What are the handover steps in WCDMA network optimization?

Reducing interference in high traffic density areas by antenna downward tilt method

introduce

In the early development of mobile communication system, the radiation pattern of base station antenna mainly depends on the gain needed to ensure reliable communication within the specified coverage area, and the omni-directional radiation mode is often adopted. With the increase of traffic, frequencies are reused in different geographical locations or wireless cells to improve spectrum utilization. In addition, wireless cells need to be subdivided into sectors.

1. 1. Horizontal beam width

In cellular mobile phone system, the first step to increase communication capacity is to use directional antennas arranged horizontally. That is, a base station uses several antennas, and each cell is divided into three or six sectors. Each sector specifies a set of dedicated frequencies.

For example, the reuse factor K=7, and each cell has 3 sectors (also called 7/2 1). This frequency reuse method is shown in figure 1, and the serial number of the used channel group is also marked in the figure (omitted). R represents the cell radius, and the frequency reuse distance d is the shortest distance between two cells using the same frequency configuration. Base stations with the same frequency are co-channel interference sources, which are indicated by shading in the figure.

Because the antenna of the base station is directional, the interference level received by the base station will be weakened. This is because the main antenna lobe is narrow, and the received interference mobile station signals are less. In [reference 1], it is suggested to adopt a three-sector system-120-degree sector, while in some hot spots, a 60-degree sector system can be adopted locally. We choose the radiation pattern of the horizontal antenna to keep the electric field intensity of each sector as constant as possible. So far, we have considered the antenna radiation pattern on the horizontal plane. Using horizontal beam antenna will increase the total number of antennas used in the system, which will lead to increased cost. With the increase of telephone traffic, we should find other ways to reduce co-channel interference. One method is to shape the horizontal radiation pattern of the antenna.

1.2. Vertical beam width

For cells using the same frequency, the required base station antenna should have as low radiation energy as possible and as high radiation as possible in the service area.

Tilting the main lobe can produce ideal effect, especially in combination with suppressing the sidelobes of adjacent main lobes. It is very important to suppress the sidelobe in the "lower sidelobe region" marked in Figure 2. (Figure omitted)

Although it is also ideal to have a steep antenna radiation pattern on the upper side of the main lobe, in practice, if the antenna is not made very large (which will also affect the cost of the antenna), it is impossible to make substantial improvement. There are two ways to lower the main beam:

Mechanical antenna tilt

Change the phase of the antenna element so that the beam tilts downward (electrons tilt downward).

The following analysis of this paper aims to investigate which downward dip method can provide better performance in reducing co-channel interference.

2. Determine which downward sloping method to choose.

2. 1. Mechanical or electronic

Two different downward sloping methods produce different surface radiation. When the inclination angle is small, this difference is not obvious; However, with the increase of dip angle, this difference is obvious. Here are some examples of surface radiation. (Figure omitted)

It can be seen that in the case of electron dip, the ground radiation pattern still maintains its shape when the dip angle increases; However, in the case of mechanical tilt, the radiation pattern appears "low depression", and at the same time, the lateral radiation increases. This effect is well known in mechanical downtilt antennas. Please refer to W. Lee's book Mobile Cellular Telecommunications (reference 1). From the point of view of reducing the interference of base station B 1 (see figure 1), there is nothing wrong with this "depression". However, with the increase of side radiation, the reception interference from B2 and B6 base stations also increases.

We quantitatively estimate this effect, and this method will be described in detail below.

We compared the electronic method with the mechanical method to improve the load-drying ratio. The antenna used for comparison is a standard 8-element antenna, and each element is separated by half a wavelength. The azimuth radiation pattern of the radiation unit is shown in Figure 6. (omitted) Two different methods are used to calculate different downtilt modes, as shown in Figure 7 (omitted). As can be seen from the frequency reuse diagram in Figure 1, there are six interference sources around a specific base station.

The worst carrier-to-interference ratio appears at the cell edge. When the main beam is downward, although the received power c from the mobile station decreases, the received interference decreases more, thus improving the carrier interference ratio C/ 1.

