Mobile Wireless Network Optimization

We have already witnessed the development of wireless networks, but we believe that we are not very clear about the mobile network optimization technology. Here we will focus on it.

The network optimization of the mobile communication system mainly includes two aspects: Wireless Network Optimization and switching network optimization. The wireless part of the system has many uncertain factors, which have a great impact on the wireless network. Its performance often determines the service quality of the mobile communication network. Wireless network optimization is a task with a large amount of tasks and complicated processes. The following are some experiences and experiences on optimizing the wireless network in actual work.

I. Ways to discover the quality of wireless networks:

1. DT (driving test, whether there is congestion, interference, or disconnection.

2. CQT (fixed-point network quality test): Multiple test points are selected in the service area for a certain number of call calls to reflect the network quality from the user's perspective. Generally, test points are used in scenarios with concentrated communications, such as hotels, airports, stations, important departments, office buildings, and gathering places.

3. OMC data analysis: OMC traffic statistics are an important way to understand network performance indicators and reflect the actual running status of wireless networks. Through the analysis of its statistical data, we can find Wireless Communities with abnormal indicators such as the connection rate and disconnection rate in the service area. In addition, we can make a comprehensive evaluation of the wireless network quality, such as switch success rate, paging success rate, congestion rate, and drop-off rate.

4. user declaration: Understanding network quality through user complaints, timely detection of problems, targeted and other characteristics, is also an important way for us to understand the status of network services.

Of course, in actual work, DT, CQT, traffic analysis, and user reporting are mutually compatible and confirmed.

Ii. Analysis and troubleshooting of wireless network faults

When problems with the quality of wireless network services are discovered through various means, we will analyze the test data and parameters to determine the cause of the problem and take appropriate measures to optimize the network.

1. common hardware faults:

(1) Adjustment of base station coverage

When the signal in the base station coverage area is poor, you can increase the coverage range by raising or downgrading the antenna height, checking the antenna pitch angle and direction angle, and checking the standing wave ratio. When interference occurs in adjacent cells, these measures can also be used to reduce the coverage of the base station to reduce interference.

For example, if a user reports that the mobile phone signal near a base station is poor, the mobile phone signal level around the base station is-85dBm, which is 500 away from the base station, the base station is 3 kilometers away from the base station and can no longer communicate normally. The terrain is flat and there is no blocking. Obviously, the coverage of the base station is significantly lower than the normal level. After inspection, both the antenna height and the antenna pitch angle and the direction angle are in the normal range, but the antenna standing wave ratio is as high as 1.7. During further checks on the base station's installation status, it is found that the loose antenna interface causes the standing wave ratio to increase, the direct cause of reduced coverage.

(2) Communication exceptions caused by misconnections of the Tianji feeder.

In the test, it is found that the signal in a company's hospital is strong and weak, ranging from-70 dBm ~ -Fluctuation between 95 dBm (both the standby and call statuses have this phenomenon), and the sound is interrupted at a time. After investigation, there is no problem with the carrier board of the base station. This should be the area covered by a base station's 2nd residential area. However, most of the time, the signal of the 3rd residential area is occupied, and switching between the 2 and 3 residential areas is frequent. After checking the antenna feeder part, the two feeder lines in the 2nd Community were mistakenly connected to the antennas in the 1 Community and the 3 Community respectively, in this way, the coverage of zone 2 overlaps with that of cell 1 and cell 3, resulting in frequent switching between cell 2 and cell 3. After the feeder is reconnected, the cell signal coverage is normal.

(3) Hardware aging causes a reduction in voice quality.

Mobile phones have high signal strength, but the voice quality is poor during calls. In addition to eliminating quality problems on the exchange side and external interference, the base station does not have alarms, but it is probably caused by hardware aging.

For example, the standby status signal of a user in a base station 1 cell is good, but the user needs to call multiple times for both called and called to connect, and the signal becomes weak when connected, sometimes it is even switched to an adjacent area. Then, we used the method of locking the three carrier frequencies of a cell, and found that normal calls can be made only when TPU0 is disabled, it is determined that there is a problem with the first frequency board of the station 1 Community. After the TPU0 is changed, the test is repeated and the call returns to normal.

(4) Determination of hidden hardware faults.

