Perceptive admission control for wireless network quality of service

As wireless networks become more widely used, there is a growing need to support advanced services, such as multimedia streaming and voice over IP. Traditional approaches to guarantee quality of service (QoS) work well only with predictable channel and network access. In wireless mobile networks, where conditions dynamically change as nodes move about the network, a stateless, high level approach is required. Since shared wireless resources are easily over-utilized, the load in the network must be controlled so that an acceptable QoS for real-time applications can be maintained. If minimum real-time requirements are not met, these unusable packets waste scarce bandwidth and hinder other traffic, compounding the problem. To enable high QoS for all admitted traffic, we propose the Perceptive Admission Control (PAC) protocol. PAC monitors the wireless channel and dynamically adapts admission control decisions to enable high network utilization while preventing congestion. Through discussion, simulations and testbed experiments, we demonstrate that PAC ensures low packet loss and delay for all admitted flows.     

Carrier Frequency Offset estimation for interleaved OFDMA uplink based on subspace processing

This paper investigates Carrier Frequency Offset （CFO）, estimation in the uplink of the Orthogonal Frequency-Division Multiple Access （OFDMA） systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.     

The theoretical BER performance analysis of a cooperative diversity scheme in frequency selective fading channel

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.     

A routing framework for providing robustness to node failures in mobile ad hoc networks

Nodes in a mobile ad hoc network are often vulnerable to failures. The failures could be either due to fading effects, battery drainage, or as a result of compromised nodes that do not participate in network operations. Intermittent node failures can disrupt routing functionalities. As such, it is important to provide redundancy in terms of providing multiple node-disjoint paths from a source to a destination. In line with this objective, we first propose a modified version of the widely studied ad hoc on-demand distance vector routing protocol to facilitate the discovery of multiple node-disjoint paths from a source to a destination. We find that very few of such paths can be found. Furthermore, as distances between sources and destinations increase, bottlenecks inevitably occur and thus, the possibility of finding multiple paths is considerably reduced. We conclude that it is necessary to place what we call reliable nodes (in terms of both being robust to failure and being secure) in the network to support efficient routing operations. We propose a deployment strategy that determines the positions and the trajectories of these reliable nodes such that we can achieve a framework for reliably routing information. We define a notion of a reliable path which is made up of multiple segments, each of which either entirely consists of reliable nodes, or contains a preset number of multiple paths between the end points of the segment. We show that the probability of establishing a reliable path between a random source and destination pair increases tremendously even with a small number of reliable nodes when we use our algorithm to appropriately position these reliable nodes.     

一个管理业务接入的模型与实现

分析了电信管理网中管理业务接入的特点,基于这些特点,提出了一个采用可扩展标记语言 (XML)技术和模型视图控制器(MVC)结构的管理业务接入模型,并给出实现的情况。     

差分空时编码CDMA系统的多用户接收机设计

利用码分多址和互满正交设计,该文针对多天线系统提出了非相干空时传输方案。它可支持满分集通信,并能有效抑制多用户干扰。基于平坦Rayleigh衰落信道,给出了差分解相关接收机,它不仅隔离了不同用户的检测,而且使不同数据符号的译码彼此独立。     

同步静态随机访问存储器常见问题解析

介绍当今正在大量使用的突发模式SSRAM,零总线反转SSRAM,二倍数据率SSRAM,四倍数据率SSRAM等类器件的差异,澄清一些容易混淆的概念。     

DVB条件接收系统中独立加扰器的设计与实现

本文介绍DVB条件接收系统的基本结构，详细分析了条件接收系统的工作原理，并给出条件接收系统中独立加扰器SAS(Stand Alone Scrambler)的具体实现方案。     

移动通信市场调查方案的选择及结果分析

为了全面了解全国移动市场状况、邮电部经济中心受邮电部移动局委托制订了全国性移动通信市场调查方案，并对北京，南宁和北海三市进行了调查。本文介绍了这一方案的实施办法，并对上述三市的调查结果进行了分析。     

运用接入新技术,组建农村用户接入网

运用接入新技术组建农村用户接入网已势在必行。本文针对我国经济水平低、地区间发展不平衡等实际情况，对组建我国农村用户接入网的有关策略进行了论述。