Switched Dual Diversity Reception of M-ary DPSK Signals on Nakagami Fading Channels

The paper deals with dual diversity reception of M-ary differential phase-shift keying modulated signals in the presence of additive white Gaussian noise and Nakagami-distributed slow and nonselective fading. The performance of a switched diversity system is analysed and compared to that of the predetection selection diversity combining scheme. The general case of correlated diversity branches is considered, without restrictions on the fading severity parameter. Average symbol error rate formulas are analytically derived in terms of integral expressions that can be easily computed via numerical integration routines. Moreover, the numerical evaluation of the optimum switching threshold is carried out and the influence of the fading severity parameter, the branch correlation, and the cardinality of the symbol alphabet is analysed. Finally, three fixed switching threshold strategies that allow to obtain a satisfactory diversity gain are considered.     

自适应递推最小二乘灰色均衡器用于时变信道

本文提出了适用于时变信道的自适应递推最小二乘灰色均衡的新思想，以收敛性比较。最小二乘灰色均衡器优于传统的最小二乘均衡器，而以时变信道上的误码率来看，其性能是盲均衡器盲均衡所不能比拟的，而且也优于传统的均衡器，理论分析及计算机模拟表明，自适应最小二乘灰色均衡器是时变信道上性能优良的均衡。     

Simulating Ion Permeation Through the ompF Porin Ion Channel Using Three-Dimensional Drift-Diffusion Theory

Ionic channels, natural nanotubes found in biological cells, are interesting to the electronics community because they display a range of device-like functions. The purpose of this paper is to illustrate how the solution methodology, developed for 3-D drift-diffusion models of semiconductor devices, can be applied to ion permeation in ionic channels. For this study we select the ompF porin channel, found in the membrane of the E. coli bacterium. The self-consistent 3-D model is based on the simultaneous solution of Poisson's equation, which captures Coulomb interactions, and a current continuity equation for each ion species, describing permeation down an electrochemical gradient. Water is treated as a uniform background medium with a specific dielectric constant. For demonstration, a simple model is assumed for the mobility/diffusivity of each ionic species and we compute the current-voltage relations for ompF porin in a wide range of conditions. Agreement with experimental measurements is surprisingly good given that the model uses the ion diffusivity as the only calibrated parameter.     

Co-Channel Interference in Cellular Mobile Radio Systems with Coded PSK and Diversity

In this paper, the performance of coding and diversity in narrowband wireless cellular systems affected by fading, shadowing and co-channel interference is analyzed. We consider low-order diversity, that can be practically realized for both coherent and differential phase shift keying. We assume that the shadowing random processes affecting all transmitted signals do not vary appreciably over the transmission duration. Fading, on the contrary, is assumed to vary more rapidly. Our main focus here is on outage probability. After choosing a performance indicator, its expectation is taken with respect to fading and co-channel interference, conditionally on shadowing. Hence, the resulting average performance indicator is a random variable. The probability that this random variable exceeds a specified threshold defines the outage probability. We consider as performance indicators (i) the channel cut-off rate R₀ and (ii) the bit error rate P_b of an actual coded scheme. As we are interested in interference-limited, rather than power-limited systems, we evaluate both R₀ and P_b for very high signal-to-noise ratios. Results are parameterized by the frequency reuse factor and the diversity order.     

河型成因研究及其应用

大水淤滩刷槽、小水淤槽、河性对河型就在这对相互矛盾过程的相互交替、相互抵消、相互消长中形成。演化。前者导向好河，后者导向坏河。两者的强弱对比，就是河性河型差异的总根据。可用来水来沙关系的ｍ值来表达这种对比，ｍ〉２．５的将形成单股窄深蠕动性河型，ｍ〈２．５的则形成多宽浅游荡河型。改变来水来沙关系的ｍ值，大水淤滩刷槽、小水淤槽过程的强弱地经也就改变，河性河型逐步改变。这就是调水调沙、改造河性的真谛。将     

Stability and Erosion in Grassed Channels

Grass is a cost-effective form of erosion control. Since grass prevents erosion, the relationship between grass properties and erosion rate in grassed open channels is highlighted and analyzed within the context of channel stability. The deformation of grass caused by the flow’s momentum has been taken into consideration. Results are in good agreement with the available experimental erosion rate data for grassed channels. The purpose of this paper is to show that the amount of deformation of a grass channel lining due to flow can be used to estimate the erosion rate, and, as a result, lining deformation can be used as an indicator of channel stability. The method is simple enough to be useful for design.     

