RET: Remote Electrical Tiling
RCU: Remote Control Unit
CCU: Central Control Unit
- Mechanical and electrically tuning antennas
1.1 Mechanical downtilt refers to the direct adjustment of the physical tilt angle of the antenna to change the beam coverage. Electrical downtilt refers to changing the beam coverage area by changing the antenna’s phase without changing the antenna’s physical position.
1.2 Principles of Electrical tuning antenna adjustment.
The vertical main beam achieves the antenna coverage, and the adjustment of the downtilt angle changes the coverage of the main beam. For the electrical tuning antenna, the phase shifter is used to change the phase of the power signal obtained by each radiating element in the antenna array to achieve the downward tilt of the vertical main beam. It is the application of radar phased array technology in mobile communication.
The principle of electronic downtilt is to change the phase of the collinear array antenna element, change the amplitude of the vertical component and the horizontal component, and change the field strength of the composite component, so as to make the vertical directivity diagram of the antenna downward. Because the field strength of each direction of the antenna increases and decreases at the same time, it is ensured that the antenna pattern does not change much after the tilt angle is changed, so that the coverage distance in the main lobe direction is shortened, and at the same time, the entire directional pattern is reduced in the serving cell sector. Area but no interference.
Electrically tuning antenna generally adjust the vibrator circuit on the physical structure of the motor to achieve the change of the vibrator path, this is the phase shifter, which changes the feed phase of each vibrator by adjusting the length of the feed network to achieve the downward tilt of the antenna beam.
2. Electrically tuning antenna
construction:
The azimuth and pitch angle of the installation seat of the antenna are controlled by mechanical.
The pitch angle of the antenna is adjusted by adjusting the phase angle.
Wire remote control
It is generally connect the base station controller through RS485, RS422, and controller will connect the remote control center via wire or wireless.
Wireless connection
It is generally direct connect with control center via wireless communication component.
2.1 structure
2.2 Antennas
Remote electrical tilt antenna is made up of antenna and remote control unit (RCU). The reason why the electrical tuning antenna can achieve continuously adjustable electrical downtilt is the use of multi-channel phase shifter which can be adjusted mechanically, the device is one input and multiple output, through the mechanical transmission mechanism can simultaneously change the output signal phase(change the path of the oscillator). Then the remote control is carried out through the remote control unit (RCU).
The phase shifter can be simply divided into two types: the difference is that the motor rotation is to adjust the transmission line’s length or adjust the location of the media.the location of the media.
Electrical tuning antenna
The interior of the antenna is as follows:
2.3 RCU(Remote control unit)
RCU is composed of a drive motor, a control circuit and a transmission mechanism. The main function of the control circuit is to communicate with the controller and control the driving motor. The driving structure mainly includes a gear which can be engaged with the transmission rod, when the gear rotates under the motor drive, the transmission rod can be pulled, thus changing the down slope angle of the antenna.
RCU is divided into external RCU and built-in RCU.
RET antenna with built-in RCU means that the RCU is already mounted to the antenna and shares a housing with the antenna.
RET antenna with the external RCU means that the RCU controller needs to install an RCU between the corresponding ESC interface of the antenna and the ESC cable, and the RCU is outside the antenna mask.
The external RCU can be relatively clear understanding of its structure, so let me introduce the external RCU. In simple terms, RCU can be understood as a remote control of the motor, one input control signal, one output motor drive, as follows:
RCU is an internal motor and control circuit, we don’t need to understand; let’s take a look at the interface of RCU.
RCU and RRU interface:
The RET interface is the interface to the AISG control line, and generally, the built-in RCU only provides this interface for connect to the RRU.
The interface between RCU and antenna, the white part in the figure below is the motor drive shaft, which is connected to the antenna.
It is obvious that the RCU drives the motor directly to control the phase shifter inside the antenna instead of controlling the phase shifter through the signal wire; the interface between RCU and the antenna is a mechanical transmission structure, not a signal wire structure.
External RCU antenna interface
After the feedback line is connected, the RCU connects to the antenna and connect to the Electrical tuning antenna as follows:
2.4 AISG cable
For the built-in RCU, because it is integrated inside the antenna mask, it is enough to directly connect the electrical tuning antenna cable between the antenna(actually the internal RCU), and the RRU. Whether the RCU is internal or external, the connection between the RCU and the RRU is via an AISG control line.