Using the radiation patterns of electronic and mechanical downtilt antennas, we calculated the functional relationship among signal level, interference level and downtilt angle. All base station antennas are inclined downward at the same angle. The calculation results are shown in Table VIII A and Table VIII B. (Figure omitted)

First, the received signal level from the mobile station is shown in fig. 7. As you can see, there is not much difference between electronic and mechanical downtilt methods. Secondly, the received interference level from the base station 1 is represented by eight B's, and there is not much difference in interference suppression between the two downward inclinations.

The reception interference of the mobile stations from the base station 2 is very different. Interference suppression is shown in Figure 9. It can be seen that the electronic downward tilt method greatly suppresses the interference, while the mechanical downward tilt method can't do this. When investigating the interference received from the mobile stations of base stations 3, 5 and 6, the electronic downward tilt method also has advantages over the mechanical method.

When the mobile station interferes, it can be seen that the electronic downtilt method has the same advantages as the mechanical downtilt method.

To sum up, the electronic declination method is much better than the mechanical declination method in improving the load-to-dry ratio. Therefore, it can be said that the electronic downtilt method is a more ideal choice for the base station antenna.

There is another factor to consider when evaluating electronic and mechanical downtilt methods. In the urban communication network, there are many man-made obstacles in the community, which is very special. These obstacles will cause multiple reflections, leading to multipath effect in the propagation channel. RMS delay range is an important parameter of propagation channel, which may be the limiting factor of high information transmission rate system. As measured in the article [Reference 2], when the main beam is tilted downward and the base station antenna is slightly higher than the general situation, the root mean square delay range can be reduced. As shown in figure 10, all signals scattered from the elliptical area will react at the receiving station with the same delay. By comparing the surface radiation patterns of electron and mechanical downtilt methods shown in Figure 1 1 (A) and Figure 1 1 (B) (omitted), it can be clearly seen that electrons are used.

In a word, the electronic downtilt method is superior to the mechanical downtilt method because:

In most cases, it can reduce more interference levels.

The ground radiation pattern is less distorted.

The rms delay range of the signal can be minimized.

2.2 Determination of the best downward inclination angle

Using the above model, we calculated the load-drying ratio C/ 1 for several different dip angles. Assume that the antenna height of the mobile station is 1.6m, the antenna height of the base station is 20-60m, the distance to the mobile station is r = 2km, and the distance to the interference source is as shown in figure 1, and figure 12 shows the improvement of the carrier-to-interference ratio C/ 1 by electronic and mechanical downtilt methods. (Figure omitted)

It can be seen that in the case of using electronic downtilt mode, the improvement brought by downtilt is more obvious, at least in frequency reuse. It can also be noted that there is an optimal value of the dip angle when the mechanical dip method is used (it is the best in the area of about four degrees), and when the dip angle of the electronic dip method increases, the carrier-to-interference ratio also increases, at least from the perspective of the dip angle (for the dip angle greater than 15 degrees, the first radiation blind area will be in the service area and should be avoided). When the antenna height of the base station increases, the advantages of downward tilt mode are more prominent.

It is clear from fig. 8 and fig. 12 that there is some compromise between signal level c and carrier-to-interference ratio C/ 1. The optimal downward tilt angle depends on the cell size, antenna radiation pattern and antenna height. In addition, due to the change of 24-hour traffic in each cell, the optimal size of each cell also changes. If you use DELTEC's Teletilt antenna product line, you can change the cell size and minimize the delay.

Although the graphs shown in Figures 8 to 12 are calculated based on a simple flat terrain model, the trends they show well predict what happens in practical applications. The increase of load-drying ratio C/ 1 will be affected on uneven ground and where there are many buildings. In practical application, the effect can be improved by slightly increasing the antenna height of the base station and adopting the mode of electronic downward tilt. In addition, if the reuse factor used in frequency reuse mode is small (for example, K=4), the reuse distance will be small, and the improvement of carrier-to-interference ratio is more significant than that of C/ 1.

