What is the difference between macro base station and micro base station?

The difference between macro base stations and micro base stations: Macro base stations are straightforward. Tower stations are relatively large ones. One station covers dozens of kilometers and has complete computer room facilities. Micro base stations are in buildings or dense areas. The installed small base stations have small coverage and low user volume, covering single villages, buildings and other scenarios.

Base station composition

Infrastructure

Communication base station is the most critical part of the mobile communication network infrastructure. Mobile communication base stations include mechanical rooms, wires, tower masts and other structural components. The base station rooms are mainly equipped with signal transceivers, monitoring devices, fire extinguishing devices, power supply equipment and air conditioning equipment, and the tower poles include lightning protection grounding systems, tower bodies, foundations, and brackets. , cables and auxiliary facilities and other several parts of the structure. According to the shape, tower masts can be divided into angle steel towers, single tube towers, top poles, cable towers and many other different forms. The antenna is a three-layer structure of antenna frame, feed system and infinite reflector, and has two different application scenarios, indoor and outdoor. According to different transmission directions, antennas can also be divided into directional and omnidirectional.

The selection of a base station needs to be comprehensively considered from various aspects such as performance, supporting facilities, compatibility and usage requirements. Special attention should be paid to the fact that the base station equipment must be compatible or supporting with the mobile switching center, so as to achieve better results. communication effect. The base station subsystem mainly includes two types of equipment: base transceiver station (BTS) and base station controller (BSC).

Base station location selection

The base station location must first consider the communication environment around the communication base station, comprehensively consider base station density, signal, traffic volume, on-site conditions and other factors, and try to avoid strong electromagnetic interference and pulse interference. Area and large quantities of flammable and explosive products near commercial and warehouse locations. In addition, the communication base station should be built within a wide field of view, and there should be no tall buildings around it to prevent signal transmission from the communication base station. In the process of base station communication construction, the construction of the computer room, the installation of equipment and the construction of towers are all mechanical structures. The level of construction machinery and technology is very high. Before construction, the geographical features of the construction area should be investigated to make full use of favorable terrain conditions to facilitate construction and maintenance.

Tower Selection

Tower selection must first consider the geological conditions of the construction area, build pile foundations scientifically, and select the appropriate tower type on this basis. Before officially carrying out the design and implementation of communication base station tower selection, it is necessary to conduct a comprehensive investigation of the geological conditions of the construction area and understand the geological conditions and possible geological risks of the construction area. On this basis, a series of effective methods are given. Respond to measures, select the appropriate tower type, comprehensively examine the economic, technical and safety indicators, and select the appropriate tower form. For pile-based communication base stations, the selection of the tower must first consider the performance, crack resistance and settlement of the pile body, and analyze and verify these performance indicators. Basically the entire load of a communications tower is applied directly to the foundation. In order to improve the stability of the tower, special attention must be paid to the foundation construction. There are three different forms of tower foundation construction: extended foundation, single pile foundation and group pile foundation. If necessary, tie beams and anchor bolts can also be added to resist the liquefaction of the foundation to further improve the bearing capacity of the foundation.

Transceiver Station

We often see the high antenna on the roof, which is part of the base station transceiver station. A complete base transceiver station includes wireless transmitting/receiving equipment, antennas and all signal processing parts unique to the wireless interface. The base transceiver station can be regarded as a wireless modem, responsible for the reception and transmission processing of mobile signals. Generally, in a certain area, multiple sub-base stations and transceiver stations form a cellular network with each other. By controlling the mutual transmission and reception of signals between the transceiver stations, the transmission of mobile communication signals is achieved. Within this range, Region is what we often call network coverage. Without a transceiver station, it would be impossible to send and receive mobile phone signals. The areas that cannot be covered by base transceiver stations are also the blind spots of mobile phone signals. Therefore, the range of the base transceiver station transmitting and receiving signals is directly related to the quality of the network signal and whether the mobile phone can be used normally in this area.

Under the control of the base station controller, the base transceiver station completes the conversion between the control of the base station and the wireless channel, and realizes the transmission and reception of mobile phone communication signals and the mobile platform through air wireless transmission and related control functions. The transceiver station decodes and transmits each user's wireless signal.

