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which operates at microwave and (ii) a coplanar strip (CPS) scheme which operates at 178.3o E), in the south pacific region, have been used to estimate, of insertions (e.g. water in the oil) and atmospheric pollutions.

     WEDNESDAY, OCTOBER 26, 2005

    09:00 12:40 Concurrent Sessions

    11:40 12:40 Tutorial D

    12:40 14:00 Lunch

    14:00 15:00 General Lecture

    15:00 18:00 Concurrent Sessions

    15:20 16:20 Tutorial C

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URSI GA Oral presentations ? Wednesday, October 26, 2005 TIME TRANSFER AND SYNCHRONISATION(A07) Convener: P. Banerjee, NPL (India) A07 Session Oral Presentation Type 26-Oct-05, 09:00 - 12:40 Schedule HALL-D Room 09:00 A07.1(01712) NEAR-TERM TIME TRANSFER TECHNOLOGIES FOR INTERNATIONAL ATOMIC TIME (TAI), Demetrios Matsakis, U.S. Naval Observatory Washington, DC USA The most precise modes of time-transfer currently used for Coordinated Universal Time (UTC) involve either GPS or Two Way Satellite Time and Frequency Transfer. This paper briefly describes their current and future capabilities, with emphasis on how their uncertainties affect UTC. Most of these uncertainties are specific to the equipment and methodology at each site, while others are specific to each baseline (pair of sites). The link topology is particularly significant when different modes are combined, and methods for reducing the overall uncertainty will be discussed. 09:20 A07.2(01592) A METHOD OF TIME SYNCHRONIZATION BETWEEN THE DIFFERENT GROUND RECEIVER STATIONS OF THE COHERENT RADIO BEACON EXPERIMENT USING GPS, Sreelatha.P., Sudha Ravindran and C V Devasia, Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, India The Coherent Radio Beacon Experiment is a national program for the study of low latitude ionosphere with participation from various national institutes and universities across the country. The program involves the simultaneous reception of beacon transmissions from Low Earth Orbiting beacon satellites at the ground receiving stations, setup at different locations of the country. Time synchronization is thus essential for the data to be valid for the generation of tomograms. An innovative method of time synchronisation using GPS is used here instead of extracting the time code from the orbiting satellites. The paper presents in detail the GUI program developed in-house for GPS synchronised data acquisition. 09:40 A07.3(01604) CLOCK RATE ESTIMATION FOR A BETTER AVERAGE ATOMIC TIMESCALE, Mizuhiko Hosokawa, Yuko Hanado, Noboru Kotake and Kuniyasu Imamura, National Institute of Information and Communications Technology Koganei, Tokyo 184-8795, JAPAN In the course of a investigation on the improvement of UTC(NICT) algorithm, we obtained an formula to estimate a rate-change of an synthesized atomic timescale when a clock drops out from the clock ensemble. The formula is well simplified and easy to handle with by introducing some appropriate assumptions and approximations. A comparison between the estimated value and the result of real event was conducted and it was confirmed the difference was a few parts in 10-15. This formula is now used to predict and confirm the rate-changes of UTC(NICT) at the drop out of a Clock. 10:00 Tea/ Coffee Break 10:20 A07.4(01605) UPDATE ON THE NATIONAL INSTITUTE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY TIME AND FREQUENCY TRANSFER RESEARCH ACTIVITIES, Mizuhiko Hosokawa, Yukio Takahashi, Shin’ichi Hama and Takao Morikawa, National Institute of Information and Communications Technology Koganei, Tokyo 184-8795, JAPAN The National Institute of Information and Communications Technology (NICT), formerly known as CRL, has been conducted the research and development on time and frequency transfer. The recent activities in NICT on this area are shown in this paper. The main subjects are (1) Global Positioning System (GPS) time and frequency transfer in various methods, (2) two way satellite time and frequency transfer (TWSTFT): development of a multi-channel modem, its operation and the establishment of new links, (3) precise time comparison using Engineering Test Satellite (ETS)-VIII and (4) the time management system in Quasi-Zenith Satellite System (QZSS). 10:40 A07.5(01608) APPLICATION OF INSAT STFS BROADCAST TO ELECTRIC POWER INDUSTRY, A. K. Hanjura and A. Sen Gupta, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi, India 91

