacji w paśmie 5 GHz w sieciach bezprzewodowych standardu 802.11a. Właściwości anteny kształtowano przez dodanie dodatkowych pasków w różnych pozycjach. (Planarna jednobiegunowa antena UWB pracująca w paśmie 5 GHz) Keywords: monopole, Ultra-wide Band, Notched Band, Parasitic Strip. Słowa kluczowe: antenna szerokopasmowa, antenna planarna Introduction High data rate in wireless communication systems is focal feature upon which bunch of research ensue and persist. To enable these features wireless communication systems created momentous demands on antenna designer. The antenna designer has to consider that the antenna should be compact and in ease to integrate with the active devices. In 2002, the FCC authorized to employ Ultra wide band from 3.1 GHz to 10.6 GHz with the limited emission power spectrum [1, 2]. After that, different types of antennas were designed for ultra wide band applications [3- 11] and at the same time many challenges cropped up in designing ultra wide band antennas. One of the main problems in ultra wide band is the interference within the ban[...]

Minimizing Unnecessary Handovers in a Heterogeneous Network Environment

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In this paper, we have provided a model to minimize the unnecessary handovers from a cellular network to a WLAN. Exploiting traveling distance prediction method, the proposed handover necessity estimation mechanism uses distance threshold parameters to avoid unnecessary handovers. Our analysis and simulation results suggest that the proposed mechanism can keep the probabilities of handover failure and unnecessary handover close to the predetermined designed values. Streszczenie. Przedstawiono model umożliwiający minimalizowanie niepotrzebnych przełączeń typu handover między siecią komórkowa a siecią bezprzewodową WLAN. (Minimalizacja niepożądanych przełączeń w niejednorodnym środowisku sieciowym) Keywords: Vertical handover, handover failure probability, unnecessary handover probability. Słowa kluczowe: przełączenie typu handover, sieci komórkowe, sieci bezprzewodowe.. Introduction Vertical handovers, which transfer a live call/session from one access technology network to another, are likely to play an important role in B3G scenario for supporting always best connectivity. However, minimizing unnecessary handovers is as important as handover triggering condition estimation and optimization of handover execution. If the unnecessary handovers are not checked, the phenomenon will have adverse effect on the system performance. Not only overhead involved in unnecessary handovers would consume network resources, but it would also increase the probability of handover failure. This problem is particularly important in the context of wireless local area network (WLAN), which has a small coverage region. Reducing unnecessary handovers in intra-technology (horizontal) handovers has widely been studied [1], [2], however, Yan et al. [3] have made first serious effort for the same in inter-technology (vertical) handover. They made an interesting contribution to the study of handover decision method based on the prediction of traveling distanc[...]

A Performance Comparison of DS-UWB Rake Receivers for different environments

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This paper focuses on the performance comparison RAKE receivers used in the Ultra wide-Band system. The simulations are based on implementation of the complete system using direct sequence spread spectrum approach. The results are obtained for the three types of RAKE receiver models, namely, All(A) RAKE, Selective (S) RAKE and Practical(P) RAKE. The driven results are based on the four cases presented in IEEE P802.15 propagation channel model. Streszczenie. W artkule przedstawiono porównanie odbiorników RAKE używanych w systemach komunikacji ultra szerokopasmowej. Zbadano trzy różne odbiorniki RAKE. Badania bazowały na normie IEEE P802.15. (Porównanie odbiorników szerokopasmowych RAKE w różnych warunkach pracy) Keywords: DS-UWB, RAKE Receivers, Channel modeling Słowa kluczowe: komunikacja szerokopasmowa, RAKE Introduction UWB has slowly developed over the past hundred years. It took years to develop such techniques that can transmit and receive data using short impulse signals between transmitter and receiver. In 1950, it was examined for military applications like radars. By late 1960s and early 1970s, the wide band non sinusoidal communications were explored for the public as well as for private sector. In 1980s research work published in [1] was about the practical implementation of low power short impulse radio using time-modulated schemes while in 1998 spread spectrum techniques for the practical implementation were presented in [2]. The concept behind the spread spectrum is that the transmitted message signal follows a random sequence and appears to be noise for an irrelevant re-ceiver. This new form of radio which uses short duration im-pulses unlike sparks and gaps can be referred as UWB [3]. The research work presented in this paper provides insight into practical implementation of UWB system. The System is composed of UWB transmitter, IEEE P802.15 propagation channel model and receiver. The System includes: [...]

