软件无线电技术及其在移动通信基站中的应用

介绍了软件无线电技术的定义和有关概念，分析了软件无线电技术在移动通信系统中应用的优越性和可能性，讨论了用软件无线电结构开发基站硬件平台的主要技术难点和研究方向。     

Intermetallic reactions in a Sn-20In-2.8Ag solder ball-grid-array package with Au/Ni/Cu pads

The intermetallic compounds formed during the reflow and aging of Sn-20In-2.8Ag ball-grid-array (BGA) packages are investigated. After reflow, a large number of cubic-shaped AuIn₂ intermetallics accompanied by Ag₂In precipitates appear in the solder matrix, while a Ni(Sn_0.72Ni_0.28)₂ intermetallic layer is formed at the solder/pad interface. With further aging at 100°C, many voids can be observed in the solder matrix and at the solder/pad interface. The continuous distribution of voids at the interface of specimens after prolonged aging at 100°C causes their bonding strength to decrease from 5.03 N (as reflowed) to about 3.50 N. Aging at 150°C induces many column-shaped (Cu_0.74Ni_0.26)₆(Sn_0.92In_0.08)₅ intermetallic compounds to grow rapidly and expand from the solder/pad interface into the solder matrix. The high microhardness of these intermetallic columns causes the bonding strength of the Sn-20In-2.8Ag BGA solder joints to increase to 5.68 N after aging at 150°C for 500 h.     

Dynamic Waveband Switching in WDM Mesh Networks Based on a Generic Auxiliary Graph Model

Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings.     

Formulation and characterization of anisotropic conductive adhesive paste for microelectronics packaging applications

There has been a steadily increasing interest in using electrically conductive adhesives as interconnecting materials in electronics manufacturing. In this paper, several anisotropic conductive adhesive (ACA) pastes were formulated, which consist of diglycidyl ether of bisphenol F or diglycidyl ether of bisphenol A as polymer matrix, imidazoles as curing agents, and different sizes of silver (Ag) powders or gold (Au)-coated polymer spheres as conductive particles. The effects of ACA resin and different curing agents, as well as different conductive particles, on flexible substrate of the flip-chip joint were studied. The results show that the size and type of different conductive particles have very limited influence on an ACA flip-chip joint. The ACA resin as well as the curing agent can affect the reliability of the joint. The same results can be applied for the failure analysis of ACA flip-chip technology.     

高超声速飞行器二维全尺寸流场数值模拟

基于有限体积法和Roe离散格式进行了数值计算,分析了不同马赫数和攻角下二维全尺寸飞行器的流场,模拟了发动机内部氢/空气燃料的燃烧反应。计算结果表明:设计马赫数条件下,通过采用三级楔形体(压缩角度8°/6°/7°)对气流进行压缩,能保证进气道有足够的气流捕获量,经过压缩后的高压气体与氢燃料充分混合反应,发动机能以良好的状态工作。     

数字有线电视机顶盒节目指南的实现

本文介绍了电子节目指南信息的构成及MPEG-PSI和DVB-SI信息规范，提出了一种EPG信息的存储结构和节目数据库的生成方案，并据此介绍了如何在数字有线机顶盒中生成电子节目指南EPG。     

The Impacts of an Electronic Marketplace with Multiple Independent Retailers for Smart Grocery Ordering Systems

This study investigates the impacts of an electronic marketplace with multiple independent retailers for a smart grocery ordering system. Apart from replenishing products from suppliers, the system can also purchase/sell products from/to the electronic marketplace through ‘spot shops’. Both static and dynamic pricing models for the electronic marketplace are developed. An extensive numerical experiment is conducted and the results show that under both static and dynamic pricing, (i) the inventory cost of the aggregated supply chain is significantly reduced; (ii) each participant also enjoys significant cost savings from employing the electronic marketplace. Furthermore, the cost savings increase as the lead times from suppliers increase and/or the variability of their demands increases. The participants’ cost savings also increase as more participants employ the electronic marketplace.     

Electromigration in a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi Solder Stripe Between Two Cu Electrodes Under Current Stressing

The electromigration behavior of a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi solder stripe between two Cu electrodes under current stressing at various densities has been investigated for a current stressing time of 72 h and a temperature of 120°C. After current stressing at a density of 1.0 × 10⁴ A/cm², the solder matrix exhibited a slight microstructural change as well as formation of a distributed Cu₆Sn₅ phase near the anode-side solder/Cu interface. Upon increasing the current density to 3.9 × 10⁴ A/cm² and 5.0 × 10⁴ A/cm², a high density of distributed Cu₆Sn₅ phase was formed across the entire solder stripe, resulting in pronounced microstructural change of the solder. Hillocks were also formed near the anode-side interface due to accumulation of a Sn-rich phase, a Bi-rich phase, and a distributed Cu₆Sn₅ phase, while voids were formed in the solder matrix and at the opposite cathode side. The mechanisms of formation of the distributed Cu₆Sn₅ phase and migration of Bi and Sn are discussed.     

A model for calculating channel share of 802.11 access points with overlapping wireless cells

Consider a collection of 802.11 access points. Each serves as the gateway to the Internet for clients in its WiFi cell. These cells have an arbitrary interference pattern, and reception at a client may be corrupted by transmissions nearby. The popularity of WiFi has made such dense deployment increasingly common. As interference can seriously degrade performance, there is much interest in optimizing the configuration of these cells. One factor to consider in optimization is channel share, defined as the useful fraction of channel bandwidth that an access point gets when there is downlink traffic saturation. Interference affects channel share on the sender side through carrier sensing and transmission deferral, and on the receiver side through collisions, which result in exponential backoff and retransmission. There exists a simple, “back-of-the-envelope” (BoE) technique to model the impact of pairwise sender-side interference. This paper tackles the harder task of determining the impact of receiver-side and non-pairwise sender-side interference. It proposes a technique for modeling the channel share of wireless links, and the accuracy is demonstrated with Qualnet simulation.     

Implementation of a High Throughput 3GPP Turbo Decoder on GPU

Turbo code is a computationally intensive channel code that is widely used in current and upcoming wireless standards. General-purpose graphics processor unit (GPGPU) is a programmable commodity processor that achieves high performance computation power by using many simple cores. In this paper, we present a 3GPP LTE compliant Turbo decoder accelerator that takes advantage of the processing power of GPU to offer fast Turbo decoding throughput. Several techniques are used to improve the performance of the decoder. To fully utilize the computational resources on GPU, our decoder can decode multiple codewords simultaneously, divide the workload for a single codeword across multiple cores, and pack multiple codewords to fit the single instruction multiple data (SIMD) instruction width. In addition, we use shared memory judiciously to enable hundreds of concurrent multiple threads while keeping frequently used data local to keep memory access fast. To improve efficiency of the decoder in the high SNR regime, we also present a low complexity early termination scheme based on average extrinsic LLR statistics. Finally, we examine how different workload partitioning choices affect the error correction performance and the decoder throughput.