Flow Resistance and Momentum Flux in Compound Open Channels

New formulations are presented for flow resistance and momentum flux in compound open channels. As implemented in the St. Venant equations, these formulations facilitate a physically enhanced approach to evaluating conveyance, roughness, stage-discharge relationship, and unsteady flood routing in compound open channels. An analysis using steady flow data from the well-controlled experiments at the large-scale Flood Channel Facility, HR Wallingford, demonstrates the ability of the present approach to properly resolve the discontinuity of overall roughness across the main-channel bankfull level. Also, the proposed formulations are shown to be conducive to obviating the long-standing computational difficulty in unsteady flood routing due to small flow depths over flat and wide floodplains. The present work should find general applications in one-dimensional computation of river flows.     

Effect of bit-to-bit dependence on packet error rate using asynchronous DS-CDMA for mobile packet radio networks

The probability of packet success for asynchronous direct sequence code division multiple access (DS-CDMA) over the multipath fading channel is investigated under different fading conditions and for different cases. We studied the bit-to-bit dependence caused by the multipath fading and by the multiple access interference (MAI) originating from the chip and phase offsets between the desired and interfering signals. We investigated the effect of using the Gaussian versus the improved Gaussian process on the computation of probability of packet success as well as the effect of the bit-to-bit dependence within a packet. The improved Gaussian approximation provides more accurate values for the probability of bit error for any number of simultaneous users, while it also allows us to incorporate the effects of bit-to-bit dependence into the calculations of the probability of packet success.This paper was presented in part at the 17th Biennial Symposium on Communiations, Kingston, June 1994. This work was supported by a strategic grant (STR-0100720) from the Natural Sciences and Engineering Research Council (NSERC) of Canada.     

Analysis of the performance of energy harvesting cognitive relay networks over κ-μ fading

Aiming at the problems of small coverage, short lifetime and diversity link channel attenuation in energy-constrained cognitive relay networks, the outage performance of energy harvesting multi-hop cognitive relay networks over complicated fading channel scenarios are studied. First, the κ-μ distribution is adopted to represent various single and mixed line-of-sight and non-line-of-sight fading channel scenarios. Then the dedicated power beacon assisted energy harvesting underlay multi-hop decode-and-forward cognitive relay networks are constructed. The exact and asymptotic unified outage probability expressions for secondary networks are derived over the κ-μ fading channels. Simulation results show that the secondary outage probability can be monotonically decreased with the increase of the power beacon signal’s power or/and primary networks’ interference constraint until it tends to saturation on the condition of various fading channel scenarios, and the secondary networks’ outage probability can be degraded with the deterioration of the channel link condition when the primary networks’ interference constraint is lower, and the secondary networks’ outage performance can also be increased with the improvement of the channel link condition when the primary networks’ interference constraint is higher. The secondary networks’ outage probability can be decreased by reasonable settings of the hop number and energy harvesting ratio according to the type of fading channel scenarios.     

流道截面与增材制造加工工艺参数对液压集成块成型质量的影响

液压系统广泛应用于工程领域,提高功率密度是其重要发展方向,其中液压集成块轻量化设计是提高功率密度的有效手段。通过增材制造(AM)灵活的加工特性能使集成块重量降低,是高功率密度液压驱动的一种有效的设计方法,但目前增材制造加工的流道存在塌陷形变、尺寸精度低、内部流道粗糙度高等问题。以提升增材制造流道成型质量为研究目标,选区激光熔融(SLM)为加工方法,探讨流道横截面及打印模型中有无支撑添加对成型质量的影响,并通过非接触测量对打印模型内部流道尺寸进行测量得到定量分析。结果表明,对于圆形流道,有支撑结构有较好的打印结果,菱形流道形变量小于圆形流道。进一步通过改变打印参数对内流道表面质量进行研究,结果显示适当选择工艺参数可以提高表面质量。