33,023 research outputs found

    Genetic Algorithm Aided Timeslot Scheduling for UTRA TDD CDMA Networks

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    It is demonstrated that genetic algorithms may be utilised for finding a suboptimum but highly beneficial uplink (UL) or downlink (DL) timeslot (TS) allocation for improving the achievable performance of the third generation UTRA system’s time division duplex (TDD) mode. It is demonstrated that this novel GA-assisted UL=DL timeslot scheduling scheme is capable of avoiding the severe BS to BS intercell interference potentially inflicted by the UTRA TDD CDMA air interface owing to allowing all TSs to be used both in the UL and DL, hence potentially quadrupling the carried teletraffic and halving the uplink power

    Genetically Enhanced Performance of a UTRA-like Time-Division Duplex CDMA Network

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    In this contribution a Dynamic Channel Allocation (DCA) algorithm is developed, which minimizes the amount of Multi-User Interference (MUI) experienced at the Base Stations (BSs) by employing Genetic Algorithms (GAs). A GA is utilized for finding a suboptimum, but highly beneficial Uplink (UL) or Downlink (DL) Timeslot (TS) allocation for improving the achievable performance of the third generation UTRA system’s Time Division Duplex (TDD) mode. It is demonstrated that a GA-assisted UL/DL timeslot scheduling scheme may avoid the severe BS to BS inter-cell interference potentially inflicted by the UTRA TDD CDMA air interface owing to allowing all TSs to be used both in the UL and D

    Loosely Synchronised Spreading Code Aided Network Performance of Quasi-Synchronous UTRA-like TDD and FDD CDMA Systems

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    It is demonstrated that loosely synchronised (LS) spreading codes exhibit a so-called interference-free window, where both the autocorrelation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both inter-symbolinterference and multiple-access-interference in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. The work reported has studied the achievable network performance and compared it to that of a UTRA-like time division duplex (TDD) and frequency division duplex (FDD) CDMA system using orthogonal variable rate spreading factor codes

    Adaptive Beamforming and Adaptive Modulation-Assisted Network Performance of Multiuser Detection-Aided FDD and TDD CDMA Systems

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    The network performance of a frequency division duplex and time division duplex (TDD) code division multiple access (CDMA)-based system is investigated using system parameters similar to those of the Universal Mobile Telecommunication System. The new call blocking and call dropping probabilities, the probability of low-quality access, and the required average transmit power are quantified both with and without adaptive antenna arrays (AAAs), as well as when subjected to shadow fading. In some of the scenarios investigated, the system’s user capacity is doubled with the advent of adaptive antennas. The employment of adaptive modulation techniques in conjunction with AAAs resulted in further significant network capacity gains. This is particularly so in the context of TDD CDMA, where the system’s capacity becomes poor without adaptive antennas and adaptive modulation owing to the high base station (BS) to BS interference inflicted as a consequence of potentially using all time slots in both the uplink and downlink of the emerging wireless Internet. Index Terms—Adaptive beamforming, adaptive modulation, code division multiple access (CDMA) systems, Universal Mobile Telecommunication System Terrestrial Radio Access (UTRA), wireless network performance

    Loosely synchronized spreading code aided network performance of quasi-synchronous UTRA-like TDD/CDMA systems

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    In this paper we investigate the achievable capacity of a UTRA-like Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes. The family of operational CDMA systems is interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the frequency selective channel. They also suffer from Multiple-Access-Interference (MAI) owing to the non-zero cross-correlations of the spreading codes. By contrast, the family of LS codes exhibits a so-called Interference Free Window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance in comparison to that of a UTRA-like TDD/CDMA system using Orthogonal Vari- MSO able Rate Spreading Factor (OVSF) codes

    Pressure induced superconductivity in CaFe2_2As2_2

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    CaFe2_2As2_2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and superconductivity has been found to exist in a narrow pressure region that appears to be at the interface between two different phase transitions. The pressure - temperature (PTP - T) phase diagram of CaFe2_2As2_2 reveals that this stoichiometric, highly ordered, compound can be easily tuned to reveal all the salient features associated with FeAs-based superconductivity without introducing any disorder. Whereas at ambient pressure CaFe2_2As2_2 does not superconduct for T>1.8T > 1.8 K and manifests a first order structural phase transition near T170T \approx 170 K, the application of 5\sim 5 kbar hydrostatic pressure fully suppresses the resistive signature of the structural phase transition and instead superconductivity is detected for T<12T < 12 K. For P5.5P \ge 5.5 kbar a different transition is detected, one associated with a clear reduction in resistivity and for P>8.6P > 8.6 kbar superconductivity is no longer detected. This higher pressure transition temperature increases rapidly with increasing pressure, exceeding 300 K by P17P \sim 17 kbar. The low temperature, superconducting dome is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity, and possibly the associated fluctuations, too dramatically

    Second language user support

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    Computer users rarely experience entirely trouble-free interaction. The natural variety ofindividuals ensures that no software systems yield constantly fluent interaction for allusers. In consequence, software designers often strive to ameliorate this situation bybuilding 'user support' into their systems. User support can take different forms but,conventionally, each aims to assist the needy end-user by means of facilities directly supporting the performance of certain operations, or through supply of information thatadvises the user on available system functionality.The present paper briefly characterises a range of user support facilities before describingone requirement in greater detail. This aspect considers the needs of users whose mother-tongue is not English, but who are obliged to use English-based information systems. Inthis context, 'helping the user' must reasonably extend beyond mere advice on systemoperation to selective elucidation of information content. We regard this move as alogical extension of the user support concept, by seeking to address specific interactionneeds in a target user population. An example of this approach is described through aninformation system, in the domain of civil engineering, for native Chinese speakers ofEnglish

    Building a 3.5 m prototype interferometer for the Q & A vacuum birefringence experiment and high precision ellipsometry

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    We have built and tested a 3.5 m high-finesse Fabry-Perot prototype inteferometer with a precision ellipsometer for the QED test and axion search (Q & A) experiment. We use X-pendulum-double-pendulum suspension designs and automatic control schemes developed by the gravitational-wave detection community. Verdet constant and Cotton-Mouton constant of the air are measured as a test. Double modulation with polarization modulation 100 Hz and magnetic-field modulation 0.05 Hz gives 10^{-7} rad phase noise for a 44-minute integration.Comment: This draft has been presented in the 5th Edoardo Amaldi Conference on Gravitational Wave
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