3. Determine the best antenna position and make full use of the tilt effect.

If the base station is located in an urban area with high traffic density, the antenna can be placed under the roof to reduce the cell size, especially in the system where microcells are limited by interference. The influence of buildings on propagation loss is usually 10- 15 dB, which is different from the diffraction screen model [Ref. 3]. In this case, due to the drainage pipe network effect of the street, the ground radiation is rhombic (see figure 13).

However, under urban conditions, the exact shape of the service area is not easy to determine, because it will be greatly affected by local obstacles, and any field strength estimation with considerable accuracy needs a high-resolution geographic database. Despite these difficulties, it is a feasible choice to install the base station antenna below the average roof line if microcells must be used to meet the requirements of high service density and capacity.

For honeycomb, the size can be reduced by installing the antenna higher than the roof and tilting the main beam downward. The advantages of this method will be detailed later.

We can estimate the change of signal strength received by the mobile station according to two factors:

(1) Change the height of the base station antenna.

(2) The main girder inclines downwards

We use the description of the diffraction screen model in reference 3 to explain the situation shown in figure 14. (Figure omitted)

The results are shown in figures XV and XVI. It can be seen that when the antenna height of the base station is lower than the average height of the roof (assuming 15m), the signal level drops sharply. The signal strength in this case is shown in figure 15.

Similar signal intensity attenuation can also be obtained by the downward inclination of the main beam. If the installation height of the antenna is higher than the average height of the roof and the beam inclines downward, the signal level will also drop, as shown in Figure 16. In order to give full play to the advantages of downward dip method, we suggest that the antenna installation of base station should be slightly higher than the average height of roof.

Advantages of these methods:

Minimize the influence of obstacles in the signal propagation path in order to properly control the cell shape.

Reducing the rms delay range through a more direct signal path [Reference 2]

The signal path loss is reduced, and the signal level variation of the whole cell is reduced.

Changing the cell size by changing the tilt angle is a more flexible means.

When the communication network develops or temporary "hot spots" appear, the cell size can be easily changed by adjusting the downward inclination angle through remote control [see. 4].

conclusion

For the communication network with high traffic density limited by interference, the downward inclination of the main beam can be an effective tool to improve the carrier-to-interference ratio C/ 1.

The electronic tilting method is superior to the mechanical tilting method because:

In most cases, it can better improve the carrier-to-interference ratio C/ 1.

Less ground radiation pattern distortion

Minimize the signal rms delay range.

The variable electronic tilt method is superior to the fixed tilt method because:

In the adjustment work to improve performance, the obstacles to reducing costs are reduced.

When the communication network develops, there is no need to change the antenna or the antenna height with the change of the site.

Cell planning can be done on site (optional)

There is greater flexibility.

The inventory of antenna can be simplified.

The service life of the antenna can be prolonged.

The remote electronic downward adjustment method is superior to the field adjustment because:

There is no need to directly touch the antenna on site.

The adjustment cost is reduced and the speed is accelerated.

When adjusting the downward tilt angle, it is not necessary to turn off the base station or expose people to RF energy radiation.

The adjustment is not affected by the weather and can be carried out independently.

By slightly increasing the antenna height and antenna inclination of the base station

The RMS delay range of the propagation path can be further reduced.

If remote downward adjustment is adopted, the cell size will be adjusted with minimum delay to change the channel load. This can be achieved by installing DELTEC's Teletilt series antenna products (Tentec New Zealand Limited).

On the relationship between network optimization and antenna feed maintenance

This paper analyzes the antenna and feeder problems encountered in daily maintenance, expounds the important relationship between antenna and feeder maintenance and network optimization, and advances some common solutions to the antenna and feeder problems.

Keywords: network optimization antenna and feeder maintenance

order

Antenna feed maintenance is an important part of mobile communication network optimization. Its technical requirements are high, and its maintenance work is long-term and arduous, which is very important for the good operation of mobile networks. In order to optimize the mobile communication network, the maintenance of antenna feed must run through the maintenance of mobile communication.

