基于FPGA的DTMF信号的产生与检测

文章以现场可编程门阵列(FPGA)为控制核心,设计并实现了双音多频信号(DTMF)的产生与检测,DTMF信号的产生是在FPGA内部将两个不同频率的正弦波形合成一个双频数字信号,通过D/A转换器变为模拟信号输出。DTMF信号的检测以Goertzel算法为核心,计算出8个频点的幅值,通过比较大小判断出相应的电话号码。经过工程测试,该设计能够达到DTMF信号的产生与检测要求,结果表明,将DTMF编解码算法集成于FPGA系统中,使DTMF信号系统变得简单灵活,充分发挥了FPGA的优势。     

DTMF信号发送/接收电路芯片MT8880及应用

本文介绍新型DTMF 信号发送/接收电路芯片MT8880的基本工作原理及其在8031单片机控制下的编程实例。该芯片集成度高、可编程控制、具有多种工作模式,可以广泛应用于有线、无线通信设备和控制系统中。     

用公共电话网构建社区紧急求助系统

介绍一种以公共电话网络PSTN(Public Switch Telecommunication Network)为传输媒介的住宅小区紧急求助系统。系统以单片机为核心,以双音多频(DTMF,Dual Tone MultipleFrequency)作为通信方式。该系统为小区内住户提供紧急求助服务,具有可靠性高、成本低、易普及等优点。文中给出系统原理图、主要硬件电路和程序框图。最后对该系统的应用前景进行了预测。     

电话远程控制系统的设计与实现

讨论了一种电话远程控制系统（TRCS）的设计与实现。该系统基于单片机和双音多频信号技术（DTMF）,具有振铃检测、模拟摘机、DTMF信号解调、开关量控制等功能,并且使用ISD4004芯片进行语音提示。详细论述了该系统的硬件组成以及软件设计。实际证明该系统性能稳定、操作方便,具有较高的实用价值。     

基于PSTN的城市电梯安全呼叫系统设计

本文介绍了一种基于公共电话网(PSTN)的电梯安全呼叫系统,采用总线拓扑结构和DTMF信号对电梯群进行组网,构成由电梯分机、机房电话和小区管理中心的管理主机组成的小区电梯安全呼叫网络,并通过管理主机实现与公共电话网通信.本文重点讲述了管理主机部分的软件设计.     

应急自动电话报警装置的实现

本系统在事主遇到紧急情况下,按下触发按钮,通过电话网络发送DTMF(双音多频)拨号信号,同时给出语音信息。可以自动及时隐蔽的报警,提高了事主的安全性。本系统采用单片机做主逻辑控制,控制键盘和显示,以及拨号和放音。同时具有一定的容错性。     

用软件编程替代DTMF芯片的应用方案

引言 传统的智能电话报警器的音频拨号功能通常采用DTMF(Dual Tone Multi Frequency,双音多频)芯片(如8880、8888等)来实现.从功能实现上来看,DTMF芯片的作用是将指定的号码生成双音多频信号,馈入电话线,实现拨号功能.本文提出一种新方案:采用软件合成方法获得DTMF信号音,采取一定的方式存放在语音模块中,由软件调用,将DTMF信号馈入电话线,实现拨号功能.这样替代了DTMF芯片,在保证系统稳定可靠的前提下,可以实现同样的功能.     

利用HMP 板卡实现IMS 媒体网关的媒体转换功能

概述IMS（IP Multimedia Subsystem）媒体网关的功能,介绍了HMP（Hos Multimedia Processing）板卡的相关知识,着重论述如何使用HMP的各种通道资源来实现不同媒体间的转换。     

一种具有来电显示及DTMF信号收发功能的智能控制模块设计

探讨了FSK来电显示技术及DTMF编解码技术,给出了具有来电显示和DTMF信号收发功能的智能控制模块的硬件结构和软件流程。采用AT89C52单片机控制HT9032C、MT8880等芯片,设计实现了基于电话网的DTMF信号的收发以及来电信息的采集智能控制模块,并通过RS232接口与上位机通信,提出了软硬件抗干扰的具体措施。     

基于AT89C51单片机的家用电器电话遥控装置

本文介绍了一种基于AT89C51单片机的家用电器电话遥控装置,该装置利用双音多频电话机,可以通过电话对家用电器及其工作状况进行控制.它是一种基于DTMF(双音多频)信号的远程智能控制器.它具有振铃检测和模拟摘机,DTMF信号解调和133秒无响应自动挂机的功能.     

