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Definition of communication
Communication: refers to the exchange and transmission of information between people or people and nature through a certain behavior or medium. Broadly speaking, it means that two or more parties that need information adopt any method and any medium without violating their own wishes Transfer information from one party to another accurately and securely.
Typical communication behavior-ancient
Beacon
Typical communication behavior-modern
Overseas: Wired telegraph, wired telephone, wireless transceiver
Domestic: Daqing Post Office, ten telephone subscriber exchanges, pager (BB machine), mobile phone (Big Brother)
Mid-1990s: GSM has entered a new milestone in mobile communications. (Nokia, Motorola, Ericsson)
With the advent of 3G, smart phones are available.
With the advent of LTE, people have embarked on the fast lane of data, and "low-headed people" have appeared.
On the morning of June 6, 2019, the Ministry of Industry and Information Technology officially issued 5G commercial licenses, and large-scale construction of 5G networks. Enter an era of interconnection of all things.
Classification of communication:
1. Classification by transmission medium
Wired communication: refers to the communication medium in the form of wires, cables, optical cables, waveguides, nano-materials, etc. It is characterized by the medium being visible and accessible (open line communication, cable communication, optical cable communication).
Wireless communication: refers to a form of communication in which the transmission medium is invisible and untouchable (such as electromagnetic waves) (microwave communication, short-wave communication, mobile communication, satellite communication, scattering communication)
2. Classification by modulation method
Baseband transmission: refers to the communication method in which the signal is sent directly to the channel for transmission without modulation.
Frequency band transmission: refers to the communication mode after the signal is modulated and then sent to the channel for transmission, and the receiver has corresponding demodulation measures.
3. Classification by working frequency band
Wave communication, medium wave communication, short wave communication, microwave communication, far infrared communication, etc.
4. Classification according to the signal transmitted in the channel
Analog signal communication, digital signal communication.
wait wait wait
Mobile communication
Mobile communication: refers to at least one of the two parties in communication is moving (or temporarily staying at a predetermined position) for information transmission and exchange. Including the communication between the mobile body (vehicle, ship, aircraft or pedestrian) and the mobile body, and the communication between the mobile body and the fixed body (fixed radio station or wired user).
China's major communications events:
On January 7, 2009, the Ministry of Industry and Information Technology issued a 3G license, with China Mobile as TD-SCDMA, China Unicom as WCDMA, and China Telecom as CDMA2000.
On December 4, 2013, the Ministry of Industry and Information Technology issued a "TD-LTE" 4G license to China Mobile, China Unicom, and China Telecom.
On February 27, 2015, the Ministry of Industry and Information Technology issued the "FDD-LTE" 4G license to China Unicom and China Telecom.
On June 6, 2019, the Ministry of Industry and Information Technology officially issued 5G commercial licenses to China Telecom, China Mobile, China Unicom, and China Radio and Television.
The mobile network has evolved for many years, and the original network was called the first generation mobile communication system. The first generation network has now been the second generation. Replaced by the third generation network. 4G or the fourth generation mobile communication system has developed rapidly in the world.
A first generation mobile communication technology ( . 1G ) - analog mobile communications
Originating in the 1980s, it mainly uses analog modulation technology and frequency division multiple access (FDMA) technology. The main disadvantages of this technology are low spectrum utilization and signaling interference with voice services. The main representatives of 1G are: the United States' advanced mobile phone system ( AMPS ) , the United Kingdom's Global Access Communication System ( TAC ) and Japan's Telegraph and Telephone System ( NMT ) . 1G mobile communication is based on analog transmission technology, which is characterized by small business volume, poor quality, poor completeness, no encryption and low speed. 1G is mainly based on cellular structure networking, using analog voice modulation technology directly, with a transmission rate of about 2.4 kbit / s. Provide 9.6kbit / s communication bandwidth, and the access technology adopts FDMA.
1G features:
- Only voice service;
- Low spectrum reuse rate and limited system capacity;
- The standards are not uniform and cannot roam (different operating frequency bands) ;
- Safety differences;
- High equipment prices ("Big Brother")
Second, the second generation mobile communication technology ( 2G ) - Digital Mobile Communication
It originated in the early 1990s and mainly uses digital time division multiple access (TDMA) and code division multiple access (CDMA) technologies. The second-generation mobile communication digital wireless standards mainly include: GSM in Europe and IS-95CDMA launched by Qualcomm in the United States. China mainly adopts GSM, and the United States and South Korea mainly adopt CDMA. Provide 9.6kbit / s-28.8kbit / s transmission rate, access technology is TDMA , CDMA .
In order to meet the needs of the development of data services, 2.5G was also born in the second-generation technology, that is, GPRS of GSM system and IS-95B technology of CDMA system , which greatly improved the data transmission capability.
The main business of 2G is voice, and its main feature is to provide digital voice services and low-speed data services. It overcomes the weakness of the analog mobile communication system, greatly improves the voice quality and security performance, and can perform automatic roaming within and between provinces. The second generation mobile communication replaces the first generation mobile communication system to complete the conversion from analog technology to digital technology .
2G features:
- The standards are not uniform, and can only roam in the coverage area of the same standard, and cannot conduct global roaming;
- Limited bandwidth, cannot provide high-speed data transmission, and cannot realize multimedia services;
- The anti-interference and anti-fading ability is not strong, and the system capacity is insufficient;
- Low frequency utilization;
GSM ( Global System for Mobile Communication ) system components: China has the world's largest GSM network.
• Mobile station (MS)
• Base station system (BSS) can be divided into base transceiver station ( BTS ) and base station controller ( BSC ).