URSI GA Oral presentations ? Wednesday, October 26, 2005

National Physical Laboratory (NPLI), New Delhi, is disseminating Standard Time and Frequency Signal (STFS) as a serial time code via Indian domestic satellite INSAT. Currently, the time service is via INSAT-3C. This one-way time transfer provides very precise time epoch to the user. Typical inaccuracy in the received time epoch is ~ 10 20 ms. This national service has been in operation since March 1988. The STFS dissemination service of NPL is being used widely in India by many agencies like research laboratories, National Television Broadcast and All India Radio. However, the single largest user is the electric power sector, that uses the precise time information for its grid management. STFS systems are used by the Eastern grid and almost the entire Western power grid. Some stations of the Northern grid are also using this service and the number is increasing every year. In this paper, we shall describe a typical STFS receiving system and its interface with the power station equipment. Distribution of noise-free time signals in the high EMI environment, that is present in the power stations, and over distances exceeding few kilometers, requires conversion of signals into potential free contacts and later converting them to electrical signals at the other end using appropriate interface. 11:00 A07.6(0757) PERFORMANCE OF GEODETIC GPS RECEIVERS FOR ON-LINE TIMING APPLICATIONS, P. Banerjee (1), Anindya Bose(2), (1)National Physical Laboratory, New Delhi 110 012, India,(2)Physics Department, Burdwan University, Burdwan 713 104, West Bengal, India Multichannel GPS receivers with one pulse per second hardware output may be used for online timing applications. Aspects, those may tell upon performance of such GPS receivers are a) lack of calibration of the receiver delay and b) phenomenon of scintillation. Observations presented in the paper dictate that the timing from a GPS receiver needs to be calibrated with respect to any standard clock, linked to BIPM timing network for absolute accuracy. During peak solar cycle, the presence of scintillation may temporarily fade the signals of satellite(s) beyond threshold limit affecting the time transfer accuracy. This paper describes the analytical observations and possible remedial measures. 11:20 End of the Session

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URSI GA Oral presentations ? Wednesday, October 26, 2005

INVERSE SCATTERING AND IMAGING(B03) Convener: Karl Langenberg (Germany) Co-convener(s): Jurgen Detlefsen (Germany) , Mitsuo Tateiba (Japan) B03 Session Oral Presentation Type 26-Oct-05, 09:00 - 12:40 Schedule HALL-R Room 9:00 B03.1(0411) TIME REVERSAL IN RANDOM MEDIA AND SUPER RESOLUTION WITH SHOWER CURTAIN EFFECTS AND BACKSCATTERING ENHANCEMENT, Akira Ishimaru, Sermsak Jaruwatanadilok, and Yasuo Kuga, Electrical Engineering Department, University of Washington, Box 352500, Seattle, Washington, 98195 USA. Time reversal has attracted considerable attention in recent years, particularly because of its potential for communication and imaging through a complex environment. When a wave is emitted by a point source and is received by an array of receivers, and time-reversed and back-propagated in the same medium, the wave is refocused near the original source. This paper presents an analytical theory of the first and second moments of time-reversed UWB pulse in a random medium. It makes use of the two-frequency mutual coherence function and shows the super resolution due to the coherence length, the shower curtain effects, and the backscattering enhancement. 9:20 B03.2(01498) A PROTOTYPE VHF/UHF TOWER RADAR FOR SUBSURFACE SENSING: SYSTEM DESCRIPTION AND DATA INVERSION RESULTS, M. Moghaddam(1) , L. Pierce(1), A. Tabatabaeenjead(1), J. Hoffman(2) and E. Rodriguez(2), (1) University of Michigan, Ann Arbor, MI,(2) Jet Propulsion Laboratory, Pasadena, CA To nondestructively obtain the characteristics of a multilayered rough ground, a multifrequency polarimetric radar backscattering approach can be used. We have developed a tower-based prototype for the Microwave Observatory of Subcanopy and Subsurface (MOSS) mission concept. The tower radar makes backscattering measurements at VHF, UHF, and L-band frequencies. To focus the beam at various incidence angles within the beam width of the antenna, the tower is moved vertically and measurements made at each position. The signals are coherently summed to achieve focusing and image formation above and below the surface. This requires an estimate of wave velocity profiles throughout the imaged region. Traditionally, radar images are formed with the assumption that waves travel in free space. Here, however, the inhomogeneous profile needs to be calculated and used in image formation in the subsurface, hence providing a physically based approach to radar processing. To solve the inverse scattering problem for subsurface velocity profile simultaneously with radar focusing, we introduce a new method using two nested iterations. The inner loop is an inverse scattering algorithm that produces subsurface wave velocity for the layered medium given an estimate of the focused radar backscattering data. The outer loop uses the results of the velocity profile inversion and forms an updated backscattering coefficient image. The process continues until convergence is achieved. Numerical results will be shown using actual radar data acquired with the MOSS tower radar system and compared with in-situ measurements. Implications of this class of measurements for Earth and outer planetary exploration will be discussed. 9:40 B03.3(0896) INVERSION OF SUBSURFACE PROPERTIES OF A LAYERED MEDIUM WITH ROUGH BOUNDARIES , Alireza Tabatabaeenejad, Mahta Moghaddam, and Leland Pierce, Radiation Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan. The focus of this work is on retrieving different parameters of a two-layer dielectric structure with rough boundaries. The scattering data consist of measurements of the wave backscattered from the surface at different frequencies and incidence angles. The inverse solution employed is based on optimization techniques. The inversion method is then applied to the problem of estimating subsurface soil properties from a tower-based radar system operating at the VHF and UHF bands. Initial images produced based on a-priori estimate of the soil dielectric constant are used to obtain the first measurement of the backscattered fields. The measured backscattered fields can now be used in the inversion algorithm to estimate soil properties. This process continues until convergence. 10:00 B03.4(0506) RECONSTRUCTION OF CYLINDRICAL METAL TARGETS USING THEIR FREQUENCY AND TIME DOMAIN RCS VALUES, Hiroshi SHIRAI and Yoshinori HIRAMATSU, Department of Electrical, Electronic, and Communication Engineering, Faculty of Science and 93 Engineering,Chuo University, 1 13 27 Kasuga, Bunkyo, Tokyo 112 8551 Japan.

