# 1. 频带和频率分配

A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. Many systems are characterized by the range of frequencies to which they respond. Musical instruments produce different ranges of notes within the hearing range (The human range is commonly given as 20 to 20,000 Hz). The electromagnetic spectrum can be divided into many different ranges such as visible lightinfrared or ultraviolet radiation, radio waves, X-rays and so on, and each of these ranges can in turn be divided into smaller ranges. A radio communications signal must occupy a range of frequencies carrying most of its energy, called its bandwidth. A frequency band may represent one communication channel or be subdivided into many. Allocation of radio frequency ranges to different uses is a major function of radio spectrum allocation.

Frequency allocation (or spectrum allocation) is the division of the electromagnetic spectrum into radio frequency bands. This spectrum management is regulated by governments in most countries.

The International Telecommunication Union (ITU) is a specialized agency of the United Nations (UN) that is responsib for issues that concern information and communication technologies. The ITU coordinates the shared global use of the radio spectrum, promotes international cooperation in assigning satellite orbits, works to improve telecommunication infrastructure in the developing world, and assists in the development and coordination of worldwide technical standards.

Fig. 1: Overview of United States Frequency Allocations Chart (image from here)

## 1.1 一些常见的电磁波

• 无线电波（radio wave）：3 kHz ~ 300 GHz
• 微波（microwave）：300 MHz ~ 300 GHz, 波长介于红外线和无线电波
• 红外线（infrared）：300 GHz ~ 430 THz, 波长介乎微波与可见光
• 可见光（visible light）：430 Thz ~ 790 THz
• 紫外线（ultraviolet）：750 THz ~ 30 PHz
• X射线（X-ray）：30 PHz ~ 30EHz
• 伽马射线（Gamma ray）：30 EHz ~ ?

PS: Hz不同单位从小到大的关系（x1000）：Hz -- KHz -- MHz -- GHz -- THz -- PHz -- EHz

Table 1: Examples of some uses of common electromagnetic waves

# 2. 无线电频谱

## 2.1 无线电频谱表

The radio spectrum is the part of the electromagnetic spectrum from 3 Hz to 3000 GHz. Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

Fig. 3: United States Frequency Allocations on the Radio Spectrum Chart (image from here)

Licensed bands means that individual companies pay a licensing fee for the exclusive right to transmit on assigned channels within that band in a given geographic area. Licensing is a way of ensuring that wireless operators do not interfere with each other’s transmissions. Without licensing, interference would garble both transmitters’ signals, preventing decent reception. With licensing, the only place where interference occurs is usually at the outer edge of the license-holder’s assigned coverage area.

## 2.3 ISM频段

ISM频段（Industrial Scientific Medical Band），各国挪出某一段频段主要开放给工业，科学和医学机构使用。应用这些频段无需许可证或费用，只需要遵守一定的发射功率（一般低于1W，对功率进行管制，使得发射台只有很短的距离，避免相互干扰），并且不要对其它频段造成干扰即可。ISM频段在各国的规定并不统一。如在美国有三个频段902-928 MHz、2400-2484.5 MHz及5725-5850 MHz，而在欧洲900MHz的频段则有部份用于GSM通信。

2.4GHz为各国共同的ISM频段。因此无线局域网（IEEE 802.11b/IEEE 802.11g），蓝牙，ZigBee等无线网络，均可工作在2.4GHz频段上。

ITU-R指定的ISM频段如下（详情见ISM band, Frequency allocation）：

ISM频段使用，最常见的是微波炉，其工作在2.45 GHz。

### 2.3.1 Non-ISM uses

In recent years ISM bands have also been shared with (non-ISM) license-free error-tolerant communications applications such as wireless sensor networks in the 915 MHz and 2.450 GHz bands, as well as wireless LANs and cordless phones in the 915 MHz, 2.450 GHz, and 5.800 GHz bands. Because unlicensed devices are required to be tolerant of ISM emissions in these bands, unlicensed low power users are generally able to operate in these bands without causing problems for ISM users.

• Bluetooth: 2.45 GHz
• IEEE 802.11 (e.g., Wi-Fi): 2.45 GHz, 5.8 GHz
• IEEE 802.15.4 (e.g., Zigbee, 6LoWPAN): 使用868(Europe)/915(North America)/2450(worldwide) MHz中的一个

# 3. 国内移动通信频谱

• DCS表示Digital Cellular System，实际上是GSM-1800。
• 电信EVDO是指CDMA2000 1x EV-DO（Evolution-Data only），已被国际电联ITU接纳为国际3G标准。
• 4G网络（LTE, Long-Term Evolution）分为TDD（time-division duplexing）和FDD（frequency division duplexing）。

## 3.1 4G

• Mobile WiMAX Release 2 (也叫WirelessMAN-Advanced）： 由IEEE主导制定，IEEE 802.16m是WiMAX（Worldwide Interoperability for Microwave Access）的升级演进，从fixed stations接收可高达1 Gbps，接收下行与上行最高速率可达到100 Mbps。是国际电信联盟承认的4G标准，不过随着Intel于2010年退出，WiMAX技术也已经被运营商放弃，并开始将设备升级为TD-LTE。

International Mobile Telecommunications-Advanced (IMT-Advanced Standard) are requirements issued by the ITU-R of the International Telecommunication Union (ITU) in 2008 for what is marketed as 4G (Or sometimes as 4,5G) mobile phone and Internet access service.

## 3.2 LTE

LTE指定的频带列表，可以参见维基百科词条LTE frequency bands

[1] Wikipedia: Frequency allocation, Frequency band, International Telecommunication Union, GSM frequency bands
[2] ITU: Frequency allocations
[3] Everything Maths and Science: Electromagnetic spectrum
[4] 百度百科：无线电波
[5] 中国无线频谱资源分配详细图解