# Overviews

## The diagram of a communication system

![](https://2889346953-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Le4Kw7maZEabKFjsC7z%2F-Lf5hWWAPXrS6pkg310z%2F-Lf5hidbOGMO6RDijZip%2Fthe_diagram_of_a_communication_system.png?generation=1558112045323192\&alt=media)

## Frequency Bands with Designations

![](https://2889346953-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Le4Kw7maZEabKFjsC7z%2F-Lf5hWWAPXrS6pkg310z%2F-Lf5hiddfU0ocf3xV2nu%2Ffrequency_bands.png?generation=1558112048286000\&alt=media)

### There are two kinds of communication by 传输信号的不同: `模拟电子` 和 `数字电子`

从我的角度看，

`模电` is kind of like 大自然中的信号，波形类似 `sine`， 可无限细分、采集（因为人的认识基于对比，而对比是无穷无尽的） ![](https://2889346953-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Le4Kw7maZEabKFjsC7z%2F-Lf5hWWAPXrS6pkg310z%2F-Lf5hidfBvFXxyZSUghB%2Fsine_wave.png?generation=1558112048698489\&alt=media)

`数电` 是经过人处理过的更精确的信号表示，它通过高与低的变化传输 `方波` (高电平为 1, 低电平为 0) ![](https://2889346953-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Le4Kw7maZEabKFjsC7z%2F-Lf5hWWAPXrS6pkg310z%2F-Lf5hidhvclxARwtQFyO%2Fsqure_wave.png?generation=1558112048390665\&alt=media)

### 无聊的表达式 与 计算

信息速率(传信率): $$R\_b$$ or $$Rate\_{bit}$$

> a small piece, part, or quantity of something.

码元速率(传码率): $$R\_B$$ or $$Rate\_{baud}$$

> a unit of transmission speed equal to the number of times a signal changes state per second.

$$R\_b = R\_B \cdot log\_2{M}$$ , (M 为`几进制系统`的`几`)

$$T = \frac{1}{R\_B}$$ , (T 为`码元宽度`)