URSI GA Oral presentations ? Wednesday, October 26, 2005

A simple target reconstruction algorithm is proposed for cylindrical metal scatterers using monostatic RCS data in the time domain as well as in the frequency domain. By using the time domain RCS response at the local frequency maxima at possible specular reflection angle, one easily estimates the locations of the facets by measuring the wavefront arrival time difference from the scattering center. one may also be able to identify more than two facets at the same direction, if they exist. We first assumed that the target is composed by plane square facets. However our algorithm can be extended to handle for curved facets. 10:20 Tea/ Coffee Break 10:40 B03.5(0192) DEVELOPMENT OF THE ESTIMATION SYSTEM OF ELECTRIC PARAMETERS FOR MANY TYPES OF MATERIALS AND ITS EVALUATION, Toshihide Tosaka(1), Isamu Nagano(2), and Satoshi Yagitani(2), (1) National Institute of Information and Communications Technology, Wireless Communications Department, EMC Measurement Group, 421 Nukui-Kitamachi, Koganei, Tokyo 1848795 Japan (2) Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 9201192 Japan We developed the estimation system of electric parameters. For the non-magnetic materials, the estimated relative permeability was the same as the nominal values. For the ferromagnetic materials, the estimated relative permeability varied 0% to 30% from the nominal values. For both types of materials, the estimated conductivities were 0% to 9.8% different from nominal values. Next, we apply our estimation method to shielding sheets, and we can estimate the electric parameters for items such as thin cloths. Then, we estimate the dielectric constant for liquid materials. The accuracy is such that the estimated value is different from the nominal value by less than 2%. These results show that we have successfully developed an estimation system of electric parameters for these cases. Using our estimation system, we can estimate considering the frequency characteristics for electric parameters in about 2 minutes. 11:00 B03.6(01007) INVERSE SOURCE CHARACTERIZATION FOR ELECTROMAGNETIC WAVE INTERACTIONS WITH THE ENVIRONMENT, A. Gati1, Y. Adane1, M. F. Wong(1), J. Wiart1 and V. Fouad Hanna(2),(1) France Télécom R&D RESA/FACE 38-40, rue du Général Leclerc - 92794 Issy Moulineaux.(2) Laboratoire Instruments et Systèmes d‟île de France - Case 252 - Université Pierre et Marie Curie 4, place Jussieu - 75252 Paris cedex 05 When modelling electromagnetic wave interactions with the environment, the source can be analysed separately from the environment which can be modelled by asymptotic methods. This hybrid approach is interesting for physical and algorithmic reasons. It allows also integrating measurement through the characterisation of the sources. We present a new inverse source characterization technique. By knowing the 3D radiation pattern of a source (measured or simulated), a reduced set of equivalent smaller sources can be found. The near field can be reconstructed and due to the smaller size of the equivalent sources interactions with objects in the near field region of the whole antenna are possible 11:20 B03.7(0122) A NEW AND EFFECTIVE MODEL FOR 3-D FORWARD AND INVERSE SCATTERING PROBLEMS IN LOSSY SCENARIOS, Lorenzo Crocco (1), Ilaria Catapano(1), Michele D’Urso (2) and Tommaso Isernia(3),(1) Istituto per il Rilevamento Elettromagnetico dell‟Ambiente IREA-CNR via Diocleziano 328, I-80124, Napoli (ITALY);(2) DIET - Università di Napoli Federico II Viale Claudio 21, I-80125 Napoli (ITALY), (3) DIMET - Univ. Mediterranea di Reggio Calabria, via Graziella, Loc. Feo di Vito,ITALY The remarkable computational requirements of 3D scattering problems push towards the development of new effective models. The CS-EB model, recently introduced for 2D scalar problems, allows to reduce computational costs in forward problems and occurrence of false solutions in inverse problems. Therefore, it is convenient to exploit this model also in the demanding 3D vectorial case. However, owing to the dyadic nature of the operators, a suitable reformulation (named CS-EB-s) is required to preserve the expected advantages. In this communication, formulation of CS-EB-s is discussed and its performances in scattering problems in lossy media are assessed through several numerical examples. 11:40 B03.8(0821) EFFECTIVE RECONSTRUCTION APPROACHES TO MILLIMETER-WAVE IMAGING OF HUMANS, J. Detlefsen, A. Dallinger, S. Schelkshorn, Hochfrequenztechnik, Techn. Univ. Muenchen, Arcisstr. 21, Muenchen, Germany 94

