Operational aspects of adsorption air‐conditioner used in diesel locomotive

A locomotive cabin adsorption air‐conditioner has been equipped in #DF4B‐2369 locomotive; and has been successfully run for 2 years. It is powered by waste heat from the exhaust of the diesel engine. The influence on heat transfer is described by the equivalent heat transfer coefficient or thermal resistance of components inside the adsorber. The variation of adsorption capacity is expressed by a non‐equilibrium adsorption function. The dynamic heat transfer process of adsorption air‐conditioning system is treated with the lumped parameter method. Some typical running experimental results are present. The diesel engine rotating speed and locomotive speed influenced on the refrigeration system are discussed. The maximum mean refrigeration power is regarded as an objective function. Based on experiments and theoretical analysis, the running characteristics of the air‐conditioning system are optimized. Some techniques of performance improvement are suggested as well. Copyright © 2006 John Wiley & Sons, Ltd.     

On scheduling and clustering in hierarchical TH-PPM UWB wireless ad hoc networks

Ultra wideband (UWB) systems are considered as the key wireless infrastructure platforms for efficient short-range communications. In particular, the UWB based mobile computing systems are envisioned to be attractive solutions to various ad hoc networking applications. However, due to UWB’s unique physical characteristics, the traditional resource management schemes for ad hoc networks cannot be applied to UWB based systems directly. In this paper, we consider the bandwidth scheduling problem in a UWB based hierarchical wireless ad hoc network, which is typically used in an enterprise-scale mobile computing environment. Based on the mathematical analysis and the computer simulations, it is demonstrated that our proposed scheduling scheme exhibits close-to-optimal performance governed by the proportional fairness (PF) constraint. Moreover, a novel self-organized clustering method is designed to improve the system throughput while meeting the PF constraint. Simulation results suggest that the proposed clustering method is effective under various system configurations.

Adaptive channel and power allocation of downlink multi-user MC-CDMA systems

The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very attractive multiple access technique for high-rate data transmission in the future wireless communication systems. This paper is focused on the joint channel and power allocation in the downlink transmission of multi-user MC-CDMA systems and considers the throughput maximization problem as a mixed integer optimization problem. For simple analysis, the problem is divided into two less complex sub-problems: power allocation and channel allocation, which can be solved by a suboptimal Adaptive Power Allocation (APA) algorithm and an optimal Adaptive Channel Allocation (ACA) algorithm, respectively. By combining APA and ACA algorithms, an adaptive channel and power allocation scheme is proposed. The numerical results show that the proposed APA algorithm is more suitable for MC-CDMA systems than the conventional equal power allocation algorithm, and the proposed channel and power allocation scheme can significantly improve the system throughput performance.     

Downlink transmission of broadband OFCDM systems-part III: turbo-coded

Orthogonal frequency and code-division multiplexing (OFCDM) systems have been introduced for high-speed data transmission in future wireless mobile communications. In this paper, a hybrid multicode interference cancellation (MCI) and minimum mean-square error (MMSE) detection scheme is presented for the turbo-coded OFCDM systems. Channel estimation based on a code-multiplexed pilot channel is employed. The weights of the hybrid detection are derived theoretically and an effective method to generate the weights in practical applications is proposed. By means of computer simulation, the effects of system parameters on the performance are studied extensively. It is shown that the hybrid detection outperforms pure MMSE detection in various channel conditions, especially for high-level modulation schemes. To carry out interference regeneration for the hybrid detection, the conventional turbo decoding algorithm which only decodes systematic bits should be extended to decode parity bits as well. Moreover, two iterations in turbo decoding are sufficient to provide good performance for the system with the multistage hybrid detection. Finally, given time-domain spreading factor N/sub T/, the system performance improves with frequency-domain spreading factor N/sub F/. However, the frequency diversity gain is saturated when N/sub F/ is large (i.e., N/sub F//spl ges/16).     