• Network Subsystem (NSS) NSS consists of Mobile Service Switching Center ( MSC ), Home Location Register ( HLR ), Visited Location Register ( VLR ), Authentication Center ( AUC ), Equipment Identification Register ( EIR ), and Operation Maintenance Center ( OMC ) Composition.
• Database (Database)-HLR, VLR, AUC, EIR, etc.
• Operation Support System (OSS)
It mainly includes:
l Network Management Center ( NMC )
l Security Management Center ( SEMC )
l Personalized Center ( PCS ) for user equipment card management
l Database processing system ( DPPS ) and other functional entities for centralized billing management .
GSM system network structure
The main interface of GSM system
Third, the third generation mobile communication technology ( 3G ) - Digital Mobile Communication
The theoretical research, technical development and standard formulation of 3G began in the mid-1980s, and the International Telecommunication Union (ITU) officially named it as International Mobile Telecommunications 2000 (IMT-2000, International Mobile Telecommunications in the year 2000). The European Telecommunications Standards Institute (ETSI) calls it Universal Mobile Telecommunication System (UMTS).
Provide 9.6kbit / s-2Mbit / s access rate. (Indoor 2Mbit / s; Outdoor 384kbit / s; Driving environment 144kbit / s)
The most basic feature of 3G is the intelligent signal processing technology. The intelligent signal processing unit will become a basic functional module, supporting voice and multimedia data communication. It can provide various broadband information services that the previous two generations of products cannot provide, such as high-speed data and slow Images and TV images, etc.
3G standards: The International Telecommunications Union (ITU) has currently identified four global 3G standards, namely WCDMA, CDMA2000, TD-SCSMA and WIMAX. In China, China Mobile uses TD-SCDMA , China Telecom uses CDMA2000 , and China Unicom uses WCDMA
- WCDMA (Wideband CDMA)-There are many manufacturers engaged in WCDMA standard research and equipment development, including Nokia, Motorola, Siemens, NEC, Alcatel, etc. The standard proposes the evolution strategy of GSM (2G)-GPRS-EDGE-WCDMA (3G).
- CDMA2000 (narrowband CDMA) was launched by Qualcomm of the United States, Motorola, Lucent and Samsung all participated, and South Korea is the leader of CDMA2000. The standard proposes the evolution strategy of CDMA (2G)-CDMA2001x-CDMA2003x (3G). Among them CDMA2001x is called 2.5G mobile communication technology. China Telecom is currently using this program to transition to 3G.
- TD-SCDMA (Time Division-Synchronous CDMA, Time Division Synchronous CDMA), a 3G standard developed by China Datang Telecom. The proposed standard does not go through the intermediate link of 2.5G, and directly transitions to 3G, which is very suitable for the upgrade of GSM system to 3G
- WIMAX (Worldwide Interoperability for Microwave Access), also known as 802.16 Wireless Metropolitan Area Network, is another broadband wireless connection solution that provides "last mile" for businesses and home users.
3G standard parameters
WCDMA：
RTT： FDD
Asynchronous CDMA system: no GPS
Bandwidth: 5MHz
Chip rate: 3.8Mcps
Chinese frequency band: 1940MHz-1955MHz (uplink), 2130MHz-2145MHz (downlink)
Modulation method: HPSK up, QPSK down.
CDMA2000
RTT FDD
Synchronous CDMA system: with GPS
Bandwidth: 1.23MHz
Chip rate: In downlink channel transmission, there are two methods of direct spread and multi-carrier transmission, the chip rate is 3.6864Mchip / s and 1.22Mchip / s respectively;
Chinese frequency band: 1920MHz-1935MHz (uplink), 2110MHz-2125MHz (downlink)
TD-SCDMA
RTT TDD
Synchronous CDMA system: with GPS
Bandwidth: 1.6MHz
Chip rate: 1.28Mcps
Chinese frequency band: 1880MHz-1920MHz (uplink), 2010MHz-2025MHz (downlink)
WiMAX
Bandwidth: 1.5MHz-20MHz
Maximum access speed 70M
Maximum i transmission distance: 50 km
Fourth, the fourth generation of mobile communications (4G)
Data transmission should be an order of magnitude higher than 3G, reaching 2-20Mbit / s. (Low-speed mobile users: indoor, walking 100Mbit / s, medium-speed mobile users: 60km / h 20Mbit / s, high-speed mobile users: 250km / h 2Mbit / s)
LTE is the evolution of 3G, not a commonly misunderstood 4G technology, but a transition between 3G and 4G technology. It is a global standard of 3.9G. It improves the 3G air access technology and uses OFDM and MIMO as its wireless The only standard for network evolution. The enhanced version of LTE-Advanced is considered as a 4G standard.
The technologies used by 4G to increase transmission rates are:
Orthogonal Frequency Division Multiplexing (OFDM);
Smart antenna technology (SA);
Multiple input multiple output (MIMO) technology;
Software Radio (SDR).
LTE can provide a peak rate of downlink 326Mbps and downlink 86Mbps under the 20MHz spectrum bandwidth. LTE needs to support transmission bandwidth higher than 5MHz.
The radio interface and radio access network architecture evolution technologies being developed by 3GPP LTE mainly include the following:
- Significantly increased transmission rate. If it is achieved on a 20MHz bandwidth: the downstream transmission rate is 100Mbit / s and the upstream transmission rate is 50Mbit / s;
- Increase the cell boundary bit rate while keeping the current base station location unchanged;
- Significantly improve spectrum utilization;
- Obviously reduce the waiting time, less than 100ms, etc.
5. The fifth generation of mobile communications ( 5G )