The following focuses on the common faults of antenna feeder installation and maintenance, and talks about the maintenance and maintenance of antenna feeder.

First of all, the maintenance and adjustment of antenna and feeder plays an important role in network optimization.

As a service industry, only by improving the communication quality can mobile communication win the satisfaction of users. The purpose of mobile network optimization is to improve network quality. The normal operation of the antenna feed system can not only expand the coverage, reduce the blind spots and improve the coverage, but also reduce interference and crosstalk, reduce the call drop rate and provide quality services for users.

When installing a base station, it is necessary not only to select the site reasonably, but also to control the antenna height of the base station reasonably, so as to reduce the interference in the system and ensure the service quality of the network. For the base stations with serious congestion and high dropped call rate, we can adjust the cell boundary, switching frequency bands, mobile phone access conditions and other related parameters, adjust the antenna direction angle and pitch angle, reduce inter-station interference, and achieve traffic balance.

For example, the antenna height of the base station of Huaxia Hotel in Suzhou is 50 meters, and the third community is seriously congested, with a dropped call rate of 3%-4%. Therefore, we organized personnel to analyze the BSC database and took the following measures:

A. Adjust the antenna pitch angle of the third cell of Huaxia Hotel base station from 6 to10;

B. reduce the power level;

C. The switching point of Huaihai Road base station has been added between Huaxia Hotel and the base station of Public Security Bureau.

After the implementation of the measures, the effect is obvious, the interference level drops to normal, the dropped call rate drops to 0.5%, and the traffic is balanced.

Second, the common fault handling of antenna feeder

1, Installation of antenna and feeder

During the installation of the antenna feeder, due to the negligence of the installer, the antenna feeder is short-circuited, the antenna feeder connector is dusty and dirty, and the seal of the antenna feeder connector is aging and damaged. These antenna and feeder faults are often difficult to find, especially the moving obstacles caused by the broken seals.

After the installation of Luling base station in the second phase of GSM project was completed, the base station could not be debugged, and Siemens personnel could not find out the problem after several visits. Is it the hardware problem of the base station, cable connection problem or antenna feed problem? After searching in many ways, it was found that it was due to the negligence of the installer that a hair-like copper skin was placed between the wire cores of the feeder when making the feeder connector, which led to the short circuit of the feeder. After reforming the feeder connector, the base station runs normally, but how much energy is spent on it and how much profit is lost to the mobile station.

Similarly, on some days, although the test index meets the requirements after the feeder is installed, the tail line of the feeder is not fastened and weathered, which leads to the seal breaking and the base station failure. The feeder tail of Zhu Xian Zhuang base station in Suzhou is not firmly bound. After eight months of normal use, the base station is often disabled because of the standing wave ratio alarm. We carefully analyzed the reasons and determined that the seal of the feeder joint was cracked by wind. We reprocessed the connector, reinforced the feeder tail, and the standing wave ratio alarm disappeared. The coverage distance is expanded from the original 1 km to 4-5 km, which improves the utilization efficiency of the base station. There are many such cases, and if they are not dealt with in time, there will be more problems.

2. The problem of feeding water from the sky.

There are both human factors and natural factors in the problem of feeding water from the sky.

The natural factor is that the feeder itself is submerged. During the second phase of GSM project, there was a flood in Suzhou, and some feeders were soaked in the water. Because the feeder was soaked in water for a long time, the outer skin of the feeder aged and rainwater infiltrated into the feeder. After the installation of the antenna feeder, the standing wave ratio test was not carried out as required, resulting in no standing wave ratio alarm on the antenna feeder in sunny days, and the standing wave ratio alarm on the antenna feeder system in cloudy days or rainy days, which led to the shutdown of the base station. For this reason, the engineering bureau and our staff went to it for more than a dozen times, but they failed to solve it. Later, the feeder was tested by standing wave ratio tester, and it was found that the reason why the base station frequently quit was that the transmitting feeder was flooded. After replacing the antenna feeder, remove the fault.