Planar Monopole Stair Case Antenna for Ultra-wide Band

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Planar monopole antennas are extensively used in many wireless communication applications due to their compact size, low weight and ease of integration with active devices. Many antennas with different band characteristics have been designed such as dual, multi, wide and ultra wide band. In this paper simple monopole antenna is proposed for Ultra wide band applications. The antenna is analysed for bandwidth increment with addition of linear multiple steps, mathematical model is also proposed. Simulation results show that the proposed design can be used for UWB applications with reasonable accuracy. Prototype of proposed design with measured results are also presented. Reasonable agreement is found between the simulated and measured results. Details of the proposed antenna design, simulated and measured results are presented and discussed. Słowa kluczowe. W artykule opisano prostą antenę mono-polarną w zastosowaniu do ultra-szerokich pasm przepustowych. Przedstawiono model matematyczny i analizę wzrostu przepustowości pod wpływem liniowych stopni mnożących. Wyniki badań symulacyjnych zostały zweryfikowane poprzez porównanie z pomiarami rzeczywistymi. (Płaska, mono-polarna antena schodowa do pasm ultra-wysokich). Keywords: Monopole Antenna,Ultra-wide Band, Stair case, Mathematical formulation. Słowa kluczowe: antena mono-polarna, pasma utra-wysokie, schody, formuła matematyczna. o szeroki Band, z karbem Band, pasożytnicze Gazy Introduction Planar monopole antennas are finding numerous applications in mobile and wireless communication due to their compact size, low weight and ease of fabrication and integration with active devices. However, inherent narrow band characteristics of monopole antennas have forced the researchers to explore and investigate the ways and means to enhance the bandwidth of UWB antennas while keeping the sizes as low as possible. Quite a few techniques as reported in [1,2] have been explored and applied to design[...]

A Host Based Autonomous Scheme for Seamless Vertical Handover

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In this paper we suggest a host based, end-to-end selfreliant scheme for handover in heterogeneous network environment. It directly involves the correspondent node in the handover process. The proposed scheme imitates the Network Address Translation. It maps a logical address to another logical address. It modifies the address information in the header of the packet while it is in transition. In principle the process is identical to the NAT box operation, but the goal is different. While NAT is primarily used in conjunction with masquerading to hide the private IP address space, HaMAT works in conjunction with MIH and serves to hide the IP address change of the mobile node encountered due to the vertical handover. HaMAT is a functional entity just like Media Independent Handover Function, and it resides inside the Mobile Node and Correspondent Node. By eliminating the need for rerouting, tunneling and route optimization as required in Mobile IP, HaMAT achieves high performance results in terms of handover delay, end to end packet latency, jitter and the overhead involved. The service disruption time for HaMAT is as low as 10 msec compared to reported handover delays of 260 msec and 1 sec for MIPv4 and MIPv6 respectively. Streszczenie. W artykule zaproponowano bazujący na hoście schemat przełączania typu handover w niejednorodnym środowisku sieciowym. Schemat imituje Network Address Translation i mapuje logiczny adres orasz modyfikuje nagłówek w pakiecie. (Bazujący na hoście autonomiczny schemat przełączania typu handover) Keywords: Heterogeneous Networks, Mobility, Mobile IP, Vertical Handover. Słowa kluczowe: przełączwenie typu handover, sieci niejednorodne Introduction As user demand of ubiquitous networks cannot be met by a single technology, the diverse technologies will have to complement each other to provide ubiquity of service. This phenomenon has introduced multi-interface mobile devices —possibility to connect to differen[...]