We can usually observe the quality and level of the residential area based on the proportion of different switchover causes, and determine the hidden hardware faults to prevent them from happening. From OMC, we can calculate Uplinkquality, downlinkquality, uplinkstrength,

The reason for downlinkstrength switching is the number of bettecell switching factors. When the proportion of the former is significantly higher than that of the latter, it may be that the base station hardware has a hidden fault. In this case, we need to consider whether it is a base station carrier board. During the test, to split the base station with frequency hopping, you must turn off the frequency hopping. Then, only one of the carrier frequencies to which the cell belongs should be opened, and the remaining carrier frequencies should be locked for testing, in this way, all the carrier frequencies in the residential area can be tested one by one, and a problematic carrier board can be found.

2. Optimization of wireless network parameters

Adjusting wireless network optimization parameters can improve and optimize many network indicators, such as improving the switching success rate, connection rate, reducing the congestion rate, and reducing the call-down rate.

(1) Adjustment of power: A road section is planned to implement segmented coverage for base stations A and B. During DT testing, the signal from Station A to Station B is still below-93dBm when it is very close to Station B. As A result, most of this section occupies the signal of Station, in addition, frequent disconnection occurs when base station A switches to Base Station B. The analysis shows that this phenomenon is caused by low transmit power of B Base Station, so the PWR value of the station is changed from 2 to 0. The road section was re-tested, and the coverage effect was also improved.

(2) increase or decrease the relationship between adjacent cells: in DT, Base Station A is driving towards Base Station B, which initially occupies the signal of Station A and Zone 2, there is A disconnection between 4 KM from Station A and 5KM from Station B. According to the relative location analysis of the base station, the signal here should be switched from Station A to Station B. Then, B station and A station return to DT. At the beginning, it occupies the signal of B station and 3 community. When the signal quality drops to 3 or above and the level is below-90dBm, the signal is still not switched. But in the idle state, you can reselect the signal to the station 2 community, and the level will gradually increase. According to the BSC database, the relationship between the B station 3 community and the station 2 community is not found. Therefore, the two sites cannot achieve cross-zone switching. After the adjacent links are added to sites A and B, the switchover is normal during the retest.

(3) Optimization of other parameters

For base stations with aging equipment or remote isolated stations, you can consider improving RXLEVMIN to ensure that the mobile phones connected to the base station have a better level and reduce the disconnection rate, from 5 to 10 to avoid updating the ping-pong position, reduce SDCCH congestion, and increase the connection rate. When the signaling traffic overload or overlap coverage is large in a region, generally, set CELLRESH to 5 as the lag value of the cells in the neighboring areas of different LAC. When the adjacent areas of different LAC are covered with gaps, set CELLRESH to 1-3.

3. Problems with the expansion of Base Stations

When the access rate within the coverage of the base station community is very low and the TCH usage is very high, it can be preliminarily determined that the wireless channel capacity is insufficient after the possibility of hardware failure is eliminated. When traffic cannot be shared by neighboring idle communities, the carrier capacity expansion of the base station must be considered.

For example, when a cell is busy with a channel, the traffic volume is 0.74Erl, and the congestion rate is 5.16%. Obviously, expansion is required. Otherwise, the connection rate and disconnection rate are directly affected.

In addition, it is worth noting that the TCH congestion rate in the OMC statistics is high and the traffic volume is small, which is generally not a capacity problem, most of which are hardware faults, check the hardware of the antenna and base station.

You can change the TCH channel to the number of SDCCH channels for cells with high SDCCH congestion and low TCH traffic. This reduces the number of TCH channels without causing congestion. However, by adding eight SDCCH channels, the congestion can be mitigated. This eliminates the need to add additional carrier boards and saves investment. For example, it is found that the SDCCH congestion rate in a cell is 4.26%, the TCH traffic per line is 0.05ERL, and the number of SDCCH channels is 16. After a TCH is set to SDCCH, the congestion rate is reduced to 0, and the traffic per line is increased to 0.18Erl.

4. Application of direct release Station

Direct release stations include indoor and Indoor layout. Their applications can save investment and effectively solve coverage problems. Outdoor direct stations are generally used in rural areas with relatively few users or on both sides of remote roads to achieve seamless highway coverage. Direct stations can also be used to absorb traffic for a long time in the field. However, the disadvantage of the direct station is that it expands the coverage radius of the base station and increases the number of calls belonging to the base station to a certain extent. Direct station commissioning and testing will directly interfere with the normal operation of the base station, resulting in paralysis of the entire community.