Cellular mobile communication system

communication system

honeycomb mobile communication The system is a mobile communication hardware architecture, which is divided into analog cellular system and Digital cellular system 。 Due to the various communications that constitute the system coverage Base platform The signal coverage of hexagon , so that the whole overlay network It is named after a cell. Next, we will introduce the relevant knowledge of cellular mobile communication system.

Chinese name: Cellular mobile communication system
Foreign name: Cellular Mobile Communication System

Alias: "Cell system" system
Division: For several cells
Nature: Further increase system capacity

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concept

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In a cellular mobile communication system, the signal coverage area is divided into cells, which can be hexagonal, square , round or some other shape, usually hexagonal Honeycomb 。 Each of these partitions is assigned multiple frequencies（ f one - f six ）, with corresponding base stations. In other partitions, repeated frequencies can be used, but adjacent partitions cannot use the same frequency, which will cause Co channel interference 。

Increase capacity. Compared with a single base station, cellular mobile communication systems can use the same frequency in different partitions to complete different data transmission （ Frequency reuse ）。 A single base station can only have one data transmission on the same frequency. However, the use of the same frequency in cellular mobile communication systems will inevitably interfere with other base stations using the same frequency. This means that in a standard FDMA system, there must be a base station with a different frequency between two base stations that use the same frequency.

Schematic diagram of frequency reuse (4 frequencies)

Figure 1 Frequency reuse Sketch Map (4 frequencies)

brief history

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First generation cellular communication system (1G): 1G is based on simulation technique , and basically oriented Analog telephone Communication system. It was born in the early 1980s mobile communication The first basic framework of Cellular cell Architecture Frequency division multiplexing , and roaming. Advanced Mobile Phone Service (AMPS) is a mainstream 1G technology.

Second generation cellular communication system (2G): 2G network marks the transition of mobile communication technology from analog to digital era. This introduces Digital signal processing technology Our communication system was born in 1992. 2G system introduced popular User identity module （ SIM ）Card. Mainstream 2G Access technology CDMA and TDMA 。 GSM is a very successful TDMA network, which has been widely used since the 2G era. 2.5G network appeared after 1995, it introduced the merger Packet switching technology The 2G system is extended.

The third generation cellular communication system (3G): The basic idea of 3G is to support higher bandwidth and Data rate While providing multimedia services. 3G also adopts Circuit switching And packet switching policies. The mainstream 3G access technologies are TDMA, CDMA and broadband CDMA（ WCDMA ）、 CDMA2000 , and time division synchronous CDMA（ TS-CDMA ）。

The fourth generation cellular communication system (4G): the widely used 4G includes several types broadband wireless access Communication system. The characteristics of 4G can be described by MAGIC, that is Mobile Multimedia , anytime, anywhere Global Roaming Support and integrate wireless solutions, and customize personal services. 4G system not only supports upgrading Mobile Services , also supports many existing wireless network 。

The fifth generation cellular communication system (5G): for 5G and ultra 4G wireless Network Communications , there are a series of assumptions. Some people think it will be high-density Network, distributed MIMO To provide a small green flexible community. advanced crosstalk And mobility management are also accompanied by different transmission points and overlapping Coverage area And the cooperation between them. For each cell Uplink and Downlink Transmission and resource usage will be more flexible. Multiple user connections are supported Wireless access technology And truly achieve seamless compatibility when switching between them. People's commonly expected cognition Wireless technology Intelligent wireless technology will enable different wireless technologies to efficiently share the same spectrum by adaptively finding and using the unoccupied spectrum when the primary user leaves. This dynamic Radio resource management Will be based on Software Defined Radio Technical realization.

In fact, there are mainly two different organizations in the world two roads —the socialist road versus the capitalist road , carrying out the technical promotion of 3G to 4G. They are:

-Worldwide Interoperability Microwave access (WiMAX)： WiMAX Mainly by Sprint , Clearwire, and Intel.

- Long term evolution （ LTE ）: LTE is mainly led by Ericsson, Nokia and other companies.^[1]

classification

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Common cellular mobile communication systems can be divided into three categories according to their functions: Macrocell 、 Microcellular And smart cell, usually the three Cellular technology Each has its own characteristics.^[2]

Macrocell technology

In the cellular mobile communication system, in the initial stage of network operation, the main goal of operators is to build large macro cellular cells and obtain the largest possible area Coverage The coverage radius of a macro cell is generally 1 km to 25 km, Base station antenna Do as high as possible. In the actual macro cell, there are usually two special micro areas. One is the "blind spot", because the radio waves Communication process The shadow area caused by obstacles in the Communication quality Seriously inferior; The second is "hot spots", because the space business load is not uniform distribution The busy service area supports most services in the macro cell. The above two "points" are often solved by setting Repeater Divide the community. In addition to economic reasons, in principle, these two methods cannot be used without limitation, because the communication quality will decline when the system coverage is expanded; To improve communication quality, capacity is often sacrificed. In recent years, with the increase of users, macro cell Cell division , becoming smaller and smaller. When the cell is small to a certain extent, the cost of building a station will increase sharply, and the reduction of the cell radius will also cause serious interference. On the other hand, blind areas still exist, and hot spots are high Traffic It can not be well absorbed. Microcellular technology is created to solve the above problems.

Microcellular technology

Compared with macro cellular technology, micro cellular technology has Coverage Small Transmission power The coverage radius of the cell is 30 m~300 m, and the base station antenna is lower than the height of the roof. The transmission is mainly along the line of sight of the street, and the leakage of the signal on the roof is small. Microcells can be used as the supplement and extension of macro cells. The application of microcells mainly includes two aspects: first, improve the coverage, and apply to some blind spots that are difficult to be covered by macro cells, such as subways and basements; The second is to increase the capacity, which is mainly used in areas with high traffic, such as busy commercial streets, shopping malls, stadiums, etc. Microcells are used to improve Network capacity In general, it forms a multi-layer network with macro cells. The macro cell covers a large area as the bottom layer of the multi-layer network, while the micro cell covers a small area Continuous coverage It is superimposed on the macro cell to form the upper layer of the multi-layer network. The micro cell and macro cell are system configuration There are different communities on the Broadcast channel 。

Smart cellular technology

Smart cell technology refers to that the base station adopts Adaptive antenna system , intelligent monitoring Mobile station And transmit the determined signal power to the cellular cell of the mobile station in a certain way. For uplink, use Adaptive antenna array Receiving technology, which can greatly reduce Multiple access interference , add system capacity ； For downlink, the validity of the signal Area control Within the radius of 100~200 wavelengths near the mobile station, the magnitude of the same channel interference is reduced. An intelligent cell can be either a macro cell or a microcell. The networking design using the concept of intelligent cell can significantly increase the system capacity and improve the system performance 。

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