Base Station Controller: It is the control and management part of the base station subsystem. It is located between the MSC and the BTS. It is responsible for wireless network management, wireless resource management, and monitoring and management of the wireless base station. It controls the establishment, continuation, and removal of the wireless connection between the mobile station and the BTS. There are mainly GSM and CDMA base stations in China.
BSC refers to the Base Station Controller.It is the base transceiver andMobile switching centerThe connection point between BTS and MSC also provides an interface for exchanging information between BTS and MSC.A base station controller usually controls several base station transceivers. Its main functions are to manage radio channels, establish and dismantle calls and communication links, and control the handover of mobile stations in the control area.
Logical composition of base station controller
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The logical composition units of the base station controller include operation and maintenance unit (OMU), access unit (AU), processing unit (PU), switching unit (SU), and peripheral equipment monitoring unit (PMU)
N Operation and Maintenance Unit (OMU)
Be responsible for handling the global process and realizing the control related to system operation and maintenance, realizing the isolation of internal and external network segments, and providing the global clock of the whole system;And contains OMM functions
N Access unit (AU)
Realize the external interface function of the system, including E1/T1, STM-1, CSTM-1, and realize some link layer processing
N Processing unit (PU)
Realize the processing of wireless control plane protocol, wireless user plane protocol and some data bearer protocols related to ATM transmission
N Switching unit (SU)
Realize the layer 2 exchange function between the frame level and the frame level, and provide a dual exchange plane for the control plane and the user plane
N Peripheral monitoring unit (PMU)
Power status collection and alarm
Temperature, humidity, smoke, water immersion, infrared and other environmental alarm processing
Function list
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The base station controller is located between the MSC and the BTS. Its task is to manage the wireless network, that is, to manage the wireless cell and its wireless channel, the operation and maintenance of wireless devices, the service process of mobile stations, and to provide the interface between the base station and the MSC.The functions related to wireless control should be concentrated on the BSC to simplify the BTS equipment. Its functions are as follows:
1．Wireless base stationRBS resources are controlled by the BSC. At the same time, the BSC can also monitor RBS performance through internal software testing and loop testing on the voice channel.Ericsson's base station uses internal software testing and loop testing to monitor TRX on the voice channel.If a fault is detected, RBS will be reconfigured to activate the standby TRX, so that the original channel group remains unchanged.
2. For radio resource management, the BSC configures services and control channels for each cell. In order to accurately reconfigure, the BSC collects various statistical data.For example, the number of lost calls, successful and unsuccessful handovers, traffic per cell, wireless environment, etc. Special recording functions can track all events in the call process, and these functions can detectNetwork failureAnd faulty equipment.
3. Process the connection with the mobile station, be responsible for the establishment and release of the connection with the mobile station, assign a logical channel to each voice, and during the call, the BSC monitors the connection. The mobile station and the transceiver measure the signal strength and voice quality, and the measurement results are sent back to the BSC.The transmission power of mobile stations and transceivers is determined by the BSC. Its purpose is to ensure good connection quality and minimize interference in the network.
4. Location and handover. The handover is controlled by the BSC. The location function constantly analyzes the quality of voice connection, so that it can decide whether to switch. The handover can be divided into handover within the BSC, handover between BSCs within the MSC, and handover between MSCs.A special handover is called intra cell handover. When the BSC finds that the voice quality of a connection is too low and no better cell is found in the measurement result, the BSC will switch the connection to another logical channel in the cell, hoping that the call quality will be improved.Handover can also be used to balance the load between cells. If the traffic in one cell is too high, while the traffic in adjacent cells is small, and the signal quality is acceptable, some calls will be forcibly switched to other cells.
5. Paging management. The BSC is responsible for distributing paging messages from the MSC. In this regard, it is actually a special transparent channel between the MSC and the MS.
6. Management of transmission network. BSC configures, allocates and monitors 64KBPS circuits with RBS. It also directly controls the switching function in RBS.This switching function can effectively use 64K circuits.
7. Code type conversion function:Full rateThe voice coding of the GSM channel multiplexed into a 64K channel is completed in the BSC. A PCM timeslot can transmit four voice connections.This function is realized by TRAU.
8. Voice coding.
9. BSC is responsible for the operation and maintenance of the whole BSS.Such as system data management, software installation, equipment blocking and unblocking, alarm processing, test data collection, transceiver testing.
working principle
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Taking the GSM system as an example, the location and function of the base station controller in the base station subsystem are shown in the figure.
Location and function of base station controller
Taking a mobile phone call as an example, the main functions of the base station controller are described as follows:
1. The call information of the mobile phone is sent to the BTS transceiver and received.
2. The BTS transceiver also sends the call information to the BTS console. The BTS controller is responsible for establishing the connection of the call, establishing a channel from the BTS subsystem to the mobile switching center for the call, so as to open up the wireless access part and the wired transmission part of the network, as shown by the dotted line in the figure.
In addition, in addition to controlling the transceiver, the BTS controller of the transceiver also controls several adjacent BTS transceivers. It selects the signal area provided by a BTS transceiver for this call according to the current status of each BTS transceiver.
3. In the process, when the signal quality becomes poor, the BTS controller is responsible for switching the call in different control areas, including intra cell handover and inter cell handover.
Intra cell handover: The BTS controller selects different logical channels for the mobile phone in the signal area provided by the BTS transceiver to improve the communication quality.
Inter cell handover: When the communication quality cannot be optimized within the signal area, the BTS controller monitors the signal quality of other BTS transceivers, and selects a signal area with good quality to transfer the call to the signal area. This is inter cell handover. At this time, the BTS controller will convert and update the cell phone area information.
4. At the end of the call, the resources occupied by the connection and the call will be released according to the end information transmitted by the transceiver.
5. At the other end of the network, the called mobile phone also has a corresponding base station subsystem to provide services. The difference is that the paging signal of the base station controller comes from the mobile switching center. Other operation management is similar to the calling end, and will not be repeated.
The above description takes the GSM system as an example. Other systems are basically the same as the GSM system, except for some different terms, which will not be described here.