URSI GA Oral presentations ? Wednesday, October 26, 2005

Millimeter-wave systems are a promising approach for the imaging of humans. Reconstruction algorithms for imaging in general are based on solutions to a linearized inverse scattering problem. Because of the short range application reconstruction algorithms imply a high computational load and require advanced focusing techniques. In the present approach scattering data only are acquired for a broad band of frequencies along circular lines surrounding the object giving limited information. Several approaches based on synthetic aperture techniques modified for cylindrical apertures including slant plane geometry are applied for this approach and will be compared to wave number domain focusing methods. Specific methods of 2D reconstruction for selected cross sections of the object including directions of maximum resolution are presented which reduce the reconstruction effort while maintaining most of the image information. 12:00 B03.9(0418) MIGRATION BASED IMAGING USING THE UWB BEAM SUMMATIONALGORITHM,, Amir Shlivinski(1), Ehud Heyman(2), and Karl J. Langenberg(1), (1) Department of Electrical Engineering, University of Kassel, 34121 Kassel, Germany,(2) School of Electrical Engineering, Tel Aviv University, Tel Aviv 69978, Israel, A migration based imaging algorithm is implemented here using the ultra wideband Gaussian beam summationmethod (UWB-GBS). A scatterer image embedded within known background medium is recovered by correlating the backpropagated pulsed scattered wavefield with the forward propagating pulsed field. The forward/backward propagations are performed by decomposing the fields into sets of Gaussian beam (G B) propagators using the UWB-GBS, and the image is formed by generating cross-beam correlation functions (XB-CF) by correlating pairs of forward/backward propagating GB‟s, and aggregating the products at each image point. Numerical efficiency is gained using a-priori beam localization. 12:20 B03.10(0966) LINEAR AND NONLINEAR INVERSE SCATTERING IN ULTRASONIC AND ELECTROMAGNETIC NON-DESTRUCTIVE EVALUATION, Langenberg Karl J(1), René Marklein(2) and Klaus Mayerk(2), (1) University of Kassel, Dept. Electrical Engineering Wilhelmshoeher Allee 71, Kassel, 34109, Germany,(2) University of Kassel 12:40 End of the session

