电子与通信工程硕士专业英语part 5

Modulation Methods (carrier modulation)
调制方式 线性 载 调制 波 调 制 非 （ 线性 连 续 调制 波 调 制 数字 ） 调制 用途举例
常规双边带调制AM 单边带调制SSB 双边带调制DSB 残留边带调制VSB 频率调制FM
相位调制PM 振幅键控ASK 频移键控FSK 其他高效数字调制 QAM、MSK等
其他编码方式 ADPCM等
Lesntensive reading：
1. Introduction Modern communication systems use digital modulation techniques. Advancements in very large integration (VLSI) and digital signal processing (DSP) technology have made digital modulation less cost than analog transmission systems. Digital modulation offers many advantages over analog modulation.
make a tradeoff between A and B
make a tradeoff among these parameters
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading：
The performance of a modulation schemes is often measured in terms of its power efficiency and bandwidth efficiency. Power efficiency describes the ability of a modulation technique to preserve the fidelity of the digital message at low power levels. … … and is often expressed as the ratio of the signal energy per bit to noise power b spectral density (Eb/No) required at the receiver input for a certain probability of error (say p 10-5). o
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading：
In digital communication systems, the modulating signal (e. g., message) may be represented as a time sequence of symbols or pulses, where each symbol has m finite states. Each symbol represents n bits of information, where n=log2mbits/symbol. Many digital modulation schemes are used in modern communication systems, and more and more are sure to be introduced. Some of these techniques have subtle differences between one another, and each technique belongs to a family of related modulation methods.
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading：
While power and bandwidth efficiency considerations are very important, other factors also affect the choice of a digital modulation schemes. For example, for all personal communication systems which serve a large user community, the cost and complexity of the subscriber receiver must be minimized, and a modulation which is simple to detect is most power efficiency attractive. The performance of the modulation scheme under various types of channel bandwidth efficiency impairments such as Rayleigh and Ricean fading and multipath time dispersion, given a particular demodulator implementation, is another key factor in selecting a modulation. the cost and complexity
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading：
Some modulation schemes are better in terms of the bit error rate performance, while others are better in terms of bandwidth efficiency. Depending on the demands of the particular application, tradeoffs are made when selection a digital modulation.
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading： Advantages:
New multipurpose programmable digital signal processors have made it possible greater noise immunity to implement digital modulators and demodulators completely in software. Instead of having a particular modern design permanently frozen as hardware, embedded software easier multiplexing implementations now allow alterations and improvements without having to redesign or greater modem. replace the security digital error-control codes complex signal conditioning and processing techniques software implementations and easier alterations and improvements
Lesson 2 数字调制 Digital Modulation
精读详解 Intensive reading：
Some advantages include greater noise immunity and robustness to channel impairments, easier multiplexing of various forms of information (e. g., voice, data, and video), and greater security. Furthermore, digital transmissions accommodate digital errorcontrol codes that detect and/or correct transmission errors, and support complex signal conditioning and processing techniques such as source coding, encryption, and equalization to improve the performance of the overall communication link.
Lesson 2
数字调制 Digital Modulation
(UNIT 7 Passage A ) Intensive reading：1. 2.
Lesson 2 数字调制 Digital Modulation
• 技术背景 Background：
Modulation—— the process of impressing low-frequency information signals onto a high-frequency carrier signal 载波调制—— carrier（continuous wave） modulation 脉冲调制—— pulse modulation Demodulation—— the reverse process
广播 载波通信、短波无线电话通信 立体声广播 电视广播、传真 微波中继、卫星通信、广播
中间调制方式 数据传输 数据传输