There are many cases where the antenna feeder is artificially flooded, mainly including poor grounding seal of the antenna feeder, scratches during installation of the antenna feeder, and poor sealing between the antenna feeder and the flexible jumper connector.

For example, the base station of Lu 'anlou in Dangshan is often out of service because of the standing wave ratio alarm. We sent someone to check and found that the feeder was artificially tightened during the first grounding, and the copper skin was exposed. Rainy or cloudy, resulting in feeder water, resulting in standing wave ratio alarm.

Since the opening of Dangshan Fan Zhuang Base Station in February 1998, the carrier frequency has remained normal. However, users near the first area reported that their mobile phones could not access the Internet. Maintenance personnel check that all hardware disks of the base station are normal, and the traffic statistics show that the number of TCH occupied in the cell is 0, indicating that the mobile phone cannot access the Internet in the cell. For this reason, we cooperated with the maintenance personnel of Siemens and Engineering Bureau to thoroughly inspect the hardware and software of the base station, and found no problems. At the end of July, 1999, cooperated with the personnel of the Engineering Bureau to inspect the base station. When checking the antenna and feeder, the test value is only 13.2 (less than 17) after testing with the standing wave ratio meter. After analysis, it was found that the feeder was scratched during installation, which caused the feeder to enter the water, which caused the ground of the base station to fail to operate normally, but it could not provide services to users. After replacing the feeder, the mobile phone in this community can access the Internet. The obstacles caused by the installation of feeders took half a year from discovery to elimination.

The connection between the feeder and the flexible jumper of Sixian base station is not well sealed, which leads to the water inflow of the feeder and gives the standing wave ratio alarm. After the connector is processed, the alarm disappears and the base station runs normally.

Feeder water inflow causes the standing wave ratio alarm of feeder system, and base stations often quit service, which affects the coverage of this area. Serious user complaints not only affect the income of mobile business, but also affect the reputation of mobile department. To nip in the bud, first of all, the installer is strict with himself and has a high sense of responsibility; Secondly, the standing wave ratio should be tested after the base station is installed, and problems should be dealt with in time; Finally, the quality inspectors should carry out acceptance according to certain procedures, including the verification of test data, and the installation and manufacturing process of antennas and feeders should be strictly controlled, so as not to let unqualified items get away with it.

Third, the maintenance of antenna and feeder

As we all know, the frequency of 900 MHz antenna is 875-960MHZ, and the transmission power is 20W. If conducted through antenna and feeder, this high-frequency electromagnetic wave and low transmission power will reduce the receiving sensitivity. Sometimes users report that the receiving sensitivity of mobile phones is very high when the base station is just opened, and it drops in less than two years, especially at the edge of the coverage area. What is the reason? After analysis and measurement, the maintenance of the antenna feed system is the key. Without maintenance, the sensitivity will decrease by about 15% every year.

How to maintain the antenna feeder?

1. Pay attention to the dust removal of antenna equipment. Due to long-term exposure to the sun and rain, all kinds of dust and dirt stick to the antenna and feeder. These dust and dirt have great resistance in sunny days, but when it is rainy or wet, they absorb moisture and connect with the antenna to form a conductive system, forming a capacitance loop between dust and core wires, between core wires and core wires, and between some high-frequency signals. In this case, the coverage of the base station will be affected, and the base station will be disabled in severe cases. Therefore, before the flood season comes every year, neutral cleaner should be used to dust the antenna and feeder equipment.

2, 2, combined parts fastening. The antenna is affected by external forces such as wind blowing and man-made collision, and the connection between the antenna combination device and the feeder is often loose, resulting in poor contact or even breakage, which leads to water ingress and dust pollution in the antenna feed, resulting in increased transmission loss and decreased sensitivity. Therefore, after the antenna is dusted, the loose part of the antenna combination should be decontaminated and derusted with fine sandpaper, and then fastened firmly with waterproof tape.