无线通信网络呼叫接纳控制策略研究综述

呼叫接纳控制（CAC）是无线通信网络无线资源管理中一个重要的组成部分,CAC策略依据一定的准则决定呼叫到达请求的允许接入或拒绝接入,其中策略设计的好坏直接影响着网络的性能和资源利用率。20多年来,CAC策略得到了广泛地研究,极大地改善了网络呼损率、中断率、分组延时、丢包率和吞吐率等性能。简要介绍了无线通信网络中与CAC的一些相关背景及CAC策略的功能定位与作用,重点介绍了近年来CAC研究的一些新的成果,并分析了这些成果仍然存在的一些问题,最后给出了对于CAC进一步研究的探讨。     

基于呼叫详细记录数据的城市功能区识别

不同城市功能区区域之间具有外在物理差异和内在功能差异,且随时间和人类活动不断发生演变。针对卫星遥感等传统监测方法存在运行周期长、成本高,不能表征内在功能差异等问题,利用通信运营商提供的用户生活数据——呼叫详细记录（CDR）,进行城市功能区识别研究。首先,以人工标注的方法对基站小区进行功能区分类,得到住宅区、办公区、商业区、高校区、景点区五类训练样本;然后,提取各功能区内用户群体的通话行为和移动行为特征,进行差异性对比分析;最后,利用高斯混合模型（GMM）设计出多特征加权判决的功能区识别算法,并用训练集对该算法进行仿真。实验结果表明,CDR数据可以对城市功能区之间的内在差异进行表征,功能区性质与用户的通话行为和移动行为存在对应关系;判决权重为0.6时,该算法在现有数据集下的功能区召回率达到了最大,为51.08%。结合误差分析表明CDR数据在城市功能区识别应用上具有可行性。     

Flexible work in call centres: Working hours, work-life conflict & health

Call-centre workers encounter major psychosocial pressures, including high work intensity and undesirable working hours. Little is known, however, about whether these pressures vary with employment status and how they affect work-life conflict and health. Questionnaire data were collected from 179 telephone operators in Sydney, Australia, of whom 124 (69.3%) were female and 54 (30.2%) were male. Ninety-three (52%) were permanent full-time workers, 37 (20.7%) were permanent part-time, and 49 (27.4%) were casual employees. Hypothesised structural relationships between employment status, working hours and work organisation, work-life conflict and health were tested using partial least squares modelling in PLS (Chin, 1998). The final model demonstrated satisfactory fit. It supported important elements of the hypothesised structure, although four of the proposed paths failed to reach significance and the fit was enhanced by adding a path. The final model indicated that casual workers reported more variable working hours which were relatively weakly associated with greater dissatisfaction with hours. The interaction of schedule control and variability of hours also predicted dissatisfaction with hours. Conversely, permanent workers reported greater work intensity, which was associated with both lower work schedule control and greater work-life conflict. Greater work-life conflict was associated with more fatigue and psychological symptoms. Labour market factors and the undesirability of longer hours in a stressful, high-intensity work environment appear to have contributed to the results.     

An HMM-based call admission control policy for supporting QoS in wireless cellular networks

The multimedia services are getting to become the major trend in next-generation cellular networks. Call admission control (CAC) plays the key role for guaranteeing the quality of service (QoS) in cellular networks. The goal which keeps both the call dropping probability (CDP) and call blocking probability (CBP) below a certain level is more difficult owing to user indeterminate mobility. In this paper, the Hidden Markov Models (HMMs) concept which is suitable for solving a dynamic situation is introduced and applied to the call admission control policy. The prediction of user mobility can be modeled and resolved as the decoding problem of the HMMs. According to the prediction result, the proposed CAC method can reserve appropriate bandwidths for a handoff call beforehand. Thus, the call dropping probability can be kept below a lower level. Moreover, the call blocking probability is not sacrificed too much since the proposed method can reserve the suitable bandwidths in the appropriate cells but not reserve stationary ones which are always adopted by traditional CAC methods. Therefore, the proposed method not only can satisfy both CDP and CBP issues, but also improve the system utilization.     

