Ant colony optimisation-based multiuser detection for direct-sequence CDMA systems with diversity reception

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.     

Optimum linear decoding of vector quantisation transmitted over a CDMA channel

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.     

Concatenated coded modulation techniques and orthogonal space-time block codes in the presence of fading channel estimation errors

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.     

On the Concatenated Structure of a Linear Code

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.     

Joint estimation and identification of lidar log power returns in a switching environment

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.     

利用二阶循环平稳性的信道自适应盲辨识

提出了利用二阶循环平稳性信道盲辨识的自适应求解方法。通过递推更新循环相关函数,从而完成了循环相关矩阵的自适应估计。利用共轭梯度搜索的方法实现信道的自适应盲辨识,并讨论了梯度算法中步长选取的问题,提出了可变步长选取的方法。由于采用二阶循环统计量,因此算法既简单又可以很好的抑制平稳加性有色噪声。计算机仿真表明,在低信噪比情况下,自适应算法能很好的工作。     

浅海中低频水声信道仿真研究

在中低频段（通常为数百至数千赫兹频率范围）,传播损失、时空相关性以及时空平稳性等水声信道特性是主、被动目标探测和远程通讯技术研究的重点。为了模拟信道的时空去相关特性,应用KrakenC传播模型得到理想信道传递函数H（r,ω）,并在此基础上,提出了新的基于信道时延的相位加扰方法。通过数值仿真,该方法可以很好地在统计特性上模拟海试LoFAR’08中的实际浅海信道测量数据。测量数据由拖曳式电火花声源（有效带宽为300Hz~2.5kHz）激励浅水信道得到。     

大气激光通信中的级联空时分组码

空时分组码虽然获得了满分集增益,但因不能提供编码增益而使系统性能受到限制.首先介绍了光MIMO系统的信道模型;其次针对Q-PPM(Q>2)调制方式,完成了对已有空时分组码的改进,并和RS码相级联而提出了一种级联空时分组编码方案.在此基础上分析了该方法的误码性能.最后,利用仿真实验进一步验证了该方法的可行性,并和级联重复码的性能进行了对比.结果表明:在大气激光通信中,随着信噪比的增加,级联空时分组码获得了较高的编码增益,有效抵御了大气湍流效应.     

Far-end crosstalk identification method based on channel training sequences

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.     

Adaptive subchannel allocation in multiuser multicarrier systems

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     

基于凸集投影的水声信道辨识算法

研究了使用凸集投影方法进行水声信道辨识的可行性,给出了凸集投影常用的凸集约束的条件,并推导了在复数域中的凸集约束的表达式。计算机仿真和实验结果证明,在较高信噪比的情况下,使用凸集投影方法可以正确估计水声信道中的多途幅度衰减和相位变化,其分辨率优于传统最大似然估计器-匹配滤波器,可作为研究水声信道的有力工具。     

采用高阶统计的水声信道盲辨识算法

1引言传统的水声信道辨识技术,需要事先发射一组训练码用以获取当时信道的响应函数,这种方法存在的问题是耽误通信时机、通信协调有一定不便。更重要的是水声信道是空时变化的,通过某时训练码     

Heat-transfer crisis in a channel

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.     

Speaker identification over telephone system based on channel‐effect cancellation

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.     

一种新颖的多用户OFDM资源分配算法

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.     

Two-layer flow in a corrugated channel

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.     

Heat transfer in a plasmotron channel

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.     

Flow in a channel rotated impulsively

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     

Turbulent flow in a cylindrical channel

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.     

Capacity analysis for a multiuser cross-layer downlink model in the presence of fading and interference

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