共查询到20条相似文献,搜索用时 9 毫秒
1.
An ant colony optimisation (ACO)-based multiuser detector assisted by spatial diversity reception using direct-sequence CDMA is proposed. By taking advantage of heuristic values and the collective intelligence of ACO, the proposed detector offers almost the same bit error rate (BER) performance as the full-search-based optimum multiuser detector does, while greatly reducing the computational complexity. The near-far resistance of the ACO-based multiuser detector is also examined. The BER performance for a ten-user system deteriorates scarcely when the interfering users' energy is 12 dB higher than that of the desired user. 相似文献
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The problem of joint source-channel and multiuser decoding for code division multiple access channels is considered. The block source-channel encoder is defined by a vector quantiser (VQ). The jointly optimum solution to such a problem has been considered before, but its extremely high complexity makes it impractical for systems with medium to large number of users and/or medium to large size of VQ codebook. Instead, the optimum linear decoder with a much lower complexity that minimises the mean-squared error is introduced. The optimum linear decoder is soft in the sense that it utilises all the soft information available at the receiver. Analytical and simulation results show that at low channel signal-to-noise ratio region, the proposed decoder's performance is almost the same as that of the jointly optimum decoder and significantly better than that of the tandem approaches that use separate multiuser detection and table-lookup decoding. 相似文献
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Performance of coding and modulation systems in fading channels is usually analysed under the assumption that the receiver has perfect knowledge of channel condition. However, various shortcomings in practical channel estimation techniques lead to imperfections, resulting in channel estimation errors. The authors analyse a practical coding and modulation scheme for multiple-antenna systems considering channel estimation errors. The novelty of this study resides in providing error probability bounds for concatenated trellis coded modulation (TCM) or bit-interleaved coded modulation (BICM) schemes with orthogonal space--time block codes (OSTBC) under imperfect channel estimation assumption. Moreover, our analytical results quantify the performance degradation associated with various levels of channel estimation error variance. The authors also show that if channel estimation quality does not improve sufficiently with SNR, there would be error floor in performance, such that the coded system could get outperformed by a system with differential signalling that requires no channel estimation. Simulation results are presented, which confirm the validity of the analytical results. 相似文献
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We address here the problem of finding a concatenated structure in a linear code ? given by its generating matrix, that is, if ? is equivalent to the concatenation of an inner code B 0 and an outer code E 0, then find two codes B and E such that their concatenation is equivalent to ?. If the concatenated structure exists and is non trivial (i.e. the inner code B is non trivial), the dual distance of ? is equal to the dual distance of B. If this dual distance is small enough to allow the computation of many small weight words in the dual of ?, it is possible to recover first an inner code B, then an outer code E whose concatenation is equivalent to ?. These two codes are equivalent respectively to the original inner and outer codes B 0 and E 0. 相似文献
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The problem of estimating the return power in a laser integrated radar (lidar) system in the presence of multiplicative noise and partially unmodeled dynamics is explored. Several nonlinear methodologies are reviewed and compared to develop a systematic approach to signal model identification and estimation. The situations considered operate in mode-switching environments, that is, the desired unknown parameters are allowed to vary according to sudden jumps exhibiting discontinuous behavior at random times. Partitioning-based, parallel-structured techniques are shown to be significantly superior to the usual extended Kalman filter algorithm. 相似文献
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Papandreou N. Antonakopoulos T. 《IEEE transactions on instrumentation and measurement》2005,54(6):2204-2212
Far-end crosstalk identification results to improved frequency spectrum utilization in asymmetric digital subscriber line (ADSL) systems. The accurate determination of the crosstalk coupling function is a demanding task that is affected by various system impairments. In this paper, we present a new real-time method that exploits the exchange of signaling information between the modems of a new activated ADSL line in order to determine the crosstalk function between this line and any other active line in the binder. Each remote modem subtracts the decoded data from the received signal, decreases the noise effect of the previously identified crosstalkers, is synchronized to the disturber's timing and then applies a least-squares estimator for identifying the new crosstalk coupling function. The method is used along with a maximum margin bit-loading algorithm in order to provide the best possible estimation results. The estimated crosstalk coupling functions, the transfer function of each line and the noise measurements can be exploited by a centralized bit-loading algorithm for maximizing the total system performance in terms of maximum achievable data rate and/or bit error rate. 相似文献
