利用FPGA实现灵活的射频调制解调器

现场可编程门阵列(FPGA)具有结构灵活的特点,介绍了如何利用FPGA构建16-QAM射频发射器的数据通道,并给出了应用实例.     

射频IC为无线连接开辟坦途

以无线链接取代电缆链接非常简单易行,其成本效益也特别高,但选用这种方法时须作多方面的考虑。     

802.15.4 ZigBee--轻松实现无线连接

设想一下，您能够在同一地点无线控剖所有设备，从而简化一天的工作．早上到达仓库时，您可以使用远程控制设备，打开照明灯、空调装置(HVAC)、制冷设备中的温度感应器，然后关闭安全系统，将货架或设备清单发送给制造产品的工人．在上班时间，您可以检查家中车库是否锁好、灯是否关闭．温度调节装置的温度设置是否过高，     

实现数据传输的调制解调器

本文介绍了调制解调器在数据传输领域中的工作原理、先进性能以及市场前景。     

ADSL调制解调器驱动器的实现

ADSL接入技术已成为终端用户最主要的宽带接入技术.ADSL技MODEM.ADSL用户端调制解调器驱动器是一个宽频带功率放大器,他能不失真放大和传输电话线上已编码的数字信号.本文通过对ADSL调制解调器驱动器特点、结构和性能的分析,给出了一种ADSL用户端MODEM驱动器的实现电路.该电路采用具有优良高频的双功率放大器LT1886,即使在配置高电平的闭环增益网络后也能保持较低的失真.     

飞思卡尔802.15.4ZigBee轻松实现无线连接

引言如果能够在同一地点无线控制所有设备,可以简化一天的工作。早上到达仓库时,可以使用远程控制设备,打开照明灯、空调装置(HVAC)、制冷设备中的温度感应器,然后关闭安全系统,将货架或设备清单发送给制造产品的工人。在上班时间,可以检查家中车库是否锁好、灯是否关闭、温度调节装置的温度设置是否过高、烤箱是否关闭、安全系统是否打开、百叶窗是否敞开。晚上回到家中,可以使用无线键盘和鼠标查收电子邮件,帮孩子打开无线学习玩具,通过远程控制设备与您的娱乐中心双路通信交流。上述功能均可通过具备灵活性、无缝移动性的智能家庭和办…     

多速率调制解调器设计与实现

现代通信系统中多种信息速率并存,多速率兼容成为一个突出的问题.基于直接序列扩频（DS-SS）和卷积编码技术,提出了一种可以满足多速率兼容的调制解调器实现方法,通过选择不同长度的伪随机序列或者卷积编码,不同的信息速率占用相同的传输带宽.对扩频、解扩以及卷积码的编码和解码部分进行了较为详细的论述,给出了关键模块的原理和实现方法,对使用此调制解调器的通信系统进行了测试,并给出了测试数据.     

PDA调制解调器的设计与实现

介绍了一种新型的PDA调制解调器的设计 ,详细地分析了该调制解调器电路的工作原理并介绍了该调制解调器驱动程序的设计。     

Modems

The rapidly rising need for computer communications has been met for the most part by utilization of the ever expanding network of voice-bandwidth channels. Transmission of digital signals over these analog channels involves a modem for modulation and demodulation of a voice-frequency carrier. The usual forms of amplitude, frequency, and phase modulations are described together with their basic characteristics, such as efficiency of bandwidth utilization. The principles of signal shaping and filtering for optimum signal-to-noise performance and minimization of intersymbol interference are discussed. Also covered are methods of synchronization, carrier recovery, effects of channel impairments, and the application of automatic equalization. The choice among modem designs is shown to be influenced by bit speed requirement, permissible error rate, type of channel, receiver startup characteristic, and tradeoff between modem and line costs. The functions of the usual transmission and control leads between a data modem and a data terminal are described, and examples are given of leased private-line and switched telecommunications network applications. A current look at the physical aspects of voice-band modems is given and future trends are considered.     

数据调制解调器（上）

本文简要地介绍了数据解调基本原理和技术，对话带数据调制解调器系列作了比较系统和完整的讨论，并对调制解调器中的新技术和发展作了简介。     

射频卡及其在自动售水机中的应用

文章介绍了射频芯片e5 5 5 0、U2 2 70B的特点和工作原理 ,叙述了它们在自动售水机系统中的具体用法和系统功能的实现。     

NEC-700型调制解调机旁路业务设备搬迁过程中的技术问题

通过分析NEC-700型调制解调机的旁路业务设备是否能从终端站搬迁到中继站,以及对两站所处区域的社会经济情况进行比较和研究,提出了搬迁的可行性和必要性,制定了搬迁方案,实施结果表明搬迁取得成功.     

多媒体调制解调器新进展

本文简单介绍高速数据调制解调器和低比特率语音与视频压缩编码解码器的最新发展 ,以及在普通公用电话网上实现多媒体通信和语音 /数据同时传输的通信。     

Modems for emerging digital cellular-mobile radio system

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation. and various architectures of π/4-QPSK (π/4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the π/4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for π/4-QPSK and other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted     

Microprocessor Implementation of High-Speed Data Modems

This paper describes the application of a commercially available microprocessor (Intel 3000 or Signetics 3000) to a flexible data transmitter and data receiver for high-speed data modems. For the transmitter a quadrature modulation scheme is chosen; the receiver is based on phase-shift compensation techniques and coherent demodulation with an externally derived digital carrier. For the realization with the given microprocessor it has been necessary to adapt the way of executing the various operations (especially the multiplications for the digital filtering) to the available computational capabilities. The resulting microprocessor implementations are also suitable for application in the current medium-speed synchronous data transmission systems.     

保护ADSL调制解调器防止电涌击穿

熟悉保护标准、指导原则和器件,可以提高设计人员保护ADSL调制解调器的电话线及数据线免遭过压冲击的能力。因为同普通电话线相连,异步数字用户线路(ADSL)调制解调器十分容易遭受电击,如雷电、电源线交叉和静电放电(ESD)。因此,必须对ADSL调制解调器进行恰当的保护,以防止破坏性过压和过流的冲击。     

消除无线调制解调器中的PCMCIA功率限制

引言 支持移动计算要求的无线网络接入的需求正在迅速增长,移动通信全球系统（GSM）电信网络,以及引中出来的通用分组无线业务（GPRS）无处不在。工程设计人员已开始转向PCMCIA总线,将其作为实现GSM调制解调器设计的一种解决方案。     

A Programmable Impedance Matching Circuit for Voiceband Modems

A line impedance-matching circuit for a voiceband modem is described. The circuit can be programmed to realize four different impedances. A switched-capacitor filter is used to generate the required transfer functions. The impedance-matching concept and circuits are described. Measured results are presented that show that the four impedances are realized with sufficient accuracy for voiceband modems. The circuit was fabricated in a standard 0.35-mum mixed-signal CMOS process.