2G/3G interoperability and neighboring cell optimization

In the construction of Qinhuangdao TD-SCDMA (hereinafter referred to as "TD") network, TD (ZTE equipment) and 2G network are closely related. The co-network of TD and GSM can expand coverage, balance load and reduce investment cost. Therefore, from the perspective of network optimization, 2G/TD collaborative optimization is very necessary. In the early stage of network construction, 2G and TD networks are optimized through collaboration, so that users cannot perceive network changes in the cross-services between 2G and 3G , thus achieving the effect of seamless network transition.

Neighbor cell optimization is the key to optimizing 2G/3G interoperability indicators. Reasonable configuration of 2G/3G neighbor cell network relationships is the prerequisite for subsequent parameter optimization in 2G/3G interoperability.

2G/3G interoperability can only be achieved by correctly configuring adjacent cells, enabling UE to select the correct target cell, and successfully completing reselection and handover operations. Neighboring cell omission, multiple configuration, and unreasonable configuration are the main factors causing 2G/3G interoperability problems:

1. Neighboring cell missed configuration means that the UE cannot switch to a better cell in time, which easily leads to handover failure, resulting in call quality deterioration or even call drop.

2. The main manifestation of multiple neighboring cell configurations is that the UE's measurement time is increased, resulting in failure to switch in time, causing dropped calls or deterioration of call quality.

3. The unreasonable configuration of neighboring cells is mainly due to the unreasonable distance of GSM neighboring cells, the unreasonable selection of GSM neighboring 900MHZ and 1800MHZ cells, and the phenomenon of the same BCCH and BSIC in the GSM neighboring cell list, which may lead to the selection of the wrong target cell, switching failure, dropped calls and deterioration of call quality.

Analysis on the Principles of 2G Neighbor Cell Quantity Configuration

By extracting statistical data of 50 NodeB cells in the existing network, analyzing the relationship between the number of 2G neighbor cells configured in the existing network and network indicators, adjustments and optimizations are made to the 2G neighbor cells of the existing TD cells.

By analyzing the trend chart of the number of neighboring cells in the existing network, the circuit domain switching success rate and the circuit domain drop rate, it can be found that: when the number of neighboring cells is configured between 4 and 7, the circuit domain drop rate is low; when the number of neighboring cells is configured between 3 and 7, the switching success rate between circuit domain systems is high.

Analysis of the trend charts of the number of neighbor cells, the packet domain drop rate, and the packet domain system switching success rate shows that when the number of neighbor cells is configured to be 3-7, the packet domain system switching success rate is high; when the number of neighbor cells is configured to be 2-6, the drop rate is low.

Based on the above research, the cells with low 2G/3G handover success rate in the existing network were screened and modified to ensure that the number of 2G neighbor cells is configured between 4 and 7. The handover statistics after the modification are shown in Figure 2, and the comparison of handover success rates between systems is shown in Figure 3.

From the comparison chart of inter-system switching success rate, it can be seen that after the optimization of the number of neighboring cells, the inter-system switching success rate of the TD cell has been improved in both the circuit domain and the packet domain, especially the inter-system switching success rate in the packet domain has increased from 91.96% before optimization to 94.25%, an increase of nearly 2.3 percentage points.

Same as BCCH principle analysis

When performing 2G/3G interoperability, the UE side uses the cell BCCH frequency + NCC + BCC to identify the cell, and does not use CELLID or RXLEV as the measurement basis. Therefore, if the same BCCH frequency appears in the 2G neighboring cell of TD or around the 2G neighboring cell, it may cause interference to the 2G neighboring cell, resulting in TD cell decoding errors, resulting in the selection of the wrong target cell, causing switching failure or disconnection, thereby affecting the entire network indicators.

From the signaling analysis, it can be seen that when the TD cell initiates a handover to a 2G neighboring cell, the network will extract the 2G neighboring cell information from the measurement control signaling sent down, including BCCH, NCC and BCC. This means that when the TD cell selects a 2G neighboring cell for handover, it uses the BCCH of the 2G neighboring cell as the measurement basis to select the target cell to be switched.