3.3. Correct the fixed antenna direction. The direction and position of the antenna must be accurate and stable. Under the influence of wind and external force, the direction and elevation of antennas will change, which will cause interference between antennas and affect the coverage of base stations. Therefore, the antenna field strength, transmitting power, receiving sensitivity and standing wave ratio should be tested and adjusted after the antenna is repaired.

4. Based on the above analysis, to fundamentally solve the problems existing in the antenna feeder, we should start with the daily maintenance of the equipment, check and test the antenna feeder regularly, and handle the problems in time when found. Maintenance personnel and installers should strengthen their own quality training, master the installation and maintenance methods of antennas and feeders, use rich maintenance methods to diagnose and eliminate faults quickly and accurately, improve maintenance efficiency, ensure the running quality of mobile networks, increase our competitiveness in the mobile communication market, and make our mobile communication network a smooth and efficient network.

Overview of network optimization

Network optimization is mainly divided into:

Community optimization yield optimization

The site with high drop rate and call establishment failure rate is investigated on the spot, and the problems such as equipment hardware failure, antenna feed system design, frequency interference and site selection are eliminated. Wireless parameter adjustment (switching, power control) and switch parameter adjustment.

Wireless planning optimization capacity optimization

Through frequency adjustment, the interference in the network is eliminated, the interference outside the network is avoided, the coverage of the cell is adjusted, the traffic distribution is more reasonable, and insufficient coverage and out-of-area coverage are avoided. Adding or deleting the relationship between adjacent cells makes the handover more reasonable and reduces dropped calls caused by inappropriate handover. Monitor the growth of system capacity, warn the network bottleneck in time, point out the shortage of system configuration, and provide technical suggestions for expansion planning.

Feasibility analysis of introducing new configuration optimization technology

Reasonable planning and configuration of switch, base station controller, location area and carrier frequency keep the load of CPU, signaling and base station controller at normal level, thus accommodating more users. The feasibility of introducing new technologies such as microcellular and concentric circles and the new functions in the new version are analyzed.

Monthly optimization work report, data and frequency plan during network expansion and cutover, check network monitoring, etc.

In order to let customers have a comprehensive and clear understanding of the network situation and optimization work, network optimization provides a monthly report of optimization projects. The main contents are as follows:-network indicators and long-term trend chart-main problems, solutions and results analysis report-main activities and progress of network optimization in the current month-work plan and optimization meeting arrangement for the next month-other issues related to optimization. Network expansion often involves a lot of data changes and comprehensive update of frequency planning. Checking the database and frequency planning is directly related to whether the network quality can maintain the original level after handover. Siemens network optimization uses rich experience in network wireless characteristics and advanced tools to help engineering and frequency planning departments set reasonable parameter values, eliminate hidden dangers, ensure smooth handover, keep abreast of the latest situation, and find and solve problems at the first time.

Optimize the network performance by adjusting the antenna depression angle.

In the process of wireless network optimization, it is often necessary to adjust the coverage of base station cells to adjust the service cells, reduce the traffic load of busy cells and eliminate co-frequency interference. Therefore, the above objectives can be achieved by adjusting the antenna depression angle, improving the antenna height, changing the transceiver equipment of the base station, increasing the channel configuration of the cell or increasing the cell, and increasing the co-frequency multiplexing distance. The method of adjusting the antenna depression angle does not require special investment, and has the advantages of high speed and small changes in network parameters, and is a common means to optimize the network.

Adjusting the antenna inclination is only for directional antennas, and it is often used for two types of directional antennas: 60 and120. The half power angle in the vertical direction is about 8 and15. This paper introduces the method of adjusting the antenna inclination angle according to different applications.

1, adjust the service area

Suppose an antenna is 50m high, with a gain of 10dB and a transmission power of 10w. Under the condition of quasi-flat terrain, the relationship between the antenna depression angle and the horizontal main direction coverage distance is shown in the following figure.