Policy support for call control

The need for policies to control calls is justified by the changing face of communications. It is argued that call control requires distinctive capabilities in a policy system. A specialised policy language called APPEL (ACCENT Project Policy Environment/Language) has therefore been developed for this purpose. However, the policy language is cleanly separated into a core plus specialisations for various application domains. The paper describes both the foundation and the call control ontologies. Sample policy examples are provided to illustrate use for call control. The paper also presents the policy system architecture in which the policy language is interpreted. The components of the policy system are described, particularly the policy server and the policy wizard.     

Outsourcing strategy in two-stage call centers

This paper considers ‘two-stage’ call centers where some incoming calls are completed by first service while others require an additional second service. Although this type of call center is not uncommon, it has not been dealt with, if any, in the call center literature. In this paper, we introduce the concept of the ‘two-stage’ call center and discuss its features. Furthermore, we develop an effective outsourcing strategy in ‘two-stage’ call centers. To this end, we model ‘two-stage’ service system and propose several call routing structures. The structures are compared through numerical test and conventional queueing theories form the theoretical basis of our study.     

QBD approximations of a call center queueing model with general patience distribution

This paper investigates a computationally practical way for analyzing a call center queueing model, i.e., a finite-capacity, multi-server queueing model, where each server goes on a single vacation. Poisson arrival process and exponential service and vacation times are assumed. We also assume that each customer may leave the queue due to impatience. Customers’ patience times are i.i.d. random variables with a general distribution. Level-dependent finite QBD (quasi-birth–death) processes are employed to approximate such a queueing model. Two approaches are considered. The first one uses the phase-type (PH) distribution to approximate the general patience distribution, whereas the second one is based on the idea of replacing the eventual reneging of customers with balking. We find that the first approach is almost impossible to compute numerically due to the exponential growth of the size of the block matrices in a level-dependent finite QBD. We examine the validity and applicability of the approximation based on the second approach and show that it gives us a practical way to obtain performance measures of call center systems in practical scale with sufficiently reasonable accuracy.     

Performability evaluation of emergency call center

Emergency call centers serve people in utmost circumstances; hence they should be highly dependable. Availability and performance are key aspects in call centers. Architectural models, service policies, and redundancies are attributes for defining and evaluating the overall operation of such systems. In this work, we performed the performability evaluation of an important emergency call center located in a large city in Brazil. The results showed that the system’s downtime is considered high, so, we proposed a new architecture to improve the system’s performability. The results obtained in this paper can be used to provide support for decisions on interventions in the emergency call center to improve its performability. It is expected that the models presented in this paper will be useful in a variety of emergency call centers.     

Power-based multi-cell call admission control scheme for wideband-CDMA systems

Wideband code division multiple access (WCDMA) systems are interference-limited. When a WCDMA system operates at nearly full capacity, admitting a new user may affect the stability of the system. Therefore, the proper call admission control (CAC) is crucial and should balance between quality of service (QoS) requirements for the new user as well as for the existing users and the required high capacity. In this paper, we investigate this trade-off in the uplink direction using a power-based multi-cell admission control (MC-AC) algorithm. Multimedia services are considered with different QoS requirements in this algorithm. Different traffic scenarios are also considered. Simulation results reveal that the proposed MC-AC algorithm has many advantages over single-cell admission control (SC-AC) in terms of the overall stability of the system and the total system throughput.     

局域网中利用Mobile Agent技术实现信息的检索

提出了一个应用于局域网中的基于MobileAgent技术的信息检索的模型,并给出了实现该系统的关键技术,整个模型是建立在已有网络协议的基础上,并且采用了概念分层结构,关键技术涉及Agent的基本结构、Agent的管理和通信、Agent的回调生成算法和安全问题。