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BEYOND 3G AND 4G WIRELESS COMMUNICATIONS(C03) Convener: Hitoshi Yoshino(Japan) C03 Session Oral Presentation Type 26-Oct-05, 09:00 - 12:40 Schedule HALL-4 Room 9:00 C03.1(0463) A GEOMETRY-BASED STOCHASTIC MIMO CHANNEL MODEL FOR 4G BROADBAND PACKET ACCESS, Ernst Bonek, Werner Weichselberger, Markus Herdin, and Hüseyin Özcelik, Institut für Nachrichtentechnik und Hochfrequenztechnik, Technische Universität When, Vienna, Austria (Invited) We present a MIMO channel modeling approach that combines the advantages of geometry-based and stochastic elements. The channel is characterized by a time- and delay-dependent MIMO channel matrix that contains the impulse responses from each transmit to each receive antenna (for both polarisations), calculated from dual-polarised double-directional wave propagation. Based on 5GHz indoor measurements it captures all essential channel parameters of a broadband MIMO system for packet access, while providing reasonable simulation times for the development of MIMO transceiver algorithms with arbitrary antenna array configurations in three-dimensional environments with interference. 9:20 C03.2(01086) MULTI-HOP VIRTUAL CELLULAR NETWORK , Eisuke Kudoh and Fumiyuki Adachi, Dept. of Electrical and Communication Engineering, Graduate School of Engineering, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai, 980-8579 Japan (Invited) There is a strong demand for higher speed data transmissions in mobile communication services. However, there will be a serious problem; as data transmission rate becomes higher, the peak transmit power becomes larger. This paper introduces the wireless multi-hop virtual cellular network (VCN) concept suitable for non-real time high speed packet data services in the future mobile communications. Each virtual cell consists of a central port, which is a gateway to the network, and many distributed wireless ports. A novel multi-hop route construction algorithm and a distributed dynamic channel allocation algorithm for multi-hop links channel are presented. 9:40 C03.3(0091) MULTI-USER DETECTION FOR SIGNALS HAVING DIFFERENT SYMBOL RATES, Koji Maeda, Takahiro Asai and Hitoshi Yoshino, Wireless Laboratories, NTT DoCoMo, Inc., Japan, 3-5 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-8536 JAPAN (Invited) This paper proposes a multi-user detector that detects signals having different symbol rates, within a reasonable level of computational complexity. The proposed multi-user detector successively detects the signals based on rejection of outof- band signals and replica generation using soft-decision output from channel decoders. A performance comparison of the proposed method to a multi-user detector based on the maximum likelihood sequence estimation (MLSE) is presented based on the computer simulations. The computer simulation results show that the proposed method can separate the signals effectively, and that its BER performance for a narrow-band signal approaches that of the MLSE-based multi-user detector when the symbol rate ratio of the wide-band signal to the narrow-band signal becomes large. 10:00 C03.4(0373) A STUDY ON SUB-CARRIER SELECTING MC-CDMA (SCS-MC-CDMA) SYSTEM IN BROADBAND WIRELESS COMMUNICATIONS, Teruya Fujii, Noboru Izuka, Hiroyoshi Masui, and Atsushi Nagate, Information and Communication Labs., Japan Telecom, 2-9-1 Hatchobori Chuo-ku, Tokyo, Japan (Invited). We recently proposed an SCS-MC-CDMA system with time domain spreading. The system adopts a sub-carrier selection method to reduce signal-processing loads at the mobile terminal; users are allocated an appropriate number of sub-carriers based on their data rate. By extracting the assigned sub-carriers with a sub-carrier selection filter, the users can make their signal processing loads match their data rate. We have also proposed an MMSE combiner with channel estimation on a chip-by-chip basis for the system to counter a high maximum Doppler frequency, which degrades the BER performance by the increase of the inter-code interference level. With our proposed method, good BER performance can be realized even when the maximum Doppler frequency is as high as 1000Hz. 96

    URSI GA Oral presentations ? Wednesday, October 26, 2005

10:20 Tea/Coffee Break 10:40 C03.5(0816) ADAPTIVE 4G UPLINK PROPOSAL BASED ON INTERLEAVE-DIVISION MULTIPLE ACCESS, Hendrik Schoeneich, Justus Christian Fricke and Peter Adam Hoeher, Faculty of Engineering, University of Kiel (Invited) Efficiency and adaptivity play a major role in the design of fourth-generation (4G) wireless systems. 4G systems should be bandwidth efficient, power efficient, and allow for low complexity transceivers. The systems should be flexible with respect to data rate (link adaptation), data reliability (QoS), and service provisioning. Moreover, they should operate on frequency-selective and fast-fading channels. In this paper, a system proposal for the 4G uplink based on Interleave-Division Multiple Access (IDMA) is presented (“KIEL Proposal”), which fulfills the mentioned requirements. Cross-layer issues are addressed. 11:00 C03.6(0933) ANALYTICAL BER COMPUTATION FOR INTERFERENCE CANCELLATION RECEIVER IN MC-CDMA SYSTEM, L.Nithyanandan and P.Dananjayan, Dept. of Electronics and Communication Engineering,Pondicherry Engineering College, Pondicherry-605014, India.