If the cell to be adjusted is at the edge of the cellular network, generally speaking, in order to expand the coverage as much as possible, the antenna depression angle should be adjusted to 0 ~ 2, and when the antenna position is higher than 50m, the antenna depression angle can be adjusted to 2 ~ 4. For occasions where there are many users near the base station and mobile phones are dense, and in order to meet the needs of important users in the outer suburbs who can use vehicle-mounted mobile stations, the antenna depression angle can be appropriately adjusted to about 5.

If the cell to be adjusted is not at the edge of the cellular network, the coverage should be well controlled. When the coverage is too large, the depression angle can be increased to correct it. When the coverage distance is above 8km or below 0.5km, it is invalid to increase or decrease the coverage distance only by changing the inclination angle. If the antenna inclination is greater than 20, the factors affecting the coverage distance may have become vertical sidelobes or even reflected waves.

2. Reduce the traffic in busy communities.

By increasing the antenna depression angle of the busy cell, the coverage area can be reduced, while the antenna depression angle of the adjacent cell can be reduced, which can expand the coverage area of the adjacent cell, and at the same time, the related data of handover can be modified, thus reducing the traffic load of the busy cell.

In addition, if the handover area is located in a densely populated area, when the dropped call rate is high due to handover failure, similar methods can be used to transfer the handover area to areas where users are scattered, such as production areas, parks, squares, rivers and other areas.

3. Eliminate co-frequency interference.

For cellular networks with directional cell structure, the angles of antennas in the same frequency cell on the horizontal plane are the same. Theoretical analysis and practice show that in the process of increasing the tilt angle of directional antenna, the gain decline in the main direction of horizontal plane is greater than that in other directions, so it is more scientific to eliminate the same-frequency interference by changing the tilt angle than simply reducing the transmission power.

The ability to resist co-frequency interference is not directly proportional to the depression angle, and the depression angle is different for different models, different manufacturers, different antenna frame heights and different application environments. For example, the ETEL-37 antenna used in Zaoyang mobile network has the best dip angles of13 and 23. Generally speaking, the adjustment should not affect the original coverage area too much, so the adjustment of depression angle should not be too big, generally between 5. In fact, the cellular network belongs to the irregular mixed cell networking mode. When the depression angle is large (above 12) and the depression angle with other sectors of the base station is small, the influence of antenna sidelobe and back lobe on other cells must be considered. Only after repeated comparison and adjustment and instrument testing can the optimized depression angle be determined. It is worth noting that when adjusting the antenna inclination, the adjustment screw on the directional antenna must be tightened to avoid the slow change of inclination due to strong winds and other environmental influences.

Research on frequency planning and optimization method in engineering

First, the frequency planning method

Frequency planning refers to the allocation of corresponding frequency resources according to the traffic distribution in a certain area in the process of network construction to achieve effective coverage. In the process of frequency planning, the following factors need to be determined:

1. Determination of base station type

The station type of the base station is the premise of frequency planning, which can be determined according to the traffic volume and the target blocking rate. According to the traffic a, carrier frequency n and blocking rate e, the corresponding table can be queried according to the traffic a and blocking rate e to obtain the number of frequency points n to be configured in a certain cell.

2. Determination of frequency planning method

The first is the setting of frequency parameters, mainly including:

(1) Controls whether channels are allocated separately.

The control channel sends some important control information and cell parameter information, and the planning requirements for the control channel are also relatively high. In planning, the same adjacent frequency interference of control channel should be given priority as little as possible. Generally speaking, in order to avoid interference between control channel and service channel as much as possible and reduce the difficulty of frequency configuration, the frequency range of control channel and service channel are often independent of each other. According to this principle, it is necessary to allocate a separate frequency band to the control channel, which can be continuous or discrete. Discrete frequency band is mainly used to separate the frequency points of control channels, which can avoid interference between control channels, but there will be interference between control channels and traffic channels. Using continuous control channel frequency band can avoid the interference between control channel and traffic channel, but it will increase the interference between control channels.