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The problem of multiuser scheduling in multicarrier (MC) systems under practical physical-layer constraints and implementations is considered. Subchannel allocation is an important resource assignment issue in multiuser MC systems. The multiuser scheduler is decoupled into a multiuser selector and a subchannel allocator, which result in a sub-optimum multiuser scheduler with significantly reduced computational complexity. Given an active user subset and a channel set, the multiuser scheduling problem then refers to the optimal subchannel allocation to maximise the instantaneous system throughput subject to certain fairness constraints. Efficient adaptive algorithms are developed for optimal subchannel allocation. The extension of the algorithms for tracking the time-varying optimum, which occurs in non-stationary environments, is also addressed. Simulation results are presented to demonstrate the performance of the proposed algorithms in terms of the throughput maximisation, the fast convergence, the excellent tracking capability in time-varying environments, the achievable throughput of the proposed multiuser scheduler as well as the long-term fairness 相似文献
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Yu. A. Kuzma-Kichta A. S. Komendantov Yu. G. Khasanov M. N. Burdunin 《Journal of Engineering Physics and Thermophysics》1988,55(6):1325-1328
Data have been obtained on the bounds to the transitional region and the maximal wall temperature fluctuations in a heat-transfer crisis.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 6, pp. 885–889, December, 1988. 相似文献
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Abstract This paper presents a method of speaker identification over telephone system based on channel‐effect cancellation. A set of inverse channel spectra is chosen as the basis for generating a channel‐effect‐cancellation filter. The speaker identification scheme is based on vector quantization where the codebooks of each speaker are trained without channel effect. When the speech signal of a speaker goes through the telephone system, a proper channel‐effect‐cancellation filter is generated to minimize the channel effect on the speech signal. The experiments show that the channel effect is mostly contributed by telephone handsets rather than by the transmission lines. By using the proposed method, an identification rate of 93.8% can be achieved for 100 speaker tests. 相似文献
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在多用户正交频分复用(OFDM)系统中设计一种新颖的子载波-功率分配方法来最大化用户数据传输速率.这个方案分成两部分,子载波分配和功率分配.其中,子载波分配方法是在信道容量矩阵中将信道容量最好的子载波首先进行分配,功率分配采用注水方法.研究和模拟结果表明,该算法在只改变各个子载波增益系数的基础上,基本保持了较低的复杂度,并且极大地提高了用户数据传输速率. 相似文献
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The flow of two superposed viscous fluid layers in a two-dimensional channel confined between a plane and a wavy or indented
wall is studied by analytical and numerical methods at arbitrary Reynolds numbers. The interface between the two fluids may
exhibit constant or variable surface tension due to an insoluble surfactant. The flow is computed from a specified initial
condition using the immersed-interface method on a curvilinear grid constructed by conformal mapping. The numerical simulations
illustrate the effect of geometrical nonlinearity and reveal that inertia may increase or decrease the amplitude of the interface
profile at steady state depending on the flow parameters. Increasing either the Reynolds number or the wall amplitude above
a certain threshold value provokes flow instability and overturning of the interface. In the Appendix, a linear perturbation
analysis is performed for arbitrary Reynolds numbers on the assumption of small-amplitude sinusoidal undulations, and results
for the amplitude and phase shift of the interfacial and surfactant concentration wave are documented for a broad range of
flow conditions. It is found that inertia may have a mixed effect on the deformation and phase shift, while the surfactant
promotes the deformation of the interface under most conditions. 相似文献
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A. M. Gonopol'skii A. I. Dautov R. Kh. Ismagilov F. A. Slobodkina 《Journal of Engineering Physics and Thermophysics》1977,33(1):774-777
The dependence of the heat-transfer coefficient in a plasmotron channel on gas flow rate, pressure, and electrical power is studied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 1, pp. 50–53, July, 1977. 相似文献
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Summary A study is made on the unsteady flow of a viscous and incompressible fluid in a channel bounded by two parallel plates for the two cases, (1) when it is rotated impulsively with the constant angular velocity and (2) when the rotating channel is stopped abruptly. In both cases exact solutions of the equations of motion are obtained. It is found that in the first case the steady state conditions are reached in an oscillatory manner, while this phenomenon is not found in the latter case.With 4 Figures 相似文献
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R. Kh. Ismagilov 《Journal of Engineering Physics and Thermophysics》1983,45(6):1394-1396
The distribution function for turbulent frictional stress is proposed for flow in a cylindrical channel. Formulas are obtained for the calculation of the velocity distribution according to the well-known law of hydraulic drag of the channel. 相似文献
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A system model that employs beamforming at the physical (PHY) layer and different scheduling algorithms at the medium access control (MAC) layer is used in a downlink environment where two users are served simultaneously. The effect of the scheduling algorithms on the system performance is assessed in terms of total system capacity. The scheduling algorithms considered, choose users either randomly, or on the basis of their instantaneous signal-to-noise ratio (SNR) and/or their angular location around the base station. A semi-analytical framework for the capacity analysis is also presented. The results obtained from the numerical model are shown to be consistent with those based on the semi-analytical framework. It is shown that explicitly taking into consideration at the MAC layer the angular location of mobile users around the base station along with instantaneous SNR for the selection of users that are served simultaneously leads to an improved system capacity. This improvement is the result of reduced interference that simultaneously served users cause on each other. The results show that joint addressing of the PHY and MAC layer issues in an integrated cross-layer framework is important for achieving maximal system performance 相似文献