铁闪锌矿与黄铁矿的分离技术进展

由于锡铁山独特的成矿条件,使一部分菱锌铁矿无法回收,为了合理利用国这矿产资源,投产以来锌硫浮选工艺从等可浮、部分优先、全优先到目前的优先混合,不断进行技术改造,并且采用大型浮选机联合机组,使矿山取得显的经济效益。本系统地论述了各个历史阶段锡铁山铁闪锌矿与黄铁矿的分离工艺及生产情况,总结了现场生产存在的不利因素,指出了今后的主要奋斗方向和目标。     

Two-Stage Acquisition in Time-Hopping Impulse Radio Systems for UWB Communications

Ultra wideband impulse radio is a promising radio technology for networks delivering extremely high data rates at short ranges. The use of extremely short duration pulses however makes synchronization task more difficult. In this paper a two-stage acquisition with serial search noncoherent correlator for time hopping impulse radio is proposed. The proposed two-stage acquisition scheme gets chip timing synchronization, and aligns phase of the local time-hopping code in two stages successively. With the aid of flow-graph approach, the analytical expressions are presented for the mean acquisition time and the probability of acquisition. Numerical results in a slow fading channel show that the proposed two-stage acquisition method can offer much shorter mean acquisition time or much higher probability of acquisition than that of the conventional acquisition.     

Approximate interference of a microcellular spread spectrum system[comment]

An approximate technique for determining the adjacent cell interference of a microcellular code division multiple access (CDMA) system is described in the original paper [see ibid., vol. 31, no. 20, p. 1782-3, 1995]. An illustration of the hexagonal cellular model is given in that paper. The argument for the proposed technique is the following: since the variance of adjacent cell interference depends on the position of the mobile user in an adjacent cell, it is difficult to evaluate the exact value of variance for this hexagonal cellular model. To avoid dependence on position, the calculated variance of adjacent cell interference is averaged over the area of the cell where the mobile user is located. Furthermore, the hexagonal cell is approximated with a circular cell of equal area criterion. However, the approximation of a hexagonal cell by a circular cell with equal area is inaccurate     

Adaptive LMS filters for cellular CDMA overlay situations

This paper extends and complements previous research we have performed on the performance of nonadaptive narrowband suppression filters when used in cellular code-division multiple-access (CDMA) overlay situations. An adaptive least mean square (LMS) filter is applied to a cellular CDMA overlay in order to reject narrowband interference. An accurate expression for the steady-state tap-weight covariance matrix is derived for the real LMS algorithm for arbitrary statistics of the overlaid interference. Numerical results illustrate that when the ratio of the narrowband interference bandwidth to the spread spectrum bandwidth is small, the LMS filter is very effective in rejecting the narrowband interference. Furthermore, it is seen that the performance of the LMS filter in a CDMA overlay environment is not significantly worse than the performance of an ideal Wiener filter, assuming the LMS filter has had sufficient time to converge     

基于立体十字阵的闪电定位方法

为获取闪电产生雷声源的相对位置信息,利用空间几何方位估计算法,建立由七个传声器组成的立体十字阵,提出一种闪电定位方法,实现基于阵列的全方位闪电探测。首先,根据雷声源到各传声器的距离,推导得出雷声源的坐标计算公式。其中,Z轴的一对传声器用以确定坐标z向参数的正负。然后,基于间接测量误差理论,对阵元间距、雷声源的角度及距离,与定位精度的关系进行研究与分析。仿真结果表明,本文方法测得雷声源的坐标误差率约为0.01%,角度误差率约为0.005%。这在取得较好定位效果的同时,有效解决现有工作运算量偏大、定位精度偏低的问题。     

Low-complexity and high-performance receive beamforming for secure directional modulation networks against an eavesdropping-enabled full-duplex attacker

Dear editor, Directional modulation (DM),as an advanced physical-layer security (PLS) transmission technique,is suitable for the line-of-sight (LoS) propagation...