    Multiple Access Interference (MAI) is a factor, which limits the capacity and performance of CDMA system. The conventional detector does not take into account the existence of MAI. Hence, a multi-user detection strategy is used for mitigating the effects of MAI. Novel receiver structures that take advantage of knowledge of MAI signal parameters are termed as Multi-user receivers and are more complex than conventional ones. This is because of their capability of using MAI signal information to help recover the desired user. Interference cancellation receivers have received a great deal of attention due to its advantages when compared with the other multi-user detectors. The interference cancellation techniques can be broadly broken into successive and parallel schemes for canceling multiple access interference. In order to utilize the advantage of both these two schemes, a Hybrid Interference Cancellation (HIC) scheme for MC CDMA system is proposed. HIC combines both SIC and PIC to the correct proportion so that the receiver performance is enhanced to reach the near optimal level. The objective of this work is to analytically compute BER for MC CDMA hybrid interference cancellation receiver and to justify its optimality. 11:20 C03.7(01036) OPTIMUM SELECTION OF CHAOTIC SPREADING CODES FOR DS-CDMA SYSTEMS USING GENETIC ALGORITHM, Mahmoud M. Gad, Said E. El-Khamy and Shawki E. Shaaban, E.E. Department, Faculty of Engineering, Alexandria University, Alexandria 1544, Egypt. This paper presents a novel method for the optimum selection of chaotic spreading code sets for Asynchronous DS-CDMA systems based on Genetic Algorithm. The generation of binary chaotic codes is briefly discussed. Classical code sets optimization methods as AO/LSE and CO/MSQCC is presented. The proposed Genetic Algorithm based code optimization method is discussed. Finally, Numerical examples are used to illustrate the performance improvement for CDMA system utilizing chaotic optimized codes over those utilizing classical codes, such as m-sequence and Gold codes, optimized using classical methods. 11:40 C03.8(01089) A NEW METHOD OF CHAOTIC CODE QUANTIZATION FOR THE GENERATION OF EFFICIENT CDMA CODE SETS, Said E. El-Khamy, Mahmoud M. Gad, and Shawki E. Shaaban, E.E. Department, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt In this paper, we propose a new method for the selection of quantization threshold value for chaotic maps based on the statistics of the map itself and not on the statistics of the individual generated codes. The new method is based selecting the invariant probability density function (PDF) median value as a threshold value, which is independent of the used initial conditions. Computer simulations are used to evaluate the balance of the generated codes. Chaotic codes generated using this method are found to have better performance in Asynchronous CDMA Applications than codes generated using zero-threshold method. 12:00 C03.9(01326) NEW MULTIPLE ACCESS METHOD FOR WIRELESS MOBILE SYSTEMS, Michael Bank, Boris Hill and Jacob Gavan, Com. Engineering, Holon Academic Institute of Technology, Golomb 52, Holon, Israel.

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Using an Orthogonal Frequency Division Multiple Access (OFDMA) system to achieve good parameters can prove to be an arduous task due to the effects of the Doppler Shift and delays. Here, favorable conditions for orthogonalityutilization are diminished. In addition, problems exist in synchronization in the uplink from the receiver, placed inside a car, which is traveling within the confines of a modern city. This article offers proposals for necessary modifications to help decrease the negative influences of using an OFDMA system. 12:20 C03.10(0925) PERFORMANCE IMPROVEMENT USING OPPORTUNISTIC SCHEDULER IN CDMA SYSTEMS, K.Jayanthi and P.Dananjayan, Department of Electronics and Communications Engineering, Pondicherry Engineering College, Pondicherry-605014, India. The unique characteristics of wireless networks, namely the time varying channel conditions and multi-user diversity necessitates new scheduling solutions to be developed. The wireless resource is scarce, and mobile users perceive time varying channel conditions. To effectively harness the precious resource and achieve higher network performance, good scheduling schemes opportunistically seeking to exploit channel conditions is absolutely essential. The prime objective of this work is to improve / maximize system performance (e.g. throughput, capacity) under various fairness and QoS constraints. Simulation analysis of the proposed scheme is carried out under CDMA environment. As expected, the obtained results prove to have higher throughput satisfying per user QoS constraints in both environments. In addition to this, system capacity and resource utilization considerably improved. Hence, this channel-based scheduler results in substantial system gain, which is the basic requirement in a multi-user wireless scenario. However, a trade off always occurs between system throughput and user fairness. 12:40 End of the Session

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