Verification of neighbor distance configuration principle

By extracting statistical data from 50 NodeB cells in the existing network, we studied the relationship between the neighboring cell distance and the 2G/3G switching success rate. The extracted statistical data analysis includes: the switching success rate between circuit domain systems at different neighboring cell distances and the comparison of the switching success rate trend charts between circuit domain systems at different neighboring cell distances. It can be seen that the configuration distance of 2G neighboring cells is basically controlled within the range of 1.5KM. Within this range, there are more switching requests and the switching success rate of the circuit domain is also higher.

By analyzing the packet domain indicators, including the packet domain system switching success rate at different neighboring cell distances and the packet domain system switching success rate trend chart at different neighboring cell distances, it is not difficult to find that: as the 2G neighboring cell distance increases, the packet domain switching success rate shows a downward trend. In the range of 1.5KM-3.0KM, it almost shows a linear downward trend. In the range of 1.0KM-1.5KM, the packet domain switching success rate is faster, decreasing by nearly 8 percentage points.

Verification of 900MHZ/1800MHZ co-site neighboring area selection principle

1.1800MHZ neighboring area advantage

Regarding the uncertainty factors in the selection of 900MHZ and 1800MHZ for 2G neighboring cells, we extracted the data statistics of 900MHZ and 1800MHZ in the existing network and compared and analyzed the assigned connection rate and interference. It can be concluded that the congestion rate and uplink interference ratio of 1800MHZ cells are significantly better than those of 900MHZ cells, which greatly increases the success rate of TD switching or reselection to 1800MHZ cells, which is beneficial to improving network indicators.

2.1800MHZ Neighborhood Disadvantages

By testing the frequency locking coverage range of TD Community Development Building 1 and the 2G neighboring cells 900MHZ and 1800MHZ that are co-located in the same direction, it was found that the signal attenuation of 1800MHZ is very fast, so that the coverage range is significantly smaller than that of 900MHZ. This means that when performing 2G/3G interoperability, the switching probability of the TD cell and the 1800MHZ neighboring cell will be significantly smaller than the switching probability with the 900MHZ neighboring cell, resulting in a reduction in the number of switching of the TD cell to 1800MHZ.

3. Theoretical Evidence

Based on the above analysis, some 900MHZ neighboring cells with low 2G/3G handover success rates and co-sites in the existing network are replaced with 1800MHZ neighboring cells. The handover statistics are shown in Figure 4. The 2G/3G handover success rate trend is shown in Figure 5.

It can be seen that after the 1800MHZ cell replaces the co-located 900MHZ neighboring cell, the switching success rate of the corresponding TD cell is greatly improved, both in the circuit domain and the packet domain.

Through the study of the above contents, we have summarized some principles and experiences on the optimization of 2G neighbor cells in the 2G/3G interoperability of TD networks. In terms of the number of neighbor cells, the network performance is optimal when the number of neighbor cells is 4-7. The circuit domain drop rate is low when the number is configured at 4-7; when the neighbor cells are configured at 3-7, the success rate of handover between circuit domain systems is high. In terms of the distance between neighbor cells, the distance between 2G neighbor cells should be controlled within the range of about 1km as much as possible. Within the range of 1.5KM-3.0KM, the packet domain handover success rate shows a linear downward trend. In terms of interference, the congestion rate and uplink interference ratio of the 1800MHZ cell are significantly better than those of the 900MHZ cell, and the handover success rate of the 1800MHZ neighbor cell is higher than that of the 900MHZ neighbor cell. In terms of the same frequency principle, the same BCCH and BSIC phenomenon cannot appear in the G network neighbor cell list of the TD cell. For more information, please log in to the Electronics Fans Network ( http://www.elecfans.com )

The above conclusions are drawn through a large number of experiments and data collection. These experiences will play a certain guiding role in optimizing 2G/3G interoperability in TD networks and improve 2G/3G interoperability performance.

Innovation Cards

Focus: 2G/3G interoperability

Innovation starting point: In the construction of TD network, 2G/3G interoperability is an important performance of TD network, which affects the user's perception.

Practice: Through the analysis and research of the KPI indicators of Qinhuangdao's existing network, the relationship between the number of 2G neighbor cells and the 2G/3G handover success rate and call drop rate is summarized; the relationship between the 2G neighbor cell configuration distance and the handover success rate, and the selection of 2G cells when 900MHZ and 1800MHZ are co-located. Through the above analysis, the experience and innovation of the number of 2G neighbor cells configured by TD, the distance between 2G neighbor cells, and the selection of 2G neighbor cells when 900MHZ and 1800MHZ are co-located are summarized.