Microstrip Antenna Array for Beamforming Systems

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A dual and quad element antenna array resonating at 2.4 GHz with narrow beam is proposed in this paper. An intention to put forward this work is to make use of microstrip patch antennas in beamforming to form directional beams in analog and digital domains; reducing co-channel / multipath interferences and improving Quality of Service (QoS) for senor arrays and 3G wireless networks. The size of dual and quad element antenna array is 60 x 130 mm2 and 60 x 240 mm2 respectively. Simulations in HFSS (High Frequency Structure Simulator) showed least mutual coupling among adjacent elements and prototypes have been fabricated using FR4 to verify the efficiency of the presented work for IEEE 802.11b/g WLAN standards. Streszczenie. W artykule przedstawiono dwu- i czteroelementowy układ anten o wąskim strumieniu promieniowania, o częstotliwości rezonansowej 2,4 GHz oraz możliwości wykorzystania w przesyle sygnału. (Układ anten mikropaskowych w systemach kształtowania strumienia promieniowania antenowego) Keywords: Antenna Array, Beamforming, Mutual Coupling, IEEE WLAN Standard. Słowa kluczowe: Układ anten, kształtowanie strumienia, sprzężenie, IEEE WLAN. Introduction The existing trend in development of latest communication systems and wireless technologies is to achieve better coverage and capacity with high data rates [1]. Typically the power consumption and interference increases when omni directional antennas transmit signals in the directions other than the desired user [2]. Thus, the capacity can be increased by placing nulls in the direction of interferers [3]. WLAN standards offer data rates up to 54 Mbps; while GSM, CDMA and GPRS are capable of high quality voice communications but on the expense of multipath fading [4] so utilization of spatial domain (i.e. through beamforming in smart antenna systems) ensur[...]

Detection of ECG T-wave Alternans Using Maxima of Continuous-Time Wavelet Transform Ridges

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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. Streszczenie. Diagnostyka sygnału TWA odgrywa du˙za˛ role˛ w badaniach jako marker arytmii powoduja˛cej zawał serca. Sygnał TWA jest wykrywany jako składowa sygnału elektrokardiogramu. W artykule opisano wykorzystanie cia˛głej transformaty falkowej do analizy tego sygnału. (Detekcja składowej TWA sygnału EKG bazuja˛ca na wykorzystaniu cia˛głej transformaty falkowej) Keywords: Continuous-Time Wavelet Transform, Detection, Electrocardiography (ECG), T-wave Alternans Słowa kluczowe: transformata falkowa, elektrokardiogram, sygnał TWA Introduction Electrocardiography (ECG) is an important clinical tool for diagnosis of cardiac diseases. It is commonly measured by placing the surface electrodes on a subject’s chest and recording the cardiac cellular potential variations. The measured voltages, graphically plotted as a function of time, represent sequential depolarization (P-wave and QRS complex) and repolarization (T-wave) of cardiac chambers. A single such heart beat is shown in Fig. 1(a). 0 0.1 0.2 0.3 0.4 0.5 0.6 -1 0 1 2 (a) ECG (mV) 0 1 2 3 4 5 -1 0 1 2 (b) ECG (mV) 0 1 2 3 4 5 -1 0 1 2 (c) time(sec) ECG (mv) P Q R S T[...]

ASIC Design Implementation of Memory Efficient Infinite Impulse Response UWB Equalizer

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Channel Equalization plays an important role in reducing distortion and Inter-Symbol Interference (ISI) to improve the quality of transmission in Ultra-Wide Band (UWB) channel. Many equalization techniques have been proposed in the past but the proposed techniques in this paper describes Infinite Impulse Response (IIR) equalizer architecture which halves the memory requirement of conventional IIR equalizers. This is achieved by exploiting the aperiodically repeated clusters of negative-exponentially decaying segments of Channel Impulse Response (CIR) and hence by providing a single delay- line between the input and output of the equalizer. Further this architecture is realized by implementing on Application Specific Integrated Circuit (ASIC) using Mentor Graphics IC Design tools. Mathematical modeling gives suitable parameters of the IIR Filter, followed by Register Transfer Level (RTL) Design using Very High Descriptive Language (VHDL), ASIC synthesis to TSMC 0.35um process technology, physical modeling using advanced layout techniques. The IIR equalization filter is designed using 8758 Metal Oxide Semi-conductor (MOS) transistors with core cell area of 0.406mm2. Streszczenie. W artykule zaproponowano architekturę ekwalizera NOI, która zmniejsza wymagania pamięci przy transmisji szerokopasmowej w układach ASIC. Zaprezentowano układ w technologii 35 nm z tranzystorami MOS przy powierzchni celki jądra 0.406 mm2. (Projekt szerokopasmowego ekwalizera NOI w układach ASIC) Keywords: Quasi-cyclic LDPC codes, Protograph LDPC codes, Low complexity LDPC codes, Vandermonde Matrix. Słowa kluczowe: układy ASIC - application specific integrated circuits, ekwalizer, filtry szerokopasmowe. Introduction The distinct clusters of dense multi path components in UWB systems results in Channel Impulse Response (CIR) potentially span over hundreds of transmitted symbols, hence imposing excessive memory requirements on the equalizers implementation. In [1] a g[...]

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