The antennas used by the base station are divided into transmitting antennas and receiving antennas, and they are divided into omnidirectional and directional. Generally, there are three configuration methods: transmitting omnidirectional and receiving omnidirectional; transmitting omnidirectional and receiving Orientation mode; send orientation, receive orientation mode. From the literal meaning, we can understand the difference between each method. Omnidirectional transmission is mainly responsible for all-round signal transmission; omnidirectional reception is naturally the reception of signals in one direction; directional means only sending and receiving from a fixed angle. . Generally speaking, base stations with fewer channels (such as those located in suburban areas) often use omni-directional transmission and omni-directional reception, while base stations with more channels use omni-directional transmission and directional reception, and the establishment of base stations is also faster than in suburban areas. More intensive.

Since the signal may be relatively weak when transmitted to the base station, and there will be certain signal interference, it must go through the preselector.

Module filtering and amplification, performing dual frequency conversion, amplification and frequency discrimination processing. The input high-frequency signal is amplified and sent to the first frequency converter. The frequency of the first local oscillation signal provided by the frequency converter is 766.9125-791.8875MHz. After down-conversion, a first intermediate frequency signal of 123.1MHz is generated. After the first intermediate frequency signal is amplified, filtered, and mixed, a second intermediate frequency signal (21.3875MHz) is generated, which is amplified, filtered, and sent to the intermediate frequency integrated block. The audio output signal and received signal strength indicator signal (RSSI) generated by the IF integrated block (including the second IF signal amplifier, limiter and frequency discriminator) are sent to the audio/control board. In the audio signal control board, the diversity signal is The switch continuously compares the odd and even signals and selects the stronger signal, which is transmitted to the mobile control center through the audio circuit.

The working principle of the base station transmitter is: filter the carrier frequency signal with the frequency of 766.9125-791.8875MHz and the modulated signal of 168.1MHz provided by the frequency synthesizer, respectively, into the double-balanced frequency converter, and obtain the frequency It is a radio frequency signal of 935.0125-959.9875MHz. This radio frequency signal is filtered and amplified before entering the driver stage. The output power of the driver stage is about 2.4W, and then added to the power amplifier module. The power control circuit uses negative feedback technology to automatically adjust the output power of the pre-drive stage or push stage to keep the output power of the driver stage at the rated value. That is to say, the received signal is stabilized and then sent out, which can effectively reduce or avoid the loss of communication signals in wireless transmission and ensure the user's communication quality. The function of the power amplifier module is to amplify the signal to 10W, but this also depends on the actual situation. If the cell transmits a larger signal radius, a 25W or 40W power amplifier module can also be used to enhance the signal transmission radius.

Controller

The base station controller includes wireless transceivers, antennas and related signal processing circuits, etc., and is the control part of the base station subsystem. It mainly includes four components: Cell Controller (CSC), Voice Channel Controller (VCC), Signaling Channel Controller (SCC) and Multi-channel End Interface (EMPI) for expansion. A base station controller usually controls several base transceiver stations. Through remote commands from the transceiver stations and mobile stations, the base station controller is responsible for all mobile communication interface management, mainly the allocation, release and management of wireless channels. When you use a mobile phone, it is responsible for opening a signal channel for you, and when the call ends, it closes the channel and leaves it for others to use. In addition, the handover of mobile stations within this control area is also controlled. For example, when you enter the signal sending and receiving range of another base station when using your mobile phone, the controller is responsible for switching between the other base stations and maintaining a constant connection with the mobile switching center.

The GSM system uses a handover method when crossing a cell. That is, when the user reaches the cell boundary, the mobile phone will first cut off contact with the original base station, and then establish contact with the base station of the new serving cell. When the new serving cell When busy, the call channel cannot be provided, and disconnection will occur. Therefore, when using a mobile phone to make calls, users should try to avoid using it in the four-corner blind spots to reduce the chance of dropped calls.

The core of the controller is the switching network and common processor (CPR). The public processor controls and manages each module within the controller and is connected to the Operation and Maintenance Center (OMC) through the X.25 communication protocol. The switching network will complete the internal switching of 64kbit/s data/voice service channels between interfaces. The controller is connected to the mobile switching center through the interface equipment digital repeater (DTC), and is connected to the transceiver station through the interface equipment terminal controller (TCU) to form a simple communication network.

In the entire cellular mobile communication system, the base station subsystem is the bridge connecting the mobile station and the mobile center, and its position is extremely important. Factors such as the number of base stations in the entire coverage area, the location of the base stations in the cell, and the performance of relevant components in the base station subsystem determine the communication quality of the entire cellular system. The selection and construction of base stations has become an important part of building a modern mobile communication network.

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