现代通信原理 周武旸
现代通信原理 周武旸
第一章绪论 冬1.1通信的概念及分类 1.2移动通信的发展历程
第一章 绪论 1.1 通信的概念及分类 1.2 移动通信的发展历程
1.1通信的概念 冬Shannon在其1948年的论文中指出：“The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point”,即由一方向另一方进行消息的有效传递。 。面对面交流、烽火、电报、电话、互联网等。 111 C.E.Shannon.A Mathematical Theory of Communication. The Bell System Technical Journal.Vol.27,1948.p379~423
1.1 通信的概念 Shannon在其1948年的论文[1] 中指出：“The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point”，即由一方向另一方进行消息的有效传递。 面对面交流、烽火、电报、电话、互联网等。 [1] C.E. Shannon. A Mathematical Theory of Communication. The Bell System Technical Journal. Vol.27, 1948. p379~423
通信链路的基本元素 发射机(TX) 信道 (CHD） 接收机RX) The transmitter (TX)element processes The receiver (RX) function is message s signal in order to produce a principally to reverse the modulation signal most likely to pass reliably and processing of the transmitter in order efficiently through the channel. This to recover the message signal, usually involves modulation of a carrier attempting to compensate for any signal by the message signal,coding of the signal degradation introduced by the signal to help correct for tranmission channel.This will normally involve errors,filtering of the i message or amplification,filtering,demodulation modulated signal to constrain the occupied and decoding and in general is a bandwidth,and power amplification to more complex task than the transmit overcome channel losses. processing. Loosley defined as the electrical medium between source and destination,e.g.cable,optical fibre,free space, the channel is characterised by its Loss/Attenuation,Bandwidth,Noise/lnterference and Distortion. 在通信中传递的信息一定要“数据化”，否则无法传递，比如气味
7 通信链路的基本元素 发射机 (TX) 信道 (CH) 接收机 (RX) The transmitter (TX) element processes message signal in order to produce a signal most likely to pass reliably and efficiently through the channel. This usually involves modulation of a carrier signal by the message signal, coding of the signal to help correct for tranmission errors, filtering of the message or modulated signal to constrain the occupied bandwidth, and power amplification to overcome channel losses. The receiver (RX) function is principally to reverse the modulation processing of the transmitter in order to recover the message signal, attempting to compensate for any signal degradation introduced by the channel. This will normally involve amplification, filtering, demodulation and decoding and in general is a more complex task than the transmit processing. Loosley defined as the electrical medium between source and destination, e.g. cable, optical fibre, free space, the channel is characterised by its Loss/Attenuation, Bandwidth, Noise/Interference and Distortion. 在通信中传递的信息一定要“数据化”，否则无法传递，比如气味
通信网络 冬如同交通系统，货物、人就像通信系统要传递的信息，道 路交通设备就像通信系统中的传输网、交换网等各种技术 体系的网络架构，道路交叉点就像交换机、路由器等。 ·为保证交通工具（无论装货、载人）能够安全、顺利到达 目的地，要符合一定的规则：遵守交通规则、货物拆分打 包、不超载、合适的交通工具、合理的交通线路等，这就 是通信网中的编解码、数据分组格式、路由等通信协议
通信网络 如同交通系统，货物、人就像通信系统要传递的信息，道 路交通设备就像通信系统中的传输网、交换网等各种技术 体系的网络架构，道路交叉点就像交换机、路由器等。 为保证交通工具（无论装货、载人）能够安全、顺利到达 目的地，要符合一定的规则：遵守交通规则、货物拆分打 包、不超载、合适的交通工具、合理的交通线路等，这就 是通信网中的编解码、数据分组格式、路由等通信协议
通信系统分类 。按传输媒介分类 按信道发送信号类型分类 有线通信 。模拟通信 无线(wireless)通信 ·数字通信 ?按消息物理特征分类 ?按终端设备固定或移动分类 。固定通信 电话 ·移动通信 电视 ·数据通信 最海●●海 图像通信 。按系统典型设备分类 光纤通信 卫星通信 a
9 通信系统分类 按传输媒介分类 有线通信 无线(wireless)通信 按消息物理特征分类 电话 电视 数据通信 图像通信 按系统典型设备分类 光纤通信 卫星通信 … 按信道发送信号类型分类 模拟通信 数字通信 按终端设备固定或移动分类 固定通信 移动通信 ……
模拟通信和数字通信模型 Analog Communication System 信道中传送的是Analog Signals x(t) s(t) r(t) x'() Source Modulation Channel Demodulation Sink n(t) Noise 10
10 模拟通信和数字通信模型 Analog Communication System 信道中传送的是Analog Signals Source Modulation Channel Demodulation Sink Noise x(t) s(t) n(t) r(t) x´(t)
模拟通信信号变换过程 >Source:信息信号x(t) (模拟基带信号) >Modulation:信息信号x(t)→发送信号s(t) ·连续波模拟调制 ·脉冲序列模拟调制 > Channel:噪声n(t),接收信号r(t)=s(t)+n(t) >Demodulation:恢复信息信号x(t)≈x(t) >Sink:信息信号x'(t) 11
11 模拟通信信号变换过程 Source: 信息信号 x(t) （模拟基带信号） Modulation: 信息信号 x(t) → 发送信号s(t) 连续波模拟调制 脉冲序列模拟调制 Channel: 噪声n(t)，接收信号 r(t) = s(t)+n(t) Demodulation: 恢复信息信号 x’ (t) ≈ x(t) Sink: 信息信号x’ (t)
数字通信系统 冬信道中传送的是Digital Signals x() Source 9s(t) Source Channel 9c(t) Modulation encode encode s() Synchronization Channel Noise n(t) r() x() 9s'(t) 9c') Sink Source Channel De- decode decode modulation 12
12 数字通信系统 信道中传送的是 Digital Signals Sink Source encode Channel encode Modulation Synchronization Channel Noise Source x(t) gc(t) s(t) n(t) r(t) x’ (t) Channel decode Source decode Demodulation gs(t) gs ’ (t) gc ’ (t)
数字通信信号变换过程 > Source:x(t) (模拟基带信号) > Source encode:x(t)->g(t) (数字基带信号) > Channel encode:gs(t)→gc(t)（编码基带信号) > Modulation:g(t)->s(t) (频带信号) 连续波数字调制 ·脉冲序列数字调制 > Channel:n(t),r(t)=s(t)+n(t)(接收信号) 13
13 Source: x(t) （模拟基带信号） Source encode: x(t) → gs(t) （数字基带信号） Channel encode: gs(t) → gc(t) （编码基带信号） Modulation: gc(t) → s(t) （频带信号） 连续波数字调制 脉冲序列数字调制 Channel: n(t), r(t) = s(t)+n(t) （接收信号） 数字通信信号变换过程