- AISG (antenna interface standards group) is a standard organization for antenna interface. The website is http://www.aisg.org.uk/, mainly used for remote control of base station antennas, and tower equipment.
- AISG includes interface specification and protocols, and defines related interface communication standards and communication procedures.
2.5 other devices
A control signal splitter is a device used to interconnect multiple drivers into a control line in parallel. It interconnects through a cable and then separates multiple signals from multiple drivers. It has a lightning protection function and is suitable for discrete control of control cables. It can also extend a single-port controller to allow simultaneous control of three antennas in a base station.
Control signal arrester is used to access the system of related equipment for lightning protection of a device, it protects multiple active signals at the same time, suitable for direct control of the driver through the control cable scheme when the system through T head to control, you can not use this arrester. The lightning protection principle of radio frequency signals is not quite the same. It is achieved through overvoltage protection. The antenna feed arrester is not the same thing, do not confuse.
A handheld controller is a kind of suggested controller designed for field debugging. It can perform some simple operations on the driver by pressing the keyboard on the panel. Basically, all functions can be tested by running test software on the computer. It can also be used to complete local control functions where the remote control is not required.
The desktop controller is a remote control controller installed in a standard cabinet. It is connected to the system through Ethernet and can manage and control the antenna equipment of the base station in the control center. The basic function of this controller is the same, but the structure is not the same. Some are made of 1U standard chassis, some other equipment, and then combined to make an integrated controller.
The antenna end T-head is connected to the antenna end in a control scheme through a feeder. It can complete the control signal modulation and demodulation, power supply feeding, and lightning protection function. In this scheme, the control signal arrester and the long cable to the controller are eliminated.
Base station terminal T head is the equipment connected to the base station terminal in the control scheme through the feeder. It can complete the control signal modulation and demodulation, power supply feeding and lightning protection function. It is used in conjunction with the t-head of the antenna end of the tower, in which the control signal arrester and the long cable to the controller are eliminated.
The tower amplifier with the built-in T-head is a tower top amplifier internally integrated with the antenna end T-head, placed near the antenna in the control scheme via the feeder. It has an AISG output interface connected to the antenna driver. It has completed the rf signal amplification but also can complete the power supply feed and control signal modulation and demodulation function and own a lightning protection circuit. This kind of tower is widely used in the 3G system.
3.The use of electrical tuning antenna
3.1 how base station use RCU
RS485
PCU+ Long AISG cable
Feature: in the tower amplifier, through AISG long cables, adjust antenna through PCU.
The base station control signal and DC signal are transmitted to the RCU through the AISG multi-core cable. The main device can control one RCU remotely and manage multiple cascaded RCU.
Modulation and demodulation mode
External CCU + AISG cable +RCU
Features: through long AISG cable or feeder, adjust antenna via CCU
The base station modulates the control signal to 2.176MHz OOK signal (baiOn-Off Keying, binary amplitude keying, which is a special case of ASK modulation) through external or built-in BT, and transmits it to SBT through RF coaxial cable together with DC signal. SBT completes the mutual conversion between OOK signal and RS485 signal.
3.2 Remote Electrical tuning antenna mode
the basic method is to control the power dispatch through the base station network management. The control information is sent to the base station through the base station network management, and the base station transmits the control signal to the RCU, the modulation of the electrical dip angle of the electrically modulated antenna is completed by RCU. The difference between the left and right sides lies in the way the base station transmits the control signal to RCU. The left side transmits the control signal to RCU through the base station radio frequency cable, and the right side transmits the control signal to RCU through the base station electric adjusting port.
In fact, the different way is the use of RCU different.
3.3 RCU cascade
Solution: SBT(STMA)+RCU+integrated network or RRU+RCU +integrated network
There is only one RET interface on each RRU/RRH, and when one/2 RRU opens multiple cells (RRU split) , the RCU needs to be cascaded.
The ESC antenna can be adjusted manually by manually pulling the stroke mark on the outside of the antenna.
3.4 Antenna Calibration
The electrically tuned antenna needs to be calibrated to determine how well the antenna is electrically tuned.
The ESC antenna supports the minimum and maximum angles to set two stuck points, but after receiving the calibration command, the slave device drives the driver to move in the entire angle range. First, measure the distance between the two stuck points, and then The total stroke in the configuration file is compared (the configuration and the actual error are required to be within 5%).
4. The relationship between AISG and electrically modulated antenna
AISG defines the interface and protocol between CCU and RCU.
