Hybrid Turbo FEC/ARQ Systems and Distributed Space-Time Coding for Cooperative Transmission

Cooperative transmission can be seen as a “virtual” MIMO system, where the multiple transmit antennas are in fact implemented distributed by the antennas both at the source and the relay terminal. Depending on the system design, diversity/multiplexing gains are achievable. This design involves the definition of the type of retransmission (incremental redundancy, repetition coding), the design of the distributed space-time codes, the error correcting scheme, the operation of the relay (decode & forward or amplify & forward) and the number of antennas at each terminal. Proposed schemes are evaluated in different conditions in combination with forward error correcting codes (FEC), both for linear and near-optimum (sphere decoder) receivers, for its possible implementation in downlink high speed packet services of cellular networks. Results show the benefits of coded cooperation over direct transmission in terms of increased throughput. It is shown that multiplexing gains are observed even if the mobile station features a single antenna, provided that cell wide reuse of the relay radio resource is possible.     

High-Speed Downlink Access in 3G Systems: A Portent for the Evolution of 4G Systems?

Due to the need of operators to protect the high levels of investment inthird generation (3G) wireless systems, it seems likely that the path tofourth generation (4G) wireless systems will be evolutionary rather thanrevolutionary. Currently there are a number of proposals beforestandardisation bodies such as 3GPP and 3GPP2 for extending the relevant3G systems to handle asymmetrical, packet-orientatedservices with very high downlink capacities. These proposals, whichinclude HDR and 1XTREME, may pave the way towards 4G systems.This paper outlines some of the salient features of HDR and 1XTREME:adaptive modulation, advanced hybrid ARQ, new fast access controlschemes, etc. On the basis of the trends inherent in theseproposals, some possible directions for the development of 4G systems arediscussed.     

SystemC:一种新的系统建模语言

文章介绍了一种国外正在研究的新的系统建模语言SystemC，因其较好地结合了面向对象的设计方法和硬件建模的特点，从而有望解决系统建模和HW／SW协同设计中等一系列问题。     

A Real Time Transport Scheme for Wireless Multimedia Communications

In wireless communications systems, a mobile station is typically equipped with limited processing capability and buffer space for transmitting and receiving. The radio link is usually found to be noisy and its propagation delay is sometimes non-negligible as compared with the packet transmission delay. And because of the necessity of flow control and packet retransmission upon error, the delay and throughput performance cannot satisfy the need of a particular traffic type, i.e., real-time multimedia. This paper presents a scheme suitable for the above condition, called the Burst-oriented Transfer with Time-bounded Retransmission (BTTR). The present scheme uses a large transmission window for sending/receiving a burst of time-sensitive data and, within this window, another smaller observation window is repeatedly used for error status feedback via the backward channel. There is time limitation on each retransmission such that the burst of data can be received in a timely manner, however, with some degradation on the packet loss rate. An analysis is given in terms of the expectations of delay, throughput, and packet drop rate. A comparison with an error-free link protocol will also be given. The result shows that the proposed scheme can meet the delay and throughput requirement under reasonable packet drop rate.     

Cooperative Hybrid‐ARQ Protocols: Unified Frameworks for Protocol Analysis

Cooperative hybrid‐automatic repeat request (HARQ) protocols, which can exploit the spatial and temporal diversities, have been widely studied. The efficiency of cooperative HARQ protocols is higher than that of cooperative protocols because retransmissions are only performed when necessary. We classify cooperative HARQ protocols as three decode‐and‐forward‐based HARQ (DF‐HARQ) protocols and two amplified‐and‐forward‐based HARQ (AF‐HARQ) protocols. To compare these protocols and obtain the optimum parameters, two unified frameworks are developed for protocol analysis. Using the frameworks, we can evaluate and compare the maximum throughput and outage probabilities according to the SNR, the relay location, and the delay constraint. From the analysis we can see that the maximum achievable throughput of the DF‐HARQ protocols can be much greater than that of the AF‐HARQ protocols due to the incremental redundancy transmission at the relay.     

SW46/D型高速卷绕机转动件平衡分析

分析了德国 Barmag公司 SW46/D型高速卷绕机转动件平衡原理 ,指出降低该机转动件许用不平衡量 ,可减小振动 ,降低噪声 ,从而延长机器的修理周期 ,降低维修费用。     

运用SW6进行双管板换热器管板的计算

由于ＳＷ６－９３（ＳＷ６－１９９８）软件包没有双管板换热器管板的计算模块,因此在设计计算时,我们将双管板换热器分成几个单管板换热器进行计算。几年来设计了数十台固定双管板换热器（卧式、立式）和Ｕ形管双管板换热器,下面介绍分解模式。     

Till which pressures the fluid phase EOS models might stay reliable?

This paper examines the performance of three fluid phase equations of state in predicting the available very high-pressure data of n-pentane, n-hexane, cyclohexane, toluene, dichloromethane, chloroform and methanol. It is assumed that the key for success at such pressures is establishing the appropriate interrelation between the densities of saturated liquids and the imaginary infinity pressure states. The recently proposed EOS that combines SAFT with the cohesive term of cubic EOS (SAFT + Cubic) most likely satisfies this criterion. According to this model, the saturated liquid densities at T_r = 0.4 are approximately 2.1 ± 0.1 times smaller than the densities predicted at the infinity pressure. With this ratio SAFT + Cubic yields reliable density estimations as far as the substances remain liquid (stable or metastable) in all the considered cases. Its pressure limit for accurate predictions of the auxiliary properties such as sound velocities and bulk moduli appear to be lower, typically around 1 GPa.     

SW6计算软件包中钢管壁厚负偏差的取值问题

无缝钢管壁厚负偏差的取值是压力容器设计中的重要环节,若钢管壁厚负偏差取值不当,会给压力容器带来安全隐患。作者根据无缝钢管标准与SW6-1998V5.0计算软件包关于无缝钢管壁厚负偏差的取值,进行了分析对比,提出了相应建议。